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PubMed2006

Morphological interrelationship between astrocytes and nerve endings in the rat spinal trigeminal nucleus caudalis.

It has been reported that the spinal trigeminal nucleus caudalis (Sp5C), which receives nociceptive information from the oro-facial regions, has four laminae. To clarify the role of glial cells in the transmission of the nociceptive information, the present study was conducted to examine the detailed distribution of astrocytes in each lamina and also to investigate a morphological interrelationship between the astrocytes and nerve endings in the rat Sp5C. After the preparation of the serial cryostat sections, immunohistochemistry for glial fibrillary acidic protein (GFAP) was employed to identify the astrocytes, and immunohistochemistry for substance P (SP), calcitonin gene-related peptide (CGRP), was used for the nerve endings. We also employed double-labeling immunofluorescence and electron microscopic immunohistochemistry for the GFAP/SP or GFAP/CGRP. GFAP-positive reactions were observed in all laminae of the Sp5C, and SP- or CGRP-positive nerve endings were observed in the lamina I and II. Additionally, we clarified the presence of GFAP/SP- or GFAP/CGRP-positive reactions by the double-labeling immunofluorescence and demonstrated the morphological interrelationship between the astrocytes and nerve endings by the double-labeling electron microscopic immunohistochemistry. These findings suggest that astrocytes might play some roles in the transmission of nociceptive information from the oro-facial region.

Animals↗

PubMed2005

Projections from the spinal trigeminal nucleus to the cochlear nucleus in the rat.

The integration of information across sensory modalities enables sound to be processed in the context of position, movement, and object identity. Inputs to the granule cell domain (GCD) of the cochlear nucleus have been shown to arise from somatosensory brain stem structures, but the nature of the projection from the spinal trigeminal nucleus is unknown. In the present study, we labeled spinal trigeminal neurons projecting to the cochlear nucleus using the retrograde tracer, Fast Blue, and mapped their distribution. In a second set of experiments, we injected the anterograde tracer biotinylated dextran amine into the spinal trigeminal nucleus and studied the resulting anterograde projections with light and electron microscopy. Spinal trigeminal neurons were distributed primarily in pars caudalis and interpolaris and provided inputs to the cochlear nucleus. Their axons gave rise to small (1-3 microm in diameter) en passant swellings and terminal boutons in the GCD and deep layers of the dorsal cochlear nucleus. Less frequently, larger (3-15 microm in diameter) lobulated endings known as mossy fibers were distributed within the GCD. Ventrally placed injections had an additional projection into the anteroventral cochlear nucleus, whereas dorsally placed injections had an additional projection into the posteroventral cochlear nucleus. All endings were filled with round synaptic vesicles and formed asymmetric specializations with postsynaptic targets, implying that they are excitatory in nature. The postsynaptic targets of these terminals included dendrites of granule cells. These projections provide a structural substrate for somatosensory information to influence auditory processing at the earliest level of the central auditory pathways.

Animals↗

PubMed1987

Tooth pulp-evoked activity in the spinal trigeminal nucleus caudalis of cat: comparison to primary afferent fiber, reflex, and sensory responses.

Tooth pulp-evoked single-neuron responses were recorded in the spinal trigeminal nucleus caudalis of the cat. The thresholds to monopolar electric pulses of various durations (0.2 to 20 ms) were determined using a constant current stimulator. With stimulus pulse durations of 10 to 20 ms, the thresholds were comparable with those of primary afferent A-fibers, although the most sensitive primary afferent fibers had lower thresholds. Primary afferent C-fibers had higher thresholds than the postsynaptic neurons studied. The threshold for the tooth pulp-elicited jaw-opening response was obtained at a lower stimulus intensity than the liminal response in most postsynaptic neurons of this study. The threshold rise of the postsynaptic trigeminal neurons with decreasing stimulus pulse duration (from 5 to 0.2 ms) was much steeper than that of primary afferent A-fibers or jaw-opening response. The strength-duration curves for tooth pulp-elicited pain sensations in man resemble those of spinal trigeminal neurons. Sixty-two percent of the units had a threshold elevation during a noxious pinch of the tail. The results indicate that the activation of postsynaptic trigeminal neurons requires a considerable temporal summation of primary afferent impulses. The jaw reflex thresholds cannot be explained by the properties of the neurons in the subnucleus caudalis of the trigeminal tract. The results support the concept that dental pain is based on the activation of spinal trigeminal nucleus caudalis neurons receiving their input from intradental A-fibers.

