Biomedical subjects

R W Rhoades

Publications and source records attributed to R W Rhoades.

At least 109 records · Page 6Linked to original sources

PubMed1990

Intracellular recording and injection study of corticospinal neurons in the rat somatosensory cortex: effect of prenatal exposure to ethanol.

The effects of prenatal exposure to ethanol on the structure and function of corticospinal neurons was investigated. The subjects were the 3-4-month-old offspring of hooded rats fed a nutritionally balanced liquid diet containing 6.7% (v/v) ethanol (Et), pair-fed a nutritionally matched isocaloric diet (Ct), or fed chow and water (Ch). Corticospinal neurons in primary somatosensory cortex were examined by intracellularly recording and filling cells that were driven by antidromic stimulation of the pyramidal decussation. In the control rats, corticospinal neurons comprised a homogeneous morphophysiological population. Morphologically, all of the antidromically driven cells examined were pyramidal neurons with cell bodies in layer Vb. The dendrites of these neurons were spinous and branched within layers I, IV, and V. Their axons arborized within layers IV, V, and VI and some collaterals extended laterally for distances up to 2.6 mm from the cell body. The mean conduction latency was 3.6 and 3.4 msec for Ch- and Ct-treated rats, respectively. In Et-treated rats, corticospinal neurons constituted a heterogeneous population. The laminar distribution of the corticospinal neurons in Et-treated rats was broad; the cell bodies of labeled neurons were in layers II, IV, V, and VI. The dendrites of layer Vb neurons were spinous; however, many of the spines appeared dysmorphic and the density of spines was significantly greater (32%) in Et-treated rats than in Ct-treated rats. Although the dendritic branching pattern for layer Vb neurons was similar to that described for the controls, a Sholl analysis showed that the complexity and extent of their dendritic trees were significantly greater in Et-treated rats. The axons of all layer Vb neurons in Et-treated rats had long horizontal processes that arborized in layers IV-VI, and some neurons also had an array of collaterals that ascended to layer I. The mean conduction latency for layer Vb neurons was 3.9 msec. The structure and function of ectopic neurons (those in layers II, IV, Va, Vc, and VI) in Et-treated rats differed markedly from those of the layer Vb neurons. Morphologically, the dendritic and axonal fields of these neurons were narrower than for the layer Vb neurons, and the ectopic neurons had a mean conduction latency of 7.1 msec. The heterogeneity of the population of corticospinal neurons in Et-treated rats may result from the effects of ethanol on early events in neuronal development such as neuronal generation and migration.

Animals↗

PubMed1990

Organization and actions of the noradrenergic input to the hamster's superior colliculus.

Immunocytochemistry using antisera directed against dopamine-beta-hydroxylase (DBH) was used to determine the organization of the noradrenergic (NE) input to the hamster's superior colliculus (SC). Immunocytochemistry for DBH was combined with retrograde transport of fluorogold (FG) to determine the sources of NE input to SC. Microiontophoretic techniques were used together with extracellular single unit recording and receptive field mapping techniques to determine the manner in which NE influenced the responses of individual SC neurons. The hamster's SC contained numerous DBH-positive fibers but no immunopositive cells. These fibers formed a plexus that was most dense in the lower stratum griseum superficiale (SGS). The density of DBH-positive fibers was very low in the stratum opticum (SO) and increased in density in the stratum griseum intermediale (SGI) and the other deep layers. When FG injections into the SC were combined with immunocytochemical detection of DBH, double-labeled cells were observed in the contralateral locus ceruleus. DBH-positive neurons were observed in several other portions of the mesencephalon and pons, but none of these were labelled with FG. The effects of NE iontophoresis were assessed for a total of 135 SC neurons. In 74% (N = 100), NE reduced spontaneous and/or stimulus evoked activity. In 3% (N = 4 cells), NE increased activity, and in 23% (N = 31 cells) it had no effect. These percentages were essentially the same for superficial layer visual cells and somatosensory neurons in the deep laminae. The effect of NE iontophoresis upon signal to noise ratios was assessed for 46 visual and 56 somatosensory neurons. For 54% (N = 25) of the visual cells and 16% (N = 9) of the somatosensory cells, NE iontophoresis decreased signal to noise ratios. For 13% (N = 6) of the visual cells and 21% (N = 12) of the somatosensory cells, NE iontophoresis increased signal to noise ratios. The effects of NE on the responsivity of SC neurons were antagonized by propranolol (86% of the 21 cells tested), sotalol (67% of the six cells tested), and atenolol (effective in the single cell tested). All these agents are beta-adrenergic antagonists. The single alpha-adrenergic antagonist that we evaluated, corynanthine, potentiated the effects of NE on the responsivity of the two SC neurons that we tested.

