Biomedical subjects

R W Rhoades

Publications and source records attributed to R W Rhoades.

At least 127 records · Page 7Linked to original sources

PubMed1989

Physiological and anatomical consequences of infraorbital nerve transection in the trigeminal ganglion and trigeminal spinal tract of the adult rat.

Single-unit recording and retrograde tracing techniques were used to assess the receptive field properties, topography, and projections of rat trigeminal primary afferent neurons subsequent to transection of the infraorbital (IO) nerve in adulthood. Four hundred and fifty-eight units were recorded in the trigeminal ganglion ipsilateral to nerve section. Of these, 66.6% had IO receptive fields. Thirty percent responded to innocuous stimulation of vibrissae, 39.1% to guard hair deflection, 8.2% to gentle indentation or stretch of the skin, and 22.3% to noxious stimuli (compared to 77.2% vibrissa, 12.0% guard hair, 4.5% skin, and 6.3% noxious in normal animals). An additional 15 units were driven by a stimulating electrode placed on the IO nerve proximal to the site of the lesion but had no receptive field. Of the cells with vibrissa receptive fields, 33.3% were slowly adapting type I (SAI), 6.6% were slowly adapting type II (SAII), 32.2% were low velocity rapidly adapting (RA-LV), 20.0% were high velocity rapidly adapting (RA-HV), and 7.7% were nociceptive (NX, in normal animals 43.8% were SAI, 10.3% SAII, 27.6% RA-LV, 16.8% RA-HV, and 1.5% NX). A number of cells had receptive field properties not seen in normal animals. The single-unit recordings indicated that the topography of mandibular and ophthalmic representations in the ganglion were essentially normal, while the organization of the maxillary region of the ganglion was slightly abnormal. The ganglion physiology experiments were augmented by records from primary afferents in the trigeminal spinal tract (TrV). Eighty-one (72.2%) of the 112 fibers recorded in the TrV of normal rats had IO receptive fields. Of these, 73.2% responded to innocuous vibrissal stimulation, 14.6% to guard hair deflection, 8.5% to gentle indentation of the skin, and 2.5% to noxious stimuli. Of the 61 vibrissa units, 37.8% were SAI, 19.7% SAII, 37.8% RA-LV, 3.3% RA-HV, and 1.6% NX. In adult-lesioned animals, 81 (61.3%) of the recorded fibers had IO receptive fields. Of this number, 38.2% responded to vibrissae, 29.6% to guard hairs, 16.0% to skin, and 19.7% to noxious simuli. Of the vibrissa-sensitive units, 16.1% were SAI, 3.2% were SAII, 45.2% were RA-LV, 35.5% were RA-HV, and 3.2% NX. As in the ganglion recording studies, a number of abnormal receptive fields were documented.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

An electron microscopic analysis of the morphology and connectivity of individual HRP-labeled slowly adapting vibrissa primary afferents in the adult rat.

The ultrastructure of 4 slowly adapting vibrissa primary afferent central terminal arbors was examined following intracellular injection of horseradish peroxidase (HRP). The terminals were found to contain clear round vesicles and formed primarily asymmetric synapses on dendritic shafts and spines. Few examples of synaptic glomeruli, with the labeled axon as the central element, were identified.

Afferent Pathways↗

PubMed1988

Neonatal infraorbital nerve transection in rat results in peripheral trigeminal sprouting.

