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R W Rhoades

Publications and source records attributed to R W Rhoades.

At least 73 records · Page 4Linked to original sources
PubMed1994

Effect of serotonin depletion on vibrissa-related patterns of thalamic afferents in the rat's somatosensory cortex.

To investigate the role of 5-HT in the development of the somatosensory cortex, this amine was depleted in newborn (P-0) rats with a single subcutaneous injection of the toxin 5,7-dihydroxytryptamine (5,7-DHT) and thalamocortical organization was assayed by application of the carbocyanine dye Di-I to the thalamocortical radiations or ventrobasal thalamus, or by staining cortical sections for AChE or cytochrome oxidase (CO). High-performance liquid chromatographic analysis of cortices from animals killed on P-6 or P > 60 demonstrated that 5,7-DHT treatment resulted in 85.04 +/- 12.6% and 72.5 +/- 1.5% reductions in cortical 5-HT, respectively. Alternate cortices from the brains of animals killed on P-6 processed for 5-HT immunoreactivity demonstrated a complete absence of the vibrissa-related pattern of immunoreactivity and only a small number of coarse immunoreactive axons. The 85% depletion of 5-HT did not alter the somatotopic organization of thalamocortical afferents in animals killed on P-6 or P > 60, but it did cause 30.5 +/- 7.3% and 19.1 +/- 3.7% reductions in the cross-sectional areas of the patches of thalamocortical afferents corresponding to the long mystacial vibrissae (p < 0.05). These reductions were not associated with significant reductions in either brain or cortical weight or with decreases in the dimensions of the thalamic representation of the vibrissa follicles. These results indicate that 5-HT plays a significant role in the development of the thalamic innervation of the primary somatosensory cortex.

5,7-Dihydroxytryptamine↗
PubMed1994

Peripheral influences on the size and organization of somatotopic representations in the fetal rat cortex.

Nerve lesions at different fetal ages and on the day of birth were used to determine the role of the periphery in establishing territories devoted to representations of different portions of the body surface in rat somatosensory cortex. Transection of the infraorbital nerve (ION), the trigeminal branch that supplies the whisker pad, resulted in a significant reduction in the area within the primary somatosensory cortex devoted to the representation of the mystacial vibrissae in fetal, but not newborn, rats. Such lesions in fetal, but not neonatal, rats also resulted in significant increases in the cortical area devoted to the representation of the lower lip and jaw. There was a significant positive correlation between the reduction in the vibrissae representation and the expansion of that of the lower lip and jaw. Damage to the ION in either neonatal or fetal rats failed to increase significantly the amount of cortex devoted to the representation of the forepaw. These results indicate that the primary afferent innervation of the periphery does influence the amounts of cortex devoted to representations of different parts of the body surface and that the representation of one region can expand significantly when that of another body part is reduced.

Animals↗
PubMed1993

NGF augmentation rescues trigeminal ganglion and principalis neurons, but not brainstem or cortical whisker patterns, after infraorbital nerve injury at birth.

Prior studies indicate that neonatal nerve injury kills many trigeminal (V) first- and second-order cells, and interrupts pattern formation in the brainstem and cerebral cortex. Yet it is not known whether effects upon cell survival and pattern formation are causally related. To determine whether axotomized V ganglion cells can be rescued by an exogenous trophic agent, rats received 5 mg/kg of nerve growth factor (NGF) prior to, and every day after, infraorbital nerve section on the day of birth until sacrifice on postnatal day (PND) 1, 3, 5, 7, or 14. Other animals received identical lesions without NGF. Ganglion cell numbers were significantly reduced by PND1 in pups not given NGF, while NGF-treated rats displayed no significant cell loss through PND7. However, NGF did not permanently rescue V neurons because ganglion cell numbers were reliably reduced by PND14. Cell numbers in V nucleus principalis were reduced by PND1 in pups not given NGF, while NGF-treated animals displayed no cell loss through PND14. NGF's rescue of second-order cells is probably an indirect effect of NGF action upon V ganglion cells because, in other newborns, NGF failed to maintain principalis cells after direct lesion of the left V ganglion. To determine whether preventing cell death permits whisker-related pattern formation, other rats also received NGF prior to and after infraorbital nerve section at birth. After 3-14 days, patterns were assessed in the brainstem and cortex with cytochrome oxidase histochemistry and serotonin immunocytochemistry. Whisker-related patterns failed to develop as in cases not given NGF. These data indicate that communication with the periphery is necessary for the maintenance of central whisker-related patterns. They also suggest that V ganglion cells can be rescued, albeit temporarily, from rapid injury-induced death by NGF, thereby delaying injury-induced cell death in nucleus principalis. However, the mechanism(s) responsible for injury-induced pattern alterations in the developing V system remains to be elucidated.

