Biomedical subjects

R W Rhoades

Publications and source records attributed to R W Rhoades.

At least 91 records · Page 5Linked to original sources

PubMed1992

Structural and functional consequences of neonatal deafferentation in the superficial layers of the hamster's superior colliculus.

Intracellular recording and horseradish peroxidase (HRP) injection techniques were used to evaluate the effects of neonatal enucleation upon the structural and functional properties of cells in the superficial retinorecipient laminae of the hamster's superior colliculus (SC). The physiological recordings confirmed previous results that normally visual superficial layer neurons develop somatosensory receptive fields in the enucleated animals. This study further showed that all of the physiological subclasses of somatosensory neurons normally encountered in the deep layers were present in the superficial laminae. With the exception of marginal cells, all of the morphological classes of neurons in the superficial SC laminae of sighted hamsters (narrowfield vertical cells, widefield vertical cells, stellate cells, horizontal cells, and giant stellate cells) were recovered from the blinded animals. Quantitative comparison of neurons within a given morphological class demonstrated only slight differences between cells from blind and sighted hamsters. However, there was a significant reduction in the percentage of neurons with dorsally directed dendrites in the neonatally enucleated animals. Additional experiments with the Golgi technique also demonstrated that neonatal enucleation altered the distribution of morphological cell types in the superficial SC laminae. These results suggest that enucleation in the hamster may result in relative reductions in specific cell types in the superficial SC laminae rather than dendritic changes in all of the cell classes present in these layers.

Animals↗

PubMed1992

Normal development and effects of deafferentation on the morphology of superior collicular neurons projecting to the lateral posterior nucleus in hamster.

Visually responsive neurons in the superficial layers of the hamster's superior colliculus (SC) can be divided into distinct morphological and functional classes. In the preceding paper (Mooney et al., '91), we showed that neonatal enucleation has only slight and insignificant effects upon the structural characteristics of cells within a given class, but results in a significant reduction of neurons (narrow and widefield vertical cells) with dorsally directed dendritic arbors. In an effort to determine whether this change reflected differential transneuronal degeneration of these cell types or alterations in the dendritic arbors of surviving cells, this study re-examined this issue by restricting the analysis to a specific and relatively homogeneous subpopulation of superficial layer neurons, those that project to the lateral posterior nucleus (LP). Physiological recordings demonstrated that most (64.7%) tecto-LP cells in neonatally enucleated hamsters develop somatosensory receptive fields. The combination of retrograde tracing and injection of cells with Lucifer yellow in a fixed slice preparation demonstrated that nearly 75% of tecto-LP cells in normal adult hamsters are widefield vertical cells while less than 25% of the neurons filled in neonatally enucleated adults are in this class. Most of the tecto-LP cells in the neonatally enucleated adult hamsters were either horizontal cells (19.5%), giant stellate cells (24.6%), or had dendrites that were directed only toward the deep SC laminae (10.3%). Differential enucleation-induced cell death could not account for all of these changes. Tecto-LP neurons were retrogradely labelled with the carbocyanine dye, Di-I, in hamsters on postnatal day (P-) 0 (the day of birth) through P-10. As early as P-0, most retrogradely labelled neurons could be identified as either widefield (44.6%) or narrowfield (18.9%) vertical cells. These results, when considered together with those from the normal adult and neonatally enucleated adult hamsters, support the conclusion that neonatal eye removal results in a reorganizaton of the dendritic arbors of some collicular neurons that have already undergone considerable development at the time of the lesion.

Afferent Pathways↗

PubMed1992

Synaptic organization of the serotoninergic input to the superficial gray layer of the hamster's superior colliculus.

