Gamma-aminobutyric acid-immunoreactive neurons in the rat trigeminal nuclei

The distribution of GABAergic neurons in the rat trigeminal nuclei was studied using a highly specific monoclonal antibody (mAb3A12) to gamma-aminobutyric acid (GABA). Immunopositive cells were relatively abundant in the marginal and gelatinosa beds of the caudal part of the trigeminal spinal tract nucleus, and in the dorsomedial areas of the oral subnucleus and the principal nucleus. A high density of GABA-immunoreactive somata was also found in the rostral part of the oral subnucleus and in the adjacent parvicellular reticular formation as well as in the supratrigeminal and intertrigeminal regions. Thus, the distribution of the GABAergic cells showed a relatively high density in areas related to the convergence of sensory stimuli, and in zones that contain interneurons inhibiting masticatory motorneurons. The results suggest, therefore, that GABA might play an important role both in discriminative sensory processing and in reflex modulation of the orofacial region.Abbreviations RF reticular formation - FRp parvicellular reticular formation - Vc trigeminal nucleus of the spinal tract, subnucleus caudalis - Vmes mesencephalic nucleus - Vmo trigeminal motor nucleus - Vo trigeminal nucleus of the spinal tract, subnucleus oralis - Vp principal trigeminal nucleus - Vsp spinal trigeminal nucleus - Vsup supratrigeminal nucleus     

Mapping of the trigeminal sensory complex of the cat. Characterization of its neurons by stimulations of peripheral field, dental pulp afferents and thalamic projections.

From a new systematic investigation of the 4 divisions of the trigeminal sensory complex, the following points are emphasized: 1. The subnucleus oralis receives a large representation from the oral cavity, a region also represented in the three other divisions of the trigeminal sensory complex. 2. Units responding to noxious mechanical stimulation have been found in two different loci: the subnucleus caudalis for the whole trigeminal area, and the subnucleus oralis for the oral cavity. 3. The dental pulp projects to the four divisions of the trigeminal sensory complex, but the heaviest projection is found in its rostral part (the main nucleus and subnucleus oralis). 4. Three distinct types of responses were found following dental pulp stimulation: primary, non primary and responses strongly enhanced by an increase in stimulus parameters.     

Localization and Central Projections of Primary Afferent Neurons That Innervate the Temporomandibular Joint in Cats

Primary afferent neurons that innervate the temporomandibular joint (TMJ) in cats were labeled by injecting a 2-5% solution of wheatgerm agglutinin bound to horseradish peroxidase into the joint capsule and capsular tissues in 14 cats and processing the brain stem and trigeminal ganglia using the tetramethylbenzidine method described by Mesulam (1978). The perikarya of ganglion cells that innervate the TMJ ranged in diameter from 15 to 109 μm and were primarily located in the posterolateral portion of the trigeminal ganglion. The central processes of these neurons entered the brain stem in middle pons and were distributed to all portions of the sensory trigeminal nuclei. However, the majority of labeled fibers and greatest density of terminal labeling were observed in the dorsal part of the main sensory nucleus and the subnucleus oralis of the spinal trigeminal nucleus. Very few labeled fibers were observed in the spinal tract of the trigeminal nerve below the obex. However, evidence for axon terminals was consistently observed in laminae I, II, and III of the medullary dorsal horn. These findings concur with physiological evidence showing that information from the TMJ influences neurons in rostral (Kawamura et al, 1967) and in caudal (Broton et al, 1985) portions of the trigeminal sensory nuclei.     

