Arrangement and connections of mesencephalic trigeminal neurons in the rat

The morphology of the mesencephalic trigeminal nucleus was examined microscopically in serial frozen sections. The nucleus extends over a length of about 4.5 mm, and its cell number was calculated to range from 1,000 to 1,600. 60% of the cells were located in the caudal third of the nucleus. Clustering of large unipolar cells was seen throughout the nucleus. Small spindle-shaped multipolar cells were found in the pontine part of the nucleus. The efferent connections of the mesencephalic trigeminal neurons were investigated by means of iontophoretically delivered Phaseolus vulgaris leuco-agglutinin or horseradish peroxidase after electrophysiological identification of mesencephalic trigeminal neurons. All projections were found ipsilateral to the injection site; they were confined to the trigeminal motor nucleus, especially to its lateral part, and to the dorsolateral reticular formation. The latter projection area included the supratrigeminal nucleus, the nucleus of Probst, and the parvocellular reticular zone. There were no direct projections to the facial or hypoglossal motor nuclei. It is concluded that proprioceptive input from one side is mediated polysynaptically to the bilateral oral final common-path neurons, with the exception of the ipsilateral trigeminal motoneurons.     

A scanning electron microscopic study of the mesencephalic trigeminal nucleus in duck and rabbit

The mesencephalic trigeminal nucleus (MTN) cells of both young and adult ducks as well as of rabbits were investigated by scanning electron microscope. The rabbit showed only ovoid unipolar cells, while the duck also presented polyhedral cells. Few of these latter revealed processes originating from their surface and were recognized as multipolar cells. Some differences between the MTN cell surface of young and adult ducks were noticed. Synaptic bulbs were observed on the MTN cells in both duck and rabbit.     

HRP-labeled masticatory neurons in the rat trigeminal mesencephalic nucleus: a light and electron microscopic study

The neurons innervating the muscles of mastication were labeled retrogradely with horseradish peroxidase (HRP) which was injected into each muscle of mastication of the rats. The TMB-HRP labeled neurons were for light microscopic and DAB-HRP labeled neurons for electron microscopic study. Many HRP-labeled mesencephalic neurons were observed in the trigeminal mesencephalic nucleus (TMEN) after HRP injection in jaw-closing muscles (JCM). On the other hand, no labeled neurons were found following the application of HRP to the lateral pterygoid and the anterior belly of the digastric muscles, with the exception of a very few from the mylohyoid muscle. The latter three muscles were jaw-opening muscles (JOM). The mesencephalic neurons of each JCM in the TMEN were rather randomly distributed, although they were concentrated more in the caudal region of this nucleus. These neurons were typically unipolar, with spherical to oval perikarya. Each neuron had a single process which coursed caudolaterally to join the mesencephalic tract of the trigeminal nerve. Ultrastructurally, mesencephalic masticatory neurons had a rather regular nucleus locating either centrally or eccentrically in the perikaryon, which is rather plump. The cytoplasm was endowed with very well developed Golgi apparatus and rough endoplasmic reticulum. Neurofilaments, varying in number, intermingled mostly with the Golgi apparatus in the cytoplasm. Somatic spines were frequently observed; however, synapses abutting upon the soma were few. Macula adherens-like structures were occassionally encountered in the contact zone between two cells.     

Masseteric Nerve Injury Increases Expression of Brain-Derived Neurotrophic Factor in Microglia Within the Rat Mesencephalic Trigeminal Tract Nucleus