Immunocytochemistry with an antibody directed against a serotonin (5-HT)-bovine serum albumin (BSA) conjugate was combined with electron microscopy and serial section analysis to examine the synaptic organization of the serotoninergic projection to the stratum griseum superficiale (SGS) of the hamster's superior colliculus (SC). Most of the 5-HT-immunoreactive swellings in the hamster's SC did not make conventional synaptic contacts. Examination of 250 such swellings in single thin sections revealed only 11 synapses. Assessment of an additional 50 swellings followed through serial sections showed that only 6% (N = 3) of these varicosities made conventional synaptic contacts. All the synapses made by serotoninergic axons were with the dendrites of SC neurons. These results demonstrate that the inhibitory effects of 5-HT on SC neurons in hamster are mainly mediated by the nonsynaptic release of this indoleamine.

Animals↗

PubMed1992

Differential effects of peripheral damage on vibrissa-related patterns in trigeminal nucleus principalis, subnucleus interpolaris, and subnucleus caudalis.

Histochemistry for cytochrome oxidase reveals a vibrissa-related pattern in trigeminal nucleus principalis, subnucleus interpolaris, and the magnocellular portion of subnucleus caudalis. This pattern is apparent in late fetal animals and is disrupted by transection of the infraorbital nerve on the day of birth. We recently reported results suggesting that the cytochrome oxidase pattern reflects primary afferent-induced clustering of second order neurons in all of these nuclei. If this conclusion is correct, it should follow that primary afferent lesions made after the cytochrome oxidase pattern became established in the brainstem might have little effect upon it. Accordingly, we transected the infraorbital nerve (the trigeminal branch that supplies the vibrissae) on postnatal days 0-10 and evaluated the vibrissa-related pattern in the brainstem with cytochrome oxidase histochemistry at varying intervals after these lesions. If the infraorbital nerve was sectioned on postnatal days 0-2, the vibrissa-related pattern was absent in trigeminal nucleus principalis, and both subnucleus interpolaris and caudalis. If such lesions were made after postnatal day 9, there was no appreciable effect upon the cytochrome oxidase pattern in any portion of the trigeminal brainstem complex. However, if lesions were made between postnatal days 3 and 8, the density and clarity of the cytochrome oxidase staining pattern were reduced in interpolaris and caudalis, but not in principalis. This difference was not due to differential transganglionic degeneration in these nuclei. Tracing with horseradish peroxidase demonstrated qualitatively equivalent primary afferent losses in principalis, interpolaris, and caudalis. Immunocytochemistry with a monoclonal antibody directed against parvalbumin also demonstrated a vibrissa-related pattern of cell bodies in principalis and interpolaris in rats killed on postnatal day 9 or later ages. The combination of retrograde tracing and immunocytochemistry revealed that the parvalbumin-immunoreactive neurons in principalis projected to thalamus while those in interpolaris were not labelled by tracer injections into the thalamus, midbrain, cerebellum or spinal cord. Infraorbital nerve transections made as late as postnatal day 8 resulted in a sharp decrease in the staining of parvalbumin-positive neurons in interpolaris, but not in principalis. Lesions made on postnatal day 10 had no qualitative effect upon parvalbumin-positive neurons in any portion of the trigeminal brainstem complex. The results of this study support the conclusion that the vibrissa-related cytochrome oxidase pattern in principalis becomes independent of primary afferent input at a very short interval after its initial appearance. In contrast, the patterns in more caudal portions of the trigeminal brainstem complex require maintenance of primary afferent input for a much longer postnatal period.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Evidence for prenatal competition among the central arbors of trigeminal primary afferent neurons.

