Persistent Fos protein expression after orofacial deep or cutaneous tissue inflammation in rats: implications for persistent orofacial pain.

This study was designed to systematically examine the effects of persistent orofacial tissue injury on prolonged neuronal activation in the trigeminal nociceptive pathways by directly comparing the effects of orofacial deep vs. cutaneous tissue inflammation on brainstem Fos protein expression, a marker of neuronal activation. Complete Freund's adjuvant (CFA) was injected unilaterally into the rat temporomandibular joint (TMJ) or perioral (PO) skin to produce inflammation in deep or cutaneous tissues, respectively. Rats were perfused 2 hours, 24 hours, 3 days, or 10 days following CFA injection. The TMJ and PO inflammation-induced Fos expression paralleled the intensity and course of inflammation over the 10-day observation period, suggesting that the increase in intensities and persistence of Fos protein expression may be associated with a maintained increase in peripheral input. Compared to PO CFA injection, the injection of CFA into the TMJ produced a significantly stronger inflammation associated with a greater Fos expression. In TMJ- but not in PO-inflamed rats, Fos-like immunoreactivity (LI) spread from superficial to deep upper cervical dorsal horn as the inflammation persisted and there was a dominant ipsilateral Fos-labeling in the paratrigeminal nucleus. Common to TMJ and PO inflammation, Fos-LI was induced in the trigeminal subnuclei interpolaris and caudalis, C1-2 dorsal horn, and other medullary nuclei. Substantial bilateral Fos-LI was found in the interpolaris-caudalis trigeminal transition zone. Further analysis revealed that Fos-LI in the ventral transition zone was equivalent bilaterally, whereas Fos-LI in the dorsal transition zone was predominantly ipsilateral to the inflammation. The differential induction of Fos expression suggests that an increase in TMJ C-fiber input after inflammation and robust central neuronal hyperexcitability contribute to persistent pain associated with temporomandibular disorders.     

Morphology of central terminations of intra-axonally stained, large, myelinated primary afferent fibers from facial skin in the rat

Horseradish peroxidase was intra-axonally injected into functionally identified primary afferent fibers within the rat spinal trigeminal tract in order to study the morphology of their central terminations. They were physiologically determined to be large, myelinated, cutaneous primary afferents by means of electrical and mechanical stimulation of their receptive fields. Ninety-three axons that innervated vibrissa follicles, guard hair follicles, and slowly adapting receptors were stained for distances of 4-12 mm at the levels of the main sensory nucleus, spinal trigeminal nucleus, and rostral cervical spinal cord. The collaterals of single axons from these receptors formed terminal arbors in the outer part of the spinal trigeminal nucleus rostral to and near the level of the obex (rostral type collaterals). In the rostral part of the subnucleus caudalis (Vc) they were confined to lamina V (caudalis type collaterals) and in the caudal part of Vc and in cervical segments they were confined to lamina III/IV (spinal-dorsal-horn-type collaterals). There were no transitional forms between the rostral and caudalis types, but there was a transitional form between the caudalis and spinal dorsal horn types. This transitional form was distributed in laminae III/IV and V. The terminal arbors of the rostral type of collaterals formed an interrupted, rostrocaudally oriented column like those seen in the lumbar dorsal horn, but the column shifted down to lamina V near the obex, and more caudally, gradually shifted upward to lamina III. Major morphological differences were not observed among the three different functional types of collaterals with respect to the rostrocaudal distribution of collaterals, and the shape and location of collaterals. The differential laminar distribution of collateral arbors of single axons along the rostrocaudal axis distinguishes the spinal trigeminal nucleus from the spinal dorsal horn where functional types of mechanoreceptive afferents form continuous or interrupted sagittal columns of terminal arbors that do not shift dorsoventrally within segments.     