Animals↗
PubMed1993

Reduction in the percentage of serotoninergic axons making synapses during the development of the superficial layers of the hamster's superior colliculus.

Immunocytochemistry with an antibody directed against a serotonin (5-HT)-bovine serum albumin conjugate was combined with electron microscopy to assess the synaptic organization of the serotoninergic projection to the stratum griseum superficiale (SGS) of the superior colliculus of hamsters killed on postnatal days (P) 0, 3, 7, 12, 15, 20 and > 60. At least 200 5-HT-immunoreactive profiles were examined at each of these ages. In the newborn (P0) animals, 36.6% of the 5-HT-positive profiles made conventional synapses. This percentage remained fairly constant until P15 when only 17.3% of the profiles made conventional synaptic contacts. On P20, this value decreased to 10.5% and in the adult animals, it fell to 4.4%. These results thus indicate a dramatic age-related change in the synaptic organization of the 5-HT input to the hamster's superior colliculus.

Aging↗
PubMed1993

Increased serotoninergic innervation of the hamster's superior colliculus alters retinotectal projections.

Anterograde tracing with horseradish peroxidase (HRP) was used to compare the organization of retinotectal projections in normal adult hamsters and in animals that sustained subcutaneous injections of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) on the day of birth. Neonatal injection of this neurotoxin decreases the density of the serotoninergic (5-HT) innervation of the cerebral and cerebellar cortices, but increases the density of these fibers in the brainstem including the superior colliculus (SC). Analysis of tissue from the retinorecipient laminae of the SC by high-pressure liquid chromatography indicated that these lesions increased the amount of 5-HT in the adult SC by 47%. The increased serotoninergic innervation of SC was associated with a marked change in the distribution of the uncrossed retinotectal projection. In normal adult hamsters, fibers from the ipsilateral eye form dense clusters in the lowermost stratum griseum superficiale (SGS) and stratum opticum (SO). A small number of uncrossed fibers are also visible in the more caudal portions of these layers. In the animals that sustained neonatal 5,7-DHT injections, uncrossed retinotectal fibers formed a nearly continuous band in rostral SO and lower SGS, and numerous labeled fibers were present in the caudal SC, primarily in the SO. Neonatal treatment with 5,7-DHT also produced alterations in the crossed retinotectal pathway and in the crossed and uncrossed retinogeniculate projections. These results indicate that the 5-HT input to the developing brainstem may strongly influence the development of retinofugal projections.

5,7-Dihydroxytryptamine↗
PubMed1993

Lesion-induced changes in the central terminal distribution of galanin-immunoreactive axons in the dorsal column nuclei.