The distribution of brain-derived neurotrophic factor was examined in the rat mesencephalic trigeminal tract nucleus after transection and crush of the masseteric nerve. In the intact mesencephalic trigeminal tract nucleus, brain-derived neurotrophic factor was detected in small cells with fine processes. These cells and processes were occasionally located adjacent to tyrosine kinase B receptor-immunoreactive sensory neurons. The transection and crush of the masseteric nerve increased expression of brain-derived neurotrophic factor in the nucleus. The number and size of brain-derived neurotrophic factor-immunoreactive cells and processes were dramatically elevated by the nerve injury. As a result, the density of brain-derived neurotrophic factor-immunoreactive profiles in the mesencephalic trigeminal tract nucleus at 7 days after the injury was significantly higher compared with the intact nucleus. Double immunofluorescence method also revealed that brain-derived neurotrophic factor-immunoreactive cells were mostly immunoreactive for OX-42 but not glial fibrillary acidic protein. In addition, the retrograde tracing method demonstrated that brain-derived neurotrophic factor-immunoreactive cells and processes surrounded retrogradely labeled neurons which showed tyrosine kinase B receptor-immunoreactivity. These findings indicate that the nerve injury increases expression of brain-derived neurotrophic factor in microglia within the mesencephalic trigeminal tract nucleus. The glial neurotrophic factor may be associated with axonal regeneration of the injured primary proprioceptor in the trigeminal nervous system.     

Localization and morphometric analysis of masticatory muscle afferent neurons in the nucleus of the mesencephalic root of the trigeminal nerve in the cat

Injections of horseradish peroxidase (HRP) were made into the ipsilateral temporal muscle and contralateral masseter muscle of 10 cats in order to identify and characterize neurons in the nucleus of the mesencephalic root of the trigeminal nerve that innervate muscle receptors in the orofacial periphery. Neurons labelled by HRP injections and unlabelled cells from 5 control cats were measured with a computer-based image analyzer, and their position was mapped on a stereotaxic graph. Cells that innervate the masseter and temporal muscles were identified throughout the rostrocaudal extent of the nucleus. There was no indication of a somatotopic pattern nor of a specific segregation within the nucleus for cells innervating muscle receptors. The nucleus contained small, rounded unipolar neurons located primarily in the dorsal border of the periaqueductal gray (PAG) matter in the rostral part of the nucleus and larger oval unipolar neurons which were scattered throughout the nucleus, but were predominant in the pontine portion of the nucleus. HRP injections labelled both large and small cells, as well as occasional multipolar cells. The last-mentioned tended to be located in the lateral margins of the PAG. The mean geometric values obtained for the control group were: area 552.7 microns2 perimeter 110.3 microns; maximum diameter 36.0 microns. and diameter of an equivalent circle 26.1 microns. The mean values of the labelled neurons were: area 606.6 microns2; perimeter 100.1 microns; maximum diameter 36.0 microns, and diameter of an equivalent circle 27.2 microns.     

Immunocytochemical localization of the AMPA receptor subunits in the mesencephalic trigeminal nucleus of the rat

The mesencephalic trigeminal nucleus is composed of large (35-50 microns) pseudo-unipolar neurons. Closely associated with them are small (< 20 microns) multipolar neurons. An unique peculiarity of the pseudo-unipolar perikarya is that they receive synaptic input from various sources, which sets them apart from the dorsal root and cranial nerves sensory ganglia neurons. Whereas glutamate is the best neurotransmitter candidate in pseudo-unipolar neurons, glutamatergic input into them has not yet been reported. AMPA glutamate receptors are implicated in fast excitatory glutamatergic synaptic transmission. They have been localized ultrastructurally at postsynaptic sites. This study demonstrates that the pseudo-unipolar neurons of the mesencephalic trigeminal nucleus express AMPA glutamate receptor subunits, which indicates that these neurons receive glutamatergic input. Serial sections from the rostral pons and midbrain of Sprague-Dawley rats were immunostained with antibodies against C-terminus of AMPA receptor subunits: GluR1, GluR2/3, and GluR4. The immunoreaction was visualized with avidin-biotin-peroxidase/DAB for light and electron microscopy. With GluR1 antibody only the smallest multipolar neurons were recognized as immunopositive within the mesencephalic trigeminal nucleus. GluR2/3 stained the pseudo-unipolar neurons intensely within the entire rostro-caudal extent of the nucleus. In addition the former antibody stained small multipolar neurons within the mesencephalic trigeminal nucleus, though with somewhat larger dimensions than those immunoreactive for GluR1. Whereas the overall staining with GluR4 antibody was scant, those pseudo-unipolar neurons that were stained, were strongly stained. Furthermore, a considerable number of microglial cells within and surrounding the mesencephalic trigeminal nucleus displayed very intense immunoreactivity for GluR4. These results are discussed in the light of the glutamate receptor subunit composition.     