Substance P-like immunoreactivity in the trigeminal sensory nuclei of an infrared-sensitive snake,Agkistrodon blomhoffi

Summary With the peroxidase-antiperoxidase immunohistochemical method we ascertained the presence of substance P-like immunoreactivity (SPLI) in fibers and cell bodies of the trigeminal sensory system of the pit viper, Agkistrodon blomhoffi. There are a few SPLI fibers each in the principal sensory nucleus and the main neuropil of the lateral descending nucleus (i.e., the infrared sensory nucleus); a moderate number in the descending nucleus; and a large number in the caudal subnucleus, the medial edges of the interpolar subnucleus, and the marginal neuropil of the lateral descending nucleus. About 30% of the cell bodies in the ophthalmic and maxillo-mandibular ganglia show SPLI, and of the two craniocervical ganglia, the proximal ganglion has many more cells with SPLI than the distal ganglion. The SPLI distribution in the common trigeminal sensory system is similar to that of mammals, and suggests that the function of this system is also similar. In the infrared sensory system, the differing distribution in the main and marginal neuropils suggests separate functions for these two structures in the system.     

c-fos expression in trigeminal spinal nucleus after electrical stimulation of the hypoglossal nerve in the rat

The expression of the immediate early gene, c-fos, was used to determine the distribution of brainstem neurons activated by stimulation of the distal hypoglossal nerve (XIIn) trunk. The traditional view of the XIIn is one of purely motor function; however, stimulation of XIIn excites neurons in the trigeminal spinal nucleus. The rationale for this study was to use c-fos expression as a marker for postsynaptic activity to define the pattern of brainstem neurons excited by XIIn stimulation. It was further hypothesized that if the afferent fibers that course within XIIn supply deep lingual tissues, then c-fos expression after direct stimulation of XIIn should display a pattern similar to that seen after chemical irritant stimulation of the deep tongue muscle. In barbiturate-anesthetized male rats electrical stimulation of XIIn produced a significant increase in Fos-positive neurons in the dorsal paratrigeminal nucleus (dPa5) and laminae I-II of caudal subnucleus caudalis (Vc) and upper cervical dorsal horn. Mustard oil injection into the deep tongue muscle also produced an increase in c-fos expression in dPa5; however, the highest density of expression occurred in laminae I-II at the dorsomedial aspect of rostral Vc. Both electrical stimulation of XIIn and mustard oil stimulation of the deep tongue increased c-fos expression in the caudal ventrolateral medulla, an autonomic relay nucleus. These results suggest that one site of innervation for afferent fibers that travel within the distal trunk of XIIn is to supply the deep tongue muscle and to terminate in the dPa5. A second group of postsynaptic neurons activated only by XIIn stimulation was located in lamina I-II in caudal portions of Vc and upper cervical dorsal horn, a laminar distribution consistent with a role for XIIn afferents in sensory or autonomic aspects of lingual function.     

Endomorphin-2 is an endogenous opioid in primary sensory afferent fibers

Evidence is presented that the recently discovered endogenous mu-selective agonist, endomorphin-2, is localized in primary sensory afferents. Endomorphin-2-like immunoreactivity was found to be colocalized in a subset of substance P- and mu opiate receptor-containing fibers in the superficial laminae of the spinal cord and spinal trigeminal nucleus. Disruption of primary sensory afferents by mechanical (deafferentation by dorsal rhizotomy) or chemical (exposure to the primary afferent neurotoxin, capsaicin) methods virtually abolished endomorphin-2-like immunoreactivity in the dorsal horn. These results indicate that endomorphin-2 is present in primary afferent fibers where it can serve as the endogenous ligand for pre- and postsynaptic mu receptors and as a major modulator of pain perception.     

c-fos expression in trigeminal spinal nucleus after electrical stimulation of the hypoglossal nerve in the rat