Animals↗

PubMedDate not supplied

Midazolam does not affect the field potentials in the caudal part of the spinal trigeminal nucleus.

The effect of midazolam on the field potentials (FPs) in the caudal part of the spinal trigeminal nucleus following strong electrical stimulation of the upper lip was investigated in Wistar albino rats. The rats received i.p. dosages of 5, 10, or 20 mg/kg midazolam, or physiological saline. Relative amplitudes of the negative deflection were not suppressed after midazolam injection. No significant differences were found in the latencies of the potentials before and after midazolam injection. It is suggested that the main action site of midazolam may be located at a higher level than the spinal trigeminal nucleus.

Animals↗

PubMed1997

Association of serotonin-like immunoreactive axons with nociceptive projection neurons in the caudal spinal trigeminal nucleus of the rat.

Serotoninergic projections to the spinal dorsal horn are implicated in the modulation of nociceptive transmission. However, morphological evidence indicating that serotoninergic projection fibers make synapses on nociceptive neurons in the medullary dorsal horn is still meager. Thus, we examined whether axonal varicosities with serotonin (5-HT)-like immunoreactivity (5-HT-LI) might make synapses on nociceptive projection neurons in the caudal spinal trigeminal nucleus (Vc) of the rat. Projection neurons were retrogradely labeled with tetramethylrhodamine-dextran amine (TMR-DA) or wheat germ agglutinin-horseradish peroxidase (WGA-HRP) that was injected into the parabrachial or thalamic region. Vc neurons in which c-fos protein-like immunoreactivity (Fos-LI) was induced by subcutaneous injection of formalin into the lip were considered nociceptive. Vc neurons in direct contact with axonal varicosities that bind isolectin I-B4 were also considered nociceptive. Triple labeling for 5-HT, TMR-DA, and Fos as well as that for 5-HT, TMR-DA, and I-B4 were done by using the immunofluorescence and fluorescence histochemical techniques. Confocal laser-scanning microscopy revealed that axonal varicosities with 5-HT-LI were in close apposition to TMR-DA-labeled neurons showing Fos-LI in lamina I and the outer part of lamina II (lamina IIo), and that both axonal varicosities with 5-HT-LI and those binding I-B4 were in close apposition to single neuronal profiles labeled with TMR-DA. The presumed nociceptive neuronal profiles in close apposition to axon terminals with 5-HT-LI were mainly those of laminae I and II neurons as well as dendrites of lamina III neurons. Electron microscopy confirmed that axon terminals with 5-HT-LI and those with I-B4 binding activity in laminae I and II made synapses on somatic and dendritic profiles that were labeled with WGA-HRP. The results indicate that serotoninergic neurons project directly on nociceptive projection neurons in the Vc.

Animals↗

PubMed2001

[A case with trigeminal herpes zoster manifesting a long lesion of the spinal trigeminal nucleus and tract on MR T2-weighted image].