The central projections of trigeminal primary afferent neurons in the cat as determined by the tranganglionic transport of horseradish peroxidase

The central projections of five peripheral branches of the trigeminal nerve were investigated by the method of transganglionic transport of horseradish peroxidase (HRP). In separate animals, the corneal, supraorbital, infraorbital, mental, or inferior alveolar branches were transected and soaked in concentrated solutions of HRP. Forty-eight to 72 hours after surgery, the brainstem, upper cervical spinal cord, and trigeminal ganglia were perfusion-fixed and processed according to the tetramethylbenzidine technique. The results show that trigeminal primary afferent neurons which innervate the cornea project mainly to the levels of caudal pars interpolaris and caudal pars caudalis. In contrast, trigeminal primary afferent neurons whose peripheral processes course through the supraorbital, infraorbital, or mental nerves project most heavily to the trigeminal main sensory nucleus, pars interpolaris, and the rostrocaudal middle three-fifths of pars caudalis. Trigeminal primary afferent neurons which give origin to the inferior alveolar nerve project heavily and in approximately equal numbers of all rostrocaudal levels of the trigeminal brainstem nuclear complex (TBNC). A small number of fibers from each of the latter four cell populations project directly to the contralateral C1-C2 dorsal horn. A small number of fibers from each cell population studied end in the reticular formation immediately adjacent to the spinal nucleus of V. It is concluded that the cornea and facial skin regions of the cat are represented nonuniformly along the rostrocaudal length of the TBNC.     

The caudal subnucleus caudalis (medullary dorsal horn) acts as an interneuronal relay site in craniofacial nociceptive reflex activity

We have recently documented that bilateral increases in electromyographic (EMG) activity of digastric (DIG) and masseter (MASS) muscles can be evoked by injection into the rat's temporomandibular joint (TMJ) region of the small-fiber excitant and inflammatory irritant mustard oil and that this increased jaw muscle activity can be significantly reduced by extensive lesions of the trigeminal subnucleus caudalis (Vc). This study was carried out in 34 anaesthetized rats to test whether neurones in the caudal Vc are indeed of critical importance in these craniofacial nociceptive reflexes. The effects of micro-injection of the cellular neurotoxic chemical ibotenic acid in histologically confirmed sites of the caudal brainstem on the mustard oil-evoked EMG activity of ipsilateral and contralateral DIG and MASS were tested. Ibotenic acid micro-injection in the left caudal Vc significantly reduced the increased EMG activity of all four muscles evoked by mustard oil injection into the left TMJ region whereas mustard oil injection into the right TMJ region in these same rats still readily evoked an increase in EMG activity. In other groups of rats, ibotenic acid micro-injection into the rostral Vc, the C2 segment or the reticular formation at the obex level did not produce any significant reduction in the reflexly evoked EMG activity. These findings suggest that neurones in the caudal Vc may be critical elements in neural pathways underlying the reflex responses evoked in jaw muscles by noxious stimulation of the TMJ region.     

The sensory trigeminal complex and the organization of its primary afferents in the zebra finch (Taeniopygia guttata)

Our knowledge of the avian sensory trigeminal system has been largely restricted to the principal trigeminal nucleus (PrV) and its ascending projections to the forebrain. Studies addressing the cytoarchitecture and organization of afferent input to the sensory trigeminal complex, which includes both the PrV and the nuclei of the descending trigeminal tract (nTTD), have only been performed in pigeons and ducks. Here we extend such an analysis to a songbird, the zebra finch (Taeniopygia guttata). We describe the cytoarchitecture of the sensory trigeminal complex, the patterns of calbindin‐like and substance P‐like immunoreactivity, and the organization of afferents from the three branches of the trigeminal nerve and from the lingual branch of the hypoglossal nerve. On the basis of cytoarchitecture and immunohistochemistry, the sensory trigeminal column can be subdivided from caudal to rostral, as in other species, into cervical dorsal horn, subnucleus caudalis, subnucleus interpolaris, subnucleus oralis, and nucleus principalis. The relative positions of the terminal fields of the three trigeminal branches move from medial to lateral in the dorsal horn to dorsomedial to ventrolateral in nTTD, whereas in PrV there is considerable overlap of mandibular and ophthalmic terminal fields, with only a small maxillary input ventrally. The hypoglossal afferents, which terminate medially in the dorsal horn and dorsolaterally in nTTD, terminate in specific cell groups in the dorsolateral nTTDo and in PrV. This work sets the grounds for further analyses of the ascending connections of the nTTD and the afferents from the syrinx to the trigeminal sensory column.     

