Intersubnuclear connections within the rat trigeminal brainstem complex

Prior intracellular recording and labeling experiments have documented local-circuit and projection neurons in the spinal trigeminal (V) nucleus with axons that arborize in more rostral and caudal spinal trigeminal subnuclei and nucleus principalis. Anterograde tracing studies were therefore carried out to assess the origin, extent, distribution, and morphology of such intersubnuclear axons in the rat trigeminal brainstem nuclear complex (TBNC). Phaseolus vulgaris leucoagglutinin (PHA-L) was used as the anterograde marker because of its high sensitivity and the morphological detail provided. Injections restricted to TBNC subnucleus caudalis resulted in dense terminal labeling in each of the more rostral ipsilateral subnuclei. Subnucleus interpolaris projected ipsilaterally and heavily to magnocellular portions of subnucleus caudalis, as well as subnucleus oralis and nucleus principalis. Nucleus principalis, on the other hand, had only a sparse projection to each of the caudal ipsilateral subnuclei. Intersubnuclear axons most frequently traveled in the deep bundles within the TBNC, the V spinal tract, and the reticular formation. They gave rise to a number of circumscribed, highly branched arbors with many boutons of the terminal and en passant types. Retrograde single- or multiple-labeling experiments assessed the cells giving rise to TBNC intersubnuclear collaterals. Horseradish peroxidase (HRP) and/or fluorescent tracer injections into the thalamus, colliculus, cerebellum, nucleus principalis, and/or subnucleus caudalis revealed large numbers of neurons in subnuclei caudalis, interpolaris, and oralis projecting to the region of nucleus principalis. Cells projecting to more caudal spinal trigeminal regions were most numerous in subnuclei interpolaris and oralis. Some cells in lamina V of subnucleus caudalis and in subnuclei interpolaris and oralis projected to thalamus and/or colliculus, as well as other TBNC subnuclei. Such collateral projections were rare in nucleus principalis and more superficial laminae of subnucleus caudalis. TBNC cells labeled by cerebellar injections were not double-labeled by tracer injections into the thalamus, colliculus, or TBNC. These findings lend generality to currently available data obtained with intracellular recording and HRP labeling methods, and suggest that most intersubnuclear axons originate in TBNC local-circuit neurons, though some originate in cells that project to midbrain and/or diencephalon.     

Projections of the optic tectum and the mesencephalic nucleus of the trigeminal nerve in the tegu lizard (Tupinambis nigropunctatus)

Summary Fibers undergoing Wallerian degeneration following tectal lesions were demonstrated with the Nauta and Fink-Heimer methods and traced to their termination. Four of the five distinct fiber paths originating in the optic tectum appear related to vision, while one is related to the mesencephalic nucleus of the trigeminus. The latter component of the tectal efferents distributes fibers to 1) the main sensory nucleus of the trigeminus, 2) the motor nucleus of the trigeminus, 3) the nucleus of tractus solitarius, and 4) the intermediate gray of the cervical spinal cord.The principal ascending bundle projects to the nucleus rotundus, three components of the ventral geniculate nucleus and the nucleus ventromedialis anterior ipsilaterally, before it crosses in the supraoptic commissure and terminates in the contralateral nucleus rotundus, ventral geniculate nucleus and a hitherto unnamed region dorsal to the nucleus of the posterior accessory optic tract.Fibers leaving the tectum dorso-medially terminate in the posterodorsal nucleus ipsilaterally and the stratum griseum periventriculare of the contralateral tectum. The descending fiber paths terminate in medial reticular cell groups and the rostral spinal cord contralaterally and in the torus and the lateral reticular regions ipsilaterally. The ipsilateral fascicle also issues fibers to the magnocellular nucleus isthmi.     