Retrograde tracing techniques were employed to determine whether transection of the infraorbital (IO) nerve in either newborn or adult rats resulted in peripheral sprouting by undamaged trigeminal (V) axons. The IO nerve was sectioned just behind the vibrissa pad, either on the day of birth or when animals reached at least 60 days of age. After an additional 60 days, the same nerve was retransected in the orbit; horseradish peroxidase (HRP) or diamidino yellow (DY) was injected into the central portion of the vibrissa pad; and animals were killed 2-3 days later. In the neonatally nerve-damaged rats, this procedure invariably labelled primary afferent neurons in both the ipsilateral and contralateral V ganglia. On the ipsilateral side, these cells were located in the caudal portion of the ophthalmic-maxillary region and, less often, in the mandibular division. Their average diameter was 22.6 micron (s.d. = 5.6). On the contralateral side, most labelled ganglion cells were visible in the anteromedial part of the ophthalmic-maxillary region but a few could also be seen in the mandibular division. Their average diameter was 21.1 micron (s.d. = 5.5). No labelled ganglion cells were observed in adult rats subjected to the same series of manipulations. In a separate series of neonatally nerve-damaged animals, the above-described procedures were combined with neonatal injection of capsaicin in an effort to determine whether the observed sprouting was dependent upon the presence of large numbers of unmyelinated axons. The addition of this treatment reduced the number of labelled cells in both the ipsilateral and contralateral ganglia, but it did not alter either their distribution or average soma diameter. In a final experiment, sequential double-labelling techniques were used to determine whether the V axons that projected to the vibrissa pad via non-IO nerve branches were the result of sprouting by undamaged ganglion cells or arose from neurons that had originally projected into the IO nerve, were axotomized by our lesions, and regenerated to the vibrissa pad via another V branch. Here, the long-lived retrograde tracer true blue (TB) was injected into the vibrissa pad 6-8 hours before the neonatal nerve cut and DY was deposited into the pad after transection of the regenerate IO nerve in adulthood. Double-labelled cells in this experiment would have projected to the vibrissa pad via the IO nerve at birth and regenerated to it via another V branch in adulthood. Nearly 55% of the DY-labelled cells in this experiment also contained TB.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Anatomical consequences of neonatal infraorbital nerve transection upon the trigeminal ganglion and vibrissa follicle nerves in the adult rat.

A large body of experimental literature has demonstrated that neonatal infraorbital nerve damage in rodents produces anatomical and/or functional alterations of the normal whisker representation in central trigeminal structures. Less is known about the organization of primary afferent components of the trigeminal system following this manipulation. Such information provides an important basis for interpreting the central changes observed following damage of infraorbital nerve fibers at birth. We have therefore examined the composition and order of peripheral innervation in the pathway from the trigeminal ganglion to the vibrissa follicles in adult rats subjected to unilateral neonatal infraorbital nerve transection. Electron microscopy was used to determine the number and diameter of myelinated and unmyelinated fibers in vibrissa follicle nerves of these animals. Wheat germ agglutinin-horseradish peroxidase and fluorescent retrograde tracers were employed to examine the number and diameter, as well as the topographic organization and branching, of ganglion cells innervating the vibrissae in these rats. The data presented below indicate that neonatal infraorbital nerve transection has the following consequences within the adult trigeminal nerve and ganglion: 1) an alteration of the gross morphology of vibrissal nerves, 2) a significant reduction in the average number (85.4%) and diameter (32.6%) of myelinated, but not unmyelinated, follicle nerve axons, 3) a significant decrease in the average number (36.8%) of trigeminal ganglion cells innervating vibrissa follicles, 4) no significant change in the distribution of ganglion cell diameters, 5) an increase in peripheral branching (1.8-fold) of these ganglion cell axons, and 6) an alteration of somatotopic order within the trigeminal ganglion. Taken together, these data indicate that neonatal infraorbital nerve transection produces a profound reorganization of the primary afferent component of the trigeminal neuraxis.

Animals↗

PubMed1988

Structure-function relationships in the rat brainstem subnucleus interpolaris: II. Low and high threshold trigeminal primary afferents.

Prior studies indicate that vibrissa, guard hair, hairy skin, mucosa, and nociceptive trigeminal primary afferents give rise to morphologically distinct terminal arbors in the medullary dorsal horn. The present study describes the extent to which similar structure-function relationships exist in the rostrally adjacent subnucleus interpolaris (SpVi). Seventy-three axons were physiologically characterized and visualized by standard intra-axonal HRP labeling techniques. They responded to guard hair (GH) or vibrissa (VIB) deflection; gentle pressure applied to hairy skin (HS), glabrous skin (GS), lingual mucosa (LM), or an incisor (PER); or a noxious pinch of the face (NOX). Response latencies to trigeminal ganglion shocks were equivalent for all categories with low threshold receptive fields (mean = 0.44 ms), and these were significantly shorter than those of fibers with high threshold NOX receptive fields (mean = 0.88 ms). All axons gave off transversely oriented collaterals into SpVi with rostrocaudal discontinuities in their arbors. Collaterals were topographically organized. Axons innervating the rostral mouth and face terminated medially, and those that supplied the caudal face innervated successively more lateral SpVi. The dorsal face was represented in the ventral SpVi, whereas the ventral face and mouth were represented more dorsally. This transverse topography extended largely throughout the rostrocaudal extent of SpVi. VIB, GH, GS, and LM collaterals had similar configurations with circumscribed arbors. HS, PER, and NOX arbors had a "stringy" shape without a clear terminal focus, save for the fact that PER and NOX collaterals often terminated in rostrally displaced substantia gelatinosa at the level of the caudal SpVi. Analysis of variance, considering only those data from mystacial VIB, GH, and HS fibers, indicated significant differences for all of the following measures: number of collaterals, number of boutons per collateral, arbor area, arbor circumference, and arbor circularity (form factor). A similar analysis, considering all fiber types, indicated significant differences for only the following measures: number of collaterals, arbor area, and arbor circumference. Individual group comparisons between the more heavily sampled functional categories indicated that GH afferents had significantly fewer collaterals, fewer boutons per collateral, smaller arbor area, shorter arbor circumference, and more circular arbors than those of HS axons. VIB fibers tended to fall between GH and HS afferents with respect to number of collaterals, arbor area, circumference, and circularity. The remaining functional groups were not as orderly.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1988