Action Potentials↗

PubMed1990

Topography of the facial musculature within the facial (VII) motor nucleus of the neonatal rat.

WGA-HRP, HRP and fluorescent tracers were used to determine the representation of the facial muscles in the facial motor nuclear complex (FMNC) of the newborn rat. Tracer injections of the superficial cervical and anterior mandibular portions of platysma, the orbicularis oculi muscle, the nasolabial musculature and the posterior auricular musculature revealed an adult-like topographic organization across FMNC subnuclei. Tracer delivery to individual vibrissa follicle loci of the whiskerpad also demonstrated an adult-like musculotopic organization within the lateral subnucleus.

Animals↗

PubMed1990

Topographic organization of the peripheral projections of the trigeminal ganglion in the fetal rat.

Retrograde tracing with true blue (TB) and diamidino yellow (DY) was used to determine the topography of the peripheral projections of the trigeminal (V) ganglion in rats on embryonic day 16 (E-16; E-0 was the day of conception). On E-16, the earliest age at which we were able to accomplish retrograde tracing successfully, the topographic organization of the V ganglionic projection to the periphery was quite adult-like. Cells projecting to the vibrissa pad were restricted to the ophthalmic-maxillary portion of the ganglion, with those innervating dorsal row follicles located medially and those supplying ventral row follicles located laterally. Injections of tracer into ophthalmic skin and/or the cornea labeled cells that were tightly clustered in the most dorsal and anteromedial portion of the ophthalmic-maxillary region. Injections of tracer into the lower jaw or the skin just rostral to the ear labeled cells that were restricted to the lateral, mandibular part of the ganglion. None of the combinations of injections we carried out resulted in large numbers of double-labeled V ganglion cells. Injection of TB into the vibrissa pad and DY into the upper lip produced a small number of double-labeled ganglion cells. This was also the case for paired injections of TB and DY into the lower jaw and lip, respectively. No more than 15 such cells were observed in a ganglion. These findings suggest that the substantial cell death that has been reported to occur in prenatal V ganglion development (Davies and Lumsden, 1984) is probably not involved in the correction of major peripheral targeting errors by the axons of V ganglion cells.

Animals↗

PubMed1990

Trigeminal projections to contralateral dorsal horn: central extent, peripheral origins, and plasticity.

Prior studies have documented a trigeminal (V) mandibular primary afferent projection to the dorsomedial portion of the contralateral medullary and cervical dorsal horns in cat, hamster, and rat. We now report the existence of a much more substantial V ophthalmic primary afferent projection to the ventrolateral portion of contralateral medullary and cervical dorsal horns in rat. Horseradish peroxidase (HRP) injections into the V ganglion or V brainstem complex anterogradely labeled a fascicle of primary afferent axons that exited the caudal ventrolateral V spinal tract to form a rostrocaudally continuous, transversely oriented, V primary afferent decussation. These fibers terminated most heavily in laminae III-V of the ventrolateral dorsal horn in contralateral caudal medulla and the first and second cervical segments. Retrograde tracing with diamidino yellow (DY) or fluorogold and anterograde tracing with Phaseolus vulgaris leucoagglutinin also demonstrated a substantial commissural projection of central origin in medullary dorsal horn laminae I-VII. The latter projection had a more diffuse trajectory and termination pattern than that of the V primary afferent decussation. Unilateral HRP injections into medullary and cervical dorsal horns also retrogradely labeled V primary afferent collaterals contralateral to the injection site in corresponding regions of dorsal horn, and also in ventromedial interpolaris, oralis, and principalis, rostral to their decussation. Axons (1.5 +/- 0.8 microns mean diameter; 0.4-3.9 microns range) therefore terminated both ipsi- and contralateral to their cells of origin. These HRP injections also labeled an average of 40.4 +/- 13.0 V ganglion cells (mean +/- SD, corrected for split somata) in dorsomedial, ophthalmic regions of the contralateral ganglion. Their mean diameter was slightly larger than that of cells labeled ipsilaterally (29.9 vs. 26.3 microns). Double-labeling studies assessed possible ophthalmic receptor surfaces innervated by centrally crossing primary afferents. DY was injected into right medullary and cervical dorsal horns, and HRP was applied to either the left cornea, the ethmoid nerve, or the dura overlying cerebral cortex. Though DY labeled from 75 to 125 left ganglion cells per animal, no cells were double-labeled. All of these findings suggest that nociceptive-specific ganglion cells are not a source of the crossed ophthalmic primary afferent projection. Unilateral transection of the infraorbital nerve on the day of birth did not alter the crossed primary afferent projection to the partially deafferented side of the brainstem. This is further evidence of an absence of central sprouting in spared V primary afferents following neonatal V deafferentation.

