A note on the medio-lateral organization of the oral subdivisions of the spinal trigeminal nucleus in the cat

Brain stem terminations of the trigeminal and upper spinal ganglia innervation of the cerebrovascular system: WGA-HRP transganglionic study

The central projections of the nerve fibers innervating the middle cerebral and basilar arteries were investigated by transganglionic tracing of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) in the rat. WGA-HRP was applied to the exposed basilar and/or middle cerebral arteries. Sections of the brain, trigeminal and upper spinal ganglia were reacted with tetramethylbenzidine for detection of the tracer. The results demonstrate that trigeminal neurons that innervate the middle cerebral artery project to the trigeminal main sensory nucleus, pars oralis, and the dorsocaudal two-fifths of pars interpolaris of the trigeminal brain stem nuclear complex. Terminals were also visible in the ipsilateral nucleus motorius dorsalis nervi vagi (dmnX) and in the lateral nucleus tractus solitarius (nTs) bilaterally at the level of the obex. The ventral periaqueductal gray, including the dorsal raphe and C2 dorsal horn, were also innervated by nerve fibers from the middle cerebral artery. Ipsilateral trigeminal rhizotomy prior to WGA-HRP application over the middle cerebral artery impeded the visualization of nerve terminations throughout the brain stem. Pretreatment with capsaicin reduced the density of labeled neurons and terminals within the trigeminal ganglion and the brain stem, respectively, following WGA-HRP application over the middle cerebral artery. Basilar artery fibers terminate in the C2 dorsal horn, the cuneate nuclei, dmnX, and nTs bilaterally. A few projections were also labeled in the ventral periaqueductal gray. Unilateral upper two spinal dorsal rhizotomy prior to WGA-HRP application over the exposed basilar artery resulted in terminal labeling within the C2 dorsal horn, the cuneate nucleus, dmnX, and nTs contralateral to the rhizotomy, whereas the ipsilateral side was devoid of any labeling. Bilateral superior cervical ganglionectomy prior to WGA-HRP administration to the middle cerebral and basilar arteries did not alter the visualization of nerve terminations throughout the brain stem.

The subnuclei and primary afferents of the descending trigeminal system in the mallard (Anas platyrhynchos L.)

The descending trigeminal tract and its nuclei were described in the mallard (Anas platyrhynchos L.). The borders of the system were established in Fink-Heimer preparations after unilateral lesions placed in the Gasserian ganglion using the distribution of degenerated particles as a criterion. Adjacent sections, stained with the Nissl, Kluver-Barrera and Haggqvist methods were used in the description of cyto- and fibroarchitecture of the descending trigeminal system and surrounding structures. Descending fibers of the trigeminal root could be traced from the sensory root, ventral to the main sensory nucleus, into the descending tract and its nuclei. Its fibers pass into the spinal cord, but not farther than the third cervical segment. Seven subdivisions (parts a-g) were recognized, but could be combined into four subnuclei, viz. in the terminology of Olszewski: subnucleus oralis containing parts a and b; subnucleus interpolaris parts c and d; subnucleus caudalis part f; dorsal horn part g, etc. No primary trigeminal fibers could be traced to structures outside the main sensory nucleus and nuclei of the descending trigeminal tract; all projections were ipsilateral with the exception of a slight bilateral projection caudal to the obex. Partial lesions in the Gasserian ganglion showed a distribution of the mandibular, maxillary and ophthalmic fibers from dorsal to ventral respectively in the subnuclei oralis and interpolaris, and from medial to lateral in the subnuclei caudalis and dorsal horn. Afferents from the petrosal ganglion project upon the medial part of subnucleus interpolaris and upon a small cell group (nucleus of the ascending glossopharyngeal tract) that may be functionally part of the subnucleus oralis. The subnucleus caudalis receives afferents from the jugular ganglion. These differences in afferentation are used in a tentative functional interpretation of the subdivisions of the nucleus of the descending trigeminal system.

