WGA-HRP was iontophoretically delivered into the habenular nuclei in 40 rats to observe the distribution of the retrograde labeled cells; and into the entopeduncular nucleus(EPN), lateral preoptic area(LPO), medial preoptic area(MPO), nucleus septalis fimbriatis(SF), nucleus triangularis septi(TS), nucleus tractus diagonalis (Broca)(DBN)and lateral hypothalamic area(LHA) in 12 rats to observe the distribution of the orthograde labeled fibers in the habenular nuclei. It was found that the afferents of various parts of the habenular nuclei were different.The lateral habenular nucleus mainly recieves the afferents from the EPN, LPO and LHA, and the medial habenular nucleus from the SF, TS and LHA. Furthermore, the lateral habenular nucleus can be divided into medial and lateral parts, the medial habenular nucleus can be divided into medial and lateral parts as well, their afferent connections are also different.

WGA-HRP was iontophoretically delivered into various parts of the habenular nuclei (the lateral segment of the lateral habenular nucleus LHb-L, the medial segment of the lateral habenular nucleus LHb-M, and the medial habenular nucleus MHb) in 40 rats to study the route and distribution of the anterograde labeled fibers and terminals in the brain. The efferent projections of the habenular nuclei follow three routes, the rostral, contralateral and caudal pathways. Along the rostral pathway fibers leave the lateral habenular nucleus, follow the stria medullaris thalami rostrally, and distribute to the thalamic dorsomedial nucleus, paratenial nucleus and lateral preoptic area. Fibers from the contralateral pathway distribute to the opposite lateral habenular nucleus by way of the commissura habenularum Fibers in the caudal pathway originate mainly from the MHb and LHb-M, and distribute to the interpeduncular nucleus with a dorsoventral topographic localization. In addition some of the caudal efferent fibers run caudally and terminate in the raphe nuclei and reticular formation etc.

0.02～0.3?l of 33％ HRP (Sigma Ⅵ) solution in sterile water were injected with a stereotaxic instrument into various sites of the caudate-putamen in 40 rats. The animals were perfused transaortically with 3％ paraformatdehyde and 1％ glutaradehyde in 0.1 M phosphate buffer solution (pH7.4). Frozen sections were dried in a container with P_2O_5 for 2～4 hours and examined for fluorescence in the nucleus nigra. After which, the sections were processed for HRP reaction according to Mesulam's method. A number of cells of substantia nigra were found to show both fluorescence and HRP-positive product, thus confirming the dopaminergic nature of the nigroneostiatum projection.Furthermore, the nigroneostriatum projection was found to be topographically organized, the ventro-medial part of compact zone of the substantia nigra projecting to the dorso-medial caudate-putamen, the dorso-medial part of compact zone to the ventral caudate-putamen, the ventro-middle of compact zone to 1be dorso-lateral and central caudate-putamen, the caudo-lateral part to the central caudate-putamen, the middle part of reticular zone to the lateral and central caudate-putamen, the lateral zone of substantia nigra to the caudal caudate-putamen. Some overlap existed.Strionigral fibers were also topographically organized, which terminated predominantly about the cells of reticular zone. These may form a feedback loop concerning with the modulation of the activity of the dopaminergic neurons in the substantia nigra.

Different fluorescent tracers, Fast Blue (FB), Nuclear Yellow(NY), Propidium iodide (PI), Bisbenzimide (Bb), Evans Blue(EB), DAPI-Primuline (Pr), were injected into the frontal cortex, hippocampus, thalamus, cerebellum and cervical cord respectively in 31 rats to observe the fluorescent retrograde double labeling cells in the nucleus raphe magnus. The results showed that the axon collaterals of the nucleus raphe magnus projected to the :thalamus-cerebellum, thalamus-hippocampus, frontal cortex-thalamus, frontal cortex-cerebellum, hippocampus-cerebellum, hippocampus-cervical cord, cerebellum-cervical cord, thalamus-cervical cord and bilateral hippocampus and thalamus. The topographical organizations of divergent projection neurons of the nucleus raphe magnus were also found.

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The divergent axon collaterals from neurons in locus coeruleus have been in vestigated by means of fluorescent double labeling technique in 36 rats.Different fluorescent tracers, Fast Blue, Nuclear Yellow, Propidium iodide, Bisbenzimide, Evans Blue, DAPI and Primuline were injected into the prefrontal cortex, the thalamus, the hippocampus, the cerebellum and cervical cord to observe the double retrograde labeling neurons of the locus coeruleus.Following unilateral or bilateral combined injections of two fluorescent tracers into the thalamus and cerebellum, the hippocampus and cerebellum, the hippocampus and thalamus, the larefrontal cortex and cerebellum, the prefrontal cortex and thalamus, the prefrontal cortex and cervical cord, the hippocampus and cervical cord, the cerebellum and cervical cord, double labeled cells were found in locus coeruleus, and some topographical organizations were also found.