We reported a 53-year-old man with the right trigeminal herpes zoster with preceding neuralgia (preherpetic neuralgia) in the right upper cervical nerve area. He developed dysesthesia and scapular pain in the right second cervical nerve area. 5 days later, herpes zoster emerged in the area of the right maxillary division of trigeminal nerve. Furthermore, he developed paralysis on the right facial muscle on the 12th day after the onset of scapular pain. Neurological examination revealed decrease in superficial sensation accompanied by pain and dysesthesia in the areas innervated by the right maxillary division of trigeminal nerve and the right second cervical nerve, and the right peripheral facial nerve palsy. Any rash was not observed in the right second cervical nerve area throughout the course. The cerebrospinal fluid showed a mild mononuclear pleocytosis. The antibody titer for varicella zoster virus (VZV) was elevated in both cerebrospinal fluid and blood serum. T2-weighted magnetic resonance (MR) image revealed a continuously long high-signal lesion corresponding to the right spinal trigeminal nucleus and tract, extending from the lower pons to the second cervical segment of the spinal cord. This lesion could have resulted from a centripetal migration of VZV from the Gasser ganglion to the spinal trigeminal nucleus and tract, which was probably related to the preherpetic neuralgia in the upper cervical nerve area without rash.

Antibodies, Viral↗

PubMed1996

Differential distribution of Fos-like immunoreactivity in the spinal trigeminal nucleus after noxious and innocuous thermal and chemical stimulation of rat cornea.

Corneal afferent nerves project to two spatially distinct sites within the spinal trigeminal nucleus: the subnucleus interpolaris/caudalis transition and the subnucleus caudalis/upper cervical spinal cord transition. The role of these two regions in processing corneal input is uncertain. To determine if neurons in these regions encode different features of an applied corneal stimulus, immunoreactivity for the immediate early gene protein product, Fos, was quantified in barbiturate-anesthetized rats. Intensity was varied across thermal (thermal probe 5, 35, 42, 52 degrees C; radiant heat of approximately 45 degrees C) stimuli and compared with that seen after mustard oil (5 microliters, 20%) or mineral oil application. All stimuli increased the number of Fos-positive neurons located at the ventrolateral pole of the subnucleus interpolaris/caudalis transition compared with unstimulated controls. By contrast, only 52 degrees C thermal probe and mustard oil produced an additional peak of Fos-positive neurons within the superficial laminae at the subnucleus caudalis/cervical cord transition. Further, the magnitudes of the bimodal peaks of Fos produced by 52 degrees C thermal probe and mustard oil stimuli were different quantitatively. Mustard oil caused a greater Fos response at the subnucleus interpolaris/caudalis transition than 52 degrees C thermal probe stimulation, whereas the opposite was true at the subnucleus caudalis/cervical cord transition. Double-labeling revealed that Fos immunoreactive neurons within the spinal trigeminal nucleus were restricted to regions densely labeled for calcitonin gene-related peptide. These results indicate that select features of corneal stimuli such as modality are encoded differently by neurons in the trigeminal subnucleus interpolaris/caudalis transition compared with those located in the subnucleus caudalis/cervical cord transition. It is likely that neurons in these two brainstem regions subserve different aspects of corneal sensation.

Animals↗

PubMed1999

Distribution of a specific calcium-binding protein of the S100 protein family, S100A6 (calcyclin), in subpopulations of neurons and glial cells of the adult rat nervous system.

S100A6 (calcyclin) is a member of the large S100 Ca2+-binding protein family, considered to activate several processes along the calcium signal transduction pathway including the regulation of cell growth, proliferation, secretion, and exocytosis. In the present study, the distribution of S100A6 in the rat nervous system was examined by immunohistochemistry with a goat antiserum against recombinant human S100A6, which recognizes the rat S100A6 homologue. The main S100A6-immunoreactive elements were 1) neuronal somata and dendrites in some specific regions of the limbic system (e.g., the basolateral amygdaloid nucleus, ventral tip of the CA1-subicular border region, entorhinal cortex, and parasubiculum), most of which were identified as a subpopulation of pyramidal cells; 2) olfactory receptor cells and olfactory nerve fibers and terminals in the olfactory bulb; 3) some tracts of the hindbrain and spinal cord (e.g., the spinal trigeminal tract, solitary tract, dorsal root fibers, and the tract of Lissauer) and their terminals (e.g., the principal sensory trigeminal nucleus, spinal trigeminal nucleus, nucleus of the solitary tract, marginal zone, substantia gelatinosa, and proper sensory nucleus of the dorsal horn), as well as some sensory neurons of their origins in the dorsal root and trigeminal ganglia; 4) a subpopulation of astrocytes in the white matter (e.g., the corpus callosum, cingulum, external capsule, internal capsule, and fimbria of the hippocampus) and around the ventricles; 5) some ependymal cells, especially around the central canal; and 6) Schwann cells. These results will improve our understanding of the diverse function of Ca2+-binding proteins in the CNS.