Orofacial deep and cutaneous tissue inflammation differentially upregulates preprodynorphin mRNA in the trigeminal and paratrigeminal nuclei of the rat

Preprodynorphin (PPD) and preproenkephalin (PPE) gene expression in a rat model of orofacial inflammation were examined in order to further characterize the neurochemical mechanisms underlying orofacial inflammation and hyperalgesia. Deep and cutaneous orofacial inflammation was produced by a unilateral injection of complete Freund's adjuvant (CFA) into the rat temporomandibular joint (TMJ) or perioral skin (PO), respectively. RNA blot analysis of the tissues including the spinal trigeminal complex revealed that the PPD mRNA level ipsilateral to TMJ inflammation was increased by 56.5+/-14.7% (n=4) when compared to the Naive group, and was significantly greater than the contralateral PPD mRNA level (p<0.05). The distribution of neurons that exhibited PPD mRNA after inflammation was localized by in situ hybridization (naive approximately 0). In TMJ-inflamed rats (n=6) PPD mRNA-positive neurons were found ipsilaterally in the medial portion of laminae I-II of the upper cervical dorsal horn (4.5+/-0.3), the dorsal portion of the subnucleus caudalis and caudal subnucleus interpolaris (5.2+/-0.3), and the paratrigeminal nucleus (6.4+/-1.2). A very localized induction of PPD mRNA was also identified in a group of neurons in the intermediate portion of the subnucleus caudalis (2.4+/-0.4) in PO-inflamed rats (n=6). The distribution of these PPD mRNA-positive neurons was somatotopically relevant to the site of injury. There were no significant changes in PPE mRNA expression in both TMJ- and PO-inflamed rats. These results indicate that TMJ inflammation resulted in a more intense and widespread increase in PPD mRNA expression when compared to PO inflammation. These changes may contribute to persistent central hyperexcitability and pain associated with temporomandibular disorders.     

Contralateral projections of trigeminal mandibular primary afferents in the guinea pig as seen by transganglionic transport of horseradish peroxidase

Transganglionic transport of horseradish peroxidase (HRP) was used to investigate contralateral projections of trigeminal mandibular fibers in the guinea pig. After application of HRP to the buccal, lingual, auriculotemporal, mylohyoid, mental and inferior alveolar nerves, crossing fibers and contralateral endings were found in the caudal region of the nucleus of the solitary tract (most of these belonging to the buccal and lingual nerves), the dorsomedial region of the subnucleus caudalis of the trigeminal sensory nuclear complex (TSNC), and the dorsal horns of the first 5 cervical spinal cord segments (C1-C5). The greatest numbers of crossing fibers in the medullary and cervical dorsal horn segments belonged to the mental and mylohyoid nerves, though these nerves did not project contralaterally to C4-C5. Contralateral buccal and lingual endings were scattered sparsely from the subnucleus caudalis to C5, and only very few contralateral auriculotemporal terminals were observed. Though laminae I-V of the dorsomedial region of the medullary and cervical dorsal horns all exhibited contralateral endings of the mental and mylohyoid nerves, most such endings were found in laminae IIi-III, followed by lamina IV, which suggests their involvement in the reception of mechanical stimuli and in the sensory motor reflexes of the orofacial region. The contralateral buccal and lingual terminals were distributed somatotopically in the first 5 cervical cord segments, with the lingual endings rostral to the buccal terminals within each segment. In C4 and C5 lingual endings appeared exclusively in laminae I and IIo, suggesting that like the ipsilateral lingual projections at this level, which also terminate in these laminae, they may be involved in pain and temperature sensation.     

Central distribution of primary afferent fibers in the Arnold's nerve (the auricular branch of the vagus nerve): A transganglionic HRP study in the cat

Central projections of the Arnold's nerve (the auricular branch of the vagus nerve; ABV) of the cat were examined by the transganglionic HRP method. After applying HRP to the central cut end of the ABV, HRP-labeled neuronal somata were seen in the superior ganglion of the vagus nerve. Main terminal labeling was seen ipsilaterally in the solitary nucleus, in the lateral portions of the ventral division of the principal sensory trigeminal nucleus, in the marginal regions of the interpolar subnucleus of the spinal trigeminal nucleus, in the marginal and magnocellular zones of the caudal subnucleus of the spinal trigeminal nucleus, in the ventrolateral portions of the cuneate nucleus, and in the dorsal horn of the C1–C3 cord segments. In the solitary nucleus, labeled terminals were seen in the interstitial, dorsal, dorsolateral and commissural subnuclei; some of these terminals may be connected monosynaptically with solitary nucleus neurons which send their axons to the somatomotor and/or visceromotor centers in the brainstem and spinal cord.     

