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M F Jacquin

Publications and source records attributed to M F Jacquin.

At least 37 records · Page 2Linked to original sources
PubMed1995

Structure-function relationships in rat brainstem subnucleus interpolaris. XI. Effects of chronic whisker trimming from birth.

Whisker trimming from birth reduces activity and alters receptive fields (RFs) in the barrel cortex and thalamus. To assess whether or not this reflects deprivation effects on trigeminal (V) first- and second-order neurons, 59 primary afferents and 343 cells in V brainstem subnucleus interpolaris (SpVi) were studied in rats whose whiskers were trimmed daily for 6-9 weeks from birth. Deprivation did not effect brainstem somatotopy or primary afferent RFs. However, many SpVi cells had abnormal RFs and higher-order inputs, resembling the changes caused by infraorbital nerve injury. For example, in controls, only 3% of whisker-sensitive local circuit neurons responded to more than one whisker, whereas 35% of the deprived and 41% of the infraorbital nerve cut samples had multiwhisker. RFs. Deprived rats also had higher than normal incidences of cells with split or absent RFs, RFs spanning more than one V division, intermodality convergence, and directional or high-velocity sensitivity. Because these changes mimic those caused by nerve section, deprivation may underlie some nerve injury effects on V brainstem RF size and character. Insofar as cytochrome oxidase, anterograde labeling, and unit recordings revealed normal topography in deprived primary afferents and SpVi cells, RF changes in SpVi cells may reflect altered SpVi circuitry. To test this hypothesis, we assessed the morphology of 32 similarly deprived V primary afferents. In SpVi, deprived fibers had normal numbers of collaterals with normal shapes, transverse arbor areas, and topography. However, the total number of boutons per collateral was significantly reduced. Thus, deprivation effects on V higher-order RFs reflect quantitative changes in V afferent terminals.

Afferent Pathways↗
PubMed1995

Developmental transformation of dendritic arbors in mouse whisker thalamus.

Neurons in slices though the somatosensory thalamus of postnatal day 6 and adult mice were injected with Lucifer yellow. Dendritic arbors on postnatal day 6 are confined to single barreloids (single whisker representations); in adults they are seven times longer, extending beyond their barreloid to adjacent barreloids. The postnatal transformation of dendritic arbors by total process growth and extension to adjacent barreloids suggests a developmental change in the role of these cells from instructing whisker pattern formation to integrating sensory information from more than one whisker.

Aging↗
PubMed1995

Structure-function relationships in rat brainstem subnucleus interpolaris: XII. neonatal deafferentation effects on cell morphology.

In the developing whisker-barrel neuraxis, it is known that pattern formation, receptive fields, axon projections, and even cell survival are under the control of peripheral signals transmitted through the infraorbital nerve. However, afferent influences upon the development of single-cell morphologies have not received thorough study. Intracellular recording, antidromic activation, receptive field mapping, dye injection, and computer-assisted cell reconstruction methods were used to assess the morphology of trigeminal (V) brainstem neurons in adult rats whose infraorbital nerves were transected at birth. Projection and local-circuit neurons in the spinal V subnucleus interpolaris (SpVi; n = 43) and local-circuit neurons in the adjacent subnucleus caudalis (SpVc; n = 11) were compared with similar cell types in normal control rats, as well as with spinal V neurons located outside of the deafferented region in experimental rats. SpVi cells displayed abnormally convergent and discontinuous receptive fields that included greater-than-normal numbers of vibrissae and other receptor organs. However, their morphologies did not differ significantly from normal on any quantitative measure, including soma size, number of proximal dendrites, or dendritic tree area, perimeter, or shape. Moreover, SpVi cells near deafferented brainstem territories did not display dendritic tree polarity toward or away from the deafferented region. In SpVc, laminae I-V cells had responses and morphologies that were indistinguishable from those of controls. Thus, (1) altered receptive fields of neonatally deafferented SpVi neurons are not attributable to changes in their morphology; (2) SpVc cells are resilient following deafferentation; and (3) the development of SpV dendrites and local axon collaterals is controlled by factors other than those directly conveyed by primary afferents.

Afferent Pathways↗
PubMed1995

Trigeminal structure-function relationships: a reevaluation based on long-range staining of a large sample of brainstem a beta fibers.