Intersubnuclear Connections within the Rat Trigeminal Brainstem Complex

Prior intracellular recording and labeling experiments have documented local-circuit and projection neurons in the spinal trigeminal (V) nucleus with axons that arborize in more rostral and caudal spinal trigeminal subnuclei and nucleus principalis. Anterograde tracing studies were therefore carried out to assess the origin, extent, distribution, and morphology of such intersubnuclear axons in the rat trigeminal brainstem nuclear complex (TBNC). Phaseolus vulgaris leucoagglutinin (PHA-L) was used as the anterograde marker because of its high sensitivity and the morphological detail provided. Injections restricted to TBNC subnucleus caudalis resulted in dense terminal labeling in each of the more rostral ipsilateral subnuclei. Subnucleus interpolaris projected ipsilaterally and heavily to magnocellular portions of subnucleus caudalis, as well as subnucleus oralis and nucleus principalis. Nucleus principalis, on the other hand, had only a sparse projection to each of the caudal ipsilateral subnuclei. Intersubnuclear axons most frequently traveled in the deep bundles within the TBNC, the V spinal tract, and the reticular formation. They gave rise to a number of circumscribed, highly branched arbors with many boutons of the terminal and en passant types.

Retrograde single- or multiple-labeling experiments assessed the cells giving rise to TBNC intersubnuclear collaterals. Horseradish peroxidase (HRP) and/or fluorescent tracer injections into the thalamus, colliculus, cerebellum, nucleus principalis, and/or subnucleus caudalis revealed large numbers of neurons in subnuclei caudalis, interpolaris, and oralis projecting to the region of nucleus principalis. Cells projecting to more caudal spinal trigeminal regions were most numerous in subnuclei interpolaris and oralis. Some cells in lamina V of subnucleus caudalis and in subnuclei interpolaris and oralis projected to thalamus and/or colliculus, as well as other TBNC subnuclei. Such collateral projections were rare in nucleus principalis and more superficial laminae of subnucleus caudalis. TBNC cells labeled by cerebellar injections were not double-labeled by tracer injections into the thalamus, colliculus, or TBNC.

These findings lend generality to currently available data obtained with intracellular recording and HRP labeling methods, and suggest that most intersubnuclear axons originate in TBNC local-circuit neurons, though some originate in cells that project to midbrain and/or diencephalon.     

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.     

The neurons of origin of non-cortical afferent connections to the oculomotor nucleus. A retrograde labeling study in the rabbit.

The cellular origin of the brainstem projections to the oculomotor nucleus in the rabbit has been investigated by using free (HRP) and lectin-conjugated horseradish peroxidase (WGA-HRP). Following injections of these tracers into the somatic oculomotor nucleus (OMC), retrogradely labeled cells have been observed in numerous brainstem structures. In particular, bilateral labeling has been found in the four main subdivisions of the vestibular complex, predominantly in the superior and medial vestibular nuclei and the interstitial nucleus of Cajal, while ipsilateral labeling was found in the rostral interstitial nucleus of the medial longitudinal fascicle (Ri-MLF), the Darkschewitsch and the praepositus nuclei. Neurons labeled only contralaterally have been identified in the following structures: mesencephalic reticular formation dorsolateral to the red nucleus, abducens internuclear neurons, group Y, several areas of the lateral and medial regions of the pontine and medullary reticular formation, ventral region of the lateral cerebellar nucleus and caudal anterior interpositus nucleus. This study provides also information regarding differential projections of some centers to rostral and caudal portions of the OMC. Thus, the rostral one-third appears to receive predominant afferents from the superior and medial vestibular nuclei, while the caudal two-thirds receive afferents from all the four vestibular nuclei. Finally, the group Y sends afferents to the middle and caudal, but not to the rostral OMC.     