Afferent Pathways↗

PubMed1990

Cell structure and response properties in the trigeminal subnucleus oralis.

Extra- and intracellular recording, electrical stimulation, receptive field mapping, and horseradish peroxidase injection techniques were used to study the structure of functionally identified neurons in trigeminal (V) brainstem subnucleus oralis of the rat. Of 15 heavily labeled cells located within oralis, 4 were local-circuit neurons with receptive fields restricted to either an incisor, guard hairs, one vibrissa, or deep facial tissue (nociceptors). Their morphologies were highly varied, with expansive and spiny dendritic trees and recurrent and intersubnuclear axon collaterals. Oralis local-circuit neurons therefore most closely resembled non-vibrissa-sensitive local-circuit cells in adjacent subnucleus interpolaris. Six other stained cells projected to contralateral thalamus, and two others projected to ipsilateral cerebellum. They typically had intramodality convergent receptive fields (i.e., spanning more than one receptor organ, such as multiple vibrissae or teeth) with widespread dendritic trees, and were therefore indistinguishable from similarly projecting cells in interpolaris. Two other cells projected to the ipsilateral spinal cord, as well as other V brainstem subnuclei. One of these responded to high-threshold mechanical stimulation of teeth; the other was discharged by deflection of one mystacial vibrissa. Their dendrites were very widespread and ended in spiny and bulbous appendages. Local axon collaterals were also extensive. The remaining oralis cell had two axons, one projecting to the thalamus, the other to the spinal cord. Its receptive field expressed convergence from multiple receptor organs, including vibrissae, guard hairs, and skin. Its somadendritic morphology was similar to that of oralis cells projecting only to thalamus. We conclude that, with some exceptions, the extensive dendritic trees, axon branching, convergence, and functional diversity of oralis cells approximate those described previously for functionally equivalent neurons in interpolaris (Jacquin et al., 1989a,b). Such anatomical and physiological properties are rarely seen, however, in nucleus principalis (Jacquin et al., 1988a). The structure and function of three atypical principalis cells with structural and functional characteristics typical of oralis cells are also described. It is argued that such cells are rostrally displaced oralis cells.

Afferent Pathways↗

PubMed1990

Intersubnuclear connections within the rat trigeminal brainstem complex.