Animals↗

PubMed1993

Adrenalectomy enhances Fos-like immunoreactivity within the spinal trigeminal nucleus induced by noxious thermal stimulation of the cornea.

Immunocytochemistry was used to assess the distribution of neurons within the spinal trigeminal nucleus that expressed the protein product of the proto-oncogene c-fos after thermal stimulation of the cornea in barbiturate-anesthetized rats. The influence of adrenal steroids on Fos-like immunoreactivity induced by corneal stimulation also was examined by comparison of the results obtained in adrenal intact rats to those in adrenalectomized rats and to those in adrenalectomized rats given corticosterone replacement therapy. Stimuli (42 or 52 degrees C, 20 s per min, 15 min) were applied unilaterally to the cornea by a contact thermode. At 2 h after stimulation animals were perfused with 4% paraformaldehyde and tissue sections were incubated with primary antiserum against the Fos protein and processed with the avidin-biotin method. The pattern of Fos-like immunoreactivity after 52 degrees C stimulation revealed a dominant group of cells ipsilaterally within the superficial laminae of the caudalmost portion of trigeminal subnucleus caudalis that was greatly enhanced in adrenalectomized rats. Low-intensity stimulation did not induce Fos-like immunoreactivity among cells in this caudal region. A second significant group of cells was seen more rostrally at periobex levels within the ventrolateral pole of the nucleus. The number of cells in the periobex grouping was increased after 52 or 42 degrees C corneal stimulation when compared to unstimulated controls and was not affected by levels of corticosterone. The results indicated a discontinuous pattern of Fos-like immunoreactivity within the spinal trigeminal nucleus after thermal stimulation of the cornea and a differential effect of adrenal steroids. The appearance of Fos-like immunoreactivity within caudal portions of the nucleus was increased only by noxious intensities of stimulation and was further enhanced in animals with low levels of corticosterone. In contrast, the Fos-like immunoreactivity at periobex levels was increased after noxious and innocuous thermal stimuli and was independent of the level of corticosterone. The results were consistent with the hypothesis that glucocorticoids modify the expression of immediate early genes among a select group of central trigeminal neurons. Such steroid modulation may contribute to the mechanisms that underlie long-term adaptation to noxious sensory input.

Adrenal Glands↗

PubMed1996

Muscarine receptor activation in the substantia gelatinosa of the spinal trigeminal nucleus of the guinea pig.

1. Intracellular recordings were made from slices of guinea pig spinal trigeminal nucleus pars caudalis (SG). 2. Muscarine [0.3-30 microM; half maximally effective concentration (EC50) = 2.9 microM] hyperpolarized 61% of SG neurons. The effect was mimicked by carbachol (0.3-30 microM; EC50 = 3.9 microM) and antagonized by pirenzepine (1 microM). Thirty-four percent of the neurons were depolarized by muscarine and carbachol (1-30 microM: EC50 = 5.7 microM), and the effect was antagonized by pirenzepine (100 nM). 3. In approximately 80% of recordings, muscarine (10-30 microM) evoked repetitive spontaneous inhibitory postsynaptic potentials (IPSPs) that were sensitive to bicuculline (10 microM). 4. Muscarine (1-30 microM; EC50 = 3 microM) decreased the amplitude of the majority of evoked excitatory postsynaptic potentials (EPSPs), and the effect was mimicked by carbachol and antagonized by pirenzepine (100 nM). 5. These results indicate that there are at least three mechanisms by which muscarine inhibits SG neurons: 1) hyperpolarization through activation of non-M1 receptors; 2) activation of gamma-amino-butyric acid-containing interneurons that mediate IPSPs in a subset of neurons; and 3) a decrease in evoked EPSP amplitude. Muscarine can also activate SG neurons via interaction with an M1-type receptor.