The Ganglionic Origins and Central Projections of Primary Sensory Neurons Innervating the Upper and Lower Lips in the Rat

Retrograde and transganglionic transport of horseradish peroxidase (HRP) was used to investigate the neurons innervating the upper and the lower lips and their central projections in the rat. Both the upper and the lower lips were observed to be innervated by a very large number of trigeminal sensory neurons, with their cell bodies located in the maxillary and the mandibular parts of the trigeminal ganglion, respectively. The central projections of neurons innervating the upper lip formed a long continuous column starting rostrally at midlevels of the trigeminal main sensory nucleus (5P) and extending caudally through the CI dorsal horn, with occasional fibers reaching the C3 segment. The heaviest projections appeared in the middle portions of 5P and nucleus interpolaris (51), as well as in the rostral part of nucleus caudalis (5C). A small but consistent projection to the solitary tract nucleus, originating from cells in the inferior vagal ganglion, was observed in the upper-lip experiments. The central projections from neurons innervating the lower lip also appeared as a long column located dorsally or dorsomedially to the projections from the upper lip. The most prominent projections from the lower lip were located in the caudal part of 5P, the middle part of 5I, and the caudal two-thirds of 5C. Sparse projections could be traced as far caudally as C4. At 5C and cervical levels, some labeling appeared contralaterally in the same location as on the ipsilateral side.     

环鸽丘脑听区传入神经投射的研究

应用神经示踪物ＰＨＡＬ和ＢＤＡ对环鸽丘脑听区的传入神经投射进行了研究。结果发现中脑外侧核背部和丘间核交界内缘区的神经元发出纤维投射至丘脑卵形核周围形成卵形壳;尾部Ｏｖ壳和Ｏｖ交界面区域接受前峡核浅区的投射;尾部Ｏｖ壳不但接受ＩＣＭ神经元的传出投射,而且有神经发出的传出纤维参与了Ｏｖ壳的形成。     

大鼠脑内代谢型谷氨酸受体5亚型(mGluR5)定位分布的免疫细胞化学研究

本研究用免疫细胞化学技术观察了大鼠脑内参与兴奋性突触传递的代谢型谷氨酸受体5亚型(mGluR5)的精确定位分布.mGluR5阳性浓染的神经元胞体和纤维密集地分布于大脑皮质浅层、嗅球、伏核、尾壳核、前脑基底部、隔区、苍白球、腹侧苍白球、海马CA1和CA2区、下丘中央核、被盖背侧核和三叉神经脊束核尾侧亚核浅层;淡染而稀疏的mGluR5阳性神经元胞体和纤维见于屏状核、终纹床核、杏仁中央核、丘脑部分核团、上丘浅灰质层、外侧丘系背侧核和延髓中央灰质.     

Collateral projections from trigeminal sensory nuclei to ventrobasal thalamus and cerebellar cortex in rats

The retrograde fluorescent labeling technique reveals that trigeminal projections to the ventroposteromedial nucleus of the thalamus (VPM) of the rat originate from the main sensory nucleus (MSN) of the trigeminal and subnuclei interpolaris (V1) and caudalis (Vc) of the spinal trigeminal nucleus. These projections are predominantly contralateral; however, the presence of a few ipsilateral labeled cells in MSN suggests an uncrossed trigeminothalamic pathway. Trigeminocerebellar fibers projecting to the paramedian lobule (PML) of the cerebellar cortex are located in Vi and caudal subnucleus oralis (Vo). This is principally an ipsilateral pathway, but several bisbenzimide-labeled cells are present in contralateral Vi. The most notable finding occurred after paired injections of Evans Blue into VPM and bisbenzimide into PML, demonstrating neurons in Vi with divergent projections to both structures. The presence of this type of projection was not found in mice (Steindler: J. Comp. Neurol. 237:155-175, 1985) and has not been reported in other species.     