Corneal sensory pathway in the rat: a horseradish peroxidase tracing study

The methods of transganglionic transport of horseradish peroxidase (HRP) and horseradish peroxidase--wheat germ agglutinin (HRP-WGA) were used to determine the location within the trigeminal ganglion of the primary afferent neurons that innervate the rat central cornea, and the brainstem and spinal cord termination sites of these cells. In each of 18 animals, solutions of HRP or HRP-WGA were applied to the scarified corneal surface and allowed to infiltrate into the corneal epithelium and stroma for 15 minutes. Postmortem examination of the corneal whole mounts from the experimental animals, and of corneas and neural tissues from several control animals, showed that the HRP/HRP-WGA remained confined to the central cornea with no spread into adjacent intra- or extraorbital tissues. HRP-labeled corneal afferent somata were located in the dorsal part of the ophthalmic region of the ipsilateral trigeminal ganglion. The central fibers of the corneal afferent neurons projected very heavily to interstitial nuclei of Cajal in the spinal tract of V at the level of caudal pars interpolaris and rostral pars caudalis, lightly to the pars caudalis/C1 transition zone, and sparsely to the dorsal horn of spinal cord segments C1-C3. The trigeminal main sensory nucleus, pars oralis, the rostral three-fourths of pars interpolaris, and an extensive midregion of pars caudalis were totally devoid of reaction product. Terminal fields in caudal pars caudalis and in the spinal cord dorsal horn were concentrated largely in the outer half of lamina II, with lesser accumulations in lamina I, the deeper half of lamina II, and in lamina III. The present study demonstrates for the first time by means of an anatomical tracing procedure the brainstem termination sites of corneal afferent neurons in the rat. The patchy, discontinuous nature of the corneal afferent projection to the caudal trigeminal brainstem nuclear complex (TBNC), and the total lack of corneal projections to rostral subdivisions of the TBNC, provide an exception to the general rule of trigeminal organization in which most areas of the head and face are represented as continuous columns throughout the rostrocaudal extent of the ipsilateral TBNC.     

Efferent projections from temperature sensitive recording loci within the marginal zone of the nucleus caudalis of the spinal trigeminal complex in the cat

The efferent projections from nucleus caudalis of the spinal trigeminal complex in cats were studied with retrograde and anterograde axonal transport techniques combined with localization of recording sites in the thalamus and marginal zone of nucleus caudalis to innocuous skin cooling. Results showed brainstem projections from nucleus caudalis to rostral levels of the spinal trigeminal complex, to the ventral division of the principal trigeminal nucleus, the parabrachial nucleus, cranial motor nuclei 7 and 12, solitary complex, contralateral dorsal inferior olivary nucleus, portions of the lateral reticular formation, upper cervical spinal dorsal horn and, lateral cervical nucleus. Projections to the thalamus included: a dorsomedial region of VPM (bilaterally) and to the main part of VPM and PO contralaterally. Neuronal activity was recorded in the dorsomedial region of VPM to cooling the ipsilateral tongue. HRP injections in this thalamic region retrogradely labeled marginal neurons in nucleus caudalis. These results show that marginal neurons of nucleus caudalis provide a trigeminal equivalent of spinothalamic projections to the ventroposterior nucleus in cats.     

Oral and facial representation within the medullary and upper cervical dorsal horns in the cat

