Biomedical subjects

W E Renehan

Publications and source records attributed to W E Renehan.

At least 37 records · Page 2Linked to original sources

PubMed1994

Structure and function of gustatory neurons in the nucleus of the solitary tract. I. A classification of neurons based on morphological features.

Prior investigations in other laboratories have provided convincing evidence that the neurons of the rostral nucleus of the solitary tract (rNST) can be grouped according to their physiological response properties or morphologic features. The present study is based on the premise that the response properties of gustatory neurons are related to, and perhaps governed by, their morphology and connectivity. In this first phase of our ongoing investigation of structure-function relationships in the rNST of the rat, we have used intracellular injection of neurobiotin to label individual physiologically characterized gustatory neurons. A total of 63 taste-sensitive neurons were successfully labeled and subjected to three-dimensional quantitative and qualitative analysis. A cluster analysis using six morphologic features (total cell volume, soma area, mean segment length, swelling density, spine density, and number of primary dendrites) was used to identify six cell groups. Subsequent analyses of variance and posthoc comparisons verified that each of these six groups differed from all others with respect to at least one variable, so each group was "typified" by at least one of the six morphologic features. Neurons in group A were found to be the smallest neurons in the sample. The cells in group B had small somata and exhibited the highest swelling density of any group. Group C neurons were distinguished by dendrites with long, spine-free branches. These dendrites were significantly longer than those of any other group except Group F. The neurons in group D had more primary dendrites than any other group. Group E neurons possessed dendrities with the lowest swelling density but the most spines of any group. The cells in group F were the largest neurons in our sample and possessed the largest somata of any group. Thus overall cell size and density of dendritic spines and swellings were found to be particularly important variables in this classification scheme. Our preliminary results suggest that the number and density of dendritic spines (as well as other morphologic features) may be related to a given neuron's most effective stimulus, indicating that it will indeed be possible to use the criteria established in the present investigation to derive structure-function relationships for gustatory neurons in the rNST.

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↗

PubMed1993

Myenteric plexus destruction alters morphology of rat intestine.

BACKGROUND: It has been shown previously that myenteric plexus destruction by benzalkonium chloride (BAC) increased villus height, crypt depth, and muscle thickness, suggesting that these neurons influence intestinal morphology. A nonspecific trophic effect of BAC, intraluminal stasis, and inflammation resulting from the chemical treatment could also be causes for these changes. Our goals were to (1) show that the morphological sequelae of BAC treatment are caused by myenteric plexus removal and not the factors listed above, and (2) determine whether segmental myenteric plexus removal alters morphology elsewhere in the small intestine. METHODS: Six groups of rats were studied: control, chemical denervation (3 mmol/L BAC), surgical denervation, intraluminal stasis produced by partial obstruction, chemical inflammation (5% acetic acid), and surgical inflammation (serosa removal only). Tissue for histological study was taken from the treated segment, 15-20 cm proximal to the treated segment, and 5-10 cm distal to the treated segment 28 days after treatment. RESULTS: Chemical and surgical denervation reduced the number of myenteric neurons by 94% and 98%, respectively. Denervation had a direct effect on morphology; it increased villus height, crypt depth, and muscle thickness in the treated and proximal segments, but only muscle thickness was increased in the distal segment. The other treatments had minimal morphological sequelae. CONCLUSIONS: Segmental myenteric plexus removal alters the mucosa in the treated and proximal segments but influences muscle thickness throughout the intestine.

Acetates↗

PubMed1993

Intestinal distension alters vagal efferent activity and small intestinal transport in vivo.

We investigated whether intestinal distension altered net water absorption by an adjacent noncontiguous segment of intestine and the mechanism for this effect. Influx and efflux catheters were placed in two intestinal loops, after which the bowel was transected between the loops. During perfusion with Ringers-HCO3-, the proximal loop efflux catheter was elevated 5, 10, or 15 cm above the plane of the rat. Net water absorption was measured in the nondistended caudal (control) loop. Elevation of the proximal loop efflux catheter caused distension and increased intraluminal pressure in this loop but did not alter the circumference or intraluminal pressure of the caudal loop. Distension increased net water absorption by the caudal loop if the vagi were intact and the splanchnic nerves transected. Afferent vagotomy prevented the distension effect. Using the intracellular recording technique, we were able to show that the increase in absorption resulted from a reduction in the activity of vagal neurons innervating the gastrointestinal tract. Intestinal distension reduced the neural activity of 24 of 26 vagal efferent neurons. Our results demonstrate that after splanchnectomy intestinal distension activates a neural circuit that includes afferent and efferent vagal fibers, resulting in increased water absorption.