Prior studies suggest that some classes of thickly myelinated (A beta) afferents have distinct morphologies in the trigeminal (V) brainstem complex, and that single fibers have collaterals with different shapes in the four V subnuclei. However, these conclusions are based upon relatively few and incompletely stained fibers and limited statistical rigor. In the present study, 104 fibers were stained more completely with neurobiotin in rats to provide within-fiber intersubnucleus comparisons, and between-fiber intrasubnucleus comparisons, of collaterals associated with a vibrissa, guard hairs, hairy skin, glabrous skin, or oral structures. Collaterals from all functional categories had similar qualitative features and were distributed somatotopically in the transverse plane according to known maps. Fiber categories were not disproportionately represented at particular sites along the brainstem's rostrocaudal axis, although most fibers adhered to an onion-leaf topography in caudalis. Surprisingly few structure-function relationships were revealed by multivariate analysis of variance and post hoc group comparisons, as follows: Arbors were larger in caudalis than in any other subnucleus; collaterals were most numerous in interpolaris; vibrissa afferents had more collaterals than oral and guard hair afferents; and oral fibers had larger arbors than vibrissa or guard hair afferents in subnucleus oralis. Peripheral receptor association and response adaptation rate failed to predict arbor shapes and terminal bouton numbers in any V subnucleus. These data confirm that the locations of V primary afferent arbors are predicted by their receptive fields. However, collateral number and morphology are predicted only to a very limited extent by the V subnucleus and peripheral receptor affiliation--a conclusion that contrasts with those of most prior studies of somatosensory primary afferents.

Afferent Pathways↗
PubMed1995

Central projections of identified trigeminal primary afferents after molar pulp deafferentation in adult rats.

It is known that removal of the tooth pulp from mandibular molar teeth in adult rats alters the mechanoreceptive field properties of many low-threshold mechanoreceptive neurons in the trigeminal brainstem nuclear complex. The present study investigates one possible way that such deafferentation-induced receptive field changes could occur: altered central projections of uninjured trigeminal low-threshold mechanoreceptive primary afferent fibers. Intra-axonal injection of horseradish peroxidase (n = 22) or neurobiotin (n = 44) into characterized fibers was performed ipsilateral to, and 10-32 days after, removal of the coronal pulp from the left mandibular molars in adult rats. Collaterals were reconstructed, quantified, and compared by means of multivariate analyses of variance to equivalent fibers stained in normal adult rats. Stained mechanosensitive fibers from experimental animals were rapidly conducting and responded to light mechanical stimulation of one vibrissa, one tooth, oral mucosa, facial hairy skin, or guard hairs. Their central projections were indistinguishable from those of control axons in all four trigeminal subnuclei. The numbers of collaterals, areas subtended by collateral arbors, numbers of boutons per collateral, and arbor circularity did not differ from those of control afferents. Collateral somatotopy was also unaffected. These data suggest that following pulpotomy, the central collaterals of uninjured trigeminal afferents display normal morphologies and maintain normal somatotopy. Changes in the morphology of low-threshold primary afferents cannot account for the changes that occur in the receptive field properties of trigeminal brainstem neurons after pulp deafferentation.

Afferent Pathways↗
PubMed1994

Differential foci and synaptic organization of the principal and spinal trigeminal projections to the thalamus in the rat.