Transganglionic transport of HRP was used to study the patterns of termination of somatic afferent fibers innervating oral and facial structures within the trigeminal nucleus caudalis and upper cervical dorsal horn of the cat. In separate animals, the superior alveolar, pterygopalatine, buccal, inferior alveolar, lingual, frontal, corneal, zygomatic, infraorbital, mental, mylohyoid, and auriculotemporal branches of the trigeminal nerve were traced in this experiment. The organization of the primary afferents innervating the oral structures is not uniform across laminae and at different rostrocaudal levels of the nucleus caudalis. The superior alveolar and pterygopalatine nerves mainly terminate in laminae I, II, and V at the level of the rostral one-third of the caudalis. By contrast, the lingual, inferior alveolar, and buccal nerve terminate in laminae I-V of, respectively, the rostral third, the entire length, and caudal two-thirds of the caudalis. In addition, the lingual, buccal, and pterygopalatine nerves terminate in the dorsal and middle parts of the interstitial islands or pockets of lamina I neuropil extending to the rostral levels parallel to the nucleus interpolaris. Mediolaterally, in laminae I, II, and V of the rostral third an extensive overlap of projections was found between the branches from each trigeminal division, and some overlap was observed between projections from the mandibular and maxillary divisions. On the other hand, the projections of primary afferents innervating the facial structures are arranged in a somatotopic fashion in rostrocaudal and mediolateral axes over the laminae (I-IV) through the nucleus caudalis and upper cervical dorsal horn. Fibers from the perioral and perinasal regions terminate most rostrally in caudalis, and fibers from progressively more posterior facial regions terminate at successively lower levels. A mediolateral somatotopic arrangement was observed, with fibers from the ventral parts of face ending in the medial regions and fibers from the progressively more dorsal parts of the face ending in successively more lateral regions of the medullary and upper cervical dorsal horns. Corneal afferent terminals are concentrated in the outer parts of lamina II at the levels of the rostral parts of the caudal two-thirds of the caudalis and the interstitial islands of lamina I. The maxillary division terminates first at the most caudal level of the caudalis, followed by the ophthalmic division descending as far as the C2 segment and the mandibular division reaching the most caudal level of the C2 segment.(ABSTRACT TRUNCATED AT 400 WORDS)     

Primary afferent projections from the upper respiratory tract in the muskrat.

The central projections of the ethmoidal, glossopharyngeal, and superior laryngeal nerves were determined in the muskrat by use of the transganglionic transport of a mixture of horseradish peroxidase (HRP) and wheat germ agglutinin (WGA)-HRP. The ethmoidal nerve projected to discrete areas in all subdivisions of the ipsilateral trigeminal sensory complex. Reaction product was focused in ventromedial portions of the principal nucleus, subnucleus oralis, and subnucleus interpolaris. The subnucleus oralis also contained sparse reaction product in its dorsomedial part. Projections were dense to ventrolateral parts of laminae I and II of the rostral medullary dorsal horn, with sparser projections to lamina V. Label in laminae I and V extended into the cervical dorsal horn. A few labeled fibers were followed to the contralateral dorsal horn. The interstitial neuropil of the ventral paratrigeminal nucleus was densely labeled. Extratrigeminal primary afferent projections in ethmoidal nerve cases involved the K?lliker-Fuse nucleus and ventrolateral part of the parabrachial nucleus, the reticular formation surrounding the rostral ambiguous complex, and the dorsal reticular formation of the closed medulla. Retrograde labeling in the brain was observed in only the mesencephalic trigeminal nucleus in these cases. The cervical trunk of the glossopharyngeal and superior laryngeal nerves also projected to the trigeminal sensory complex, but almost exclusively to its caudal parts. These nerves terminated in the dorsal and ventral paratrigeminal nuclei as well as lamina I of the medullary and cervical dorsal horns. Lamina V received sparse projections. The glossopharyngeal and superior laryngeal nerves projected to the ipsilateral solitary complex at all levels extending from the caudal facial nucleus to the cervical spinal cord. At the level of the obex, these nerves projected densely to ipsilateral areas ventral and ventromedial to the solitary tract. Additional ipsilateral projections were observed along the dorsolateral border of the solitary complex. Near the obex and caudally, the commissural area was labeled bilaterally. Labeled fibers from the solitary tract projected into the caudal reticular formation bilaterally, especially when the cervical trunk of the glossopharyngeal nerve received tracer. Labeled fibers descending further in the solitary tract gradually shifted toward the base of the cervical dorsal horn. The labeled fibers left the solitary tract and entered the spinal trigeminal tract at these levels. Retrogradely labeled cells were observed in the ambiguous complex, especially rostrally, and in the rostral dorsal vagal nucleus after application of HRP and WGA-HRP to either the glossopharyngeal or superior laryngeal nerves. In glossopharyngeal nerve cases, retrogradely labeled neurons also were seen in the inferior salivatory nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Projection of jaw-muscle spindle afferents to the caudal brainstem in rats demonstrated using intracellular biotinamide

