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Efferent Projections of the Nucleus Caudalis of the Spinal Trigeminal Complex in the Cat

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Efferent Projections of the Nucleus Caudalis of the Spinal Trigeminal Complex in the Cat Okajimas Fol. anat. iap., 47 : 377-405, 1971 Efferent Projections of the Nucleus Caudalis of the Spinal Trigeminal Complex in the Cat By Syosuke Kawamura The Third Department of Anatomy, Okayama University Medical School, Okayama, Japan (Director : Prof. Kahee Niimi) Introduction The spinal nucleus of the trigeminal nerve can be divided into the nucleus oralis, interpolaris and caudalis arranged in a rostrocaudal sequence. Contrary to the first two nuclei, the nucleus caudalis shows a laminated structure and consists of the marginal, gelatinous and magnocellular parts, which are comparable with those of the posterior gray of the spinal cord (0 1 s z e w s k i, '50). Many attempts have been made to clarify the correlation be- tween the structural difference of the spinal trigeminal nucleus and its functional characteristics by many authors (B r o w n, '58 ; C a r- penter and Hanna, '61; Wall and Taub, '62; Stewart and King, '63; Darian-Smith and Mayday, '63; Eisenman et al., '64 ; N o r d, '67). It is now accepted that the nucleus caudalis is primarily concerned with pain and temperature sense of the face. This is of interest in view of the exclusive pain and thermal function of the similar spinal 'cord structures. Other data, with regard to the fiber connections of the subnuclei of the spinal trigeminal nucleus, are further indications of a certain functional segregation within the nucleus (T or vi k, '56 ; C a r p e n t e r andHanna,'61 ; Stewart andKing,'63 ; Dunn and Matzke, '68). Nevertheless, as yet there has been no study to analyze the fiber projections of the different parts of the nucleus caudalis. The present study is designed to fill this lack in our knowledge, by means of the N a u t a-G y g a x technique following localized losions in various parts of the nucleus caudalis in the cat. Meterial and Methods Ten adult cats were used in the present study. Under Nembutal anesthesia, posterior fossa craniotomy was performed, and various 377 378 Syosuke Kawamura parts of the tuber cinereum of the medulla were destroyed with a small scalpel at different levels below the obex. After survival for 7 days, the animals were killed, under deep Nembutal anesthesia, by intracarotid perfusion with normal saline followed by a solution of 10% neutral formalin. The brains and upper spinal cords were removed, fixed in 10% neutral formalin for five days, and sectioned about 10 mm thick transversely. These cut blocks of the brains and spinal cords were stored in 10% neutral formalin for one month, sectioned serially at 30-40p on the freezing microtome and impreg- nated by the N a u t a and G y g a x ('54) technique. The terminology here employed has followed most closely that of Olszew ski ('50). Observations 1. A case with the lesion in the pars marginalis of the nucleus caudalis (cat 8). The lesion in this case lies in the pars marginalis of the nucleus caudalis and the adjacent spinal trigeminal tract at rostral levels of the pyramidal decussation. There is a slight invasion into the pars gelatinosa (Text-fig. 1). The ascending degenerated fibers from the lesion are divided Text-fig. 1. Transverse sections showing the site and extent of lesions (cross- hatched areas) in the nucleus caudalis in cats 8, 3, 5 and 10. Efferents of Caudal Spinal Trigeminal Nucleus in Cat 379 roughly into the intranuclear ascending, the crossed medial lemniscal and the crossed reticular ascending pathways. The intranuclear ascending pathway. Although some degenerated fibers ascend through the medial part of the spinal trigeminal tract, most of the degenerated fibers are directed medialward from the lesion and ascend through the pars magnocellularis of the nucleus caudalis where many degenerated preterminals are found. Rostrally they begin to form small bundles. At caudal levels of the inferior olivary complex, some of the degenerated fibers spread medially to end in the parvocellular reticular nucleus, and a few fibers continue further medially into the intercalated nucleus. In addition, some degenerated fibers are found to pass dorsomedially into the ventro- lateral part of the cuneate nucleus, but no fibers can be traced to the nucleus of the solitary tract, the dorsal nucleus of the vagus, the hypoglossal nucleus or the lateral reticular nucleus (Text-fig. 3). Reaching the nucleus interpolaris, many small fascicles of de- generated fibers ascend through this nucleus where abundant preter- minals are present. The degenerated fibers spreading into the reticular formation are relatively few in number. Only a few fibers run dorsally into the inferior vestibular nucleus. In the facial nucleus occasional fibers of passage are encountered. As the nucleus oralis is reached, the small fiber bundles begin to disperse within the nucleus and are distributed to the parvocellular reticular