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Following injection of HRP into contralateral thalamus, retrogradely labeled cells were observed in principal sensory trigeminal nucleus (Vp) and an area of juxtatrigeminal nucleus (JX) formerly described by John and Tracey (1987). When PHA-L was delivered to dorsomedial part of the subnucleus oralis (Vodm), PHA-L labeled terminals were seen in dorsomedial part of the Vp (Vpdm) and in the JX region. Comparing the distribution of PHA-L labeled terminal field with that of HRP labeled JX neurons showed that the labeled terminals and neurons were overlapped closely in the JX. The distribution patterns of the labeled terminals and JX neurons were also the same: viewed on the coronal planes caudal-rostrally, both of the labelings began to appear at the levels where the facial nerve root was just broken. Rostrally, at middle levels of the motor trigeminal nucleus (Vmo), the labelings showed their typical view covering dorsal and ventral JX (dJX, vJX). The labelings disappeared at rostral poles of the Vmo and Vp. When injections of PHA-L into the Vodm and HRP into the contralateral thalamus was made in one rat, the contacts between Vodm projecting terminals labeled with PHA-L and HRP labeled trigemino-thalamic neurons were seen in the JX and also in the Vpdm. Then, electron microscopic (EM) study was done, injections of kainic acid into the Vodm and HRP into the contralateral thalamus was performed simultaneously. After EM embedding, the JX and Vpdm regions were selected, ultrathin sections were cut and observed with EM. In both areas, axo-somatic and axo-dendritic synapses were seen between degenerated boutons and HRP labeled somata or dendrites. Namely, the Vodm projecting terminals synapsed on trigemino-thalamic neurons in the JX and Vpdm. Anyway, axo-dendritic synapses was the main type of observed synapses. Thus, the present work demonstrated 1. the JX containing a group of trigemno-thalamic neurons was a target of special projections froin the Vodm; 2. The Vodm neurons projected to the contralateral thalamus through the relay of JX and Vpdm neurons.

The cobalt labelling technique was applied to different branches of the frog trigeminal and facial nerves and the representation of muscle supplied by these nerves were studied. (1) The levator bulbi muscle is innervated by a small group of neurons localised in its rostromedial part of the trigeminal motor nucleus (nV). (2) The jaw closer muscles are represented in the rostral two thirds of the nV. (3) Muscles of the floor of the mouth, which contribute to the jaw opening, and the depressor mandibulae muscle are innervated from the caudal one third of the nV and from the facial motor nucleus, respectively. There were distinct differences in the shape and size of perikarya innervating these three functionally different muscle groups.

The purpose of this study was to determine whether pontine and mesencephalic reticulospinal nuclei like those of the medulla, can be differentiated on the basis of neuronal morphology. Accordingly, neurons of the various pontine and mesencephalic brainstem reticulospinal nuclei (BRN) of adult albino or hooded rats were either backfilled with horseradish peroxidase (HRP) from spinal injections, stained with a Nissl method or impregnated with a Golgi-Kopsch variant. The results suggest that at least 13 BRN can be distinguished in the pons and mesencephalon of the rat on the basis of neuronal morphology. The dendritic arborizations (DA) of neurons in nucleus reticularis (NR) pedunculopontinus pars compacta (RPpc), NR pedunculopontinus pars dissipatus (RPpd), NR cuneiformis (RCf) and NR subcuneiformis (RScf) are radially symmetrical. The DA of neurons in NR pontis caudalis pars beta (RPoCb) and alpha (RPoCa), as well as those of NR subcoeruleus (RSc) and the A5 cell group, exhibit a pronounced dorsomedial to ventrolateral slant. The dendrites of locus coeruleus (LC) neurons slant from dorsolateral to ventromedial. The DA of NR pontis oralis pars medialis (RPoOm) neurons course medially, while those of NR pontis oralis pars lateralis (RPoOl) course laterally. The DA of Kolliker-Fuse neurons (KF) course horizontally. Finally, the DA of the nucleus raphe dorsalis (RaD) are either symmetrically multipolar or fusiform. The neurons of RPoCb, RPpc, KF and RCf project to the spinal cord with a strong ipsilateral predominance, while those of LC, RSc, RPoOm and RPpd project to the spinal cord with a weak ipsilateral predominance. The axons of A5, RPoOl and RaD neurons exhibit no lateral predominance in their spinal projections. Finally, RPoCa neurons, as well as neurons in RScf, project to the spinal cord with a strong contralateral predominance. The neurons of RPoCb, RPoCa, RPoOl, RPpd and RScf project to the spinal cord via the mlf and sulcomarginal fasciculus. The neurons of RSc, KF, RPoOm, RPpc and RCf project to the spinal cord via the lateral funiculus.