Absorption↗

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

Physiology and morphology of neurons in the dorsal motor nucleus of the vagus and the nucleus of the solitary tract that are sensitive to distension of the small intestine.

We have recently shown that distension-sensitive vagal afferents are part of a neural circuit affecting absorption of water in the rat small intestine. Our results indicated that vagal afferent activity directly or indirectly influences the activity of neurons in the dorsal motor nucleus of the vagus (DMNV). In the present study we pursued this interaction by examining the structure and function of neurons in the DMNV and nucleus of the solitary tract (NST) that responded to moderate distension of the small intestine. Distension-sensitive cells were filled by intracellular iontophoretic injection of horseradish peroxidase. A total of 43 distension-sensitive brainstem neurons were successfully characterized and labeled. Sixteen of the 17 NST neurons were excited by distension of the small intestine. Ten of the seventeen were restricted to the ipsilateral NST. Only two NST neurons possessed axons that terminated in the subjacent DMNV. In contrast to the response profile of the NST neurons, 24 of 26 DMNV neurons were inhibited by intestinal distension. Fourteen of the DMNV neurons appeared to contribute to the vagus nerve and 15 extended dendrites into the overlying NST. We propose that distension-induced inhibition of DMNV activity is accomplished by inhibitory NST neurons, which synapse on the dendrites of DMNV neurons in the NST.

Afferent Pathways↗

PubMed1992

Restoration of orbicularis oculi function by contralateral orbicularis oculi innervated muscle flap vs neuromuscular pedicle technique.

In preliminary experiments with dogs and cats, unilateral paralysis of the orbicularis oculi muscle group was produced by a section of the seventh nerve that included the posterior auricular branch. Either one of two procedures was then employed in attempts to reinnervate the paralyzed eyelid. In one group of animals, a neuromuscular pedicle was employed and in another, a contralateral orbicularis innervated muscle flap was used. Both methods restored synchronous, reflex blinking to the denervated eyelid. Of the two procedures, neurotization appears to offer the greater promise because the use of a neuromuscular pedicle requires an expendable nerve that is functional, and no such suitable substitute is available in humans.

Animals↗

PubMed1991

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

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

Aging↗

PubMed1990

The development of Meissner corpuscles in primate digital skin.

Digital skin from fetal and neonatal primates was examined using light and electron microscopic techniques to document the development of the Meissner corpuscle. Generation of the receptor was initiated early in the third trimester by fine neurites which left the superficial dermal nerve plexus, ascended the dermal papillae and entered the basal epidermis. As maturation of the Meissner corpuscle continued, the axons were confined to the apex of the dermal papilla, where they were oriented parallel to the surface to the surface of the skin and terminated among cytoplasmic extensions of presumptive lamellar cells. During late fetal life the complexity of the lamellar cell stacking increased and the lamellar cell bodies were found solely at the base of the receptor. Numerous axon terminals were evident between the cytoplasmic lamellae. The appearance of the neonatal Meissner corpuscle was indistinguishable from that of the adult, indicating that the complete cycle of development is concluded before birth.

Animals↗

PubMed1990

Structure-function relationships in rat brain stem subnucleus interpolaris. VIII. Cortical inputs.