Rats that sustained forelimb removal on either embryonic day (E) 16, on the day of birth (P-0), or transection of the brachial plexus in adulthood had brainstem sections stained for galanin, calcitonin gene-related peptide (CGRP), or substance P (SP) at various intervals after these lesions were made. In normal adult rats, only a few galanin-immunoreactive fibers are present in the cuneate nucleus and most are located in its caudal portion. CGRP-positive axons are also sparse in the cuneate and are distributed mainly in the periphery of the nucleus. SP-positive axons are seen throughout the cuneate nucleus. In rats that sustained forelimb removals at birth or transection of the brachial plexus in adulthood, dense galanin immunoreactivity was present throughout the cuneate nucleus at all rostrocaudal levels on the side of the brainstem ipsilateral to the lesion. The changes after lesions that were made in the adult animals were apparent within 1 week, the earliest time analyzed. Increases in galanin immunoreactivity in the cuneate of animals that sustained forelimb removals on P-0 were first visible on P-2. Neither forelimb removal at birth nor brachial plexus lesions in adulthood had any qualitative effect upon the distribution or density of CGRP- or SP-immunoreactivity in the cuneate nucleus. Removal of a forelimb on E-16 did not increase the density of galanin-immunoreactive fibers in the cuneate nucleus. Such lesions also failed to produce any appreciable change in the density of either CGRP- or SP-positive fibers in the cuneate nucleus. The present data raise the possibility that large caliber, non-peptidergic primary afferent axons which innervate the cuneate nucleus may express galanin after damage at birth or in adulthood.

Animals↗
PubMed1993

2-DG uptake patterns related to single vibrissae during exploratory behaviors in the hamster trigeminal system.

Stimulation of one or several whiskers activates discrete foci throughout the trigeminal (V) neuraxis. These foci contribute to patterns, corresponding to the patterns of vibrissae, that have been directly related to aggregates of cells and axon terminals in the "barrel" cortex. Here, we combine high-resolution, 2-deoxyglucose (2DG) mapping and cytochrome oxidase (CO) staining to determine whether the known pattern of V primary afferent projections is sufficient to deduce the functional activation of their targets during exploratory behavior. Four adult hamsters had all of their large mystacial vibrissae trimmed acutely, except for C3 on the left, and B2 and D4 on the right; in two others, the left C3 and right A1 and E4 whiskers were spared. After fasting overnight, 2DG was injected and the animals behaved freely in the dark for 45 minutes. The brainstem, thalamus, and cortices were sectioned, then processed for both CO staining and 2DG autoradiography. Image-processing microscopy was used to separate the autoradiographic silver grains from the histochemical staining. CO patches were patterned in a whisker-like fashion in the full rostrocaudal extent of V nucleus principalis and in caudal portions of spinal V subnuclei interpolaris and caudalis, but absent in subnucleus oralis. 2DG silver grains were densest above those CO patches in the pattern corresponding to the active whiskers. There were no consistent 2DG foci in subnuclei oralis or rostral caudalis. In these same cases, prominent 2DG labeling was restricted to the appropriate barrels in the contralateral cortex. Only one case, however, displayed a clear and appropriate region of heightened 2DG uptake in contralateral ventroposteromedial thalamus (VPM) and the adjacent part of the reticular thalamic nucleus. Patterns of increased glucose utilization with single whisker stimulation are well matched to the CO patterns that mirror distributions of neurons associated with a vibrissa in the V brainstem complex, thalamus, and cortex. Single whiskers are represented by relatively homogeneous longitudinal columns of 2DG labeling in the V brainstem nuclei. The columns are not continuous through the axial extent of the V brainstem complex; rather, they occur separately within principalis, interpolaris, and caudalis. While whisker columns were consistently labeled in interpolaris and caudalis in all animals, the labeling was increasingly variable in principalis, barrel cortex, and VPM, respectively. This suggests that the behaving animal can and does significantly modulate activity in this major, synaptically secure pathway.

Afferent Pathways↗
PubMed1993

Selective sparing of later-born ganglion cells after neonatal transection of the infraorbital nerve.