Animals↗

PubMed1995

Acute injection of adrenal steroids reduces cornea-evoked expression of c-fos within the spinal trigeminal nucleus of adrenalectomized rats.

The influence of transient increases in adrenal steroid hormones on the number of Fos-positive neurons after nociceptor activation was assessed in adrenalectomized rats. Fos protein, the product of the immediate early gene, c-fos, was detected immunocytochemically within the spinal trigeminal nucleus 2 h after noxious thermal stimulation of the cornea. Adrenalectomized rats displayed an enhanced number of Fos-positive neurons within the caudal-most portions of trigeminal subnucleus caudalis compared to that seen in adrenal-intact animals, an effect reversed by a single acute injection of corticosterone (1 mg/kg, i.p.) given 5 min prior to stimulation. Acute injection of the selective mineralocorticoid receptor agonist, aldosterone, or the selective glucocorticoid receptor agonist, RU28362, also reduced the number of Fos-positive neurons. Aldosterone and RU28362 had an additive effect on Fos when given concurrently. In contrast, adrenal status or acute injections of adrenal steroid receptor agonists had no effect on the number of Fos-positive neurons after corneal stimulation located within the ventrolateral pole of the spinal trigeminal nucleus at the level of the subnucleus interpolaris/caudalis junction. Acute administration of adrenal steroids to adrenalectomized rats greatly attenuated the number of Fos-positive neurons seen after corneal stimulation within select portions of trigeminal subnucleus caudalis. The contribution of both glucocorticoid and mineralocorticoid receptor subtypes in reducing Fos suggested a central site of action rather than an anti-inflammatory effect on peripheral tissue. These results are consistent with the hypothesis that transient increases in adrenal steroids, such as occur after injury, are sufficient to modify the production of Fos protein in central neurons that process nociceptive information.

Adrenal Cortex Hormones↗

PubMed1985

The autoradiographic localization of substance P receptors in the rat and bovine spinal cord and the rat and cat spinal trigeminal nucleus pars caudalis and the effects of neonatal capsaicin.

Substance P (SP) is a putative neurotransmitter in the central nervous system. In the present report we have used autoradiographic receptor binding techniques to investigate the distribution of SP receptor binding sites in the rat and bovine spinal cord and in the rat and cat spinal trigeminal nucleus pars caudalis. Although some quantitative differences were evident, all species appeared to have a similar distribution of SP receptor binding sites in both the spinal cord and in the spinal trigeminal nucleus pars caudalis. In the spinal cord the heaviest concentration of SP receptors is located in lamina X, while moderate to heavy concentrations were found in laminae I, II and V-IX. Very low concentrations of SP receptors were present in laminae III and IV. Examination of the cat and rat spinal trigeminal nucleus pars caudalis revealed a moderate density of SP receptor binding sites in laminae I and II, very low concentrations in laminae III and IV, and low to moderate concentrations in lamina V. Rats treated neonatally with capsaicin showed a small (11%) but significant (P less than 0.02) increase in the levels of SP receptor binding sites in laminae I and II of the cervical and lumbar spinal cord while in all other laminae the levels remained unchanged.

Animals↗

PubMed1990

Intracellular response properties of neurons in the spinal trigeminal nucleus to peripheral and cortical stimulation in the cat.