Intracellular staining with biotinamide was used to study the axonal projection and synaptic morphology of rat jaw-muscle spindle afferents. Intracellular recordings in the mesencephalic trigeminal nucleus (Vme) were identified as spindle afferent responses by their increased firing during stretching of the jaw-elevator muscles. Biotinamide-stained axon collaterals with boutons were found in the trigeminal motor nucleus (Vmo), Vme, the region dorsal to Vmo including the supratrigeminal region, the dorsomedial portion of the trigeminal principal sensory nucleus, and the dorsomedial part of the rostral spinal trigeminal subnucleus oralis. Additional, previously undescribed projections of jaw-muscle spindle afferents were found to the dorsomedial portiori of the caudal spinal trigeminal subnucleus oralis (Vodm), the dorsomedial part of the spinal trigeminal subnucleus interpolaris (Vidm), the caudal parvicellular reticular formation, laminae IV and V of the spinal trigeminal subnucleus caudalis (Vc), and the dorsal division of the medullary reticular field. Labeled spindle boutons in Vodm formed predominately axodendritic synapses. Some of these boutons received presynaptic inputs from unlabeled P-type boutons containing clear, spherical, or flattened vesicles. In Vidm, labeled collaterals and boutons were densely clustered into glomerular-like structures. Labeled boutons in Vidm made axodendritic, axosomatic, and axoaxonic synapses and received synaptic contacts from unlabeled boutons containng clear, spherical, or flat and pleomorphic vesicles. Unlabeled presynaptic boutons in Vidrn occasionally contained dense core vesicles. Labeled boutons in Vc mainly formed synaptic contacts with large diameter dendrites. This projection of jaw-muscle spindle afferents to caudal brainstem regions may play a significant role in masticatory-muscle stretch reflexes and in the integration of trigeminal proprioceptive information and its transmission to higher centers. © 1995 Wiley-Liss, Inc.     

Somatic and visceral afferents to the 'vasodepressor region' of the caudal midline medulla in the rat

Previous research has found that the integrity of a restricted region of the caudal midline medulla (including caudal portions of nucleus raphé obscurus and nucleus raphé pallidus) was critical for vasodepression (hypotension, bradycardia, decreased cardiac contractility) evoked either by haemorrhage or deep pain. In this anatomical tracing study we found that the vasodepressor part of the caudal midline medulla (CMM) receives inputs arising from spinal cord, spinal trigeminal nucleus (SpV) and nucleus of the solitary tract (NTS). Specifically: (i) a spinal-CMM projection arises from neurons of the deep dorsal horn, medial ventral horn and lamina X at all spinal segmental levels, with approximately 60% of the projection originating from the upper cervical spinal cord (C1-C4); (ii) a SpV-CMM projection arises primarily from neurons at the transition between subnucleus caudalis and subnucleus interpolaris; (iii) a NTS-CMM projection arises primarily from neurons in ventrolateral and medial subnuclei. In combination, the specific spinal, SpV and NTS regions which project to the CMM receive the complete range of somatic and visceral afferents known to trigger vasodepression. The role(s) of each specific projection is discussed.     

Trigeminal nuclear complex of the ferret: Anatomical and Immunohistochemical studies

In order to establish the ferret as an animal model for studies of trigeminal pain, we describe the cytoarchitecture and neurochemistry of the trigeminal nuclear complex in the ferret and compare them to those of the cat and rat. The complex was divided as previously described, but the ferret differed in the extent of the nuclear boundaries. The neuroantomical distribution of substance P-, calcitonin gene-related peptide-, galanin-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and neurotensin-immunoreactivity was determined throughout the rostrocaudal extent of the complex. In subnucleus caudalis, substance P-, calcitonin gene-related peptide-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and galanin-immunoreactivity was densest in laminae I and II. In subnucleus interpolaris, immunoreactivity for all the above neurochemicals was most dense along the lateral border and the ventral third of the caudal part of the subnucleus. Enkephalin-immunoreactive cell bodies were present in subnucleus caudalis and interpolaris. In subnucleus oralis, labelling for substance P, calcitonin gene-related peptide, galanin, enkephalin, and serotonin was most prominent in the dorsomedial part of the subnucleus. Somatostatin-immunoreactive cell bodies were distributed throughout the spinal nucleus. Labelling of serotonin, substance P, calcitonin gene-related peptide, galanin, enkephalin, and somatostatin was present in the main sensory nucleus. The motor nucleus contained fibers immunoreactive for substance P, enkephalin, serotonin and neuropeptide Y, and cell bodies immunoreactive for calcitonin gene-related peptide. The majority of neurotensin-immunoreactivity was found at the level of subnucleus caudalis, where it was densest in the trigeminal extension of the lateral cervical nucleus. The distribution of peptides in this species throughout the spinal nucleus is consistent with the notion that all the subnuclei may be involved in the processing of nociceptive inputs. © 1993 Wiley-Liss, Inc.     