A combination of [3H]thymidine labelling and retrograde tracing with either horseradish peroxidase (HRP) or true blue (TB) was used to determine whether V primary afferent neurons born on different embryonic (E) days were differentially susceptible to neonatal transection of the infraorbital nerve (ION). In one experiment, rat fetuses were exposed to [3H]thymidine on E-8.5, 9.5, 10.5, 11.5, 12.5, 13.5, 14.5, or 15.5, the left infraorbital nerve (ION) was transected on the day of birth, and both the regenerate and intact IONs were labelled with HRP when the animals reached adulthood. The percentage of HRP labelled cells that were also heavily labelled by [3H]thymidine was calculated for both the intact ganglion and that ipsilateral to the damaged nerve for each animal. A consistently higher percentage of double labelled cells on the lesioned rather than on the intact side for a given E-day was taken as an indication that cells born on the day in question had an increased probability of survival relative to the entire population of V ganglion cells that contributed axons to the ION. Cells born late in gestation on E-12.5 through 14.5 were significantly more likely than early born (E-9.5 through 11.5) cells to survive neonatal axotomy. In a second experiment, fetuses were exposed to [3H]thymidine on either E-9.5, E-10.5, or E-14.5, the vibrissa pads on both sides of the face were injected with TB within 6 hours of birth, and the ION was transected 6-8 hours later.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Galanin immunoreactivity reveals a vibrissae-related primary afferent pattern in perinatal rats after neonatal infraorbital nerve transection.

Immunocytochemistry was used to demonstrate the distribution of galanin immunoreactivity in the trigeminal (V) brainstem complex of normal rats and rats that sustained neonatal transection of the infraorbital nerve (ION, the V branch that supplies the mystacial vibrissae). In normal adult and perinatal (postnatal day [P-] 7) rats, there is very little galanin immunoreactivity in the rostral part of the V brainstem complex. However, there is dense immunoreactivity for this peptide in layers I and II of V subnucleus caudalis (SpC). There was a marked upregulation of galanin immunoreactivity at all levels of the V brainstem complex of P-7 rats that sustained ION transection on P-0. In V subnucleus interpolaris and the magnocellular part of SpC, this immunoreactivity occurred in clusters which had a pattern resembling that of the mystacial vibrissae. In animals examined at 30 days or more after ION transection, there were a few more galanin-immunoreactive fibers on the deafferented side of the brainstem than on the intact side, but there was no evidence of a vibrissae-related pattern. Our interpretation of these results is that galanin immunocytochemistry reveals a vibrissae-related pattern in the central arbors of axotomized primary afferents for at least 1 week after they have been disconnected from the periphery.

Animals↗
PubMed1993

Serotonin 1B receptors in the developing somatosensory and visual cortices are located on thalamocortical axons.

Serotonin (5-HT)-immunoreactive axons are densely distributed in the primary visual and somatosensory cortices of rats, mice, and hamsters for the first 2 weeks of life, and a recent study from this laboratory has demonstrated that 5-HT1B receptors assume a pattern that exactly matches that of the serotoninergic axons. The differential distribution of these receptors is also transient. In the present study, we combined receptor binding autoradiography with neurochemical ablation of 5-HT axons or electrolytic lesions of the dorsal thalamus in an effort to determine the neural elements upon which the 5-HT1B receptors were located. Subcutaneous injections of the toxin 5,7-dihydroxytryptamine, made on the day of birth, totally eliminated the dense and patterned 5-HT innervation of the somatosensory and striate cortices of rats killed on postnatal day 8 but had no qualitative effect upon the distribution or density of 5-HT1B receptors in either of these cortical regions in animals killed at the same age. Conversely, electrolytic lesions of the dorsal thalamus made on postnatal day 6 resulted in a complete loss of the dense and patterned distribution of 5-HT1B receptors in rats killed on postnatal day 8. These results indicate that thalamocortical axons transiently express 5-HT1B receptors.

5,7-Dihydroxytryptamine↗
PubMed1993

Prenatal development of the receptive fields of individual trigeminal ganglion cells in the rat.