Prior intracellular recording and labeling experiments have documented local-circuit and projection neurons in the spinal trigeminal (V) nucleus with axons that arborize in more rostral and caudal spinal trigeminal subnuclei and nucleus principalis. Anterograde tracing studies were therefore carried out to assess the origin, extent, distribution, and morphology of such intersubnuclear axons in the rat trigeminal brainstem nuclear complex (TBNC). Phaseolus vulgaris leucoagglutinin (PHA-L) was used as the anterograde marker because of its high sensitivity and the morphological detail provided. Injections restricted to TBNC subnucleus caudalis resulted in dense terminal labeling in each of the more rostral ipsilateral subnuclei. Subnucleus interpolaris projected ipsilaterally and heavily to magnocellular portions of subnucleus caudalis, as well as subnucleus oralis and nucleus principalis. Nucleus principalis, on the other hand, had only a sparse projection to each of the caudal ipsilateral subnuclei. Intersubnuclear axons most frequently traveled in the deep bundles within the TBNC, the V spinal tract, and the reticular formation. They gave rise to a number of circumscribed, highly branched arbors with many boutons of the terminal and en passant types. Retrograde single- or multiple-labeling experiments assessed the cells giving rise to TBNC intersubnuclear collaterals. Horseradish peroxidase (HRP) and/or fluorescent tracer injections into the thalamus, colliculus, cerebellum, nucleus principalis, and/or subnucleus caudalis revealed large numbers of neurons in subnuclei caudalis, interpolaris, and oralis projecting to the region of nucleus principalis. Cells projecting to more caudal spinal trigeminal regions were most numerous in subnuclei interpolaris and oralis. Some cells in lamina V of subnucleus caudalis and in subnuclei interpolaris and oralis projected to thalamus and/or colliculus, as well as other TBNC subnuclei. Such collateral projections were rare in nucleus principalis and more superficial laminae of subnucleus caudalis. TBNC cells labeled by cerebellar injections were not double-labeled by tracer injections into the thalamus, colliculus, or TBNC. These findings lend generality to currently available data obtained with intracellular recording and HRP labeling methods, and suggest that most intersubnuclear axons originate in TBNC local-circuit neurons, though some originate in cells that project to midbrain and/or diencephalon.

Animals↗

PubMed1990

Relationships between physiological and morphological properties of retinocollicular axons in the hamster.

Intracellular recording and HRP injection were used to characterize retinocollicular axons in the hamster. Eighteen retinotectal axons were filled with HRP. The type of axon recovered most often (N = 10) had a receptive field with center-surround organization, gave sustained responses to flashed spots, had linear spatial summation, and responded only to more slowly moving stimuli. These fibers had a mean axonal diameter of 0.58 microns (SD = 0.21) and an average conduction latency of 3.4 msec (SD = 1.2) to optic chiasm (OX) stimulation. They gave rise to circular or vertically elongated arbors with an average cross-sectional area of 33,238 microns2 (SD = 12,763) and were almost completely restricted to the stratum griseum superficiale (SGS). We recovered 6 fibers with very different structural and functional properties. The receptive fields of these axons also had center-surround organization, but gave phasic responses to flashed stimuli, had nonlinear spatial summation, and responded to rapidly moving stimuli. These axons had an average diameter of 0.84 micron (SD = 0.09) and an average latency of 2.1 msec (SD = 0.40) to OX stimulation. They had elongated arbors with an average cross-sectional area of 78,045 microns2 (SD = 14,252) and innervated the SGS, the stratum opticum (SO), and upper stratum griseum intermediale (SGI). We also recovered 2 fibers that had thin (0.3 and 0.6 micron) axons and latencies of 4.2 and 3.6 msec to OX stimulation. They both gave rise to horizontally oriented arbors in the stratum zonale (SZ) and upper SGS.

Animals↗

PubMed1989

Organization of the projections from the trigeminal brainstem complex to the superior colliculus in the rat and hamster: anterograde tracing with Phaseolus vulgaris leucoagglutinin and intra-axonal injection.

Anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHA-L) and intra-axonal recording and injection techniques were employed to describe the projection from the trigeminal (V) brainstem complex to the deep laminae of the superior colliculus (SC) in the hamster and the rat. The organization of these projections was the same in the two species. Deposits of PHA-L into V nucleus principalis (PrV) produced labelled axons and boutonlike swellings in the lower stratum griseum intermediale (SGI) and upper stratum album intermedium (SAI) in the SC bilaterally. Plots of boutonlike swellings indicated that the terminals of this projection were arrayed in clusters. Nucleus principalis also projected to the stratum griseum profundum (SGP) and stratum album profundum (SAP). This deeper projection did not terminate in clusters and it was most prominent in the lateral SC. The ipsilateral PrV-SC projection appeared to arise mainly from axons that recrossed the midline at the level of the SC commissure. Reconstruction of individual PHA-L labelled fibers demonstrated that single axons gave rise to terminals on both sides of the midline. Deposits of PHA-L into V subnucleus interpolaris (SpI) yielded results that were identical to those obtained with PrV injections with one exception: none of these deposits produced any labelled terminals in the ipsilateral SC. Deposits of PHA-L into V subnucleus caudalis (SpC) produced only sparse labelling in SC. Most labelled swellings were located in the SGP and SAP and they were visible only in the SC contralateral to the PHA-L injection site. Single axons arising from cells in SpI were recorded and injected with horseradish peroxidase (HRP) in the hamster's SC. These fibers all responded to stimulation of multiple mystacial vibrissae and gave rise to 2-5 clusters of bouton-like swellings in the lower SGI and upper SAI.