The expression of the immediate early gene, c-fos, was used to determine the distribution of brainstem neurons activated by stimulation of the distal hypoglossal nerve (XIIn) trunk. The traditional view of the XIIn is one of purely motor function; however, stimulation of XIIn excites neurons in the trigeminal spinal nucleus. The rationale for this study was to use c-fos expression as a marker for postsynaptic activity to define the pattern of brainstem neurons excited by XIIn stimulation. It was further hypothesized that if the afferent fibers that course within XIIn supply deep lingual tissues, then c-fos expression after direct stimulation of XIIn should display a pattern similar to that seen after chemical irritant stimulation of the deep tongue muscle. In barbiturate-anesthetized male rats electrical stimulation of XIIn produced a significant increase in Fospositive neurons in the dorsal paratrigeminal nucleus (dPa5) and laminae I-II of caudal subnucleus caudalis (Vc) and upper cervical dorsal horn. Mustard oil injection into the deep tongue muscle also produced an increase in c-fos expression in dPa5; however, the highest density of expression occurred in laminae I-II at the dorsomedial aspect of rostral Vc. Both electrical stimulation of XIIn and mustard oil stimulation of the deep tongue increased c-fos expression in the caudal ventrolateral medulla, an autonomic relay nucleus. These results suggest that one site of innervation for afferent fibers that travel within the distal trunk of XIIn is to supply the deep tongue muscle and to terminate in the dPa5. A second group of postsynaptic neurons activated only by XIIn stimulation was located in lamina I-II in caudal portions of Vc and upper cervical dorsal horn, a laminar distribution consistent with a role for XIIn afferents in sensory or autonomic aspects of lingual function.     

Intersubnuclear connections within the rat trigeminal brainstem complex

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

Ulex europaeus agglutinin-I binding to dental primary afferent projections in the spinal trigeminal complex combined with double immunolabeling of substance P and GABA elements using peroxidase and colloidal gold

Ulex europaeus agglutinin I (UEA-I) is a plant lectin with an affinity for L-fucosyl residues in the chains of lactoseries oligosaccharides associated with medium- and smaller-diameter dorsal root ganglion neurons and their axonal processes. These enter Lissauer's tract and terminate within the superficial laminae of the spinal cord overlapping projections known to have a nociceptive function. This implies that the surface coatings of neuronal membranes may have a relationship with functional modalities. The present investigation further examined this concept by studying a neuronal projection with a nociceptive function to determine whether fucosyl-lactoseries residues were incorporated in its primary afferent terminals. Transganglionic transport of horseradish peroxidase (HRP) following injection into tooth pulp chambers was employed to demonstrate dental pulp terminals in the trigeminal spinal complex, while peroxidase and fluorescent tags were used concomitantly to stain for UEA-I. Double immunolabeling for substance P (SP) and gamma-aminobutyric acid (GABA) using peroxidase and colloidal gold allowed a comparison of the distribution of a known excitatory nociceptive transmitter with that of UEA-I binding in specific subnuclei. Synaptic interrelationships between UEA-I positive dental pulp primary afferent inputs and specific inhibitory terminals were also examined. SP immunoreactivity occurred in laminae I and outer lamina II (IIo) of subnucleus caudalis (Vc) and in the ventrolateral and lateral marginal region of the caudal half of subnucleus interpolaris (Vi), including the periobex area in which Vi is slightly overlapped on its lateral aspect by cellular elements of Vc. The adjacent interstitial nucleus (IN) also showed an intense immunoreactivity for this peptide antibody. UEA-I binding displayed a similar distribution pattern in both Vc and Vi, but extended into lamina IIi and the superficial part of Lamina III in Vc. Dental pulp terminals were found to have a comparable distribution; however, many extended into the dorsal portion of the caudal half of Vi and the ventromedial quadrant of rostral Vi. Electron-microscopic analysis showed that transganglionically labeled dental pulp terminals contained ovoid, complex membrane-bound vacuoles laden with transported HRP. The preterminal axon and synaptic membranes of those dental pulp terminals located in zones of Vc and Vi displaying an affinity for UEA-I were usually characterized by a patchy, electron-dense coating of the peroxidase tag. SP was demonstrated ultrastructurally with Protein-A colloidal gold (3-nm particles), whereas GABA immunoreactivity was revealed by the avidin-biotin-peroxidase method.(ABSTRACT TRUNCATED AT 400 WORDS)     

