Projections of the anterior ectosylvian gyrus to the thalamus, the dorsal column nuclei, the trigeminal nuclei and the spinal cord in cats.
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Direct projections from the dorsal column nuclei and the spinal trigeminal nuclei to the cochlear nuclei in the cat.
A retrograde and anterograde wheat germ agglutinated horseradish peroxidase WGA-HRP study in the cat indicated that some neurons in the dorsal column nuclei and the interpolar and caudal spinal trigeminal nuclei send fibers to the dorsal and ventral cochlear nuclei; to the pyramidal cell layer of the dorsal cochlear nucleus and to the cochlear granule cell domain, bilaterally with an ipsilateral dominance.
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Autoradiographic localization of neurotransmitter binding sites in the hypoglossal and motor trigeminal nuclei of the rat.
The hypoglossal and motor trigeminal nuclei contain somatic motoneurons innervating the tongue, jaw, and palate. These two cranial motor nuclei are myotopically organized and contain neurotransmitter binding sites for thyrotropin-releasing hormone, substance P, and serotonin. Quantitative autoradiography was used to localize thyrotropin-releasing hormone, substance P, and serotonin-1A and serotonin-1B binding sites in the hypoglossal and motor trigeminal nuclei and to relate the relative distributions of these binding sites to the myotopic organizations of the two nuclei. In the hypoglossal nucleus, high-to-moderate concentrations of all four binding sites were present in the dorsal and ventromedial subnuclei, whereas low concentrations were noted in the ventrolateral subnucleus. In the motor trigeminal nucleus, high concentrations of serotonin-1B, moderate densities of thyrotropin-releasing hormone, and low levels of substance P and serotonin-1A binding sites were present in both the ventromedial and dorsolateral subnuclei. These observations demonstrate that neurotransmitter binding sites in the hypoglossal and motor trigeminal nuclei are heterogeneously localized and that their distributions correspond to the previously described myotopic organizations of each nucleus.
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An electron microscopic description of glutamate-like immunoreactive axon terminals in the rat principal sensory and spinal trigeminal nuclei.
The spinal and principal sensory trigeminal nuclei relay noxious and nonnoxious stimuli from the orofacial region to the thalamus. Physiological studies have implicated glutamate as an important neurotransmitter in this region. Despite its importance as a potential transmitter, few studies have examined the anatomical distribution of glutamate within these nuclei. We therefore chose to use a monoclonal antibody raised against glutamate conjugated to a carrier protein to identify and describe glutamate-like immunoreactive processes at the electron microscopic level. Glutamate-like immunoreactive axon terminals were identified throughout the spinal trigeminal and principal sensory trigeminal nucleus. In subnucleus caudalis glutamate-like immunoreactive terminals occurred frequently in all laminae and were morphologically heterogeneous. In lamina I, glutamate-like immunoreactive terminals were primarily ovoid, contained spherical synaptic vesicles, and participated in synaptic complexes with both dendritic and axonal profiles. In laminae II and III many glutamate-like immunoreactive axon terminals were identified as the central element in synaptic glomeruli. Within discrete patches of lamina II, large numbers of glutamate-like immunoreactive terminals contained dense core vesicles. The majority of glutamate-like immunoreactive terminals in subnucleus interpolaris, subnucleus oralis, and principal sensory trigeminal nucleus were similar in morphology and synaptic interaction to the glutamate-like immunoreactive terminals found in subnucleus caudalis. Glutamate-like immunoreactive terminals that were the central presynaptic element in glomerular complexes were seen in all subnuclei. In sections from subnucleus interpolaris and subnucleus oralis central glutamate-like immunoreactive terminations within glomerular complexes had much smoother profiles, and in subnucleus interpolaris participated primarily in axodendritic synaptic junctions. In the principal sensory trigeminal nucleus central glutamate-like immunoreactive terminations were highly scalloped and participated in numerous axoaxonic synaptic junctions. The above observations are consistent with the hypothesis that glutamate-like immunoreactivity is present in some primary afferent terminations and functions as an important excitatory transmitter involved in the relay of sensory information to the spinal trigeminal and principal sensory trigeminal nucleus.
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Distribution of axons showing calcitonin gene-related peptide- and/or substance P-like immunoreactivity in the sensory trigeminal nuclei of the cat.