The responses of the secondary neurons in the spinal trigeminal nucleus oralis (STNo) were recorded intracellularly to peripheral and cortical stimulation in chloralose-anesthetized cats. Electrical stimulation of the trigeminal sensory nerves (the frontal, infraorbital and inferior alveolar nerves) evoked an EPSP superimposed by one or a few spikes followed by a biphasic IPSP in one group of STNo neurons (Type I), and a prolonged EPSP superimposed by a burst of spikes in the other group of STNo neurons (Type II). Nearly half of Type I neurons were trigeminothalamic neurons projecting to the contralateral ventral posteromedial nucleus, while the remaining Type I and all the Type II neurons were non-projection neurons. A majority of Type I neurons responded with spike potentials to stimulation of only one sensory nerve, while most Type II neurons responded to stimulation of more than one nerve. Stimulation of the contralateral primary somatosensory cortex evoked IPSPs in most Type I projection neurons, and EPSPs in all Type II as well as most Type I non-projection neurons. In Type I neurons touch or pressure applied to a circumscribed area in the facial skin evoked an EPSP superimposed by one or a few spikes followed by a biphasic IPSP, and IPSPs were evoked from a wide surrounding area in the face by the same mechanical stimulation. In Type II neurons innocuous mechanical stimulation within a wide area evoked an EPSP, while IPSPs could not be induced from anywhere. The results indicate that postsynaptic inhibition is involved in the surround inhibition as well as corticofugal descending inhibition of sensory transmission in the trigeminal sensory nucleus.

Action Potentials↗

PubMed2004

Organization of diencephalic projections from the spinal trigeminal nucleus oralis: an anterograde tracing study in the rat.

The organization of the efferent projections from the spinal trigeminal nucleus oralis (Sp5O) to the diencephalon was studied in the rat using the anterograde tracer Phaseolus vulgaris leucoagglutinin. The present study confirms the existence of trigemino-thalamic pathways originating from the Sp5O and details their distribution. The main diencephalic targets of the Sp5O are the ventral posteromedial thalamic nucleus (VPM), the posterior thalamic nuclei (Po) and the ventral part of the zona incerta (ZIv), contralaterally, and the parvicellular part of the ventral posterior thalamic nucleus (VPpc), bilaterally. The distribution of these projections varies according to the dorso-ventral location of the injection sites: the dorsal part of the Sp5O projects to the medial part of the VPM and the Po, and to the caudal part of the ZIv, as well as to the VPpc. The ventral part of the Sp5O projects to the lateral part of the VPM and the Po and to the rostral part of the ZIv. These results suggest that the trigemino-diencephalic pathways originating from the Sp5O are involved in the processing of gustatory and somatosensory information.

Animals↗

PubMed1995

Inhibition by 5-hydroxytryptamine and noradrenaline in substantia gelatinosa of guinea-pig spinal trigeminal nucleus.

1. Whole-cell and intracellular recordings were made from neurons in slices of guinea-pig spinal trigeminal nucleus pars caudalis. 2. 5-Hydroxytryptamine (5-HT) hyperpolarized 70% of neurons by activating 5-HT1A receptors. The effect was mimicked by 5-carboxamidotryptamine (5-CT) and (+/-)-2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydronapthalene hydrobromide (8-OH-DPAT) and antagonized by 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)-butyl]-piperazine hydrobromide (NAN 190) and pindobind-5-HT1A. Nine per cent of the neurons were depolarized by 5-HT. 3. In about 20% of recordings, 5-HT also evoked repetitive inhibitory postsynaptic potentials that were mediated by glycine. 4. Noradrenaline (NA) hyperpolarized 71% of neurons. This effect was mediated by activation of alpha 2-adrenoceptors, since 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK14304) also caused a hyperpolarization and idazoxan (1 microM) blocked the hyperpolarization to both NA and UK14304. Phenylephrine depolarized a subset of neurons and this depolarization was blocked by prazosin, suggesting an action mediated by activation of alpha 1-adrenoceptors. 5. NA also evoked repetitive GABAA-mediated inhibitory postsynaptic potentials in about 20% of recordings. The increase in synaptic activity was mimicked by phenylephrine and blocked by prazosin. 6. These results indicate that there are at least two mechanisms through which 5-HT and NA inhibit neurons: (i) in many cells both 5-HT and NA mediate a hyperpolarization through an increase of a potassium conductance; (ii) 5-HT and NA also activated GABA- and glycine-containing interneurons to cause IPSPs in separate groups of cells.