The Central Projections of the Monkey Tooth Pulp Afferent Neurons

Transganglionic transport of horseradish peroxidase conjugated to wheatgerm agglutinin (HRP:WGA) entrapped in hypoallergenic polyacrylamide gel was used to study the patterns of termination of primary afferents that innervate the upper and lower tooth pulps within the trigeminal sensory nuclear complex (TSNC) of the monkey. HRP:WGA injections were also made into the lower incisors and molars, in order to examine the topographic arrangement of pulpal afferent projections. HRP-labeled pulpal afferents innervating lower and upper teeth projected ipsilaterally to the rostral subnucleus dorsalis (Vpd) and caudal subnucleus ventralis (Vpv) of the nucleus principalis (Vp); the rostrodorsomedial (Vo.r) and dorsomedial (Vo.dm) subdivisions of the nucleus oralis (Vo); the dorsomedial subdivision of the nucleus interpolaris (Vi); and laminae I—II and/or V of the nucleus caudalis (Vc) at its rostralmost level. The HRP-labeled terminals from upper and lower pulpal afferents formed a rostrocaudal column from the midlevel of Vp to the rostral tip of Vc. The label in Vp and Vo was considerably dense, but the column of terminals was interrupted at the Vpd-Vpv transition. The label in Vi and Vc was much less dense compared to that in the rostral nuclei, and the column of terminals was interrupted frequently. The representation of the upper and lower teeth in TSNC was organized in a somatotopic fashion that varied from one subdivision to the next, though their terminal zones overlapped within Vpd. The upper and lower teeth were represented in Vpv, Vo.r, Vo.dm, Vi, and Vc in a ventrodorsal, dorsoventral, lateromedial, lateromedial, and lateromedial sequence, respectively. Topographic arrangement was also noticed for the projections of pulpal afferents from the lower incisors and molars: The representations of the lower incisors and molars in Vpv, Vo.r, Vo.dm, Vi, and Vc were organized in a lateromedial, dorsoventral, ventrodorsal, ventrodorsal, and lateromedial sequence, respectively. The present results indicating sparse projections from pulpal afferents in the monkey's Vc are in good correspondence with a clinical report that trigeminal tractotomy just rostral to the obex has no significant effect on dental pain perception in patients. Furthermore, the present study indicates that projection patterns of pulpal afferents—which include the termination sites, the density of terminations between nuclei, and topographic arrangement—differ among animal species.     

Intersubnuclear Connections within the Rat Trigeminal Brainstem Complex

Prior intracellular recording and labeling experiments have documented local-circuit and projection neurons in the spinal trigeminal (V) nucleus with axons that arborize in more rostral and caudal spinal trigeminal subnuclei and nucleus principalis. Anterograde tracing studies were therefore carried out to assess the origin, extent, distribution, and morphology of such intersubnuclear axons in the rat trigeminal brainstem nuclear complex (TBNC). Phaseolus vulgaris leucoagglutinin (PHA-L) was used as the anterograde marker because of its high sensitivity and the morphological detail provided. Injections restricted to TBNC subnucleus caudalis resulted in dense terminal labeling in each of the more rostral ipsilateral subnuclei. Subnucleus interpolaris projected ipsilaterally and heavily to magnocellular portions of subnucleus caudalis, as well as subnucleus oralis and nucleus principalis. Nucleus principalis, on the other hand, had only a sparse projection to each of the caudal ipsilateral subnuclei. Intersubnuclear axons most frequently traveled in the deep bundles within the TBNC, the V spinal tract, and the reticular formation. They gave rise to a number of circumscribed, highly branched arbors with many boutons of the terminal and en passant types.

Retrograde single- or multiple-labeling experiments assessed the cells giving rise to TBNC intersubnuclear collaterals. Horseradish peroxidase (HRP) and/or fluorescent tracer injections into the thalamus, colliculus, cerebellum, nucleus principalis, and/or subnucleus caudalis revealed large numbers of neurons in subnuclei caudalis, interpolaris, and oralis projecting to the region of nucleus principalis. Cells projecting to more caudal spinal trigeminal regions were most numerous in subnuclei interpolaris and oralis. Some cells in lamina V of subnucleus caudalis and in subnuclei interpolaris and oralis projected to thalamus and/or colliculus, as well as other TBNC subnuclei. Such collateral projections were rare in nucleus principalis and more superficial laminae of subnucleus caudalis. TBNC cells labeled by cerebellar injections were not double-labeled by tracer injections into the thalamus, colliculus, or TBNC.