1. Extracellular single-unit recording and receptive-field mapping techniques were used to evaluate the response characteristics of trigeminal (V) ganglion cells in unanesthetized, decerebrate, fetal rats between the ages of embryonic (E-) day 15 and E-20 (E-0 is the day of conception). 2. The receptive-field properties of the cells (n = 282) recorded at all of these ages except E-15 were remarkably similar; V primary afferents were generally silent in the absence of peripheral stimulation (94.3%) and gave rapidly adapting responses to innocuous tactile stimuli (97.5%). Rapid response decrements to repeated stimuli were observed in 9 of the 14 cells (64%) tested. 3. None of the cells recorded were activated by either heat or cold. No attempt was made to evaluate responses to noxious mechanical stimuli. 4. Particular attention was paid to neurons whose receptive fields involved mystacial vibrissae follicles. At all ages, neurons were recorded that responded to indentation of the skin at the base of the vibrissae, but vibrissa deflection was not an adequate stimulus for any of the cells tested. At all ages, nearly all (89.0%) of the 127 cells with vibrissa-related receptive fields responded to indentation of one and only one follicle. 5. These results indicate that the response properties (e.g., adaptation characteristics, ability to respond to repeated stimuli) of V primary afferents in fetal rats differ substantially from those of V ganglion cells in adult animals, but that the receptive-field size for these neurons in prenatal rats is, with very rare exceptions, adult-like from the earliest age at which they can be recorded. 6. These results, when considered together with the results of previous retrograde tracing experiments in fetal animals, suggest that the initial projections of V primary afferents to their peripheral targets may be quite accurate.

Animals↗
PubMed1993

Effects of serotonin on retinotectal-, corticotectal-, and glutamate-induced activity in the superior colliculus of the hamster.

1. Single-unit recording and iontophoretic techniques were used to test the effects of serotonin (5-HT) on the responses of neurons in the superficial layers (the stratum griseum superficiale and stratum opticum) of the hamster's superior colliculus (SC). 2. Iontophoresis of 5-HT produced a visual response suppression of 40% or greater in 78.1% (n = 50) of 64 neurons tested. 5-HT did not augment the visual responses of any of the cells tested. The average response suppression was 75.3 +/- 21.2% (mean +/- S.D.). 3. Iontophoresis of 5-HT had significantly different effects on activation of SC cells by optic chiasm (OX) and visual cortical (CTX) stimulation. Application of 5-HT suppressed the OX-evoked responses of 96.9% (n = 31) of the 32 SC cells tested by at least 40%, and the average response suppression for all 32 neurons tested was 87.1 +/- 22.5%. Application of 5-HT suppressed the responses of only 35.7% (n = 10) of the 28 cells tested with CTX stimulation by at least 40%. The average response suppression for all 28 cells was 35.3 +/- 38.8%. 4. The effects of 5-HT on the glutamate-evoked responses of SC cells that were synaptically "isolated" by concurrent application of Mg2+ were also evaluated. Application of 5-HT produced a response suppression > or = 40% in 29.7% (n = 19) of the 64 neurons tested under these conditions. The average response suppression for all of the cells tested was 28.4 +/- 35.7%. This effect of 5-HT was significantly weaker than that on visually evoked responses of these neurons. 5. The present results demonstrate that 5-HT markedly depresses the visual responses of most superficial layer SC neurons. They suggest further that much of this effect is mediated by presynaptic inhibition of retinotectal transmission.

Animals↗
PubMed1993

Morphology and topography of identified primary afferents in trigeminal subnuclei principalis and oralis.

