The Journal of comparative neurology
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Immunocytochemical localization of tyrosine hydroxylase (TH) was used to determine the ultrastructural morphology and synaptic associations of catecholaminergic terminals in the nucleus accumbens of the rat. The brains were fixed by vascular perfusion with 4% paraformaldehyde and 0.2% glutaraldehyde. Coronal sections cut with a vibrating microtome were incubated with rabbit antiserum to TH then immunocytochemically labeled by the peroxidase-antiperoxidase method. ⋯ The recipient perikarya were usually 10-20 micrometers in diameter and contained an indented nucleus and abundant cytoplasm. The content of large dense vesicles and synaptic associations with somata and proximal dendrites suggest that a certain proportion of the TH-containing terminals within the nucleus accumbens are morphologically distinct from catecholaminergic terminals within the dorsal striatum. These differences are discussed in relation to neuropeptides and functions of the dopaminergic mesolimbic and nigrostriatal pathways.
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The motor nuclei and sensory connections of the IXth, Xth, XIth, and XIIth cranial nerves of the reptile Varanus exanthematicus were studied with the methods of anterograde degeneration and anterograde and retrograde axonal transport. The motor nuclei of nerve IX are located ventrally in the rhombencephalon and are constituted medially by the large-celled glossopharyngeal part of the nucleus ambiguus and laterally by the small-celled nucleus salivatorius inferior. The motor nuclei of nerve X consist of the dorsomedially located dorsal motor nucleus of the vagus and the laterally located vagal part of the nucleus ambiguus. ⋯ A separate spinal component of nerve XI could not be found. The bulbar component of this nerve forms part of nerve X and takes its main origin from a detached caudal element of the nucleus ambiguus. The motor nuclear complex of nerve XII consists of a large dorsal nucleus and a small ventral nucleus that extend from the medulla oblongata into the first segment of the cervical spinal cord.
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Direct projections from the forebrain to the nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus in the rat medulla were mapped in detail using both retrograde axonal transport of the fluorescent tracer True Blue and anterograde axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). In the retrograde tracing studies, cell groups in the medial prefrontal cortex, lateral prefrontal cortex (primarily ventral and posterior agranular insular cortex), bed nucleus of the stria terminalis, central nucleus of the amygdala, paraventricular, arcuate, and posterolateral areas of the hypothalamus were shown to project to the NTS and in some cases also to the dorsal motor nucleus of the vagus. The prefrontal cortical areas projecting to the NTS apparently overlap to a large degree with those cortical areas receiving mediodorsal thalamic and dopaminergic input. ⋯ In contrast, the subcortical projections, which travel through the midbrain and pontine tegmentum, terminate most heavily in the ventral portions of the NTS, i.e., the area immediately dorsal and lateral to the dorsal motor nucleus of the vagus. Only the paraventricular hypothalamic nucleus has substantial terminals throughout the dorsal motor nucleus of the vagus. Hypothalamic cell groups innervate the area postrema and, along with the prefrontal cortex, innervate the zone subjacent to the area postrema.(ABSTRACT TRUNCATED AT 400 WORDS)
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Omnipause neurons (OPNs) are midline pontine neurons that are thought to be instrumental in the generation of saccadic eye movements. Inhibition of the tonically active OPNs is postulated to disinhibit the burst neurons that cause the saccadic discharge in motoneurons, leading to a saccade. To test whether the anatomical connections of OPNs are consistent with this scheme, we studied the efferent projections of the OPN region by using the technique of anterograde transport of tritiated amino acids. ⋯ Thus, there are direct projections from the OPN region to all areas known to contain burst neurons. In addition, OPNs also apparently have indirect access to the spinal cord and cerebellum. Many of the latter connections parallel the efferent projections of the superior colliculus.
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In the light of hypotheses related to the evolution of pain-carrying systems in mammals, terminal projection fields in brainstem and diencephalon of efferents of nucleus caudalis (NC) of the spinal trigeminal complex and spinal cord were determined in hedgehog by using Nauta-Gygax and Fink-Heimer silver techniques for degeneration. Unilateral NC lesions resulted in medullary degeneration in the ventral portion of NC contralaterally and bilaterally in cuneate nucleus (CU) and reticular formation. Pontine degeneration was noted ipsilaterally in medial (PBM) and lateral (PBL) parabrachial, facial motor (VII), and interpolar, oral, and main sensory trigeminal nuclei; degeneration in reticular formation was bilateral. ⋯ These results are consistent with the thesis that specific sensory thalamic nuclei evolved from a diffuse sensory region. Response properties of neurons in the dorsomedial portion of the ventral nuclear field, an area which are also received NC efferents, are not known. Last, NC projections to MD and LH implicate the role of "limbic" aspects of nociception.