Previous studies have shown that damage to vibrissa follicles in newborn rats and mice does not alter the brainstem representations of the remaining vibrissa as demonstrated by staining for mitochondrial enzymes such as cytochrome oxidase (CO) succinic dehydrogenase. This study asked whether this lack of effect might be due to the fact that the trigeminal primary afferents in rodents are already quite well developed at birth. We assessed this possibility by using CO staining the evaluate patterns in the brainstems of pre- and postnatal rats. A vibrissa-related pattern began to emerge in trigeminal nucleus principalis and subnucleus interpolaris (Spl) by embryonic day (E-) 19 and appeared fully developed by the day of birth (P-0). We also made partial lesions of the vibrissa pad on E-15-20 and on P-0, killed pups on P-5-7, and measured the size of the CO-stained patches in Spl on both sides of the brainstem. The correspondence between CO patches and clusters of primary afferent terminal arbors was verified in some animals by combining transganglionic horseradish peroxidase tracing and CO staining. Vibrissa pad damage on E-15-18 resulted in significant (20.1-36.9%) increases in the average area of the remaining CO patches in Spl ipsilateral to the lesion. Vibrissa pad damage on E-19, E-20, and P-0 produced small (6.2-8.9%), but insignificant, increases in patch size in Spl ipsilateral to the lesion. We used anatomical and electrophysiological methods to determine whether our lesions altered the trigeminal innervation of surviving vibrissa follicles. We recorded single trigeminal ganglion cells from 12 rats that sustained vibrissa pad lesion on E-17. As in normal rats, all of the 49 vibrissa-sensitive ganglion cells isolated in the lesioned animals were responsive to deflection of one and only one vibrissa. We also dissected 11 deep vibrissal nerves from intact follicles in adult rats that sustained fetal vibrissa pad damage on E-17, and counted numbers of myelinated axons in 1 microns plastic sections. These data were compared with counts from corresponding follicles on the intact side of the face. The average number of myelinated axons innervating follicles in the damaged vibrissa pads was 196.8 +/- 27.9, and that for the corresponding contralateral nerves was 194.6 +/- 25.7. These data suggest that competitive interactions among the central arbors of trigeminal primary afferents in fetal life may influence the development of central vibrissa representations and, further, that lesion-induced central changes need not be correlated with alterations in the peripheral innervation of undamaged follicles.

Animals↗

PubMed1992

Functional influence of interlaminar connections in the hamster's superior colliculus.

The aim of this study was to determine the functional importance of intrinsic connections within the hamster's superior colliculus (SC) in the development of the visual responses of neurons in the deep layers of this nucleus. We used localized injections of lidocaine to block action potentials of fibers that passed through the superficial layers and injections of CoCl2 to block synaptic transmission in these layers. We also determined the morphology of a number of the deep layer cells recorded in these experiments by intracellular injection of HRP. Injection of lidocaine into the superficial layers completely abolished the visual- and/or optic chiasm-evoked responses of all 40 deep layer cells tested. Thus, fibers that either pass through or synapse in the superficial layers are necessary for the visual responses of deep layer neurons. Injections of CoCl2 restricted to the superficial layers significantly reduced the visual responsivity of 86% of 92 deep layer neurons tested and abolished the visual responses of 68% of these cells. Superficial layer injections of CoCl2 were equally effective in reducing the responses of neurons with dendrites that ascended into the superficial layers (all seven cells tested and recovered) and those of cells with dendrites restricted to the deep layers (six of seven cells tested and recovered). Injections of CoCl2 into the deep layers, in the region of the cell being recorded, significantly reduced the visual responses of 59% of 37 cells and abolished the visual responses of 40% of the neurons tested. Deep CoCl2 injections abolished the visual responses of three of four cells with dendrites restricted to the deep layers and only one of four cells with dendrites that ascended into the superficial layers. These results indicate that descending interlaminar axons from visually responsive superficial layer cells may be responsible for the visual responsivity of most neurons in the deep SC layers of hamster. Also, some deep layer neurons in this species may receive effective visual input through their dendrites that ascend into the superficial layers, where they are likely to be contacted by retinal axons or axon collaterals of superficial layer cells.

Animals↗

PubMed1991

Thalamic processing of vibrissal information in the rat. I. Afferent input to the medial ventral posterior and posterior nuclei.