Projection sites of superficial and deep spinal dorsal horn cells in the nucleus tractus solitarii of the rat

By using anterograde transport of biotin dextran amine injected into the cervical spinal dorsal horn, we have shown that fibres from superficial and deep dorsal horn project to the nucleus tractus solitarii via two distinct pathways. Afferent fibres from the superficial lamina (I-III) were found to course in the dorsal funiculus and terminate bilaterally in the caudal zone of the nucleus tractus solitarii (NTS), mainly within the commissural subnucleus. In contrast, afferents from the deeper dorsal horn laminae (IV-V) were found to course in the dorsolateral fasciculus and terminate ipsilaterally, mostly in the lateral areas of the caudal nucleus tractus solitarii. Similar, but more extensive patterns of labelled fibres were produced by injections into the white matter of the dorsal funiculus and dorsolateral fasciculus, respectively. These observations suggest that the caudal NTS not only serves as a location of visceral afferent convergence and integration, but may also be a receptive area for monosynaptic projections from dorsal horn neurons receiving sensory afferent inputs. Such projections may represent pathways through which NTS neurons are influenced by nociceptive and non-nociceptive information from the dorsal horn and thereby can co-ordinate the appropriate autonomic response, including adjustments in cardiorespiratory reflex output.     

Trigeminal primary afferent projections to "non-trigeminal" areas of the rat central nervous system.

The central projections of rat trigeminal primary afferent neurons to various "non-trigeminal" areas of the central nervous system were examined by labeling the fibers with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) transported anterogradely from the trigeminal ganglion. This technique produced a clear and comprehensive picture of trigeminal primary afferent connectivity that was in many ways superior to that which may be obtained by using degeneration, autoradiography, cobalt labeling, or HRP transganglionic transport techniques. Strong terminal labeling was observed in all four rostrocaudal subdivisions of the trigeminal brainstem nuclear complex, as well as in the dorsal horn of the cervical spinal cord bilaterally, numerous brainstem nuclei, and in the cerebellum. Labeling in the ipsilateral dorsal horn of the cervical spinal cord was very dense at C1, moderately dense at C2 and C3, and sparse at C4-C7. Numerous fibers crossed the midline in the medulla and upper cervical spinal cord and terminated in the contralateral pars caudalis and dorsal horn of the spinal cord from C1-C5. The latter axons terminated most heavily in the mandibular and ophthalmic regions of the contralateral side. Extremely dense terminal labeling was observed in the ipsilateral paratrigeminal nucleus and the nucleus of the solitary tract, moderate labeling was seen in the supratrigeminal nucleus and in the dorsal reticular formation, and small numbers of fibers were observed in the cuneate, trigeminal motor, lateral and superior vestibular nuclei, and in the cerebellum. The latter fibers entered the cerebellum in the superior cerebellar peduncle and projected to the posterior and anterior lobes as well as to the interposed and lateral deep cerebellar nuclei. Most projections in this study originated from fibers in the dorsal part of the spinal tract of V, suggesting a predominantly mandibular origin for these fibers. Projections from the ophthalmic and maxillary divisions, in contrast, were directed mainly to the cervical spinal cord bilaterally, to contralateral pars caudalis, and to certain areas of the reticular formation. In conclusion, this study has demonstrated that somatosensory information from the head and face may be transmitted directly to widespread and functionally heterogeneous areas of the rat central nervous system, including the spinal cord dorsal horn, numerous brainstem nuclei, and the cerebellum.(ABSTRACT TRUNCATED AT 400 WORDS)     

The central projections of tooth pulp afferent neurons in the rat as determined by the transganglionic transport of horseradish peroxidase