The thalamus is known to receive single-whisker 'lemniscal' inputs from the trigeminal nucleus principalis (PrV) and multiwhisker 'paralemniscal' inputs from the spinal trigeminal nucleus (SpV), yet the responses of cells in the thalamic ventroposteromedial nucleus (VPM) are most similar to and contingent upon inputs from PrV. This may reflect a differential termination pattern, density and/or synaptic organization of PrV and SpV projections. This hypothesis was tested in adult rats using anterograde double-labelling with fluorescent dextrans, horseradish peroxidase (HRP) and choleragenoid, referenced against parvalbumin and calbindin immunoreactivity. The results indicated that PrV's most robust thalamic projection is to the whisker-related barreloids of VPM. The SpV had robust projections to non-barreloid thalamic regions, including the VPM 'shell' encapsulating the barreloid area, a caudal and ventral region of VPM that lacks barreloids and PrV inputs, the posterior thalamic nucleus, nucleus submedius and zona incerta. Within the barreloid portion of VPM, SpV projections were sparse relative to those from PrV, and most terminal labelling occurred in the peripheral fringes of whisker-related patches and in interbarreloid septae. Thus, PrV and SpV have largely complementary projection foci in the thalamus. Intra-axonal staining of a small sample of trigeminothalamic axons with whisker or guard hair receptive fields revealed highly localized and somatotopic terminal aggregates in VPM that spanned areas no larger than that of a single barreloid. In the electron microscopic component of this study, HRP transport to the barreloid region of VPM from left SpV and right PrV in the same cases revealed PrV terminals contacting dendrites with a broad range of minor axis diameters (mean +/- SD: 1.51 +/- 0.10 microns). SpV terminals were indistinguishable from those of PrV, but they had a disproportionate number of contacts on narrow dendrites (1.27 +/- 0.07 microns, P < 0.01). PrV endings were also more likely to contact VPM somata (11.0 +/- 4.2% of all labelled terminals) than those from SpV (3.0 +/- 1.0%, P < 0.01). Insofar as primary dendrites are thicker than distal dendrites in VPM, these data suggest a differential distribution of PrV and SpV inputs onto VPM cells that may account for their relative efficacies in dictating the responses of VPM cells to whisker stimulation. Multiwhisker receptive fields in VPM may also reflect direct transmission of convergent inputs from PrV.

Animals↗
PubMed1994

Primary afferent plasticity following partial denervation of the trigeminal brainstem nuclear complex in the postnatal rat.

Although interaxonal competition is believed to be an essential component of the normal development of numerous mammalian neuronal populations, there is considerable debate regarding the role of competition in the development and maintenance of the somatic sensory system. The results of recent investigations suggest that trigeminal primary afferents may compete for target territory in the brainstem, but it is unclear whether these interactions continue after birth. The present study explored this important issue by examining the response of individual trigeminal primary afferent neurons to partial denervation of the trigeminal brainstem nuclear complex at early postnatal ages. We utilized intracellular recording and HRP injection techniques to label primary afferent central terminal arbors in rats that sustained electrocautery of mystacial vibrissae in rows A, C, and E on the day of birth. A total of 42 low-threshold trigeminal primary afferent neurons were labeled in subnucleus interpolaris. Twenty-eight of these afferents supplied undamaged B or D row vibrissae while 14 supplied lesioned vibrissae. Qualitative and quantitative analyses revealed that the arbors associated with undamaged afferents were enlarged (mean arbor area of 13512 +/- 790.67 microns 2 vs normal area of 6130 +/- 214 microns 2) and were oriented toward the adjacent (partially denervated) territory. There was no significant change in the size of the lesioned afferent arbor area. The perimeter of the lesioned afferent arbors was increased, however, suggesting that the arbor shape had changed. This was confirmed with a form factor calculation that indicated that the circularity of the arbors associated with lesioned vibrissae was significantly reduced. Thus, while the arbors of undamaged afferents were enlarged and oriented in the direction of the partially denervated territory, the lesioned afferent arbors were not enlarged but assumed a flattened/elongate morphology within their appropriate row. The lesion-induced increase in the size of the undamaged afferent arbors was not associated with an increase in the number of bouton-like fiber swellings. The density of boutons was only 25% the value seen in normal animals. Thus, while the area supplied by the undamaged afferent arbors increased, there was no evidence that the absolute amount of terminal arbor was similarly increased (as would be the case if sprouting had occurred; see Renehan et al., 1989). We would therefore conclude that the undamaged afferents had undergone arbor expansion, but not sprouting. These data are consistent with prior suggestions that trigeminal primary afferents utilize some form of competitive interaction(s) to establish their final form and disposition. This competition would appear to continue into early postnatal periods.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1994

Fetal NGF augmentation preserves excess trigeminal ganglion cells and interrupts whisker-related pattern formation.