Solution of the cobaltic lysine complex compound injected into the bulbar pyramid was taken up by pyramidal tract (PT) fibres and intraaxonally transported as far rostral as the internal capsule, and as far caudal as segment C4 of the spinal cord. With sulfide-precipitation of the cobalt and silver-intensification of the CoS, terminal branches of corticobulbar and corticospinal fibres could be shown in the following structures: In the pons the medial, ventral and the medial part of the lateral pontine nuclei are supplied with collaterals of PT fibres. The medial pontine nucleus receives contralateral PT fibres as well. The nucleus raphe magnus receives PT fibre collaterals from both sides. In the reticular formation contralateral fibres terminate in n. reticularis pontis caudalis, n. gigantocellularis, n. paramedianus, n. reticularis ventralis and dorsalis. Ipsilateral fibers terminate in the n. gigantocellularis and n. reticularis ventralis. The inferior olive receives both ipsilateral and contralateral PT fibres. All parts of the central gray substance are supplied by ipsi-and contralateral fibres which emerge from the PT at the level of the pyramidal decussation. The caudal nucleus of the spinal nucleus of the trigeminus receives a strong bundle of crossing PT fibres which terminate in the subnucleus magnocellularis. The dorsal column nuclei are virtually outlined by the numerous terminals of PT fibres. An oval area at ventrolateral aspect of the cuneate nucleus is innervated by PT fibres. The neurones of this area send their axons to the dorsal white column. In the spinal cord PT fibre terminals delineate four areas of termination. The first is the internal basilar nucleus which is the most richly supplied. The second lies lateral and ventral to this nucleus including segments of laminae V, VI, and VII. The third area extends into the ventral horn including a small zone of the ventral part of lamina VII. Thin PT fibre collaterals may establish here direct contacts with motoneurone dendrites. The fourth area includes laminae III and IV and receives individual terminal formations of thicker PT fibres. Findings which corroborate and which extend previous results are discussed. A few notes are made on the functional significance of some of these fibre connections.

Position, form, dimensions and fine structure of the mesencephalic trigeminal nucleus of the domestic chicken are described. It consists of round to oval large and rare medium sized pseudo-unipolar neurons. The Nissl bodies are scattered throughout the perikaryon of both cell types in a dust like way. Electronmicroscopically the neurons are characterized by numerous neurofilaments, lysosomes and mitochondria. The cell surface shows a moderate distribution of synapses, and few somatic spines and invaginations of the plasmalemma.

Cresyl violet- and thionin-stained sections of the rat brain stem were used to study the cytoarchitectonics of the parabrachial nuclear complex consisting of nuclei parabrachiales and ncl. Koelliker-Fuse. As suggested by comparisons of the cytoarchitectonic structure and connections, the parabrachial nuclei can be divided into the following independent subnuclei: dorsalis (D), dorsomedialis (DM), dorsolateralis (DL), interstitialis (I), lateralis (L), ventralis (Ve) and medialis (M). According to conventional nomenclature, D, DM, DL, I and L are parts of ncl. parabrachialis lateralis (or dorsalis), while M and Ve belong in the ncl. parabrachialis medialis (or ventralis). Cytoarchitectonically, the Koelliker-Fuse nucleus can be divided into the pars oralis and pars caudalis. The cytoarchitectonic division and the position of afferent cells for specific target structures are in very good agreement while permitting comparisons of experimental findings in different animals with differently formed subnuclei. In the Discussion section, the hitherto known connections of the parabrachial nuclei complex are cross-referred to the relevant subnuclei.

The group "k" of Meessen and Olszewski (1949) was identified in the brain stems of normal rabbits and cats. In the rabbit, a topographical subdivision of the group "k" into the well defined cell aggregations k1, k2 and k3 was found. In the cat, the nucleus corporis pontobulbaris was subdivised into a posterodorsal and a anteroventral part. The former was located ventrally to the motor and principal sensory trigeminal nuclei, the latter was wedgeshaped and situated more anteriorly at the lateroventral margin of the pons. In 9 rabbits and 7 cats the neurons of origin for cerebellar paramedian lobule afferents were identified with retrograde transport of horseradish peroxidase within the nucleus "k" and nucleus corporis pontobulbaris, respectively. In both species, most projections to the paramedian lobule were seen as originating ipsilaterally with only a small contralateral component. The study suggests that there are certain segregated projections of the nucleus "k" or the nucleus corporis pontobulbaris to the cortex of the anterior and posterior parts of the paramedian lobule, with some valid species differences. In the cat, the whole projection was found to originate in the more anterior and ventral parts of the nucleus "k" (nucleus corporis pontobulbaris). The posterior part of the paramedian lobule in the rabbit receives afferents from the homolateral subdivisions k3 and, to a minor degree, from k2; while in the cat, afferents are bilateral with an ipsilateral preponderance and originate from the posterior cellular group of the nucleus corporis pontobulbaris dispersed among and medially to the exiting motor root of the trigeminal nerve. The anterior part of the paramedian lobule afferents in the rabbit originates bilaterally within subdivision k1, to a minor degree ipsilaterally in the dorsal region of subdivision k3, and occasionally in subdivision k2, whereas in the cat afferents originate from the anterior and posterior levels of the corpus pontobulbaris. Additionally, some afferents for the rabbit anterior paramedian lobule originate within the homolateral nucleus "n". No evidence for a longitudinal zonal pattern of the projection onto the paramedian lobule was found. The study is discussed in the light of present information on the connections of the nucleus "k" (nucleus corporis pontobulbaris).

Following an autoradiographical study on the projections from the feline sensorimotor cortex (representation of the limbs) to the brain stem, new projections to nucleus pretectalis posterior, the coerulear nuclei, nuclei corporis pontobulbares, nucleus intertrigeminalis, nucleus f, x and z of the vestibular nuclear complex, nucleus parvocellularis compactus, nucleus parasolitarius, nuclei insulae cuneati laterales, the nuclei of the raphé, nucleus reticularis lateralis and nucleus fastigii were found besides the well known projections to the tectal nuclei, the reticular formation, nucleus ruber, griseum pontis, the sensory trigeminal nuclei and the dorsal column nuclei. There was no evidence of projections to nucleus tractus solitarii. The amounts of radioactivity within the nuclei seem to be in favour of EM autoradiographical studies on the synaptology of these projections, apart from faintly labelled structures like most of the reticular nuclei, the sensory trigeminal nuclei, the coerulear nuclei and nucleus fastigii.