These findings lend generality to currently available data obtained with intracellular recording and HRP labeling methods, and suggest that most intersubnuclear axons originate in TBNC local-circuit neurons, though some originate in cells that project to midbrain and/or diencephalon.     

Blockage of vibrissae afferents: II. Footshock threshold increments

Because of their dense innervation rat vibrissae have been regarded as a very important sensory system. Many behavioral deficits have been reported by other authors after rat vibrissal afferent blockades. In the present work we found significant threshold increments to footshock following either reversible nerve block (procaine or nerve pressure) or section of the vibrissal afferent nerves, but not following vibrissae trimming. These results are discussed in reference to the tonic or level-setting function of afferent systems.     

Histological changes in the somatosensory thalamus after unilateral coagulation of vibrissa follicles of the muzzle of the newborn mouse

Light microscopic study of the thalamic ventro-basal complex (VB), after unilateral coagulation of vibrissae follicles in newborn mouse, revealed an excess of neuronal perikarya on the controlateral "deafferented" side as compared to the normal side. The higher density of nerve cells was confined to the vibrissal relay in the medial part of VB nucleus (VBm), whereas the cell number in the non vibrissal-lateral part of this nucleus (VB1) remained on the control level. Electron microscopic investigation of the thalamic vibrissal relay has shown signs of a modified synaptogenesis on the "deafferented" side: (a) the number of specific afferents has diminished and in contrast to the normal side, most of the specific sensory terminals contain small spheroid synaptic vesicles and (b) the number of axon terminals with ovoid pleomorphic vesicles has been doubled.     

Neck muscle and trigeminal input to the upper cervical cord and lower medulla of the cat.

Experiments on chloralose-anaesthetized cats have shown that low-threshold neck muscle afferents project to laminae IV and V in the dorsal horn of the upper cervical cord, to lamina VI including the region which encompasses the central cervical nucleus, as well as to extensive regions of the ventral horn. At posterior medullary levels projections also exist to laminae IV, V, and VI of the spinal nucleus of V (although those to lamina IV are circumscribed), to the deep layers and lateral margin of the cuneate nucleus, and to the inferior olive. These projections are both from low- and high-threshold afferents. Evidence of a functional relationship between the trigeminal and neck muscle afferent system was found both in the upper cervical cord and lower medulla. About 40% of units in both regions receive a convergent input and when convergence could not be demonstrated, prior stimulation of one modality in some instances affected the responsiveness of the unit to the other modality. A motor role was found for some trigeminal afferent projections to the upper cervical cord. Trigeminal afferents consistently activated antidromically identified motoneurons of splenius, biventer cervicis, and complexus.     

Blockage of vibrissae afferents: I. Motor effects

In the past, it has been proposed that the rat vibrissae play an important role in other hand, postural abnormalities, muscle tone decreases and hypomotility after sensory organ destructions were proposed as evidence supporting the "level setting" or "tonic" hypothesis. This hypothesis postulates that afferent activity, besides its well know transductive functions, sets the excitability state of the central nervous system. We thought the vibrissal system to be a good model to dissect these two postulated roles because vibrissae trimming would annul the transductive function without affecting the integrity of nerve activity. Thus we compare the effects of trimming the whiskers with blocking the vibrissal afferent nerves on two types of motor behavior: activity in an open field and walking over a rope connecting two elevated platforms. We found that only vibrissal afferent blockage (both nerve section and local anaesthesia) produced severe failures in the motor performances studied. These effects could not be fully explained by the abolition of the vibrissae as a sensory modality because cutting the whiskers did not significantly affect the motor performance. These data are discussed in reference to a tonic or general excitatory function of sensory inputs upon the central nervous system.     

Response properties of periodontal mechanosensitive neurons in the trigeminal spinal tract nucleus of the cat.

