Anterior thalamic afferents from the mamillary body and the limbic cortex were studied by using single and double retrograde transport methods in the rat. The medial mamillary nucleus was divided on the basis of the cytoarchitecture into four subnuclei: the pars medialis centralis, pars medialis dorsalis, pars lateralis, and pars basalis. Extensive connections were seen between each of these subdivisions of the mamillary body and the anterior thalamic nuclei, topographically organized so that the anteromedial thalamic nucleus receives projections exclusively from the pars medialis centralis, while the anteroventral thalamic nucleus receives projections from the pars medialis dorsalis and pars lateralis. Nuclei in the dorsal half of these two mamillary subdivisions project predominantly to the medial half of the anteroventral thalamic nucleus, and those in the ventral half to the lateral half of the nucleus. The pars basalis was found to have numerous projections to the magnocellular part of the anteroventral nucleus. All limbic cortical areas send projections bilaterally to all regions of the anteromedial nucleus as well as to the parvicellular parts of the anteroventral thalamic nucleus, while the anterodorsal nucleus receives ipsilateral projections originating exclusively from the preagranular, anterior limbic, and cingular regions. The magnocellular part of the anteroventral nucleus, however, receives only ipsilateral projections from all of the limbic cortex. Some neurons in the infralimbic region also project bilaterally to all of the anterior thalamic nuclei except the anterodorsal nucleus. All of these cortical projections to the anterior thalamus originate in layers V and VI of the limbic cortex.
We investigated the direct projections from the paraventricular hypothalamic nucleus (PVH) to the spinal cord. When Phaseolus vulgaris leucoagglutinin (PHA-L) was injected into the PVH, labeled descending fibers were observed running bilaterally through three pathways. The first pathway ran into the dorsal longitudinal fasciculus and projected to the central gray matter, Edinger-Westphal nucleus, pedunculopontine tegmental nucleus, nucleus of the locus ceruleus and parabrachial nucleus. The second and third pathways coursed through the medial forebrain bundle, ventral tegmental area, and ventral part of the medulla oblongata. At the medulla oblongata, the second pathway curved dorsolaterally and joined Rexed's lamina V of C1 after giving many projections to the nucleus ambiguus, nucleus of the solitary tract, dorsal motor nucleus of the vagus, and a few to the area postrema. The fibers descended through lamina V until C5, and coursed through lamina I from C6 to the upper coccygeal segments. They gave collateral projections to lamina I from the cervical through the upper coccygeal segments. The third pathway coursed laterally and descended through the lateral funiculus after giving projections to the lateral reticular nucleus and the marginal layer of the spinal trigeminal nucleus. These fibers gave off many projections to the intermediolateral cell column of the thoracic cord and the sacral parasympathetic nucleus. Lamina X received many projections from the fibers of the lateral funiculus at C5 through the b-segment of sacral spinal cord. These results indicate that the PVH may integrate directly with the medullary and spinal autonomic regulatory nuclei, including the vagus complex, sympathetic intermediolateral cell column, laminae I and X, and sacral parasympathetic nucleus.
Collateral axonal branching from the medial or lateral mammillary nuclei to the anterior thalamus, Gudden's tegmental nuclei, the nucleus reticularis tegmenti pontis, and the medial pontine nucleus was studied using the fluorescent retrograde double-labeling method. One day after injection of Fast Blue into the anterior thalamic nuclei or Gudden's tegmental nuclei, Nuclear Yellow was injected into Gudden's tegmental nuclei or the nucleus reticularis tegmenti pontis and the medial pontine nucleus. Following 1 day survival, single- and double-labeled neurons were examined in the mammillary nuclei. The lateral mammillary nucleus contains neurons whose collateral fibers project to both the dorsal tegmental nucleus of Gudden and the ipsilateral or contralateral anterodorsal thalamic nucleus, to both the medial pontine nucleus and the anterodorsal thalamic nucleus, and to both the dorsal tegmental nucleus of Gudden and the medial pontine nucleus. The pars medianus and pars medialis of the medial mammillary nucleus contain neurons whose collateral fibers project to both the anteromedial thalamic nucleus and the ventral tegmental nucleus of Gudden, to both the anteromedial thalamic nucleus and the medial part of the nucleus reticularis tegmenti pontis, and to both the ventral tegmental nucleus of Gudden and the medial part of the nucleus reticularis tegmenti pontis. The dorsal half of the pars posterior of the medial mammillary nucleus contains a few neurons whose collateral fibers project to both the anteromedial thalamic nucleus and the rostral part of the ventral tegmental nucleus of Gudden, and to both the caudal part of the anteroventral thalamic nucleus and the rostral part of the ventral tegmental nucleus of Gudden, while the pars lateralis of the medial mammillary nucleus contains no double-labeled neurons and projects only to the anteroventral thalamic nucleus.
We examined the regions projecting to the supramammillary nucleus of the rat with retrograde transport of WGA-HRP and WGA, and anterograde transport of Phaseolus vulgaris leucoagglutinin. The supramammillary nucleus receives major descending afferents from the infralimbic cortex, the dorsal peduncular cortex, the nucleus of the diagonal band of Broca, the medial and lateral preoptic nuclei, bilaterally. The major ascending afferents come from the pars compacta of the nucleus centralis superior, the ventral tegmental nucleus, and the laterodorsal tegmental nucleus. The supramammillary nucleus also receives a few (but distinct) fibers from the anterior and lateral hypothalamic nuclei, the ventral premammillary nucleus, the interpeduncular nucleus, the cuneiform nucleus, the dorsal raphe nucleus, the incertus nucleus, and the C3 region including the prepositus hypoglossi nucleus. All descending fibers run through the medial forebrain bundle. Almost all ascending fibers from the pars compacta of the nucleus centralis superior and the laterodorsal tegmental nucleus run through the mammillary peduncle, and terminate throughout the supramammillary nucleus. A few fibers from the laterodorsal tegmental nucleus and the C3 region run through the fasciculus longitudinalis dorsalis and terminate in the dorsal part of the supramammillary nucleus including the supramammillary decussation.
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