The afferent projections of the prefrontal cortex'from the brainstem werestudied by using WGA-HRP technique in 25 rats. Following WGA-HRP injections into the dorsal part of anterior cingulate cortex, prelimbic cortex, and dorsal agranular insular cortex, three groups of retrograde labeled neurons were observed in the brainstem. First group was the monoaminergic neurons, in which the locus coeruleus, ventral tegmental area, compact part of substantia nigra, nucleus raphe dorsalis, nucleus eentralis superior, nucleus linearis caudalis widely projected to the every part of the prefrontal cortex, but the quantitative difference of the projections to different parts of the prefrontal cortex from the lateral reticular nucleus, commissural nucleus, nucleus raphe magnus, A_4, A_5, parabrachial nuclei, reticular part of substantia nigra and the nucleus linearis rostralis was also found. Second group was the nuclei related with oculomotor action, such as E-W nucleus, periventricular gray substance, reticular formation of mesencephalon and the nucleus pontis oralis. Third group was-the sensory nucleus, such as parabrachial nucleus, main sensory nucleus of the trigeminal nerve and the commissural nucleus.

The afferent projections of the prefrontal cortex(PFC) from the cerebral cortex were studied using WGA-HRP technique in 25 rats. The PFC of the rat re- cieved the afferent projections widely arising from the frontal, parietal,temporal, occipital, cingulate, piriform and retrohippocampal cortex. Furthermore,the dif- ferent organizations of the cortical afferent projections of the medial and lateral part of the PFC were also found. Besides the afferents from the somatic and visceral sensory cortex, the PFC of rat also recives afferents of visual and auditory cortex and it appears to be a multiple sensory convergence area.

Using immunohistochemical method, the distribution of eight kinds of peptidergic neurons, i. e. cholecystokinin(CCK),vasoactive intestinal polypeptide (VIP), substance P(SP), neurotensin (NT), galanin (GAL), calcitonin gene-related peptide (CGRP), corticotropin-releasing factor(CRF) and thyrotropin-releasing hormone(TRH), of the thalamus in the rat was investigated. Immunoreactive cell bodies and fiber terminals were mainly located in the midline nuclei, intralaminar nuclei, habenular nucleus and posterior nuclei of the thalamus, but a few of positive structures in the anterior nuclei, ventral nuclei and reticular nucleus were also found. The distribution of different peptidergic neurons in the thalamus was different from each other. A large quantity of SP-, NT- and GAL- like cell bodies and all of above-mentioned eight peptidergic fiber terminals were observed in the midline nuclei and intralaminar nuclei. More CCK and CGRP positive cell bodies were seen in the posterior nuclei. Some VIP, SP, NT, GAL and CRF positive cell bodies and all kinds of the positive terminals, except CGRP, were found in the habenular nucleus. The immunoreactive structures which were found in present study, particularly the distribution of positive terminals, were more widely than those were reported. The distribution of some CCK, VIP, NT, GAL, CGRP and TRH positive cell bodies and terminals in the thalamus have not been reported previously.

Aging changes of neurotensin-like (NT-L) and galanin-like (GAL-L) cell bodies and fiber terminals in the central amygdaloid nucleus between the young and old rats were studied by means of immunohistochemical and microspectrophotometric techniques. NT-L cell bodies were mainly located in the central part (CeLn) of, centrolateral amygdaloid nucleus, a few of NT-L neurons were also found in the centrolateral amygdaloid nucleus, capsular part (CeLc) and centromedial amygdaloid nucleus (CeM). NT-L fiber terminals were seen mainly in the CeLn and CeLc. GAL-L cell bodies were observed only in the CeM. A marked decrease of density of NT-L cell bodies and fiber terminals in the central amygdaloid nucleus was found in the old rats as compared with young animals. No significant age difference in number of GAL-L cell bodies was observed in the central amygdaloid nucleus, but the staining intensity of GAL-L cell bodies was reduced remarkably. The results show that there are apparent changes with aging of the NT-L and GAL-L neurons in the central amygdaloid nucleus of the rat. The significance of the changes remains to be studied further.