Retrograde tracing with true blue (TB) and diamidino yellow (DY) and anterograde tracing with either wheatgerm agglutinin-conjugated horseradish peroxidase (WGA-HRP) or Phaseolus vulgaris leucoagglutinin (PHA-L) were employed to investigate the projections from trigeminal nucleus principalis (PrV) and trigeminal subnucleus interpolaris (SpI) to their targets in the medial ventral posterior (VPM) and posterior (POm) nuclei of the thalamus. Many more cells in both PrV and SpI were labeled by tracer injections into VPM than into POm. Only a very small number of double-labeled neurons were observed in either PrV or SpI. However, a significantly higher percentage of SpI cells projected to POm or to both POm and VPM than was the case for PrV. Anterograde tracing with WGA-HRP showed that the projections from both PrV and SpI to VPM were much denser than those from the same nuclei to POm. Small injections of PHA-L into either PrV or SpI produced a focus of fairly dense labeling in VPM and much more diffuse terminal labeling in POm. These anatomical data provide evidence for two separate trigeminothalamic pathways, one originating from PrV and the second originating from SpI. Both of these pathways converge and diverge at the thalamic level. That is, information from the PrV pathway and from the SpI pathway are both provided to VPM in a morphologically restricted fashion and to POm in a morphologically widespread fashion.

Afferent Pathways↗

PubMed1991

Thalamic processing of vibrissal information in the rat: II. Morphological and functional properties of medial ventral posterior nucleus and posterior nucleus neurons.

Extracellular recording, intracellular recording, intracellular horseradish peroxidase injection, and receptive field mapping techniques were employed to evaluate the physiological and morphological properties of medial ventral posterior nucleus (VPM) and posterior nucleus (POm) neurons in normal adult rats. Overall, we physiologically characterized 148 VPM and 121 POm neurons. Over 82% of the VPM cells were excited only by deflection of one or more mystacial vibrissae, 10% were activated by displacement of guard hairs, and the remainder were either excited by indentation of the skin or were unresponsive. Less than 40% of the POm cells were activated by vibrissa deflection, 18% were excited by displacement of guard hairs, and another 17% were unresponsive. Most of the rest of the POm cells were excited by stimulation of skin, mucosa, or activation of muscle-related afferents. Small percentages of POm cells responded only to noxious stimulation, were classified as having a wide dynamic range, or were inhibited by peripheral stimulation. Electrical stimulation of either PrV or SpI activated most neurons in both VPM and POm. This excitation was almost invariably followed by a long-lasting hyperpolarization which was generally strong enough to prevent responses to either electrical stimuli delivered in the brainstem or mechanical stimulation of the periphery. The receptive fields of vibrissa-sensitive cells in POm were generally much larger than those of cells in VPM. Data obtained with extracellular recording indicated that VPM and POm cells responded to an average of 1.4 and 4.0 vibrissae, respectively. Intracellular recording from smaller samples of VPM and POm cells demonstrated the existence of inputs that were insufficient to produce spikes from the cell, but did yield epsp's. When both sub- and suprathreshold excitation were considered, the average number of vibrissa in the receptive field of a VPM cell was 2.7 and the value for POm cells became 7.8. HRP-filled neurons recovered in POm (N = 20) generally had much larger dendritic arbors than neurons in VPM (N = 31). For the former cells, the size of the dendritic tree was significantly correlated with the number of vibrissa to which the cell responded; for the latter neurons, it was not.

Afferent Pathways↗

PubMed1991

Birthdates of trigeminal ganglion cells contributing axons to the infraorbital nerve and specific vibrissal follicles in the rat.