Primary projections of the trigeminal nerve in two species of sturgeon: Acipenser oxyrhynchus and Scaphirhynchus platorynchus

Horseradish peroxidase histochemical studies of afferent and efferent projections of the trigeminal nerve in two species of chondrostean fishes revealed medial, descending and ascending projections. Entering fibers of the trigeminal sensory root project medially to terminate in the medial trigeminal nucleus, located along the medial wall of the rostral medulla. Other entering sensory fibers turn caudally within the medulla, forming the trigeminal spinal tract, and terminate within the descending trigeminal nucleus. The descending trigeminal nucleus consists of dorsal (DTNd) and ventral (DTNv) components. Fibers of the trigeminal spinal tract descend through the lateral alar medulla and into the dorsolateral cervical spinal cord. Fibers exit the spinal tract throughout its length, projecting to the ventral descending trigeminal nucleus (DTNv) in the medulla and to the funicular nucleus at the obex. Retrograde transport of HRP through sensory root fibers also revealed an ascending bundle of fibers that constitutes the neurites of the mesencephalic trigeminal nucleus, cell bodies of which are located in the rostral optic tectum. Retrograde transport of HRP through motor root fibers labeled ipsilateral cells of the trigeminal motor nucleus, located in the rostral branchiomeric motor column.     

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

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

Afferent projections of the trigeminal nerve in the goldfish,Carassius auratus

The horseradish peroxidase (HRP) histochemical technique was used to examine the peripheral distribution and afferent projections of the trigeminal nerve in the goldfish, Carassius auratus. Sensory fibers of the trigeminal nerve distribute over the head via four branches. The ophthalmic branch distributes fibers to the region above the eye and naris. The maxillary and mandibular branches innervate the regions of the upper and lower lip, respectively. A fourth branch of the trigeminal nerve was demonstrated to be present in the hyomandibular trunk. Upon entering the medulla the trigeminal afferent fibers divide into a rostromedially directed bundle and a caudally directed bundle. The rostromedially directed bundle terminates in the sensory trigeminal nucleus (STN) located within the rostral medulla. The majority of fibers turn caudally, forming the descending trigeminal tract. Fibers of the descending trigeminal tract terminate within three medullary nuclei: the nucleus of the descending trigeminal tract (NDTV), the spinal trigeminal nucleus (Spv), and the medial funicular nucleus (MFn). All projections, except for those to the MFn, are ipsilateral. Contralateral projections were observed at the level of the MFn following the labeling of the ophthalmic and maxillomandibular branches. All branches of the trigeminal nerve project to all four of the trigeminal medullary nuclei. Projections to the STN and MFn were found to be topographically organized such that the afferents of the ophthalmic branch project onto the ventral portion of these nuclei, while the afferents of the maxillo- and hyomandibular branches project to the dorsal portion of these nuclei. Cells of the mesencephalic trigeminal nucleus were retrogradely labeled following HRP application to the ophthalmic, maxillary, and mandibular branches of the trigeminal nerve. In addition to demonstrating the ascending mesencephalic trigeminal root fibers, HRP application to the above-mentioned branches also revealed descending mesencephalic trigeminal fibers. The descending mesencephalic trigeminal fibers course caudally medial to the branchiomeric motor column and terminate in the ventromedial portion of the MFn.     

Colchicine causes intrasomatic neurofilament bundles in the mesencephalic trigeminal nucleus and intradendritic bundles in other brain regions

The effect of a single intracerebroventricular injection of colchicine on the distribution of organelles in neurons of the mesencephalic nucleus of the trigeminal nerve, the inferior colliculus and the deep cerebellar nuclei was studied. In the mesencephalic nucleus of the trigeminal nerve colchicine produced a dramatic accumulation of neurofilament bundles in the soma of these neurons and did not produce a reduction in the number of lysosomes. In other neuronal populations studied, colchicine produced neurofilament bundles in the dendrites and a reduction of lysosomes from the soma of neurons.     