Receptive-field properties and morphological characteristics of the superior collicular neurons that project to the lateral posterior and dorsal lateral geniculate nuclei in the hamster.

1. Intracellular recording, antidromic activation, and horseradish peroxidase (HRP) injection techniques were employed to characterize the receptive-field properties and morphology of the superior collicular (SC) neurons in the hamster that projected to the lateral posterior nucleus (LP) or the dorsal lateral geniculate body (LGNd). 2. Twenty-three tecto-LP and 21 tecto-LGNd cells were successfully characterized, filled with HRP, and recovered. Additional physiological information was obtained from four tecto-LP and five tecto-LGNd neurons in which HRP injections did not completely label the cell, but did provide information as to the laminar location of the soma. Recovered neurons were classified as wide-field or narrow-field vertical cells, marginal cells, stellate cells, or horizontal cells on the basis of their soma-dendritic morphology. They were categorized as stationary responsive (SR), movement sensitive (MV), or directionally selective (DS) on the basis of their physiological responses (3, 37). 3. The somas of the recovered tecto-LP cells were located, with two exceptions, in, or near, the borders of the stratum opticum (SO). Tecto-LGNd neurons, with two exceptions, had their cell bodies in the upper one-half of the stratum griseum superficiale (SGS). Fifty-two percent of the recovered tecto-LP cells were wide-field vertical cells, 22% were narrow-field vertical cells, 13% were stellate cells, 9% were horizontal cells, and 4% could not be classified according to the scheme that we employed. Twenty-four percent of the recovered tecto-LGNd cells were marginal cells, 24% were stellate cells, 38% were narrow-field vertical cells, 5% were horizontal cells, 5% were wide-field vertical cells, and 5% could not be classified. The difference between the distributions of morphological cell types that contributed to the tecto-LGNd and tecto-LP pathways was statistically significant (chi 2 = 15.8, P less than 0.01). 4. Sixty-seven percent of the tecto-LP cells had MV receptive fields, 11% were DS, 7% had SR fields, and 15% were unresponsive. The distribution of receptive-field types for tecto-LGNd cells was somewhat different: 54% had SR fields, 15% were MV, 19% were DS, 4% were somatosensory, 4% were unresponsive, and 4% were incompletely classified. These differences between tecto-LP and tecto-LGNd cells were statistically significant (chi 2 = 18.4, P less than 0.001). The strongest correlation between morphology and receptive-field type was observed for the wide-field vertical cells that projected to LP. All but one of these had MV receptive fields.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Effect of neonatal infraorbital nerve transection on substance P- and leucine enkephalin-like immunoreactivities in trigeminal subnucleus caudalis of the rat.

The distributions of substance P-like immunoreactivity (SPLI) and leucine-enkephalin-like immunoreactivity (LENKLI) in subnucleus caudalis of normal adult rats were compared with those observed in the adult rats that sustained transection of the infraorbital (IO) nerve either on the day of birth or in adulthood. All immunocytochemical experiments in the neonatally nerve damaged rats were carried out at least 60 d after the nerve transection. In the animals that sustained nerve transections as adults, brains were processed for immunohistochemistry between 7 and 60 d after the lesions. In the rats that sustained IO nerve transections as adults, there was a transient reduction in the density of the SPLI in layers I and II of ipsilateral subnucleus caudalis. It was most apparent about 2 weeks after the nerve transection and returned to near normal values by 60 d after the lesion. In the rats that sustained IO nerve transections on the day of birth, there was no reduction in the density of SPLI in caudalis, and the band of staining on the deafferented side of the brain stem was actually 40% wider than that on the intact side. Neither neonatal nor adult IO nerve transection had appreciable effects upon the distribution of LENKLI in the rat's trigeminal brain-stem complex. In another series of experiments, rats that sustained neonatal transection of the IO nerve had this same nerve recut in adulthood. Twelve days after the second lesion, the brains of these animals were processed for SPLI. There was a marked reduction in the density of the staining for this peptide on the deafferented side. This last result is consistent with the interpretation that the increased distribution of SPLI in the neonatally nerve damaged rats is due, at least partially, to reorganization of primary afferents.