Prenatal labelling with [3H]-thymidine was combined with retrograde tracing techniques in adult rats to determine the birthdates of the trigeminal (V) ganglion cells that contributed axons to the infraorbital nerve (ION) and the generation of the subsets of ION cells that innervated specific vibrissae follicles (C-1 and C-5). The V ganglion cells contributing axons to the ION are born between embryonic (E-, E-0 = the day of conception) days 9.5 and 14.5. The percentages (normalized so that they total 100%) of the total V ganglion population born on E-9.5 through E-14.5 were 5.8, 25.7, 19.8, 23.4, 21.0, and 4.4%, respectively. The distribution of birthdates for the V ganglion cells that were retrogradely labelled from the ION closely matched that for the ganglion as a whole. All of these neurons were also born on E-9.5 through E-14.5, and the percentages born on each day were 6.3, 23.6, 18.1, 24.0, 23.6, and 4.4%. Finally, a similar distribution of birthdates was obtained for the V ganglion cells that were retrogradely labelled after injection of retrograde tracers into either the C-1 or C-5 vibrissae follicles. We were unable to detect any distinctive spatial distributions for either all V ganglion or ION cells born on a specific embryonic day. Furthermore, neurons with a given birthdate and that innervated a given follicle were distributed throughout the entire region containing all of the ganglion cells supplying the follicle in question. Therefore, it appears that the V ganglion cells contributing axons to the ION are born over the entire period of ganglion neurogenesis and further that the organization of the ION's innervation of the periphery is not a function of cell birthdate.

Animals↗

PubMed1991

Effects of cortical and thalamic lesions upon primary afferent terminations, distributions of projection neurons, and the cytochrome oxidase pattern in the trigeminal brainstem complex.

Early postnatal lesions of the primary somatosensory cortex alter the vibrissa-related cytochrome oxidase (CO) pattern in nucleus principalis (PrV) of the rat's trigeminal (V) brainstem complex (Erzurumlu and Ebner, '88: Dev. Brain Res. 44:302-308). At present, the reason for this change is not clear. It may be that the corticotrigeminal projection is necessary for the maintenance of vibrissa-related patterns in PrV. However, it is also possible that the loss of the normal pattern of CO activity reflects a change in the organization of brainstem cells resulting from transneuronal retrograde degeneration. In order to address this question, we made lesions of either the primary somatosensory cortex (S-I) or ventrobasal thalamus (VB) in newborn rats and directly assayed distribution of V primary afferents by transganglionic transport of horseradish peroxidase and V-thalamic neurons by retrograde transport of either fluorogold or true blue. Neonatal cortical and thalamic lesions produced no qualitative change in the distribution of primary afferent terminals in either PrV or V subnucleus interpolaris (SpI) beyond that which could be attributed to shrinkage of the brainstem resulting from retrograde degeneration. Most importantly, the "patchy" pattern of terminations observed in normal rats remained apparent in the brain-damaged animals. The normal distribution of V-thalamic neurons in PrV was disrupted by both cortical and thalamic lesions. These cells are normally patterned in a way that matches the distribution of primary afferent terminals and thus that of the mystacial vibrissae. This was not the case in the neonatally brain-damaged rats. Taken together, these results are consistent with the conclusion that neonatal cortical and thalamic lesions disrupt the normal CO pattern in PrV primarily because of their effects upon the patterning of brainstem cells. The present findings demonstrate further that clustering of primary afferents does not require a normal complement of postsynaptic neurons.

Afferent Pathways↗

PubMed1991

A transient projection from the trigeminal brainstem complex to the superficial layers of the hamster's superior colliculus.

Anterograde tracing with the carbocyanine dye, Di-I, was used to describe the normal postnatal development of the projection from the trigeminal (V) brainstem complex to the superior colliculus (SC) in hamster. In adult hamsters, this projection is completely restricted to the deep laminae, primarily the stratum album intermedium. Trigeminal fibers were present in the SC by the day of birth, and at this time, they terminated mainly in the deep layers. However, labelled fibers also extended into the superficial laminae (the stratum griseum superficiale and stratum opticum) reaching as far as the SC surface. Trigeminal projections to the superficial SC laminae were visible as late as postnatal day (P-) 6, but were absent by P-8. During the period when V axons were present in the superficial SC laminae, they could not be detected in the dorsal lateral geniculate nucleus.