Cerebellar afferents to paramedian lobule from the trigeminal complex in Tupaia glis: a horseradish peroxidase (HRP) study

Projections from the trigeminal complex to paramedian lobule (PML) were studied in the tree shrew (Tupaia glis) by means of retrograde transport of horseradish peroxidase (HRP). Neurons which project to both dorsal and ventral folia of PML are located primarily in those areas of the trigeminal nuclear complex interpreted as nucleus interpolaris (Vi) and caudal areas of the nucleus oralis (Vo). The majority of HRP-labeled neurons lie in ventral and ventrolateral regions of Vi/Vo. No HRP-reactive cells are present in the principal (Vp), mesencephalic, or motor nuclei nor in nucleus caudalis or rostral portions of oralis. The majority of trigeminocerebellar (TC) cells are found in ipsilateral Vi; however, sparse numbers of labeled somata are present in this subnucleus on the contralateral side. Within Vi/Vo, small fusiform and medium-and large-sized multipolar neurons contain HRP-reaction product. Large multipolar cells are found primarily in ventrolateral portions of Vi/Vo, while medium and small neurons are scattered throughout the ventral half of the nucleus. Small-sized neurons are also present dorsally within Vi/Vo. Axons of labeled TC cells course laterally through the spinal trigeminal tract, enter medial aspects of the restiform body, and arch dorsally into the cerebellum.     

Carbonic anhydrase enzyme histochemistry of cranial nerve primary sensory afferent neurons in the rat

Hanssons' enzyme histochemical method for the demonstration of carbonic anhydrase has been used to examine primary sensory neurons of cranial nerves in the rat (cochlear ganglion cells excluded). Numerous carbonic anhydrase positive neurons were present in the trigeminal and geniculate ganglia as well as in the mesencephalic trigeminal nucleus. A few carbonic anhydrase positive ganglion cells were found in the nodose ganglion, but none in the petrosal and vestibular ganglia. However, in the latter ganglia, satellite cells surrounding the neurons frequently showed staining for carbonic anhydrase.     

Distribution of synaptic boutons in the mesencephalic trigeminal nucleus of the rat--a quantitative electron-microscopical study.

The distribution of synapses and synaptic bouton types in the mesencephalic trigeminal (Me5) nucleus was examined in a quantitative electron-microscopical study. Of 588 terminal boutons that were counted in the compact caudal part of the Me5 nucleus, less than 8% formed synapses on the somata of the predominantly unipolar Me5 neurons. About 79% formed synapses on fibres located between the Me5 somata, while about 13% of the vesicle-containing terminals had no clear synaptic specialization. All of these non-synaptic terminals were G type boutons, with pleomorphic and large characteristic dense-core vesicles. Approximately 60% of the axosomatic synapses were of the S type, containing spherical vesicles and an asymmetrical or symmetrical synaptic specialization. About 20, respectively 15% of the axosomatic synapses, were of the F, respectively P type; both are symmetrical synapse types containing either a majority of flat or pleomorphic vesicles. Less than 10% of the axosomatic synapses were of the G type. Although some proportional differences were noted, an almost similar bouton type distribution pattern was found for the axodendritic synapses suggesting that the axosomatic and axodendritic synapses in the Me5 nucleus are part of the same afferent fibre plexus covering the Me5 nucleus.     

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

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

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

Afferent and efferent components of the facial nerve in the bullfrog (Rana catesbeiana).

The afferent and efferent components of the facial nerve were traced within the brain stem of Rana catesbeiana, using three different neuroanatomical techniques. Primary afferent fibers could be traced to the spinal tract of trigeminal nerve and to fasciculus solitarius as far caudally as the first or second spinal segment, using silver degeneration methods. Cobalt filling of of the entire nerve showed the same distribution of afferent fibers, as well as the filling of the cells within the mesencephalic nucleus of trigeminal, indicating the origin of a proprioceptive component of the facial nerve. Cobalt iontophoresis and horseradish perioxidase experiments showed that the motor nucleus of the facial nerve was located just ventral to the fourth ventricle, and caudal to the motor nucleus of trigeminal. The distribution of afferent fibers to fasciculus solitarius and the spinal tract of trigeminal is similar in some respects to the distribution of afferent fibers from the trigeminal and vagal nerves in the bullfrog. The afferent fibers from the three cranial nerves are found as far caudally in the brain stem as the second spinal segment.     