Aging↗

PubMed1988

The projection from the superficial to the deep layers of the superior colliculus: an intracellular horseradish peroxidase injection study in the hamster.

Intracellular recording and horseradish peroxidase (HRP) injection techniques were employed to examine the projections of superficial layer [stratum griseum superficiale (SGS) and stratum opticum (SO)] superior collicular (SC) neurons in the hamster that sent axon collaterals into the deep laminae (those ventral to the SO) of this structure. Sixty-nine neurons were studied, selected from a sample of over 185 HRP-filled superficial layer cells on the basis of having heavily stained axons. Of the 69 cells included in the study, 43.4% (n = 30) sent at least one axon collateral to the deep laminae. Not all cell types in the superficial layers contributed equally to this interlaminar projection: 78.6% (n = 11) of the recovered wide-field vertical cells, 55.0% (n = 11) of the narrow-field vertical cells, 16.7% (n = 2) of the stellate cells, 40.0% (n = 2) of the marginal cells, 18.2% (n = 2) of the horizontal cells, and 28.6% (n = 2) of neurons we could not classify on the basis of their somadendritic morphology projected to the deep layers. Within a given cell class, there were no significant morphological or physiological differences between the neurons that possessed deep axon collaterals and those that did not. The deep axon collaterals of most of the interlaminar projection neurons were restricted to the stratum griseum intermediate (SGI). In this layer, the largest segment of the axon arbor was located lateral to a projection line that was orthogonal to the SC surface and that passed through the soma of the cell in question. These results, along with those of a previous study (Mooney et al., 1984), which demonstrated that the dendrites of deep layer cells may extend through the SO and into the SGS, indicate that there is an extensive anatomical substrate by which sensory information may be communicated from superficial to deep layer SC neurons.

Animals↗

PubMed1987

Transection of the infraorbital nerve in newborn hamsters alters the somatosensory but not the visual representation in the superior colliculus.

The experiments described in this report were designed to determine whether changing the somatosensory representation in the deep laminae of the hamster's superior colliculus would result in a corresponding reorganization in the visual map in the overlying superficial layers. The somatosensory representation was altered by transecting the infraorbital (IO) nerve on the day of birth. This trigeminal branch supplies, among other targets, the snout and mystacial vibrissa follicles. These peripheral structures compose a major portion of the somatosensory representation in the deep collicular laminae. The effects of these lesions were assessed in anatomical and physiological experiments when the animals reached adulthood. Retrograde tracing with true blue demonstrated a 48% reduction in the number of trigeminocollicular neurons in the partially deafferented subnucleus interpolaris (the main source of trigeminal input to the rodent colliculus--e.g., Killackey and Erzurumlu: J. Comp. Neurol. 201:221-242, '81), but anterograde tracing with horseradish peroxidase (HRP) and wheat germ agglutinin-conjugated HRP showed that the terminal field of the trigeminocollicular projection from the deafferented subnucleus was essentially normal. This pathway terminated as a series of patches along the border between the stratum griseum intermediale and stratum album intermedium and encompassed approximately 75% of the rostrocaudal extent of the colliculus. The electrophysiological experiments revealed a marked change in somatosensory collicular topography. There was an under-representation of the vibrissae and the entire IO peripheral field in the deep laminae of the nerve-damaged animals, and neurons with trigeminal ophthalmic and mandibular receptive fields were recorded from portions of the colliculus in which only whisker-sensitive neurons would be normally isolated. There were no corresponding changes in the organization of the visual representation. These results support the conclusion that the organization of the visual representation in the superficial laminae and the organization of the somatosensory map in the deep layers of the mammalian superior colliculus follow independent developmental programs.

Animals↗

PubMed1987

Morphological characteristics of low-threshold primary afferents in the trigeminal subnuclei interpolaris and caudalis (the medullary dorsal horn) of the golden hamster.