1. Intra-axonal recording, receptive field mapping, horseradish peroxidase injection, cytochrome oxidase staining, and computer-assisted reconstruction/morphometric methods were used to elucidate the structure and topography of trigeminal primary afferent collaterals in the normal adult rat. Prior studies focused on trigeminal brain stem subnuclei interpolaris and caudalis. This work is extended here to the remaining 2 subnuclei, principalis (PrV) and oralis (SpVo), where collaterals from 66 axons in 37 adult rats were studied. In nine rats, three to five axons were stained for within-nucleus comparisons of different fibers. Quantitative analyses were restricted to vibrissa sensitive fibers. 2. All of the axons conducted rapidly with small, low-threshold receptive fields. The majority responded to vibrissa deflection (n = 47); the remainder responded to guard hair deflection; gentle pressure applied to hairy skin, glabrous skin, lingual mucosa, or an incisor; or jaw movement. All descended in the trigeminal sensory root where some bifurcated into ascending and descending branches. Each well-stained fiber gave rise to transversely oriented collaterals in PrV and SpVo. 3. Within PrV and SpVo, fibers with differing adaptation properties and receptive fields had indistinguishable collateral morphologies. Arbors from single axons were rostrocaudally discontinuous, small relative to collaterals in subnuclei interpolaris and caudalis, circumscribed and topographically organized in a manner consistent with cytochrome oxidase and bulk-labeled primary afferent staining patterns. In SpVo and caudal PrV, the map is inverted with the nose pointing medially. In rostral PrV, the map turns 90 degrees such that the nose points dorsally. 4. Axons had different quantitative properties along the rostrocaudal axis of the trigeminal brain stem complex. Whereas arbors subtended similar transverse areas throughout PrV and SpVo, collaterals in the rostral third of PrV had a relatively low bouton density. Arbors in the caudal two thirds of PrV had the highest bouton density. Arbors in SpVo tended to be more variable in size and shape than those of caudal PrV, and their bouton numbers were significantly lower than in PrV. 5. In PrV, arbors were largely confined to somatotopically corresponding cytochrome oxidase patches, precluding significant overlap of neighboring whisker projections. In SpVo, termination sites were not as strictly confined and numerous examples of within- and between-row overlap were obtained for whisker afferents in cases where multiple axons were stained.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1993

Anatomical and functional changes in the organization of the cuneate nucleus of adult rats after fetal forelimb amputation.

A previous study has shown that fetal forelimb removal in the rat results in an increase in the size of the hindlimb representation in primary somatosensory cortex and suggested that this anomalous cortical organization may have resulted from alterations in the primary afferent innervation of the dorsal column nuclei (Killackey and Dawson, 1989). The present study used both anatomical and electrophysiological techniques to examine the effects of fetal forelimb amputation on the dorsal column nuclei. Rats sustained forelimb removals on embryonic day 16 and were used in terminal experiments when they reached adulthood (> 60 d of age). Analysis of cytochrome oxidase-stained sections demonstrated that the cuneate nucleus ipsilateral to the lesion decreased in volume by an average of 36.7% (N = 7, p < 0.001, paired t test), but there was no corresponding increase in the volume of the gracile fasciculus and nucleus. Bilateral application of HRP to the sciatic nerves demonstrated that axons that innervate only the gracile nucleus on the intact side of the brainstem were present in the cuneate nucleus on the deafferented side. Injection of HRP into the skin overlying the point of the amputation (the stump) indicated that axons innervating this region filled most of the dorsal one-half of the shrunken cuneate nucleus and overlapped with the sciatic nerve afferents innervating the cuneate on this side. Mapping the receptive fields of multiple unit clusters demonstrated that most recording sites in the shrunken cuneate nucleus were activated by inputs from the stump and adjacent skin. In addition, 9.1% (N = 30) of such unit clusters (N = 328) could also be excited by stimulation of the hindlimb. These were observed in only three of the nine experiments. Unit clusters with split receptive fields including the skin overlying the stump and the hindlimb were located throughout the rostrocaudal extent of the cuneate nucleus. These results indicate that fetal forelimb amputation results in anatomical expansion of the central projections of hindlimb afferents into the cuneate nucleus. This anatomical organization appears weakly expressed in the receptive fields of cuneate neurons.

Afferent Pathways↗
PubMed1992

Serotonin 1B receptors form a transient vibrissa-related pattern in the primary somatosensory cortex of the developing rat.