Animals↗

PubMed1991

Development of the occipital corticotectal projection in the hamster.

Anterograde and retrograde labelling with the carbocyanine dye, Di-I, was used to assess the development of the visual cortical projection to the superior colliculus (SC) in pre- and postnatal hamsters. Posterior cortical axons arrive in the SC on postnatal (P-) day one (the first 24 hours after birth = P-0) and begin to arborize in the superficial laminae (the stratum griseum superficiale [SGS] and stratum opticum [SO]) within one day after they enter the tectum. Over succeeding days, the density of the projection increases and numerous labelled fibers are visible throughout the depth of the SGS and SO. Beginning on P-6, there is a decrease in the density of labelled fibers in the upper SGS and by P-10, the laminal distribution of the occipital corticotectal pathway appears adult-like. Anterograde tracing with Di-I also revealed the presence of a few corticotectal fibers that crossed the midline in both the SC and posterior commissures to terminate mainly in the superficial tectal laminae contralateral to the injection site. Crossed corticotectal fibers were visible in hamsters aged between P-3 and P-12. Retrograde tracing with Di-I in hamsters killed between P-3 and P-12 demonstrated that both the ipsilateral and crossed corticotectal projections arose exclusively from pyramidal cells in developing lamina V.

Animals↗

PubMed1991

Serotonin immunoreactive neurons are present in the superficial layers of the hamster's, but not the rat's, superior colliculus.

Immunocytochemistry for serotonin (5-HT) was carried out in both hamsters and rats in order to determine whether or not 5-HT-positive cells existed in the superior colliculus (SC) of either species. In both hamster and rat, the superficial and deep SC laminae contained dense networks of 5-HT-positive fibers. The rat's SC contained no 5-HT-positive neurons. In hamster, numerous 5-HT-immunoreactive cells were visible throughout the depth of the stratum griseum superficiale (SGS). These neurons had a variety of morphological characteristics and included marginal cells, horizontal cells, and neurons with vertically oriented dendritic trees. No 5-HT-positive neurons were found in any other portion of the hamster's SC. 5-HT-positive SC cells were observed with antisera from two different sources and they were not seen in animals that were pretreated with reserpine. Pretreatment with fluoxetine (an inhibitor of 5-HT uptake) also resulted in a disappearance of 5-HT-positive neurons in the hamster's SC. This result indicated that "serotonergic" cells in the colliculus of this species are capable of taking up, but probably not synthesizing, this indoleamine. The dorsal and ventral lateral geniculate nuclei (LGNd and LGNv, respectively) both contain numerous 5-HT-positive fibers and both of these structures receive input from the SGS. Combination of retrograde tracing with fluorogold and immunocytochemistry indicated that 5-HT-accumulating SC neurons were not the source of these fibers. Unilateral ablation of the superficial SC laminae also failed to reduce 5-HT immunoreactivity in either the LGNd or LGNv. These results are consistent with the possibility that 5-HT-accumulating cells in the hamster's SC may be interneurons that take up this transmitter after it is released by afferents to this nucleus.

Animals↗

PubMed1991

The source of the transient serotoninergic input to the developing visual and somatosensory cortices in rat.