Ascending and descending projections to the inferior colliculus in the rat

The ascending and descending projections to the central nucleus of the inferior colliculus (IC) were studied with the aid of retrograde transport of horseradish peroxidase (HRP). HRP-labelled cells were found in contralateral cochlear nuclei, where the majority of different cell types was stained. Few labelled cells were observed in the ipsilateral cochlear nuclei. HRP-positive neurones were found in all nuclei of the superior olivary complex on the ipsilateral side with the exception of the medial nucleus of the trapezoid body, which was never labelled either ipsilaterally or contralaterally. The largest concentration of HRP-labelled cells was usually observed in the ipsilateral superior olivary nucleus. Smaller numbers of labelled cells were present in contralateral nuclei of the superior olivary complex. Massive projections to the inferior colliculus were found from the contralateral and ipsilateral dorsal nucleus of the lateral lemniscus and ipsilateral ventral nucleus of the lateral lemniscus. Many neurones of the central and external nuclei of the contralateral inferior colliculus were labelled with HRP. Topographic organisation of the pathways ascending to the colliculus was expressed in the cochlear nuclei, lateral superior olivary nucleus and in the dorsal nucleus of the lateral lemniscus. HRP--positive cells were found in layer V of the ipsilateral auditory cortex, however, the evidence for topographic organisation was lacking.     

Olivary projections from the pretectal region in the cat studied with horseradish peroxidase and tritiated amino acids axonal transport

The organization of the projection from the pretectal region to the inferior olive in the cat was studied with autoradiographic and horseradish peroxidase (HRP) methods. After injections of HRP into the olive in six cats, cells were labeled ipsilaterally in the anterior pretectal nucleus (NPA), the posterior pretectal nucleus (NPP), the nucleus of the optic tract (NOT), and the dorsal terminal nucleus of the accessory optic tract (DTN). In three experiments, tritiated amino acids were injected into those parts of the pretectal region which contained labeled cells in the HRP experiments, and the projections to the olive were plotted. Both NPA and NPP projected to the rostral half of the dorsal accessory olive, the rostromedial margin of the ventral lamella, and the lateral part of the ventrolateral outgrowth. NOT projected to the caudal half of the dorsal cap, while DTN projected to both the dorsal cap and nucleus beta. The projections are entirely ipsilateral.     

Afferent connections of the dorsal magnocellularis area of the cat red nucleus

Location within the brain of retrogradely labeled neurons putting out projections from the dorsal magnocellularis area of the red nucleus was investigated by means of microiontophoretic injection of horseradish peroxidase into the dorsal magnocellularis area of the cat red nucleus. Projections were found from a number of hypothalamic nuclei, the centrum medianum, parafascicular and subthalamic nuclei, zone incerta, Forel's field, nucleus medialis habenulae, pontine and bulbar reticular formation, and the following midbrain structures: the central gray matter, superior colliculus, Cajal's interstitial nucleus, reticular formation, and the contralateral red nucleus. Projections were also identified proceeding from more caudally located structures: the cerebellar fastigial nucleus, facial nucleus, medial vestibular and dorsal lateral vestibular nuclei, and ventral horns of the spinal cord cervical segments. Connections between the substantia nigra and the red nucleus were clarified. Projections to the red nucleus from the cerebral cortex, interstitial and dentate (lateral) cerebellar nuclei, the nucleus gracilis and cuneate nucleus were found, confirming data presented in the literature. Bilateral trajectories of retrogradely labeled fiber systems are described.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 810–816, November–December, 1987.     

福尔马林致痛提高大鼠中枢μ阿片受体密度及电针的加强作用

用放射自显影方法观察到;（１）大鼠脚掌注射福尔马林后,某些与镇痛有关的脑区如尾核头部、伏隔核、杏仁核、中央灰质、脚间核、中缝大核、脊髓背角等结构中μ阿片受体密度明显增加（Ｐ＜０．０５,Ｐ＜０．０１）;（２）给予电针抑制痛反应的大鼠,在其大部分上述结构及扣带回、隔区、视前内侧区、内膝体、上丘、中缝背核及中央上核受体密度明显增加;与福尔马林注射组相比,脚间核、中央灰质尾端腹外侧区、腰膨大背角的受体密度进一步增加。从而在受体水平支持伤害性刺激可以激活体内内阿片肽能活动,而电针可以加强这一活动的设想。     

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.     