Action Potentials↗

PubMed1989

Structure-function relationships in rat brainstem subnucleus interpolaris: VII. Primary afferent central terminal arbors in adults subjected to infraorbital nerve section at birth.

Prior studies in this series have clarified the normal organization of subnucleus interpolaris and the response of higher-order neurons to neonatal deafferentation. The present report describes the response of individual rat trigeminal primary afferents to transection of the infraorbital (IO) nerve on the day of birth. Physiologically characterized afferents in adult animals were labeled by intraaxonal injection of horseradish peroxidase (HRP). Qualitative and quantitative examination of the interpolaris collaterals of 62 recovered neurons revealed: 1) an increase in the transverse area of vibrissa afferent terminal arbors, 2) a decrease in the number of boutons per collateral of vibrissa afferents, 3) a decrease in the bouton density of both vibrissa and guard hair primary afferents, 4) a decrease in the circularity of guard hair afferent arbors, 5) an increase in the number of collaterals given off by nociceptive fibers, and 6) abnormal primary afferent topography. The data support the hypothesis that vibrissa afferents respond to neonatal axotomy by central arbor expansion, but not by sprouting. Arbor expansion provides a morphological substrate for the abnormal histochemical staining patterns seen in animals subjected to IO damage in the early postnatal period.

Animals↗

PubMed1989

A substance P projection from the superior colliculus to the parabigeminal nucleus in the rat and hamster.

Immunocytochemical staining with antisera directed against substance P (SP) demonstrated the existence of numerous immunoreactive neurons throughout the mediolateral and rostrocaudal extents of the stratum griseum superficiale (SGS) of the superior colliculus (SC) of both rat and hamster. In both of these species, very dense SP-like immunoreactivity (SPLI) was also visible in the parabigeminal nucleus. Combination of retrograde tracing with True blue or Fluorogold and immunocytochemistry demonstrated that SP-positive SC neurons projected to the parabigeminal nucleus in both hamster and rat. Retrogradely labelled and double-labelled cells were most numerous in the rostromedial portion of the SC and rare in the caudal portion of the colliculus. Destruction of the superficial layers of the SC resulted in a virtually complete loss of SPLI in the ipsilateral parabigeminal nucleus in both species. SPLI was also visible in two other targets of the superficial SC laminae: the intergeniculate leaflet and the ventral lateral geniculate nucleus. Ablation of the dorsal SC laminae did not reduce SPLI in either of those nuclei. Our results thus indicate that at least some tectoparabigeminal neurons in hamster and rat contain SPLI and further that the SC appears to be the sole source of SP-positive input to this nucleus.

Animals↗

PubMed1989

Effect of fetal infraorbital nerve transection upon trigeminal primary afferent projections in the rat.