Subcellular Distribution of α1 and β2/3 GABAA Receptor Subunits in Sensory Neurons of the Bovine Trigeminal Mesencephalic Nucleus: Evidence Suggesting Their Axoplasmic Transport

Neurons were free-hand isolated under the stereomicroscope from the bovine trigeminal mesencephalic nucleus. These neurons were challenged with monoclonal antibodies against the alpha1 and the beta2/3 subunits of the GABA(A) receptor. The neurons showed a strong reaction to both antibodies. The reaction was mainly intracellular in the round cell bodies and in the axoplasm of the axon emerging from these pseudounipolar cells. This suggests the synthesis of these subunits in the cell body and their transport along the axon.     

Topographical representation of the jaw muscles within the trigeminal motor nucleus. An HRP study in the mallard, Anas platyrhynchos

The location of the trigeminal motoneurons of the jaw muscles has been determined in the brainstem of the mallard utilizing retrograde axonal transport of horseradish peroxidase (HRP). Injections with HRP into the jaw muscles or application of HRP to the mandibular nerve showed that the trigeminal motor nucleus can be subdivided into five subnuclei, mV1-mV5. Three functional groups of jaw muscles are represented in separate subnuclei. The most lateral subnucleus mV2 innervates all but one adductor muscles, the intermediate mV1 innervates the pterygoid muscles + one adductor and the medial mV4 the two protractor muscles. The most ventral subnucleus mV3 contains the neurons innervating two extrinsic tongue muscles as well as some perikarya of adductor muscles. Subnucleus mV5 lies dorsomedial to mV4 and contains the motoneurons of the depressor muscle of the lower eye lid. Elements of the proprioceptive system, viz. presumptive gamma-neurons and mesencephalic trigeminal nucleus cells, could also be visualized. The topological and functional aspects of the subdivision of the motor nucleus are discussed.     

The sensory trigeminal system in birds: input, organization and effects of peripheral damage. A review.

The primary sensory trigeminal system in birds comprises the mesencephalic trigeminal nucleus and the trigeminal ganglion with projections to the principal sensory nucleus (PrV) and the descending tract with its subnuclei. Other cranial nerves can contribute to PrV and the descending system that together form the somatosensory system of the head. There is also a proprioceptive component. The somatosensory system comprises a component serving tactile sense and a nociceptive component. The former processes information from many mechanoreceptors in beak and tongue; both PrV and subnuclei of the descending system are involved. The nociceptive component consists of small ganglion cells projecting presumably to layers I and II of the caudal subnucleus of the descending trigeminal system and cervical dorsal horn; this is the only trigeminal region showing immunoreactivity for substance P. The effects of amputation of the tips of the beak of chickens (debeaking) are estimated by fiber counts in electron microscopic preparations of the trigeminal branches innervating that area, and by cell counts in Nissl stained sections of the trigeminal ganglion. Our data indicate that debeaking causes a loss of exteroceptive units, but not of nociceptive units. Comparison of sections stained for the presence of substance P (immunohistochemistry) did not reveal a long-term effect on the nociceptive system suggestive of the occurrence of chronic pain.     

Action of high and superhigh doses of fission neutrons and gamma quanta on the central noradrenergic formation of the brain--on the locus coeruleus (the blue spot)

Most of the blue spot neurons of Wistar rats exhibited a pronounced central chromatolysis 24 h following irradiation with fission neutrons (above 100 Gy) and gamma-quanta (above 200 Gy). The changes in the mesencephalic nucleus of the trigeminal nerve were distinct on day 2 after 200 Gy gamma-irradiation. The number of the modified nervous cells in these regions was higher than that in other brain parts.