An autoradiographic study of the retinal projections in the Formosan monkey

This study investigated the retinal projections of the adult Formosan rock monkey by monocular injection of radioactive proline and fucose. We found that the retinofugal fibers terminated bilaterally in the suprachiasmatic, pregeniculate, lateral geniculate, pretectal complex, pulvinar nucleus, superior colliculus, dorsal and lateral terminal nuclei of the accessory optic system. More crossed retinal terminations were observed, with the exception that the suprachiasmatic nucleus received almost equally of both retinal projections. The existence of the retinal projection to the medial terminal nucleus of the accessory nucleus was in doubt. In the geniculate nucleus, the retinal fibers terminated contralaterally in layers 1, 4 and 6; and ipsilaterally in 2, 3 and 5. In the superior colliculus, most retinal fibers were aggregated superficially in a band located in the contralateral striatum griseum superficialis of the superior colliculus, and had few gaps on the ipsilateral one. The present investigation shows that the Formosan rock monkey has a similar pattern of optic fiber distribution to that of other macaques.     

Autoradiographic distribution of 125I calcitonin gene-related peptide binding sites in the rat central nervous system

Using autoradiographic method and 125I-Tyro rat CGRP as a ligand, receptor binding sites were demonstrated in the rat central nervous system. Saturation studies and Scatchard analysis of CGRP-binding to slide mounted tissue sections containing primarily cerebellum showed a single class of receptors with a dissociation constant of 0.96 nM and a Bmax of 76.4 fmol/mg protein. 125I-Tyro rat CGRP binding sites were demonstrated throughout the rat central nervous system. Dense binding was observed in the telencephalon (medial prefrontal, insular and outer layers of the temporal cortex, nucleus accumbens, fundus striatum, central and inferior lateral amygdaloid nuclei, most caudal caudate putamen, organum vasculosum laminae terminalis, subfornical organ), the diencephalon (anterior hypothalamic, suprachiasmatic, arcuate, paraventricular, dorsomedial, periventricular, reuniens, rhomboid, lateral thalamic pretectalis and habenula nuclei, zona incerta), in the mesencephalon (superficial layers of the superior colliculus, central nucleus of the geniculate body, inferior colliculus, nucleus of the fifth nerve, locus coeruleus, nucleus of the mesencephalic tract, the dorsal tegmental nucleus, superior olive), in the molecular layer of the cerebellum, in the medulla oblongata (inferior olive, nucleus tractus solitarii, nucleus commissuralis, nuclei of the tenth and twelfth nerves, the prepositus hypoglossal and the gracilis nuclei, dorsomedial part of the spinal trigeminal tract), in the dorsal gray matter of the spinal cord (laminae I-VI) and the confines of the central canal. Moderate receptor densities were found in the septal area, the "head" of the anterior caudate nucleus, medial amygdaloid and bed nucleus of the stria terminalis, the pyramidal layers of the hippocampus and dentate gyri, medial preoptic area, ventromedial nucleus, lateral hypothalamic and ventrolateral thalamic area, central gray, reticular part of the substantia nigra, parvocellular reticular nucleus. Purkinje cell layer of the cerebellum, nucleus of the spinal trigeminal tract and gracile fasciculus of the spinal cord. The discrete distribution of CGRP-like binding sites in a variety of sensory systems of the brain and spinal cord as well as in thalamic and hypothalamic areas suggests a widespread involvement of CGRP in a variety of brain functions.     

Organization of bilateral spinal projections to the lateral reticular nucleus of the rat