nucleus, but they cannot be traced medially beyond the root of the abducens nerve. A few degenerated fibers are directed dorsally to terminate in the medial part of the lateral vestibular nucleus (Text-fig. 3). Further rostrally the degenerated fibers spill over heavily into the main sensory trigeminal nucleus. Some of them are directed medially just ventral to the mesencephalic root of the trigeminal nerve to terminate in the dorsal part of the pontine reticular for- mation. No degenerated fibers can be followed to the motor trigeminal nucleus. At these levels a few degenerated fibers extend ventrally from the main sensory nucleus into the lateral lemniscus and are distributed in the ventral part of the inferior colliculus (Text-fig. 3). The crossed medial lemniscal pathway. This pathway, running ventromedially from the lesion, crosses the midline among the fiber bundles of the pyramidal decussation and then runs rostrally along the lateral edge of the uncrossed pyramidal tract . At inferior olivary levels the degenerated fibers are situated medial, ventral and ventrolateral to the inferior olivary complex, but do not enter there . At these levels a few degenerated fibers are seen to cross the midline to join the medial lemniscal pathway . Proceeding rostrally, the degenerated fibers of this pathway migrate laterally within the 380 Syosuke Kawamura Text-fig. 2. Lesions in cats 1, 4, 6 and 7. For notes see Text-fig. 1. medial lemniscus. As the nucleus of the facial nerve appears, most of the degenerated fibers are concentrated in the region between the pyramid and the ventral spinocerebellar tract (Text-fig. 3). At levels of the trapezoid body the degenerated fibers ascend through the medial lemniscus between the root of the abducens nerve and the medial superior olivary nucleus. In the lower pons they are found mostly in the lateral portion of the medial lemniscus and partly in the lateral lemniscus. In more rostra! sections some of the fibers are seen to enter the ventral part of the inferior colliculus, but the majority ascend through the most lateral part of the medial lemniscus. At superior collicular levels a fair number of degenerated fibers leave the medial lemniscus in the dorsomedial direction to distribute in the superior colliculus, particularly in the stratum griseum inter- medium. In addition, some fibers pass medially through the reti- cular formation to terminate in the lateral part of the central gray (Text-fig. 3). At the most rostral level of the superior colliculus, the degenerated fibers are crowded irregularly in the region among the red nucleus, the substantia nigra, the medial geniculate body and the central gray. A considerable number of degenerated fibers run laterally into the magnocellular part of the medial geniculate Efferents of Caudal Spinal Trigeminal Nucleus in Cat 381 Text-fig. 3. Drawings of transverse sections (unequal intervals) through the medulla oblongata, pons and mesencephalon of cat 8. In this and subsequent figures, degenerated fibeys of passage are indicated by coarse dots and preterminal degeneration by fine stipples. body, particularly its ventromedial portion (Text-fig. 4). In the posterior region of the thalamus, most of the degenerated fibers are found in the ventral part of the posteromedial ventral nucleus. Rostrally they divide into medial and lateral groups of fibers. The medial group consists of fine fibers crowded in the medial part of the posteromedial ventral nucleus, whereas the lateral group is composed of a small number of coarse fibers scattered in the lateral part of this nucleus. These two groups of fibers decrease in number rostrally and disappear at the level a little rostral to the middle of the posteromedial ventral nucleus. No degenerated fibers are seen in the other thalamic nuclei (Text-fig. 4). Other projection fibers. Besides the above two main pathways, the crossed reticular ascending pathway can be distinguished, though 382 Syosuke Kawamura Text-fig. 4. Drawings of transverse sections through the diencephalonof cat 8. it is small in amount in this case. Fibers of this pathway run ventromedially from the lesion together with those of the crossed medial lemniscal pathway to cross the midline among the fiber bundles of the pyramidal decussation. After crossing the midline, they diverge from the crossed medial lemniscal pathway to pass dorsolaterally and ascend through the reticular formation ventrolateral to the hypoglossal nucleus. Some of them are distributed to the adjacent portion of the reticular formation, a few to the nucleus interpolaris, and others to the nucleus reticularis pontis caudalis medial to the root of the facial nerve (Text-fig. 3). Moreover, some degenerated fibers are seen to run medially from the lesion and cross the midline dorsal to the central canal. A few of them enter the contralateral gracile nucleus, but the majority course laterally just dorsal to the nucleus of the solitary tract and terminate in the pars magnocellularis of the contralateral nucleus caudalis (Text-fig.
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