Adrenergic alpha-1 Receptor Agonists↗

PubMed2004

Organization of parabrachial projections from the spinal trigeminal nucleus oralis: an anterograde tracing study in the rat.

In recent years, we have accumulated data showing that the spinal trigeminal nucleus oralis (Sp5O) contributes to the processing of somatosensory inputs from the orofacial region. Although the parabrachial area (PB) represents the main brainstem relay for autonomic, nociceptive, and gustatory afferents, few data are available regarding the topographical distribution of the efferent projections from the Sp5O to the PB. We have addressed this question with the rat, by using the anterograde tracer Phaseolus vulgaris leucoagglutinin. A dense trigeminoparabrachial pathway from the Sp5O toward, predominantly, the ipsilateral PB was revealed. Projections come mainly from the dorsal part of the Sp5O that was found to innervate densely the medial, external medial, and ventral lateral subnuclei. In contrast, the ventral part of the Sp5O projected almost exclusively to an as yet not formally described region, located dorsally and laterally to the lateral tip of the brachium conjunctivum, close to the Kölliker-Fuse nucleus. These results suggest that distinct regions within the Sp5O may be involved in the processing of gustatory and nociceptive information.

Animals↗

PubMed1981

[Oblongata in the spinal trigeminal nucleus of the adult rat (author's transl)].

The substantia gelationsa has been noted as a region of central pain control, In 1979, we reported that an intense thiamine monophosphatase (TMPase) activity was specifically localized on the plasma membrane of the synaptic glomeruli, especially dense sinusoid axon terminals (DSA). In the present investigation, the ultracytochemical localization of TMPase activity was studied in the spinal trigeminal nucleus of the adult rat. Vibratome sections of aldehyde-fixed specimens were incubated in the incubation medium (veronal-acetate buffer, pH 5. 8, 27 mM, thiamine monophosphoric acid chloride 2mM, lead nitrate 2.7 mM, sucrose 146 mM, final pH 5.4) for 30 min at 37 degrees C, and processed for light as well as electron microscopy. At the light microscopic level, the reaction products, lead sulfide, were observed to be localized in the substantia gelatinosa of the caudal medulla oblongata in the spinal trigeminal nucleus. At the electron microscopic level, the TMPase activity was positive on the plasma membrane of DSA in the region where is particularly concerned with the relay of thermal and noxious stimuli. It has been suggested by us previously that there may be some relationship between the TMPase activity and pain, mechanism in the spinal cord, and the results that the situation seems to be hold true in the spinal trigeminal nucleus, also.

Animals↗

PubMed1991

Projections from neurons innervating the masseter muscle to the subnucleus oralis of the spinal trigeminal nucleus and adjacent lateral reticular formation in the rat.

The projection from the masseter to the subnucleus oralis of the spinal trigeminal nucleus (Vo) and adjacent parvicellular reticular nucleus (PCRt) was studied with retrograde and transganglionic transport of horseradish peroxidase (HRP) combined with fluorescent double labeling method. The labeled axons and terminals within the medulla showed a specific distribution. The field of labeling formed a continuous band from rostro-laterally to caudo-medially. At the level of caudal Vo the labeling region became the most expanded in the medulla, which occupied dorso-medial Vo (Vodm) and adjacent PCRt about half by half. The ratio of masseter primary afferent neurons in the mesencephalic trigeminal nucleus (Vme) to that in the trigeminal ganglion (TG) was found to be 7.7-8.5:1 following injection of HRP into the masseter nerve. However, the proportion between the Vme and the TG neurons which build up the pathway from the masseter to the Vodm and the adjacent PCRt was 8.7-10:1, revealed by means of fluorescent double labeling when different tracers were applied at the peripheral and central targets.

Animals↗