Intra-axonal recording and horseradish peroxidase (HRP) injection techniques were employed to define the response characteristics of low-threshold, rapidly conducting trigeminal primary afferents and the morphological features of their axon arbors in subnucleus interpolaris and subnucleus caudalis (or the medullary dorsal horn; these last two terms are used synonomously throughout the paper). A total of 61 such afferents were characterized and recovered. Of these, ten gave rapidly adapting (RA) and 17 slowly adapting (SA type I) responses to vibrissa deflection. Twenty were sensitive to guard hair deflection and 14 were responsive to indentation of the hairy skin. The vibrissa-sensitive primary afferents were all quite similar morphologically. Primary collaterals proceeded directly, in a radial fashion, to their zone of termination and gave rise to dense and compact arbors. These tended to be larger in the medullary dorsal horn (MDH) than in interpolaris and they also gave rise to more boutons in the former nucleus. Guard hair afferents generally had smaller arbors and gave rise to fewer boutons than vibrissa-sensitive axons. Like vibrissa afferents, their arbor were generally circumscribed in both interpolaris and MDH, but they were larger in the latter nucleus. Skin-sensitive afferents had arbors that tended to be somewhat larger than those of vibrissa- or guard-hair-related fibers. Unlike the other fiber types, the arbors of skin-sensitive afferents were on average larger in interpolaris than MDH. Quantitative analysis of the morphological data from well-filled examples from each of these four functional types verified our qualitative impressions regarding differences between interpolaris and MDH collaterals of a given fiber-type. Statistical comparison of data from different functional classes indicated trends that supported our qualitative impressions, but none of these was statistically significant. The topography of the trigeminal primary afferent input to interpolaris was organized such that the head was inverted and fibers with caudal receptive fields terminated in the lateral portion of the nucleus. This was true for all of the functional afferent types that we examined. Vibrissa-related fibers differed from nonvibrissa afferents in that they tended to avoid the most rostral portion of interpolaris. In the MDH, the primary afferent representation of the head was also inverted, but fibers with caudal facial receptive fields tended to terminate medially rather than laterally.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

The spinal and commissural projections from the superior colliculus in rat and hamster arise from distinct neuronal populations.

Multiple retrograde labelling techniques were used to determine whether the superior collicular (SC) cells that project to the spinal cord in hamster and rat also innervate the contralateral colliculus. In 25 rats and 13 hamsters, various combinations of the tracers horseradish peroxidase, True blue, Diamidino yellow, fluorogold and rhodamine-labelled latex microspheres were used to label tectospinal and SC commissural neurons. No double-labelled cells were observed in any of these experiments. Analysis of neurons that were retrogradely labelled with horseradish peroxidase showed further that SC commissural neurons were much smaller than tectospinal cells. The average soma area for tectospinal cells in hamster was 225.9 micron 2 and that for such neurons in rat was 214.4 micron 2. The mean soma areas for SC commissural neurons in hamster and rat were 85.4 micron 2, respectively. In additional experiments (6 rats and 6 hamsters), True blue was injected into the left predorsal bundle and Diamidino yellow was deposited into the left SC. In both hamsters and rats, these injections invariably produced a small number of double-labelled cells in the deep layers of the right SC. In a final group of animals (7 rats and 2 hamsters), large thalamic deposits of Diamidino yellow were combined with bilateral injections of True blue into the spinal cord. This combination also produced small numbers of double-labelled neurons in both colliculi. These results indicate that the tectospinal and SC commissural pathways arise from distinct neuronal populations, but that a small number of cells that send axons into the predorsal bundle also have commissural collaterals. They demonstrate further that some tectospinal cells also send axon collaterals to the thalamus.

Animals↗

PubMed1987

The structural and functional characteristics of tectospinal neurons in the golden hamster.