Distribution of axons with calcitonin gene-related peptide (CGRP)-like and/or substance P (SP)-like immunoreactivity (LI) within the sensory trigeminal nuclei was examined in the cat before and after trigeminal rhizotomy. Axons with CGRP-LI or SP-LI were seen throughout the principal sensory trigeminal nucleus (Vp) and spinal trigeminal nuclei, including the medullary dorsal horn (MDH). They were densely distributed particularly in the dorsolateral part of the dorsal subnucleus of the Vp, ventromedial marginal zone of the ventral subnucleus of the Vp, dorsomedial and ventromedial parts of the oral spinal trigeminal nucleus, ventromedial and lateral marginal zones of the interpolar spinal trigeminal nucleus, and lamina I, outer part of lamina II and lamina V of the MDH. Most of the CGRP-LI axons exhibited SP-LI, while many SP-LI axons did not show CGRP-LI. After trigeminal rhizotomy, almost all CGRP-LI axons disappeared from the ipsilateral sensory trigeminal nuclei, while a considerable number of SP-LI axons remained intact throughout the nuclei; these SP-LI axons did not show CGRP-LI. The results indicate that CGRP-LI axons within the sensory trigeminal nuclei exhibit SP-LI and are of peripheral origin, and that SP-LI axons without CGRP-LI are of central origin.
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An anatomical demonstration of projections to the medullary dorsal horn (trigeminal nucleus caudalis) from rostral trigeminal nuclei and the contralateral caudal medulla.
This study demonstrates that the medullary dorsal horn (MDH), the most caudal subdivision of the spinal trigeminal nucleus, receives input from neurons located in the trigeminal main sensory nucleus, the more rostral subdivisions of the spinal trigeminal nucleus, and the contralateral MDH. Using the retrograde transport of horseradish peroxidase (HRP), we show here that the MDH receives ipsilateral projections from rostral trigeminal nuclei but not from adjacent areas of the retricular formation. The rostral pole of spinal trigeminal nucleus oralis (nucleus oralis, pars beta) contains the highest density of MDH projection neurons. In addition, the MDH on one side receives projections from contralateral MDH neurons located in layers I, III, IV, V, VII and VIII but not from neurons in layers II and VI. We conclude that: (1) specific subdivisions of rostral trigeminal nuclei send projections to the MDH that could modulate the activity of MDH neurons; (2) projections from trigeminal nuclei to layers V and VI of the MDH, but not from adjacent areas of the reticular formation, provide further evidence that these deeper layers are related functionally to the MDH and trigeminal sensory processes; and (3) several populations of MDH neurons send axons across the midline into the contralateral MDH and may mediate contralateral inhibitory effects.
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[Corticofugal pathways from different fields of the cat auditory cortex to the sensory trigeminal nuclei and ventrobasal complex of the thalamus].
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Projection from trigeminal nuclei to neurons of the mesencephalic trigeminal nucleus in rat.
The mesencephalic trigeminal nucleus contains cell bodies of primary somatic sensory neurons that innervate the head region. The neurons resemble dorsal root ganglion cells but a striking difference is the presence of synaptic boutons in the nucleus. The present report demonstrates with anterograde tracers, the existence of a direct trigeminal projection from secondary sensory neurons of the principal and spinal nuclei to the mesencephalic nucleus. Our observations strongly suggest that synaptic contact may be established on the cell bodies as well as on the neurites of the mesencephalic neurons. These pathways could play a modulatory role in the processing of sensory afferent information and in the control of orofacial and/or oculomotor functions.
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Properties of different functional types of neurones in the cat's rostral trigeminal nuclei responding to sinus hair stimulation.
1. Properties of neurones in the trigeminal nuclei principalis and oralis responding to movements of facial sinus hairs were studied in cats anaesthetized by I. V. infusion of pentobarbitone.2. Using electrophysiological methods trigeminal neurones were classified into primary afferent fibres, trigeminothalamic relay neurones, interneurones and other unspecified higher order neurones.3. When receptive fields of synaptically activated neurones were compared with those of primary afferent fibres, an often extensive convergence from first order on to higher order neurones was established. Out of 119 relay neurones six received input from one sinus hair only. Spontaneous activity was encountered about twice as often in synaptically activated neurones than in primary afferent fibres.4. The responsiveness of single neurones was unstable over time in about one fifth of the population and then the total number of impulses discharged in successive responses could vary by as much as 500%. Unstable responsiveness occurred sometimes alone but was often accompanied by marked changes in the size or the configuration of the receptive field. Such instabilities were observed in all kinds of synaptically activated neurones but not in primary afferent fibres.5. Afferent inhibition in relay neurones could be elicited from within the excitatory receptive field and appeared to be related to the activation of distinct receptor populations responding to specific stimulus parameters. Inhibition was also seen in interneurones following both mechanical stimulation of the skin and electrical stimulation of lemniscal fibre terminals in the contralateral ventromedial thalamus.6. The results are discussed and compared with previous findings about sinus hair representation in the trigeminal nucleus and the ascending lemniscal projection. The findings indicate that the concept of the ;static properties' of relay neurones is not adequate for all trigeminothalamic relay neurones and may require a critical reconsideration.7. It is suggested that the afferent input from sinus hairs is effectively controlled at the level of the rostral trigeminal nuclei. This control may affect the spatial input to relay neurones, the temporal components of their responses and the intensity dimension of their transmission capacity. It is postulated that by these mechanisms tactile information from the sinus hair system is modulated according to the instantaneous sensory requirements of the behaving cat.