Trigeminal primary afferent neurons projecting directly to the solitary nucleus in the cat: a transganglionic and retrograde horseradish peroxidase study

After applying horseradish peroxidase to peripheral branches of the trigeminal nerve in the cat, the lingual and pterygopalatine nerves were found to contain fibers which ended ipsilaterally in the rostral portions of the solitary nucleus (SN); massively in the medial and ventrolateral SN, moderately in the intermediate and interstitial SN and sparsely in the ventral SN. The rostralmost part of the SN was free from labeled terminals. After injecting the enzyme into the SN portions rostral to the area postrema, small neurons were scattered in the maxillary and mandibular divisions of the trigeminal ganglion.

The posteromedial ventral nucleus of the thalamus (VPM) of the cat: direct ascending projections to the cytoarchitectonic subdivisions

The posteromedial ventral nucleus (VPM) of the cat is divided cytoarchitectonically into the magnocellular (VPMmc), lateral parvocellular (VPMpcl), and medial parvocellular (VPMpcm) divisions. Cell bodies of neurons in the VPMpcm are small, while those in the VPMpcl are small to medium-sized. The VPMmc contains large neurons. Direct projections from the lower brain stem structures to each of the three divisions of the VPM were examined by the retrograde horseradish peroxidase (HRP) method. When HRP injection was done into the VPMmc, labeled neurons were mainly located contralaterally in the ventral division of the principal sensory trigeminal nucleus (Vp), in the rostral part of the oral subnucleus in the spinal trigeminal nucleus (Vsp), and in the interpolar subnucleus of the Vsp; a few labeled neurons were also found contralaterally in lamina I of the caudal subnucleus of the Vsp. When HRP injection was restricted to the VPMpcl or VPMpcm, HRP-labeled neurons were mainly observed ipsilaterally, respectively, in the dorsal division of the Vp, or in the parabrachial nucleus (PBN) regions dorsomedial and ventromedial to the brachium conjunctivum. After HRP injection into the parvocellular part of the VPM (VPMpc), labeled neurons were also seen contralaterally in the Vsp, but these were far less numerous than those seen after HRP injections into the VPMmc. Thus, each of the three divisions of the VPM receives main ascending afferent fibers from different brain stem structures; the VPMpcm, VPMpcl, or VPMmc receives afferent fibers, respectively, from the PBN ipsilaterally, from the dorsal division of Vp ipsilaterally, or from the ventral division of the Vp and the Vsp contralaterally.

Amygdala and masseteric reflex. II Mechanism of the diphasic modifications of the reflex elicited from the "defence reaction area". Role of the spinal trigeminal nucleus (pars oralis)

It has been demonstrated (Gary Bobo and Bonvallet 1975) that long-lasting stimulation of the "amygdaloid area for the defence reaction" (basal nucleus, pars magnocellularis) elicits, after an initial facilitation, a delayed inhibition of the monosynaptic masseteric reflex (MR), while stimulation of the amygdalofugal fibers running in the ansa lenticularis provokes an immediate inhibition of the reflex. In present study, the structure which mediates these inhibitions has been identified. Using combined techniques of limited transections, localized coagulations and localized stimulation and recording, it has been demonstrated that these ingibitions are mediated by the rostral portion of the spinal trigeminal nucleus, the subnucleus oralis (NO). After localized coagulation of this nucleus, or after lesions which interrupt slectively the connections between the NO and the masticatory nucleus, long-lasting stimulation of the basal nucleus elicits only well maintained facilitation of the MR. Hence, the delayed decrease in amplitude of the reflex, observed during stimulation of the basal nucleus in the preparations with intact brain, cannot be explained by the reversal of an initial facilitatory influence to an ingibitory one. The one ingibition of the reflex is due to the superimposition, on a background of sustained facilitation of the masseteric motoneurons, of the inhibitory influence exerted on the monosynaptic masseteric circuit by a trigeminal sensory nucleus, itself activated by delayed discharges of the basal nucleus. A tentative representation of the dual control exerted on the masseteric activity by the basal nucleus is given in Fig. 9. The functional implications of this dual control during the "defence reaction" are briefly discussed.