Intracellular recording and horseradish peroxidase (HRP) injection techniques were used to delineate the structural and functional characteristics of the superior collicular cells in the hamster, which could be antidromically activated from the first cervical segment of the spinal cord. Thirty-one such neurons were characterized, filled with HRP, and recovered. Complete physiological data were obtained from another 21 tectospinal cells for which anatomical data were sufficient only to define the laminar location of the cell body from which recordings were made. Of the total sample of 52 cells, 7.7% had their somata in the stratum griseum intermediale (SGI), 50% were in the stratum album intermedium (SAI), 36.5% were in the stratum griseum profundum (SGP), and 5.8% were in the stratum album profundum (SAP). The tectospinal cells were fairly uniform morphologically. They had large (27.7 +/- 5.5 microns diameter) cell bodies, which gave rise to an average of 6.7 +/- 1.2 primary dendrites. These were generally smooth and extended up to 500 microns away from the cell body. In many cases, they ascended out of the deep laminae into the stratum opticum (SO) and/or stratum griseum superficiale (SGS). The axons of TS cells averaged 3.4 +/- 0.8 microns in diameter, and they generally coursed radially to the SAP where they curved around the periaqueductal gray and entered the predorsal bundle. These axons often gave rise to collaterals that arborized in the deep laminae of the ipsilateral superior colliculus and subjacent reticular formation. The tectospinal cells were also fairly uniform physiologically. Their average conduction latency was 2.0 +/- 2.3 ms, and this variable had a strong negative correlation (-.81) with axon diameter for the recovered cells. Most (63.5%) of the TS cells were exclusively somatosensory and gave rapidly adapting responses to deflection of vibrissae and/or guard hairs; 7.7% were bimodal (visual-somatosensory); 11.5% had complex (Rhoades et al., '83) somatosensory receptive fields; 1.9% were discharged only by a noxious pinch, and 15.4% were unresponsive. A common feature of all bimodal tectospinal neurons was dendrites that extended at least as far dorsally as the SO. Whereas there were no other clear-cut correlations between the structural and functional characteristics of these tectal neurons, we did note that all of the cells with complex somatosensory receptive fields received inhibitory input from axons that either originated from, or passed through, the contralateral superior colliculus.

Animals↗

PubMed1987

Preventing regeneration of infraorbital axons does not alter the ganglionic or transganglionic consequences of neonatal transection of this trigeminal branch.

Retrograde and transganglionic tracing with a combination of horseradish peroxidase (HRP) and wheatgerm agglutinin (WGA)-conjugated HRP (WGA-HRP) was employed to determine whether transection of the infraorbital (IO) nerve on the day of birth and prevention of regeneration by retransecting it at weekly intervals until the time of a terminal anatomical experiment had effects upon ganglion cell survival and innervation of the brainstem by this trigeminal (V) branch that differed from those which followed a single transection of the same nerve on the day of birth without any attempt to prevent peripheral regeneration of the cut axons. Counts of labelled ganglion cells and examination of the brainstem labelling produced by application of HRP and WGA-HRP to the IO nerve proximal to the point of transection(s) at 6 weeks of age demonstrated no differential effects of preventing regeneration of the cut nerve. In animals subjected to a single transection of the nerve (n = 9), we counted an average of 5001.2 (S.D. = 1286.9) labelled ganglion cells and these had an average diameter of 22.7 micron (S.D. = 6.3). In the rats (n = 9) that sustained multiple nerve cuts, the average number of labelled ganglion cells was 4447.8 (S.D. = 1060.9). The mean diameter for these primary afferent neurons was 21.5 micron (S.D. = 6.6). Neither of these values were significantly different from those from the rats subjected to a single nerve cut. The cell counts from both of these groups were significantly lower than those obtained after application of HRP and WGA-HRP to the IO nerve in normal rats (n = 3, X = 12,553.3, S.D. = 1454.8), but the average cell diameter in the normals (X = 23.2, S.D. = 6.6) was not significantly greater than that in the nerve-damaged animals. The pattern of brainstem labelling observed in the rats subjected to multiple nerve cuts was the same as that in the rats which sustained a single transection of the IO nerve on the day of birth. Very little terminal labelling was observed in nucleus principalis, subnucleus oralis, subnucleus interpolaris or the magnocellular portion of caudalis. There was, however, very heavy labelling in laminae I and II of the latter nucleus.

Animals↗

PubMed1987

Distribution of visual callosal projection neurons in hamsters subjected to transection of the optic radiations on the day of birth.

The optic radiations of hamsters were transected on the day of birth and visual callosal projections in these animals were traced using retrograde transport of either horseradish peroxidase (HRP) or the fluorescent tracers True blue (TB) or Diamidino yellow (DY) when the animals reached maturity (greater than 45 days of age). In the hemisphere ipsilateral to the neonatal lesion, the distribution of callosal cells was markedly altered. These neurons were almost completely restricted to a continuous band in lower lamina V and the upper portion of layer VI. Anterograde HRP transport to the deafferented hemisphere also revealed an abnormal distribution of callosal terminals. The band of labelling that is located along the 17-18a border in the normals was much broader than is normally the case. In the hemisphere contralateral to the lesion, the distributions of callosal cells and terminals were essentially normal. Labelled neurons were located in the infragranular layers (primarily lower layer V and the upper part of lamina VI) throughout area 17 and also in layers II-IV in the 17-18a border region. Anterograde labelling was visible in layers V and VI throughout the mediolateral extent of the dorsal posterior neocortex and supragranular labelling was restricted to the lateral portion of area 17 and medial 18a. These results suggest that the normal thalamic projection to the visual cortex is necessary for the establishment of the strip of supragranular callosal projection neurons which is normally located in the 17-18a border region, but not for the establishment (or maintenance) of callosal projections by large numbers of neurons in the infragranular laminae. They show further that neonatal transection of the optic radiations results in reduction in the correspondence between the distributions of callosal cells and terminals in the deafferented hemisphere.