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Non-motoneurons in the facial and motor trigeminal nuclei projecting to the cerebellar flocculus in the cat. A fluorescent double-labelling and WGA-HRP study.
The cerebellar projection from the facial and motor trigeminal nuclei was studied in the cat by means of retrograde axonal transport of wheat germ agglutinin-horseradish peroxidase and fluorescent tracers. The feline facial nucleus was cytoarchitectonically subdivided into ventromedial, ventrolateral, lateral, dorsal, intermediate and medial divisions (see Papez 1927), and the motor trigeminal nucleus into medial, ventral, intermediate, lateral and dorsal divisions. The neurons in the facial and motor trigeminal nuclei were classified as small (ovoid to round cells with a maximum diameter of the cell body of about 20 microns) or large (polygonal to round cells with maximum diameter of about 40 microns). After floccular injections of the wheat germ agglutinin-horseradish peroxidase complex, retrogradely labelled cells were found throughout the facial nucleus, but especially in its medial and dorsal divisions. In the motor trigeminal nucleus, labelled neurons were found only in the ventral, intermediate and lateral divisions. Cases with tracer deposition (implants or injections) in other parts of the cerebellar cortex or nuclei were all negative. All facial and motor trigeminal neurons labelled after floccular injections were smaller than the neurons labelled after injections in the facial mimic and masticatory muscles, and only single-labelled neurons were found following floccular injections of Fluoro-Gold and muscular injections of rhodamine-B-isothiocyanate in the same animals. These observations strongly suggest that the neurons in the facial and motor trigeminal nuclei which project to flocculus are of the non-motoneuron type.
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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 motoneurons. The results suggest, therefore, that GABA might play an important role both in discriminative sensory processing and in reflex modulation of the orofacial region.
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Development of metabotropic glutamate receptors from trigeminal nuclei to barrel cortex in postnatal mouse.
Expression patterns of group I (mGluR1alpha and mGluR5) and group II (mGluR2/3) metabotropic glutamate receptor subtypes were examined immunocytochemically in the trigeminal system of mice during the first 3 weeks of postnatal development, when somatotopic whisker representations are sequentially established from brainstem through thalamus to cerebral cortex. Immunostaining for all three epitopes formed whisker-related patterns in the trigeminal nuclei from postnatal day (P) 0, in the ventral posterior thalamic nucleus from P2, and in the posteromedial barrel subfield of somatosensory cortex (SI) from P4. The appearance of whisker-related patterns was preceded by increased levels of immunostaining of the neuropil, which subsequently declined from the trigeminal nuclei upward. In SI, mGluR1alpha-positive neurons were observed in all cortical layers from P2. mGluR5 was localized in neurons, glial cells, and neuropil from P2. mGluR2/3 immunostaining was distributed only in the neuropil at all ages. The three receptor subtypes showed moderate to high expression in deep layer V throughout development. Transient expression peaked in the hollows of layer IV barrels from P4 to P9, and then fell off as expression increased in supragranular layers from P14 to P21. The deep aspect of the cortical subplate (layer VIb) showed dense mGluR5 and less dense mGluR1alpha immunostaining throughout development. Up-regulation of expression of group I and II mGluRs is correlated with the growth and refinement of connectivity and the establishment of somatotopic patterns in the three main relay stations of the trigeminal system. This finding suggests roles for mGluRs in the early processing of sensory information and in developmental plasticity.
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Collateral projections of single neurons in the nucleus raphe magnus to both the sensory trigeminal nuclei and spinal cord in the rat.