Periodontal mechanosensitive (PM) units were recorded from the trigeminal spinal tract nucleus (Vst) of the cat. The Vst is divided into three subnuclei: oralis (Vo), interpolaris (Vi), and caudalis (Vc). The receptive fields of PM units in Vo and Vi were arranged in a dorsoventral sequence in the mandibular to maxillary divisions, and those in Vc were arranged in a mediolateral sequence. The majority of Vo units were single-tooth ones, whereas more than half the Vi units and all the Vc ones were multitooth units. The PM units in each subnucleus were predominantly responsive to canine tooth stimulation. Most of the PM units in Vo and Vi gave sustained responses to pressure applied to the tooth, were directionally selective, and were most actively excited by canine tooth stimulation in the caudomedial or rostrolateral direction. Vc units, however, were transient. The threshold intensity for firings by canine tooth stimulation was less than 0.05 N. These findings indicate that only the response properties of PM units in the rostral part of Vst resemble those of the trigeminal main sensory nucleus neurons and primary afferent nerves.     

Ulex europaeus Agglutinin-I Binding to Dental Primary Afferent Projections in the Spinal Trigeminal Complex Combined with Double Immunolabeling of Substance P and GABA Elements Using Peroxidase and Colloidal Gold

Ulex europaeus agglutinin I (UEA-I) is a plant lectin with an affinity for L-fucosyl residues in the chains of lactoseries oligosaccharides associated with medium and smaller-diameter dorsal root ganglion neurons and their axonal processes. These enter Lissauer's tract and terminate within the superficial laminae of the spinal cord overlapping projections known to have a nociceptive function. This implies that the surface coatings of neuronal membranes may have a relationship with functional modalities. The present investigation further examined this concept by studying a neuronal projection with a nociceptive function to determine whether fucosyl-lactoseries residues were incorporated in its primary afferent terminals. Transganglionic transport of horseradish peroxidase (HRP) following injection into tooth pulp chambers was employed to demonstrate dental pulp terminals in the trigeminal spinal complex, while peroxidase and fluorescent tags were used concomitantly to stain for UEA-I. Double immunolabeling for substance P (SP) and γ-aminobutyric acid (GABA) using peroxidase and colloidal gold allowed a comparison of the distribution of a known excitatory nociceptive transmitter with that of UEA-I binding in specific subnuclei. Synaptic interrelationships between UEA-I positive dental pulp primary afferent inputs and specific inhibitory terminals were also examined.

SP immunoreactivity occurred in laminae I and outer lamina II (II_o) of subnucleus caudalis (Vc) and in the ventrolateral and lateral marginal region of the caudal half of subnucleus interpolaris (Vi), including the periobex area in which Vi is slightly overlapped on its lateral aspect by cellular elements of Vc. The adjacent interstitial nucleus (IN) also showed an intense immunoreactivity for this peptide antibody. UEA-I binding displayed a similar distribution pattern in both Vc and Vi, but extended into lamina II; and the superficial part of Lamina III in Vc. Dental pulp terminals were found to have a comparable distribution; however, many extended into the dorsal portion of the caudal half of Vi and the ventromedial quadrant of rostral Vi.

Electron-microscopic analysis showed that transganglionically labeled dental pulp terminals contained ovoid, complex membrane-bound vacuoles laden with transported HRP. The preterminal axon and synaptic membranes of those dental pulp terminals located in zones of Vc and Vi displaying an affinity for UEA-I were usually characterized by a patchy, electron-dense coating of the peroxidase tag. SP was demonstrated ultrastructurally with Protein-A colloidal gold (3-nm particles), whereas GABA immunoreactivity was revealed by the avidin—biotin—peroxidase method. This combined approach labeled a variety of simple axodendritic to large complex scalloped dental terminals which contained SP and were shown to have a UEA-I affinity. In addition, many of the larger terminals formed contacts with GABA-ergic dendrites and received inputs from GABA-ergic synapses. These complexes were most concentrated in lamina II_o of Vc and the ventrolateral zone of Vi. Many terminals in laminae II_i; and III with a UEA-I-positive surface coating failed to bind with the antiserum for SP, indicating that other transmitters may colocalize with UEA-I and suggesting that absolute correlations between specific oligosaccharide plasmalemmal coatings and functional modalities should be approached with caution. Further studies employing antisera to different transmitters are currently underway to better define the relationship between transmitter localization and anatomical substrates within this circuitry. These studies should eventually provide additional clues about relationships between functional properties and oligosaccharide coatings of primary afferent projections.     