1. Spinal trigeminal (SpV) subnucleus interpolaris (SpVi) receives inputs from trigeminal (V) first- and second-order neurons, monoamine-containing brain stem nuclei, and somatosensory cortex. Prior studies suggest that SpVi receptive-field (RF) properties cannot be predicted solely on the basis of primary afferent inputs. To assess the cortico-V projection and its role in SpVi RFs, anatomic and electrophysiological experiments were conducted. 2. Phaseolus vulgaris leucoagglutinin (PHA-L) or wheat-germ-agglutinized horseradish peroxidase (WGA-HRP) were used as anterograde tracers to study cortico-V axons in 24 normal adult rats. Injections into SI barrel cortex-labeled pyramidal fibers that decussated at all levels of the V brain stem complex, though crossing fibers were most numerous in the pyramidal decussation and pons. A small number of axons projected to ipsilateral V brain stem subnuclei. PHA-L-labeled pyramidal fibers did not give rise to collaterals in their descent through the pons and medulla. 3. Heaviest terminal labeling occurred contralaterally and in the maxillary portion of caudalis laminae III-V. Moderately dense reaction product was seen in ventral portions of all other contralateral V brain stem subnuclei, as well as in laminae I and II of caudalis. Subnucleus oralis contained the least amount of label contralateral to the injection site. Ipsilateral projections were weak and most dense in principalis. 4. Cortico-V projections were topographic between matching whisker representations. Axons most commonly had longitudinal orientations and stringy shapes. Terminal boutons occurred at the ends of short collateral branches. Many of these collaterals were derived from axons that ascended through caudal V brian stem subnuclei after crossing in the lower medulla. 5. Cortico-V labeling was heavier in septal regions between single whisker representations. This "honeycomb-like" termination pattern was most pronounced in contralateral caudalis and SpVi and ipsilateral principalis. 6. In 13 other adult rats, right SI cortex was aspirated followed by single-unit recordings in left SpVi under pentobarbital sodium anesthesia. In 9 of these, chronic effects were evaluated by recording the responses of 346 left SpVi cells 4-55 days after the lesion. In the remaining four rats, acute effects were analyzed by recording the responses of 190 SpVi cells on the day of the lesion.(ABSTRACT TRUNCATED AT 400 WORDS)

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

Degeneration and regeneration of peripheral nerve in the rat trigeminal system: III. Abnormal sensory reinnervation of rat guard hairs following nerve transection and crush.

The present study was undertaken in an attempt to better understand the abnormalities of cutaneous sensibility that are present in patients following nerve injury with concomitant cutaneous denervation and subsequent reinnervation. Reinnervated intervibrissal pelage of the rat mystacial pad was studied in silver-impregnated sections 3 and 5 months after transecting and 2 and 5 months after crushing the infraorbital nerve. The sensory terminals on guard and vellus hairs were analyzed in serial paraffin sections and in thick frozen sections. In normal rat mystacial skin, approximately nine/ten of innervated guard hairs have a typical piloneural complex consisting of a palisade of highly regular lanceolate terminals surrounded by circularly arranged Ruffini terminals and free nerve endings (FNEs). The remaining one of ten innervated guard hairs has only circularly arranged presumptive FNEs and Ruffini terminals. Vellus hairs, either singly or in clusters, typically have only circularly arranged terminals that in many cases are simple FNEs. We first recognized abnormalities in innervation of hairs following nerve transection and fully expected nerve terminals to be completely normal following nerve crush. Almost all reinnervated sensory nerve terminals associated with guard hairs were markedly abnormal following nerve transection and quantitatively abnormal following nerve crush. Following nerve transection, lanceolate terminals were almost completely absent, and they were remarkably reduced in number following nerve crush. Vellus hairs when reinnervated typically lacked the complex circular presumptive Ruffini terminals. These findings may be in part the basis for the abnormal cutaneous sensory perceptions (dysasthesias and paresthesias) noted in human subjects following damage to nerves with subsequent sensory reinnervation of the skin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

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

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

Animals↗

PubMed1988

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

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

Afferent Pathways↗

PubMed1988

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

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

Animals↗

PubMed1988

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

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

Afferent Pathways↗

PubMed1987

Renewed growth of identified brainstem axons into fetal cortical transplants in adult rat.

Transplantation of fetal neocortex into the site of trigeminal brainstem injury induces regeneration of trigeminal primary afferent axons in adult rats. Renewed growth of injured primary afferent fibers into donor cortex can be extensive, though the innervation pattern does not resemble that normally seen in either brainstem or somatosensory cortex. Examination of the structural and functional characteristics of individual regenerate axon collaterals suggests that their morphology is determined by both intrinsic and postsynaptic target factors. Marked topographic alterations, however, question the utility of fetal cortical transplantation procedures in effecting functional recovery from brainstem injury.

Animals↗