In the developing nervous system, precisely patterned connections result from mechanisms that remodel initially diffuse connections. For example, ocular dominance column formation depends upon activity-based competitive interactions. In the developing trigeminal (V) somatosensory system, injury to afferent inputs prevents somatotopic pattern formation; however, afferent impulse blockade does not. What establishes central V patterns remains unclear. As a first step in assessing the role of neurotrophins in naturally occurring death of V ganglion cells and whisker-related pattern formation, the consequences of prenatal NGF injections were evaluated. Fetal rats given NGF on both embryonic day (E) 15 and E18 had 36% more V ganglion cells than normal and lacked whisker-related patterns in the V brainstem complex at birth and through postnatal day 3, as determined by cytochrome oxidase histochemistry. Rats injected with NGF on E16 or on E18, or with vehicle had normal ganglion cell numbers and brainstem patterns. Animals injected with antibodies to NGF or an NGF receptor had reduced ganglion cell numbers and normal brainstem patterns. These findings suggest that naturally occurring cell death in the V ganglion is neurotrophically regulated and that this process impacts upon somatotopic pattern formation in the V brainstem complex. Results of anterograde tracing experiments in NGF-augmented animals suggest that pattern disruptions are due to an absence of whisker-related patterning in the central projections of V ganglion cells. Moreover, single primary afferent collaterals labeled by Neurobiotin injections in the V ganglion did not have widespread or unusually complex arbors. Thus, NGF may affect V pattern formation by preserving or inducing projections to brainstem regions that normally come to lack such projections, such as the spaces normally demarcating neighboring whisker primary afferent projections.

Animals↗
PubMed1993

Organization of the proximal, orbital segment of the infraorbital nerve at multiple intervals after axotomy at birth: a quantitative electron microscopic study in rat.

Although much is known of the central consequences of infraorbital nerve (ION) transection at birth, little is known about the effects of this lesion on the organization of the ION itself. To advance our understanding of how deafferentation alters the developing trigeminal neuraxis, 19 newborn rats were subjected to left ION section and perfused 1, 2, 4, 7, 17, or 90 days later. Left IONs were removed in the orbit proximal to the nerve injury site, and axon numbers, types, and fasciculation patterns were assessed with light and electron microscopic methods. Complete axon counts demonstrated that the axotomized ION contained an average (+/- SD) of 13,945 +/- 10,335, 14,112 +/- 3,501, 16,531 +/- 1,904, 9,045 +/- 1,465, 7,018 +/- 4,212, and 8,672 +/- 1,030 axons at the above-listed ages, respectively. These values are well below the 33,059 axons in the normal adult ION (Jacquin et al. [1984] Brain Res. 290:131-135) and the 42,219 axons in the newborn ION (Renehan and Rhoades [1984] Brain Res. 322:369-373). The axotomized ION also contained lower than normal percentages of myelinated axons (26.7% +/- 6.3% on postnatal day 90 vs. 59.7% +/- 6.2% in normal adults). Unmyelinated fibers constituted the vast majority of the remaining fiber types; degenerating fibers never accounted for > 1.6% of all the axons. The number of fascicles making up the axotomized ION overlapped significantly with those found in the normal newborn and adult ION. We conclude that 1) extensive, though variable, axon elimination occurs proximally within one day of the lesion; 2) the 74% reduction in fiber number seen at 90 days is not reliably achieved until postnatal day 7; 3) the higher than normal proportion of unmyelinated axons in the injured ION may underly many of the known effects of neonatal ION injury on the developing whisker-barrel neuraxis; 4) gross changes in ION fasciculation patterns are not prerequisite to injury-induced pattern alterations in the developing trigeminal system.

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

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

Lucifer Yellow staining in fixed brain slices: optimal methods and compatibility with somatotopic markers in neonatal brain.

Developing dendritic trees often acquire their mature form by selective pruning and reorientation relative to anatomical boundaries, such as cortical 'barrel' walls. Whether similar constraints are imposed on the developing dendrites of subcortical somatosensory neurons is not clear, although it is known that the cells in trigeminal nucleus principalis (PrV) of adult rats have polarized trees. In attempting to resolve this issue we adopted and subsequently optimized a strategy of intracellular injection of Lucifer Yellow into PrV neurons and cerebellar granule cells in slices of fixed brain. Postinjectionally, immunohistochemical staining produced a stabilized image of the Lucifer Yellow injected cells and created the opportunity to apply also an antiserum to J1-tenascin in order to detect whisker-related compartmental boundaries in the neonatal PrV. In 6-day-old rats, most PrV dendrites are polarized and they do not cross tenascin-stained, whisker-related, patch borders. Notable exceptions are dendrites from the minority of PrV cells that have large somata and are responsive to multiple whiskers.