Transganglionic tracing with a combination of horseradish peroxidase (HRP) and wheat germ agglutinin-conjugated HRP (WGA-HRP) was employed to compare the trigeminal (V) innervation of the brainstem in adult rats that sustained transection of the infraorbital nerve (ION) on either the day of birth or just prior to the beginning of the 17th embryonic day (E-17). The same methods were also employed to assess the effects of such lesions upon the innervation of the brainstem by the lingual, inferior alveolar, mylohyoid, and auriculotemporal V branches. Previous experiments (Chiaia et al.: Dev. Brain Res. 36:75-88, '87) showed that application of HRP and WGA-HRP to the ION in normal adult rats (N = 3) labelled 12,553 +/- 1,455 (mean +/- s.d.) V ganglion cells while application of these tracers to the regenerated ION after neonatal transection (N = 9) labelled 5,001 +/- 1,287 ganglion cells. Application of HRP and WGA-HRP to the regenerated ION in adulthood (N = 6) after fetal transection labelled 5,476 +/- 3,056 ganglion cells. Thus, the numbers of ganglion cells giving rise to the regenerated ION after fetal and neonatal transection were equivalent (P greater than .05). The central projections of the ION after fetal transection were qualitatively different from those observed after neonatal injury. After neonatal transection, the central terminal field of regenerated ION fibers in adulthood is almost completely restricted to layers I and II of subnucleus caudalis (SpC; Jacquin and Rhoades: Brain Res. 269:137-144, '83; Chiaia et al.: Dev. Brain Res. 36:75-88, '87). After fetal transection, regenerated ION axons terminate heavily in all portions of the V brainstem complex. After neonatal ION transection, we (Jacquin and Rhoades: J. Comp. Neurol. 235:129-143, '85) have been unable to detect central sprouting of undamaged V mandibular axons by means of transganglionic tracing with HRP and WGA-HRP. Such sprouting was evident in both V subnucleus interpolaris (SpI) and SpC after fetal ION transection. We carried out one additional experiment to determine whether ION ganglion cells that survived fetal axotomy were more resistant to axonal damage than the population of neurons that normally contribute to this nerve on the day of birth. Rats (N = 5) sustained transection of the ION on E-17 and again on the day of birth. The regenerated ION was then labelled with HRP and WGA-HRP when the animals reached adulthood.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗

PubMed1989

Structure-function relationships in the rat brainstem subnucleus interpolaris: VI. Cervical convergence in cells deafferented at birth and a potential primary afferent substrate.

Possible substrates for peripheral injury-induced receptive field (RF) changes were assessed in the trigeminal (V) subnucleus interpolaris (SpVi). In adult rats with infraorbital nerve section at birth, 449 cells were studied ipsilateral to the lesion by using electrophysiological methods. Of these, 33 (7.4%) had RFs that included facial vibrissae, guard hairs, and skin, as well as ipsilateral regions normally innervated by cervical primary afferents (ear, neck, shoulder, arm, forepaw). Such non-V convergence was never seen in 373 normal SpVi cells or in 641 V ganglion cells ipsilateral to the lesion. SpVi cells with cervical RFs discharged to V ganglion shocks and their latencies (1.6 +/- 0.7 ms, mean +/- s.d.) did not differ from normal (1.4 +/- 0.5). Most (71%) projected to the thalamus. None were nociceptive-biased, and many had unusually discontinuous RFs (48%). Possible pathways by which cervical inputs might reach SpVi neurons were investigated in additional anatomical and electrophysiological experiments. Eight SpVi cells with cervical RFs were intracellularly labeled with HRP. Although all had dendrites that were polarized toward SpVi regions containing spared mandibular and/or ophthalmic primary afferents, none had dendrites which extended out of SpVi. In other neonatally nerve-damaged adults, WGA-HRP was injected bilaterally into forepaw, arm, and shoulder regions. Transganglionic transport was restricted to normal targets. However, WGA-HRP injections into SpVi retrogradely labeled a total of 46 +/- 20 (mean +/- s.d.) cells in ipsilateral C1-3 dorsal root ganglia, and 24 +/- 8 cells in C4-8 ganglia. In controls, labeled cells were seen only in C1-3 ganglia (32 +/- 9). The distribution and number of labeled cells in the somatosensory cortex did not differ in experimental and control cases. No labeled cells were visible in the dorsal column nuclei of either the normal or experimental rats. Thus, retrograde labeling studies suggest that a cervical primary afferent projection to SpVi is a potential substrate for cervical convergence expressed in neonatally deafferented SpVi cells.

Action Potentials↗

PubMed1989

Organization of the projection from the superficial to the deep layers of the hamster's superior colliculus as demonstrated by the anterograde transport of Phaseolus vulgaris leucoagglutinin.

Anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHA-L) was employed to describe the projection from the superficial to the deep layers of the hamster's superior colliculus (SC). Deposits of PHA-L in the stratum griseum superficiale (SGS) resulted in labelled terminal swellings in the stratum opticum and all of the deep laminae (the stratum griseum intermediate [SGI], stratum albumin intermedium [SAI], stratum griseum profundum [SGP], and stratum albumin profundum [SAP]). Labelled terminals were also visible in the periaqueductal gray (PAG). Reconstructions of individual axons showed that many collateral in the deep laminae arose from axons that projected to targets outside the colliculus. The projection from the superficial to the deep laminae had a loose topographic organization, and the trajectories of interlaminar axons were generally deflected laterally from "projection" lines that were orthogonal to the SC surface. Physiological recording and receptive field mapping were used to determine actual projection lines, which connect neurons in the superficial and deep layers that have receptive fields with the same elevation. These projection lines closely matched the trajectory of the pathway from the superficial to the deep laminae.

Animals↗

PubMed1989

Structure-function relationships in rat brainstem subnucleus interpolaris: III. Local circuit neurons.

Intracellular recording, electrical stimulation, receptive field mapping, and intracellular injection of horseradish peroxidase were used to assess the response properties, collateral projections, and morphology of 44 local circuit (LC) neurons in the subnucleus interpolaris (Sp Vi) of the trigeminal brainstem complex of the rat. LC neurons were defined as those with axons restricted to brainstem areas receiving trigeminal primary afferent fibers. Thus, none were antidromically activated from the thalamus, tectum, or cerebellum, and their axons could be seen terminating exclusively within the trigeminal brainstem complex or reticular formation. All neurons sampled were discharged by innocuous or noxious mechanical stimulation of a restricted portion of the face or mouth. They were classified functionally as sensitive to vibrissae (N = 22), nociceptors (N = 9), guard hairs (N = 7), hairy skin (N = 3), or periodontia (N = 3). Fifty percent of the stained neurons were vibrissa sensitive. Twenty-one of these 22 responded to deflection of only one vibrissa. The remaining functional groups also had small receptive fields. Intracellular staining revealed a consistency in vibrissa-sensitive LC morphology. Somata were small to medium in size and multipolar. Their axons had an initial transverse trajectory and gave off recurrent collaterals which arborized extensively in the region of the soma. The parent axon then bifurcated. One branch traveled rostrally to subnucleus principalis while the other branch traveled caudally to subnucleus caudalis. The branches periodically sent collaterals into regions of the trigeminal complex corresponding to the transverse position of the soma. Dendrites extended 440 +/- 140 microns rostrocaudally, forming a tree with a transverse perimeter of 459 +/- 226 microns. Distal dendrites were thin and sinuous, had few spines, and extensively arborized adjacent to the soma. They ended in multiple swellings connected by slender processes. The stereotyped morphology of vibrissa-sensitive LC neurons differed from the variable morphologies of LC neurons activated by nociceptors, guard hairs, hairy skin, or periodontia. Although no group of neurons in one of these categories displayed a distinguishing morphological characteristic, they collectively had features which distinguished them from the vibrissa-sensitive neurons. Non-vibrissa-responsive neurons generally had more expansive, but less circular, dendritic and recurrent axonal arbors; dendrites had more spines, and axons often sent endings into the reticular formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1989

Structure-function relationships in rat brainstem subnucleus interpolaris: IV. Projection neurons.

In a companion paper (Jacquin et al., '89), the structure and function of local circuit (LC) neurons in spinal trigeminal (V) subnucleus interpolaris (Sp Vi) were described. The present report provides similar data for 44 projection neurons in Sp Vi. Of these, 25 thalamic, 16 cerebellar, 2 superior collicular, and 1 inferior olivary projecting neurons were studied. The majority responded to vibrissa(e) deflection, and all except 4 of these had multivibrissae receptive fields. The remainder were responsive to either guard hair deflection or indentation of glabrous skin. Latencies to V ganglion shocks were suggestive of monosynaptic activation from the periphery. Sp Vi projection neurons were topographically organized in a manner consistent with that of their primary afferent inputs. Nonvibrissa sensitive cells had diverse morphologies. Morphometric analyses of the more heavily sampled thalamic and cerebellar projecting, vibrissa(e)-sensitive cells indicated the following. (1) As compared to LC neurons, projection neurons had bigger receptive fields, cell bodies, dendritic trees, and axons; less circular dendritic trees; a greater preponderance of spiny dendrites and fewer axon collaterals in Sp Vi. (2) Dendritic tree extent correlated significantly with receptive field size, thus suggesting that dendritic tree size is one mechanism contributing to receptive field size in vibrissae-sensitive projection neurons. (3) V thalamic cells had significantly bigger receptive fields and dendritic trees, and also give off more local axon collaterals, than V cerebellar neurons. Collicular and inferior olivary projecting neurons shared structural and functional attributes with other Sp Vi long-range projecting cells. Structure-function relationships exist for vibrissa-sensitive projection neurons in Sp Vi. The relevant parameters correlating with projection neuron morphology are receptive field size and projection status, whereas for Sp Vi LC neurons the relevant correlative parameter is peripheral receptor association.