Animals↗

PubMed1987

Development and plasticity in hamster trigeminal primary afferent projections.

At birth (gestational day 16), the hamster infraorbital nerve projects to the appropriate portion of the brainstem, though the projection lacks adult-like internal organization (patchiness). Infraorbital nerve damage at this time does not produce appreciable transganglionic atrophy in the central projections of the infraorbital nerve, but it does result in a failure to develop normal infraorbital primary afferent patches. Such damage also produces a more widespread central projection of spared mandibular afferents into regions occupied by 'regenerate' infraorbital terminals (J. Comp. Neurol., 235 (1985) 129-143). In the present study, transganglionic transport techniques were again used to show that, by postnatal day 5 (gestational day 21), rostrocaudally continuous aggregates of horseradish peroxidase-labelled infraorbital terminals are visible throughout the trigeminal brainstem nuclear complex. This aggregation pattern is nearly adult-like and isomorphic with the distribution of the mystacial vibrissae on the face. A similar infraorbital lesion performed on postnatal day 5, however, markedly decreased the density of the adult central projection of the infraorbital nerve to subnuclei principalis, oralis, interpolaris, and the magnocellular laminae of caudalis. The projection to superficial laminae of caudalis and the cervical dorsal horn was maintained. A postnatal-day-5 infraorbital lesion also failed to produce a more widespread central projection from spared mandibular primary afferents. These data suggest a relationship between the postnatal maturity of trigeminal primary afferents and the response of damaged and undamaged trigeminal afferents to infraorbital nerve transection in hamster. The similarity in the central primary afferent response to lesions at equivalent gestational times (postnatal days 5 and 0, respectively) in hamster and rat, suggests that this plasticity gradient may be a general characteristic of mammalian trigeminal primary afferents.

Afferent Pathways↗

PubMed1987

Effects of altered visual input upon the development of the visual and somatosensory representations in the hamster's superior colliculus.

The right superior colliculus and right eye were ablated in hamsters within 12 h of birth and the visual and somatosensory representations in the remaining (left) superior colliculus were evaluated using standard single unit recording and receptive field mapping techniques when the animals reached adulthood (at least 3 months of age). In a number of the hamsters used for recording, injections of [3H]leucine were made into the left eye 6-10 days prior to the terminal experiment. This was done to insure that the neonatal lesions did, in fact, produce the extensive recrossing of retinal fibers demonstrated by others who have employed this preparation. All of the hamsters which received [3H]leucine injections prior to the recording experiment exhibited a markedly expanded ipsilateral retinocollicular projection and retinal axons which recrossed the midline at the level of the tectum. The recording experiments showed further that this projection resulted in a visual map which was generally mirror symmetric to that in normal hamsters. There were, however, numerous irregularities and discontinuities in this representation and, in a few hamsters, it appeared almost completely disorganized. There were also a number of abnormalities in the somatosensory representation in the deep tectal laminae of the neonatally brain damaged hamsters. There was a substantial increase in the number of cells with receptive fields that extended onto the ipsilateral side of the body, neurons with split receptive fields were recorded and there were changes in the magnification of different portions of the body surface. These alterations did not, however, change the organization of the somatosensory map in a manner which brought it into alignment with the visual representation in the superficial laminae. Nevertheless, additional recording experiments in animals subjected to enucleation of both eyes and ablation of the superficial laminae of one superior colliculus did indicate that the existence of the aberrant retinal projection was a necessary condition for the somatosensory abnormalities which we observed. Additional anterograde and retrograde tracing experiments demonstrated only one abnormality in the organization of the somatosensory afferent input to the remaining colliculus. In 75% of the brain damaged hamsters, there was a weak crossed projection from the sensorimotor cortex that was never observed in normal animals. Ablation of this cortex at the time of the recording experiment did not, however, reduce the incidence of abnormal somatosensory receptive fields in these hamsters.