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

Structure-function relationships in rat brainstem subnucleus interpolaris. X. Mechanisms underlying enlarged spared whisker projections after infraorbital nerve injury at birth.

Prior studies indicate that the central projections of noninfraorbital vibrissae occupy greater than normal transverse areas in the rat trigeminal brainstem complex after infraorbital nerve section at birth. Here, we assessed the development of this phenomenon and possible underlying mechanisms. Cytochrome oxidase patches representing spared supraorbital (SO) or posteroorbital (PO) whiskers in the trigeminal subnucleus interpolaris (SpVi) were not reliably larger than those on the control side 24 hr after the infraorbital lesion. By 72 hr, SO and PO patches were 91% and 28% larger than those on the control side. Reliable increases were also observed on postnatal day 5 (PND5), PND7, and PND10 for the SO (59%, 65%, 66%) and PO (23%, 44%, 51%) patches. To test the hypothesis that central reorganization reflects the maintenance of peripheral supernumerary axons, myelinated and unmyelinated axons in SO vibrissa follicles were counted at PND0, PND7, PND17, and PND60. A corollary hypothesis, that peripheral regeneration errors result in both SO and surviving infraorbital axons, contributing to central SO patches, was tested with retrograde double-labeling methods. Both hypotheses were rejected. Thus, enlargement of SO patches is not due to either the maintenance of an immature peripheral innervation pattern, or regeneration of infraorbital axons into SO follicles. To determine if the enlargement of SO and PO patches produced by infraorbital nerve section is due to an activity-dependent competitive disadvantage imposed upon infraorbital afferents, TTX or bupivicaine was applied to the intact infraorbital nerve over the first 5-9 postnatal days. Brainstem maps developed normally and SO and PO patch areas were unaffected. Thus, impulse activity-based mechanisms do not appear to contribute to injury-induced patch enlargement. To test the hypothesis that patch enlargement is due to central collateral reorganization, intra-axonal recording and staining methods were applied to control and spared-whisker primary afferents in adult rats. Total bouton or collateral numbers did not differ in SpVi; however, arbor areas were reliably larger in experimental (14,879 +/- 350 microns 2) versus control (5527 +/- 1811 microns 2) fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1992

Cholecystokinin concentrations and peptide immunoreactivity in the intact and deafferented medullary dorsal horn of the rat.

To further address the hypothesis that cholecystokinin (CCK) in the medullary dorsal horn (MDH) arises from intrinsic or higher-order neurons, CCK-8-specific radioimmunoassay (RIA) and immunohistochemical (IHC) experiments were carried out in adult rats after trigeminal tractotomy. RIA of punches from deafferented superficial layers of the MDH revealed no significant change in CCK levels vs. the control right side. In this same area, IHC revealed modest reductions in CCK, gastrin, and substance P staining. Calcitonin gene-related peptide (CGRP) staining was reduced substantially. Gastrin immunoreactive cell bodies, present normally in inner lamina II, were reduced in number. RIA and IHC methods were also used to assess MDH CCK concentrations in adult rats subjected to left infraorbital nerve section at birth. The left medulla contained significantly higher levels of CCK than the control right medulla (1.27 +/- 0.19 vs. 0.97 +/- 0.11 ng/mg protein). IHC revealed a dense band of CCK-like staining in laminae I and II ipsi- and contralateral to the lesion. Thus, neonatal deafferentation elevates medullary CCK. To determine if the neonatal lesion-induced increase in medullary CCK is due to primary afferent or higher-order reorganization, RIA and IHC experiments were run after infraorbital nerve section at birth and trigeminal tractotomy in adulthood. RIA revealed no significant change in CCK levels caudal to the tractotomy, although they were higher than control levels in 9 of 12 cases. IHC revealed modest reductions in CCK, substance P, and gastrin staining that resembled the reductions observed in tractotomy-alone cases. These data suggest that 1) most MDH CCK is of non-primary afferent origin, 2) gastrin immunoreactivity in layer II probably originates in CCK-containing cells intrinsic to layer II, the expression of which is dependent upon trigeminal primary afferent input, 3) neonatal V deafferentation induces increased CCK in the superficial MDH, reflecting reorganized intrinsic or higher-order inputs, and 4) higher-order substance P in the MDH is robust.

Animals↗