Experimental morphological study of primary afferent terminals at the base of the dorsal horn of the cat spinal cord

The distribution and ultrastructure of primary afferent terminals in the gray matter of the cervical and lumbar regions of the cat spinal cord were studied by the experimental degeneration method of Fink and Heimer. Most preterminals of primary afferents were shown to be concentrated in the region of the intermediate nucleus of Cajal (central part of Rexed's laminae VI–VII), in the substantial gelatinosa (laminae II–III), and in the nucleus proprius of the dorsal horn (central and medial parts of lamina IV). Fewer are found in the region of the motor nuclei. The number of degenerating axon terminals in the lateral parts of laminae IV and V differed: 31.5 and 0.4% respectively of all axon terminals. Many terminals of primary afferents in lamina IV contribute to the formation of glomerular structures in which they exist as terminals of S-type forming axo-axonal connections with other terminals. These results are in agreement with electrophysiological data to show that interneurons in different parts of the base of the dorsal horn differ significantly in the relative numbers of synaptic inputs formed by peripheral afferents and descending systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 406–414, July–August, 1973.     

The Distribution of Afferent Neurons in the Trigeminal Mesencephalic Nucleus and the Central Projection of Afferent Fibers of the Mylohyoid Nerve in the Rat

Horseradish peroxidase conjugated to wheatgerm agglutinin (HRP:WGA) was injected into the proximal cut ends of three branches of the mylohyoid nerve in rats: the branch to the mylohyoid muscle (BrMh), the branch to the anterior belly of the digastricus muscle (BrDg), and the cutaneous branch (BrCu). HRP-labeled cells were detected in the ipsilateral caudal portion of the trigeminal mesencephalic nucleus (Vmes) and the ipsilateral ventromedial division of the trigeminal motor nucleus, except when HRP:WGA was applied to the BrCu. Morphologically, all labeled Vmes cells were of the pseudounipolar type.

Projections of the primary afferents of the BrMh were observed in the ipsilateral trigeminal nucleus caudalis, the upper cervical dorsal horns of laminae I -III, and the dorsolateral recticular formation (Rf), whereas the primary afferents of the BrDg terminated in the ipsilateral trigeminal nucleus principalis and Rf. These observations suggest that the role of the afferent inputs of the mylohyoid muscle differs from that of those of the anterior belly of the digastricus muscle in terms of several functions associated with jaw-closing and infrahyoid muscles.     

Peripheral axotomy of the rat mandibular trigeminal nerve leads to an increase in VIP and decrease of other primary afferent neuropeptides in the spinal trigeminal nucleus

In the vasoactive intestinal polypeptide (VIP)-rich lumbosacral spinal cord, VIP increases at the expense of other neuropeptides after primary sensory nerve axotomy. This study was undertaken to ascertain whether similar changes occur in peripherally axotomised cranial sensory nerves. VIP immunoreactivity increased in the terminal region of the mandibular nerve in the trigeminal nucleus caudalis following unilateral section of the sensory root of the mandibular trigeminal nerve at the foramen orale. Other primary afferent neuropeptides (substance P, cholecystokinin and somatostatin) were depleted and fluoride-resistant acid phosphatase activity was abolished in the same circumscribed areas of the nucleus caudalis. The rise in VIP and depletion of other markers began 4 days postoperatively and was maximal by 10 days, these levels remaining unchanged up to 1 year postoperatively. VIP-immunoreactive cell bodies were absent from trigeminal ganglia from the unoperated side but small and medium cells stained intensely in the ganglia of the operated side after axotomy. These observations indicate that increase of VIP in sensory nerve terminals is a general phenomenon occurring in both cranial and spinal sensory terminal areas. The intense VIP immunoreactivity in axotomised trigeminal ganglia suggests that the increased levels of VIP in the nucleus caudalis are of peripheral origin, indicating a change in expression of neuropeptides within primary afferent neurons following peripheral axotomy.