Transganglionic transport of horseradish peroxidase (HRP) or horseradish peroxidase-wheat germ agglutinin conjugate (HRP-WGA) was used to map in detail the central projections of trigeminal primary afferent neurons that innervate the dental pulp organ of the rat. In each of ten animals, 0.5-2.0 microliters of enzyme solution was injected into the pulp chamber of the first maxillary molar tooth. Postmortem examination of the decalcified teeth in all cases showed that the HRP/HRP-WGA remained confined to the pulp chamber and pulp roots, with no spread of enzyme into periapical tissues. HRP-labeled tooth pulp afferent fibers projected to all four rostrocaudal subdivisions of the ipsilateral trigeminal brainstem nuclear complex (TBNC) and to the upper cervical spinal cord. The labeled terminal fields formed a column that stretched relatively uninterrupted from just caudal to the rostromedial tip of the trigeminal principal sensory nucleus to at least the C2 segment of the spinal cord. The density of the afferent projection varied markedly from one rostrocaudal level of the TBNC to the next but was heaviest in an area encompassing the caudal one-half of the principal sensory nucleus and the rostral two-thirds of pars oralis. Fibers projected only lightly to pars caudalis, where they terminated preferentially in laminae I, IIa, and the junctional zone between laminae IV and V. HRP-labeled terminals in C1 and C2 were located almost exclusively in laminae I. In the dorsoventral axis, the terminal fields in the TBNC were located in a surprisingly dorsal part of the complex, well within what has been shown by others to be largely an area of termination for mandibular division fibers. Most fibers ended in medial parts of the TBNC, with the exception of two modestly labeled terminal fields located in the lateral aspects of rostral pars oralis and rostral pars caudalis. No labeled fibers terminated in the contralateral TBNC or contralateral cervical spinal cord.     

Peripheral and central terminations of hypoglossal afferents innervating lingual tactile mechanoreceptor complexes in Fringillidae.

Injections of cholera toxin B subunit conjugated to horseradish peroxidase (CTB-HRP) were made into the lingual branch of the hypoglossal nerve in four species of finch in order to identify the innervation of the mechanoreceptors of the dermal papillae of the tongue, and simultaneously to determine the pattern of central projections of lingual hypoglossal afferents. The results showed that hypoglossal fibers innervate all the Herbst corpuscles and terminal cell receptors of the elaborately organized papillae of the dorsum of the tongue, of the shorter papillae in the ventral tongue, and the loose collection of Herbst corpuscles in the subpapillary region. Labelled fibers were also observed in the intralingual glands, in the intrinsic tongue muscles, and in the posterodorsal epithelium where they formed budlike structures. Retrogradely labelled cell bodies were located in the jugular ganglion and their central processes ascended and descended throughout the brainstem within the descending trigeminal tract (TTD). Terminal fields were observed within the dorsolateral part of the nucleus caudalis of TTD, predominantly ipsilaterally, and within the medial part of the dorsal horn of the first 4-6 cervical segments bilaterally. There were dense patches of termination over a dorsolateral subnucleus of the interpolated nucleus of TTD, and within two regions of the principal sensory trigeminal nucleus: a large one laterally and a small one medially. Terminal fields were also observed within the nucleus ventralis lateralis anterior of the rostral solitary complex, and within adjacent nuclei, which are probably equivalent to the dorsal sensory nuclei of the facial and glossopharyngeal nerves of other avian species. The results are interpreted in the light of the role of the tongue in species-specific patterns of feeding in finches, and the possible requirement for the central integration of touch and taste.     

Tooth pulp-evoked potentials in the trigeminal brainstem nuclear complex

The surface and depth distributions of mandibular canine, tooth pulp-evoked potentials (TPEPs) in the trigeminal brainstem nuclear complex were studied in anesthetized cats. Three pairs of positive-negative waves or components were elicited from each trigeminal brainstem nucleus (main sensory, MSN; oralis, NO; interpolaris, NI; caudalis or medullary dorsal horn, NC). The location and dipole orientation of the current generator source for each pair of components in each nucleus were determined by using the topographic amplitude distribution of TPEPs in both their normal-reference and inverted polarities and the isoelectric contour line. The current sources for all components were the following: MSN--dorsomedial subnucleus; NO--dorsolateral portion; NI--dorsomedial portion; NC--medial part of superficial and intermediate laminae. These loci are consistent with the central terminal zones of mandibular tooth pulp afferents reported in previous neuroanatomical studies. Measurements of mean peak latencies suggest that tooth pulp A beta afferents contribute to the putatively presynaptic (P1-N1) and monosynaptic (P2-N2) components found in all trigeminal brainstem nuclei and that A delta afferents contribute to the later and possibly polysynaptic components (P3-N3) in the same nuclei. The pertinence of these findings to the theory that both non-nociceptive and nociceptive intradental inputs project to rostral and caudal nuclei are discussed.