Serotonin (5-HT)-immunoreactive axons have a patterned distribution in the primary sensory cortices of developing rodents. This distribution becomes apparent shortly after birth and disappears around the end of the second postnatal week. We employed binding of [125I]cyanopindolol in the presence of isoproterenol to determine whether 5-HT1B receptors have a similar transient spatiotemporal distribution. In rats killed on postnatal day (P-) 8, 5-HT1B receptors have a distribution closely matching that of 5-HT-immunoreactivity. The receptors are very dense in lamina IV of both the primary visual and somatosensory cortices and, like 5-HT immunoreactive axons within the somatosensory cortex, form patches matching the distribution of the mystacial vibrissae. In adult animals, the density of these receptors in lamina IV and the supragranular layers of the visual and somatosensory cortices is reduced relative to that in the surrounding cortex. Autoradiograms of the flattened cortices of adult rats yield a 'negative image' of the pattern observed in perinatal animals. Thus, one subclass of 5-HT receptors, the 5-HT1B receptor, has a spatial distribution in cortex which changes in development much like that for serotoninergic axons.

Animals↗
PubMed1992

Parvalbumin and calbindin immunocytochemistry reveal functionally distinct cell groups and vibrissa-related patterns in the trigeminal brainstem complex of the adult rat.

Immunocytochemistry for calbindin (CA) and parvalbumin (PA) was combined with retrograde tracing from the thalamus, superior colliculus (SC), and cerebellum to define the ascending projections of neurons in the rat's trigeminal (V) brainstem complex that express immunoreactivity for these calcium binding proteins. Many PA-immunoreactive neurons were observed in trigeminal nucleus principalis (PrV). Many of these cells projected to thalamus and a few sent axons to SC. In ventral PrV, PA-immunoreactive neurons were arranged in a vibrissa-related pattern. A very small number of large CA-immunoreactive neurons were observed in dorsomedial PrV. None of these cells were labeled by our tracer deposits. Small neurons in V subnucleus oralis (SpO) were also immunoreactive for PA, but none were retrogradely labeled. A small percentage of the large neurons in SpO were CA-immunoreactive; many of these were retrogradely labeled by tracer injections in the thalamus and/or SC. In V subnucleus interpolaris (SpI), many small to medium sized cells were PA-positive and they were arrayed in a vibrissae-like pattern. None of these neurons were retrogradely labeled from any of the above-listed targets, but many were retrogradely labeled by tracer injections into ipsilateral PrV. SpI also contained many large CA-immunoreactive cells. Many of these projected to the thalamus and/or SC and some were also retrogradely labeled by tracer injections into ipsilateral PrV. In V subnucleus caudalis (SpC), very dark PA-immunoreactive neurons were located in the inner part of lamina II and less often in laminae I. Lightly labeled cells were located in the magnocellular laminae and formed vibrissa-related aggregates. None of these neurons were retrogradely labeled by our tracer injections. CA-immunoreactive cells were located throughout the depth of lamina II in SpC and smaller numbers were also visible in lamina I and layers III-V. A small percentage of the CA-positive cells in lamina I and in the magnocellular layers were retrogradely labeled from the thalamus. These data indicate that PA and CA antisera identify two cell populations in whisker-related regions of the V brainstem complex and that PA cells are somatotopically patterned in PrV, SpI, and SpC. These markers also distinguish two cell groups in superficial laminae of the medullary dorsal horn.

Afferent Pathways↗
PubMed1992

Postnatal blockade of cortical activity by tetrodotoxin does not disrupt the formation of vibrissa-related patterns in the rat's somatosensory cortex.

Neuronal activity has been shown to influence pattern formation in the visual system. In the present study, we determined whether or not this was also true in the somatosensory system by silencing the primary somatosensory cortex of rats with tetrodotoxin (TTX) for the first 7-11 days of life. Application of TTX during this period did not prevent the formation of the normal vibrissa-related pattern in S-I as visualized by either staining cortical sections for cytochrome oxidase, demonstration of the pattern with an antibody directed against serotonin, or labelling of thalamocortical axons with the carbocyanine dye, Di-I. These results indicate that neither peripherally evoked nor spontaneous activity are required for qualitatively normal pattern formation in the rat's primary somatosensory cortex.

Animals↗