The present study was carried out to analyze the topography of bilateral spinal projections to the lateral reticular nucleus (LRN). We used retrograde transport of fluorescent tracers Fast Blue and Diamidino Yellow to identify spinal neurons projecting to the ipsilateral and/or contralateral LRN, as well as orthograde transport of Phaseolus vulgaris leucoagglutinin to identify the LRN areas where spinoreticular axons terminate. Orthograde labeling confirmed that bilateral spinoreticular projections coming from cervical and upper-thoracic segments terminate in the magnocellular division of LRN, while those coming from the lower-thoracic, lumbar and sacral segments end in the parvocellular division of the nucleus; only a sparse spinal input has been observed in the subtrigeminal division of LRN. Retrograde labeling showed that labeled neurons were present at all spinal levels and in particular large numbers in the cervical and lumbar enlargements. Retrogradely single-labeled cells were located, with contralateral predominance, in all segments of the spinal cord, within laminae IV, V, VI, VIII, and X, whereas in laminae III and VII labeled neurons were mainly observed ipsilaterally. Furthermore, a small fraction of double-labeled cells (7.4%) was observed throughout the spinal cord, mainly in laminae III, IV, VII and VIII.     

Selective spread of herpes simplex virus in the central nervous system after ocular inoculation.

The spread of herpes simplex virus (HSV) was studied in the mouse central nervous system (CNS) after ocular inoculation. Sites of active viral replication in the CNS were identified by autoradiographic localization of neuronal uptake of tritiated thymidine. Labeled neurons were first noted in the CNS at 4 days postinoculation in the Edinger-Westphal nucleus, ipsilateral spinal trigeminal nucleus, pars caudalis, pars interpolaris, and ipsilateral dorsal horn of the rostral cervical spinal cord. By 5 days postinoculation, additional sites of labeling included the seventh nerve nucleus, nucleus locus coeruleus, and the nuclei raphe magnus and raphe pallidus. None of these sites are contiguous to nuclei infected at 4 days, but all are synaptically related to these nuclei. By 7 days postinoculation, no new foci of labeled cells were noted in the brain stem, but labeled neurons were noted in the amygdala, hippocampus, and somatosensory cortex. Neurons in both the amygdala and hippocampus receive axonal projections from the locus coeruleus. On the basis of these findings, we conclude that the spread of HSV in the CNS after intracameral inoculation is not diffuse but is restricted to a small number of noncontiguous foci in the brain stem and cortex which become infected in a sequential fashion. Since these regions are synaptically related, the principal route of the spread of HSV in the CNS after ocular infection appears to be along axons, presumably via axonal transport rather than by local spread.     

Retinal projections in the catfish,Mystus vittatus (Bloch) as revealed by tracer studies with horseradish peroxidase

Summary The retinal efferents of the catfish, Mystus vittatus, were investigated with the use of the horseradish peroxidase (HRP) technique. Most retinal fibres extended contralateral to the eye that had received HRP label, while a few fascicles projected to the ipsilateral side without decussation in the optic chiasma. The contralateral fibres projected to the suprachiasmatic nucleus, the nucleus opticus dorsolateralis, the nucleus of the posterior commissure, the nucleus geniculatus lateralis, pretectal nuclear complex, and to two layers of the optic tectum, i.e., stratum fibrosum et griseum superficiale and stratum griseum centrale. The accessory optic tract arose from the inner area of the optic tract and extended ventromedially to the accessory optic nucleus. The ipsilateral fascicles projected to almost all the above mentioned nuclei, but these projections were comparatively sparse. The ipsilateral retinal projection was restricted to the rostral tectum.     

Sources of ascending afferent projections to the midbrain central tegmental area and centrum medianum thalami in cats

After microinjections of horseradish peroxidase into the central tegmental area of the midbrain and centrum medianum thalami in cats, labeled neurons were found in the nucleus of the tractus solitarius, gracile and cuneate nuclei, spinal nuclei of the trigeminal nerve, the external nucleus and nucleus of the brachium of the inferior colliculus, the medial pretectal region, nucleus of the posterior commissure and stratum intermediale of the superior colliculus, and reticular structures of the medulla and pons. Comparison of the location of the sources of ascending afferent projections in the central tegmental area of the midbrain and centrum medianum thalami showed that the reticular formation receives mainly visceral projections through the nucleus of the tractus solitarius, whereas the centrum medianum thalami is innervated mainly by the system of sensory somatic nuclei.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 172–178, March–April, 1982.