After injecting Diamidino yellow and Fast blue respectively into the sensory trigeminal nuclei and spinal cord, we observed doubly labeled cells in the nucleus raphe magnus (NRM). Combining the fluorescent retrograde double labeling with serotonin (5-HT) immunofluorescence histochemistry, we further found that about 30% of the doubly labeled NRM neurons showed 5-HT-like immunoreactivity (5-HT-LI). Such 5-HT-LI NRM neurons may modulate nociceptive activities simultaneously in the sensory trigeminal nuclei and spinal cord by sending axon collaterals to these regions.
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Behaviour-dependent variability of potentials in the somatosensory cortex evoked by stimulation of the trigeminal nuclei in freely moving rats.
Nine hooded rats with chronically implanted epidural recording electrodes on the right primary somatosensory cortex, the olfactory bulb and bipolar stimulating electrodes in the left ponto-mesencephalic trigeminal nuclei and parabrachial region were investigated during different patterns of spontaneous behaviour. The early positive-negative component of the TNEP with peak times P5 and NII (ms) appeared about 1 ms earlier than after tooth pulp stimulation. The amplitude P5-N11 was slightly increased during drowsiness, decreased during slow wave sleep and was strongly decreased in behavioural patterns with movements, always compared with relaxed wakefulness. The behaviour-dependent changes of cortical EP to stimulation of trigeminal nuclei (TNEP) were analogous to those after tooth pulp stimulation.
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The location of brainstem neurons which project bilaterally to the spinal trigeminal nuclei as demonstrated by the double fluorescent retrograde tracer technique.
Cells with possible dual projections to both spinal trigeminal nuclei were identified in the rat brainstem following separate injections of different retrogradely transported markers into the right and left spinal trigeminal nucleus. The greatest number of double-labeled cells was located in the nucleus reticularis gigantocellularis. Several double-marked cells were also observed in the nucleus raphe magnus, the nucleus paragigantocellularis and the periaqueductal gray. These results suggest that some cells in the above brainstem nuclei may have a bilateral modulating effect on the spinal trigeminal nuclei.
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[Effect of the destruction of the oral and caudal trigeminal nuclei on pain sensitivity in cats].
Structural changes of nociceptive response after separate lesions of the oral and caudal trigeminal nuclei were studied in chronic experiments on adult cats. The lesion of the oral nucleus was shown to increase pain response and that of the caudal nucleus--to cause its inhibition. A relationship between the specific and non-specific projection systems of the brain in the development of pain is discussed.
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Ascending projections from the lateral descending and common sensory trigeminal nuclei in python.
The primary sensory trigeminal system of Python is characterized by the presence of an additional nucleus which is involved in processing data obtained by infrared sensors. This so-called lateral descending nucleus (LTTD) is strictly separated from the nuclei of the common sensory trigeminal system. The present study was undertaken in order to establish the relation between the two sensory trigeminal systems and higher brainstem structures. Further we studied whether the projections of these two systems remain separated at higher brainstem levels. It is shown that the organization of particularly the thalamus is characterized by the presence of specific projection areas of each of the two trigeminal systems: a) the ability of infrared preception is reflected particularly in the presence of an unique thalamic nucleus: the nucleus pararotundus and probably also in the enlargement of nucleus rotundus; and b) distinct subnuclei in the thalamic ventral nuclear complex are related to the various nuclei of the common sensory trigeminal system. The main ascending projection of LTTD runs via a distinct tract to the central gray layer (SGC) of the contralateral tectum mesencephali and the nucleus pararotundus (PR). Rostrally, numerous fibres decussate again via the tectal commissure and terminate ipsilaterally in the rostral part of SGC and in PR. The ascending projections of the common sensory trigeminal nuclei resemble those of mammals by gaining thalamic nuclei (ventral nuclear complex). No projections of the tectum nor to the striatum (like in birds) were observed. The two sensory trigeminal systems remain separately organised, in their projections as well as in their structure. No major connection between the two trigeminal system is present.
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Excitatory amino acid binding sites in the trigeminal principal sensory and spinal trigeminal nuclei of the rat.
Quantitative autoradiography was used to examine the density and distribution of excitatory amino acid (EAA) binding site subtypes in the principal sensory and spinal trigeminal nuclei of the rat trigeminal complex. The highest densities of N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), kainate and metabotropic receptors were found in the superficial laminae (I and II) of subnucleus caudalis, a region known to be densely innervated by primary afferent nociceptive terminals. Lower densities of EAA binding sites were observed in spinal subnuclei interpolaris and oralis and within the principal sensory nucleus. These results are consistent with the hypothesis that EAAs are involved in primary afferent nociceptive neurotransmission.
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