For approximately the first two weeks of life, dense serotonin immunoreactivity closely matches the pattern of thalamocortical axons innervating both the granular portion of the primary somatosensory cortex and area 17 in rodents [D'Amato et al. (1987) Proc. natn. Acad. Sci. 84, 4322-4326; Fujimiya et al. (1986) J. comp. Neurol. (1986) 246, 191-201; Rhoades et al. (1990) J. comp. Neurol. 293, 190-207]. This serotonin immunoreactivity is not contained in thalamocortical axons [Rhoades et al. (1990) 293, 190-207] but its source has never been demonstrated. In the present study, a variety of approaches were used to address this issue. The combination of electron microscopy and immunocytochemistry showed that all serotonin immunoreactivity in the developing cerebral cortex was contained in axons and that the terminals of many of these fibers made synapses with the dendrites of cortical cells. Treatment with fluoxetine, a specific inhibitor of serotonin uptake, did not result in a loss of the cortical pattern of serotonin immunoreactivity, indicating that immunoreactive fibers were not labeled solely as a result of serotonin uptake. The combination of retrograde tracing from the primary somatosensory cortex and area 17 with immunocytochemistry demonstrated numerous double-labeled cells in nucleus raphe dorsalis and the median raphe nucleus. Smaller numbers of double-labeled neurons were located in the B9 cell group and the region of the lateral midbrain tegmentum. Large electrolytic lesions that included most of the nucleus raphe dorsalis and median raphe nucleus, but which left the B9 group and more caudal serotoninergic cells undamaged, caused either a substantial reduction in density or complete disappearance of the serotonin pattern in both hemispheres. Unilateral electrolytic lesions of the medial forebrain bundle resulted in a loss of the pattern only on the side of the damage. Injection of the neurotoxin 5,7-dihydroxytryptamine directly into the mesencephalon either abolished or substantially reduced the density of the cortical serotonin immunoreactivity. Injections that produced substantial cell loss in the median raphe nucleus, but only minor cell loss in the nucleus raphe dorsalis had little effect upon the cortical pattern of serotonin immunoreactivity. These results indicate that the dense serotonin immunoreactivity which appears transiently in the visual and somatosensory cortices of perinatal rodents is contained in serotoninergic axons that arise from cells in the nucleus raphe dorsalis and perhaps also the median raphe nucleus.

5,7-Dihydroxytryptamine↗

PubMed1991

Numbers of axons innervating mystacial vibrissa follicles in newborn and adult rats.

Electron-microscopic techniques were used to determine the numbers of axons in the deep vibrissal nerves innervating the C1 and C4 follicles in newborn and adult rats. All counts were made from thin sections taken after the nerve had entered the follicle capsule (FC). In newborn animals, the nerves supplying the C1 (n = 10) and C4 (n = 10) follicles contained an average (means +/- standard deviation) of 355.0 +/- 40.0 and 233.9 +/- 19.2 axons, respectively. In the adult animals (n = 10 for C1 and n = 9 for C4), the respective values were 314.4 +/- 26.2 and 233.3 +/- 34.4 axons. There were no significant differences between the values for the counts from the neonates and adults for either follicle (p greater than 0.01, independent t tests). In the vibrissal nerves of neonates, both degenerating axons and occasional growth cones were visible. Such profiles were not observed in the nerves taken from adults.

Aging↗

PubMed1990

Tectospinal neurons in hamster contain glutamate-like immunoreactivity.

Immunocytochemistry with a monoclonal antibody directed against glutamate revealed numerous immunoreactive cells in the hamster's superior colliculus (SC). A large number of these neurons were located in the deep layers and many were in the stratum album intermedium (SAI). These neurons appeared similar to the large multipolar cells that have been shown to project to the cervical spinal cord in this species. The combination of retrograde tracing using either Fluoro-Gold- or FITC-labelled latex beads with immunocytochemistry for glutamate revealed that many of the immunoreactive cells did, in fact, project into the predorsal bundle and extend axons as far as the cervical spinal cord.

Animals↗

PubMed1990

Neonatal infraorbital nerve transection in the rat: comparison of effects on substance P immunoreactive primary afferents and those recognized by the lectin Bandierea simplicifolia-I.