Action Potentials↗

PubMed1989

The orientation of horizontal cell dendrites in the superior colliculus of the hamster: an analysis based on three-dimensional reconstruction of intracellularly injected neurons.

We have employed intracellular injection of horseradish peroxidase (HRP) and 3-dimensional, computer-assisted reconstruction to delineate the organization of the dendrites of horizontal cells in the superficial laminae (the stratum griseum superficiale-SGS, and stratum opticum-SO) of the hamster's superior colliculus. Fifteen well-filled cells were analyzed. The dendrites of these cells were generally parallel to the frontal plane. An average of 74.8 +/- 13.0% of the total dendritic arbor of the recovered horizontal cells was located within 30 degrees of this plane. The long axis of horizontal cell dendritic trees deviated an average (mean +/- s.d.) of 21.7 +/- 13.2 degrees from the frontal plane and the average extent of the dendritic tree in this plane was 637 +/- 216 microns. This differed significantly from the average dendritic extent in the rostrocaudal axis (358 +/- 146 microns, p less than 0.001). In some cases, portions of the dendritic arbors of horizontal cells appeared to be oriented along lines of isoelevation or isoazimuth of the visual field representation in the superficial laminae. For other cells, there was no clear relationship between dendritic orientation and the visual field map.

Animals↗

PubMed1989

Neonatal transection alters the percentage of substance-P-positive trigeminal ganglion cells that contribute axons to the regenerate infraorbital nerve.

Neonatal transection results in a marked reduction of the number of trigeminal (V) ganglion cells that contribute axons to the regenerate infraorbital nerve (ION; Jacquin and Rhoades, 1985; Chiaia et al., 1987). Such lesions also produce a profound deafferentation of the V brain stem complex that appears to spare the innervation of layers I and II of subnucleus caudalis (SpC) by substance-P-positive (SP-positive) primary afferents (Jacquin and Rhoades, 1985; Rhoades et al., 1988). In the present study, we combined retrograde tracing with immunocytochemistry to determine whether neonatal transection of the ION alters the percentage of SP-positive V ganglion cells that contribute axons to this V branch upon regeneration. In V ganglia ipsilateral to the intact ION (n = 8), 11.6% +/- 3.2% of the cells labeled after application of true blue (TB) to the ION were also SP-positive. In ganglia ipsilateral to the neonatally damaged nerve (n = 8), 18.6% +/- 4.7% of the cells labeled after application of TB to the regenerate ION were also SP-positive (p less than 0.001). We also compared the SP content of intact ganglia (n = 10) with that of ganglia ipsilateral to the damaged nerve (n = 10) by means of radioimmunoassay. The normal V ganglia contained (mean +/- SD) 3496 +/- 774 pg SP/mg protein. The value for the ganglia ipsilateral to the damaged nerve was 5533 +/- 1746 pg SP/mg protein (p less than 0.01). There was no significant difference between SP levels on the control and partially deafferented sides of the brain stem in neonatally nerve-damaged adult rats. In one additional experiment, we injected TB into both vibrissa pads of seven rats on the day of birth prior to transection of the ION. After an 8-hr delay, the nerve on one side was then cut and allowed to regenerate, and both V ganglia were then processed for immunocytochemistry. On the nerve-damage side, 25.8% of the TB-labeled cells were SP-positive. The value for the intact side was 12.0% (p less than 0.000001). This result demonstrated that the lesion-induced change in the percentage of SP-positive ION cells was not the result of either late-growing axons from SP-positive ganglion cells that may have been missed by our nerve cuts or collateral sprouting into the regenerate ION by undamaged SP-positive ganglion cells.

Animals↗