Afferent Pathways↗

PubMed1987

Receptive-field properties of rat ventral posterior medial neurons before and after selective kainic acid lesions of the trigeminal brain stem complex.

Single neurons were recorded from the ventral posteromedial thalamic nucleus (VPM) of urethan-anesthetized rats. Six of these animals were intact, 28 sustained kainic acid (KA) lesions of trigeminal nucleus principalis (PrV), and 9 received similar lesions of trigeminal subnucleus interpolaris (SpVi). Four animals sustained PrV lesions that were followed, at an interval of 1-3 mo, by KA injections into SpVi. Special attention was paid to the receptive-field characteristics of neurons that were sensitive to deflection of the mystacial vibrissae. In normal animals, we recorded a total of 167 VPM neurons, 85% (n = 142) of which were vibrissa sensitive. The remaining VPM cells were excited by either guard hair deflection (8.4%), indentation of the skin (0.6%), or deflection of either vibrissae or guard hairs (1.8%). Seven cells (4.2%) were unresponsive. The topography of the trigeminal representation in VPM was similar to that reported previously by Waite (59). Vibrissa-sensitive neurons in intact rats generally gave rapidly adapting responses (84.5%), and only 16.2% were directionally selective. The vast majority (80.3%) of the vibrissa-sensitive cells were activated by deflection of only one whisker (1.2 +/- 0.5, mean +/- SD); none were excited by deflection of more than four vibrissae. Injections of KA into SpVi of otherwise intact rats (n = 9) had no appreciable effect on the receptive-field characteristics of vibrissa-sensitive VPM neurons. Injections of KA into PrV markedly altered the receptive-field properties of VPM cells. Recordings were made from 45 VPM neurons over a period extending from 0 to 10 h after KA injections into PrV in five rats. Of these cells, 4.4% were excited by vibrissa deflection and the remainder were unresponsive. Additional recordings from SpVi and the superior colliculus of these same animals indicated that the neurotoxin probably did not damage interpolaris neurons or their axons. Recordings were made from 394 VPM cells in 22 rats that survived 1-6 days after KA lesions of PrV. These experiments demonstrated an increase in the number of thalamic cells that were responsive to peripheral stimulation over this period. By 6 days after the lesion (4 animals), 52.8% of the 73 VPM neurons we recorded were excited by somatosensory stimuli. Of these, 89.5% were activated by deflection of one or more mystacial vibrissae. The average number of whiskers that excited a given VPM cell in these rats was 6.3 +/- 2.0 (SD). Recordings were made from VPM in five rats that survived 30-90 days after KA injections in PrV.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

Reorganization of the peripheral projections of the trigeminal ganglion following neonatal transection of the infraorbital nerve.

Two different anatomical techniques were used to obtain evidence that transection of the infraorbital (IO) nerve on the day of birth would result in reorganization of the peripheral projections of the trigeminal nerve. In 14 of 19 neonatally nerve-damaged adult rats, injection of horseradish peroxidase (HRP) directly into the IO nerve, proximal to the point of the neonatal transection, resulted in labeled cells in the ophthalmic-maxillary portion of the ganglion and labeled fibers in mandibular sensory nerves. In an additional 28 neonatally nerve-damaged adult rats, double-labeling techniques were employed to document the reorganization suggested by the HRP tracing experiments. In these experiments, one fluorescent tracer, diamidino yellow (DY), was injected directly into the regenerate IO nerve, proximal to the point of the neonatal transection; a second tracer, true blue (TB), was deposited into peripheral ophthalmic and/or mandibular fields. These combinations of injections invariably resulted in the demonstration of a small number (46-401) of double-labeled cells that were located in the ophthalmic-maxillary part of the ganglion. Identical combinations of injections in normal adult rats and the intact sides of nerve-damaged animals never produced more than 6 double-labeled cells per ganglion. In two additional series of experiments, sequential double-labeling techniques were employed to demonstrate that the multiply projecting ganglion cells probably arose in at least two ways: (1) development of non-IO projections by ganglion cells that contributed axons to the IO nerve at the time of the lesion; (2) elaboration of IO axon branches by primary afferent neurons that had non-IO projections at the time of the lesion. A final two-stage double-labeling experiment demonstrated that approximately 75% of the ganglion cells that projected to the whisker pad at birth, and survived transection of the IO nerve on the first postnatal day, regenerated axons into this trigeminal branch.

Amidines↗