Retrograde tracing, immunocytochemical, and histochemical methods were used to determine the manner in which different classes of trigeminal (V) ganglion cells respond to transection of their axons during infancy. Retrograde tracing with true blue (TB), histochemistry using the plant lectin Bandieraea simplicifolia-I (BS-I), and immunocytochemistry using an antiserum directed against substance P (SP) were carried out in the V ganglion and V brainstem complex of normal adult rats. In the adult V ganglion, 11.9 +/- 1.9% of the cells that sent axons into the infraorbital nerve (ION) contained SP-like immunoreactivity (SPLI) and 26.9 +/- 3.6% bound the lectin BS-I. Only 2.7 +/- 1.6% of ION cells were labelled by both the SP antiserum and BS-I. Transection of the ION on the day of birth had very different effects upon primary afferent neurons containing SPLI and those labelled by BS-I. We have previously shown that such lesions result in a significant expansion of the portion of SpC innervated by primary afferents containing SPLI and we have also provided data consistent with the proposal that ganglion cells recognized by an antiserum directed against SP are more likely than other primary afferent neurons to survive neonatal axotomy. In the present study, combination of retrograde tracing with TB and lectin binding histochemistry showed that cells recognized by BS-I were selectively lost after neonatal ION transection. Only 14.2 +/- 4.4% of the ION ganglion cells that projected into this nerve at the time of the lesion and that survived neonatal axotomy were BS-I positive when the animals reached adulthood. Neonatal ION transection also resulted in a permanent reduction in the density of BS-I binding in SpC. Bandieraea simplicifolia-I binding in the brainstem ipsilateral to the damaged nerve was almost completely gone within 1 day of the nerve transection and recovered only partially by the time the rats were 2 months of age. In alternate sections tested with the SP antiserum, there was a slight reduction in the density of SPLI in the deafferented SpC on postnatal days 4 and 5, but this change never approached that observed for BS-I binding.

Animals↗

PubMed1990

Development and plasticity of the serotoninergic projection to the hamster's superior colliculus.

Immunocytochemical techniques were employed to investigate the normal adult organization, development, and effects of both neonatal and adult eye removal upon the organization of the serotoninergic projection to the hamster's superior colliculus. Immunocytochemistry, both alone and in combination with retrograde tracing with true blue and fluorogold, was used to determine the organization of the serotoninergic projection to the superior colliculus in normal adult hamsters. Immunoreactive fibers were present in all laminae of the superior colliculus, but they were most dense in the lower part of the stratum griseum superficiale, the stratum opticum, the stratum griseum profundum, and the stratum album profundum. When retrograde tracing from the colliculus was combined with immunocytochemistry for serotonin, cells containing both labels were found in the lateral portions of the nucleus raphe dorsalis and also in periaqueductal gray, the median and pontine raphe nuclei, and in the region of the medial lemniscus. Such cells were visible both ipsilateral and contralateral to the injection site. Serotonin immunoreactive fibers were visible in the superior colliculus by embryonic day 14 (2 days prior to birth). On the day of birth, a small number of immunoreactive fibers were present just below the pial surface and others were generally oriented either parallel or orthogonal to the collicular laminae. At this age, there were also many immunoreactive fibers that crossed from one side of the brainstem to the other in the commissure of the superior colliculus. Some serotonin-positive axons appeared to terminate as growth cones in fetal and newborn hamsters. Over the next 2 weeks, the serotoninergic innervation of the SC increased in density and assumed the laminar distribution observed in adult animals. By this age, only a very few immunoreactive fibers were present in the commissure of the superior colliculus. Removal of one eye on either on the day of birth or in adulthood resulted in reorganization of the serotoninergic innervation of the partially deafferented colliculus. There was a marked increase in the density of serotonin-positive fibers in the upper stratum griseum superficiale on the side ipsilateral to the remaining eye. This change was apparent within 2 weeks after enucleation in either neonatal or adult animals. Quantitative analysis demonstrated that the magnitude of this effect was greater after adult enucleation than after neonatal eye removal. Both neonatal and adult enucleation also resulted in an increase in the density of the serotoninergic projection to the dorsal and ventral lateral geniculate nuclei ipsilateral to the remaining eye.

Animals↗