The Journal of comparative neurology
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Subcortical projections to the anterior thalamic nuclei were studied in the rat, with special reference to projections from the mammillary nuclei, by retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. The medial mammillary nucleus (MM) projects predominantly ipsilaterally to the entire anterior thalamic nuclei, whereas the lateral mammillary nucleus projects bilaterally to the anterodorsal nucleus (AD) of the anterior thalamic nuclei. A topographic relationship was recognized between the MM and the anterior thalamic nuclei. ⋯ The rostrodorsal part of the nucleus reticularis thalami was found to project to the anterior thalamic nuclei; cells located rostrally in this part project to the IAM and AM, whereas cells located caudodorsally project to the AV and AD. The laterodorsal tegmental nucleus projects predominantly ipsilaterally to the AV, especially to its dorsolateral part. The present study demonstrates that subdivisions of the subcortical structures are connected to the subnuclei of the anterior thalamic nuclei, with a clear-cut topography arranged in the dorsoventral and the rostrocaudal dimensions.
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Amphibians have two auditory organs specialized for reception of airborne sounds: the amphibian papilla and the basilar papilla. In this report we examine the morphology of the ganglion cells and the afferent innervation of the sensory epithelium in both auditory organs of the leopard frog, Rana pipiens pipiens. Extracellular injections of either biocytin or horseradish peroxidase (HRP) were made into the VIII nerve; they labeled ganglion cells, their axons, and their terminal fibers within the papillae. ⋯ In the basilar papilla labeled fibers were thick (around 4 microns) and terminated on as many as nine hair cells. Consistent with studies from the bullfrog, Rana catesbeiana, our results suggest that the amphibian papilla of R. pipiens pipiens has a convergent innervation (i.e., multiple hair cells provide input to a single ganglion cell) and is topographically organized. However, in contrast to reports in other ranid species, a highly convergent innervation like that found in the amphibian papilla is also found in the basilar papilla.
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The vertebrate dorsal mesencephalon consists of the superior colliculus, the dorsal portion of the periaqueductal gray, and the mesencephalic trigeminal neurons in between. These structures, via their descending pathways, take part in various behavioral responses to environmental stimuli. This study was undertaken to compare the origins and trajectories of these pathways in the cat. ⋯ In summary, neurons in the PAG and in the deep layers of the SC give rise to a massive ipsilateral descending pathway, in which a medial-to-lateral organization exists. A similar topographical pattern occurs in the crossed SC projections. The possibility that these completely different descending systems cooperate in producing specific defensive behaviors is discussed.
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Immunohistochemical visualization of Fos protein, the nuclear phosphoprotein product of the early-immediate gene c-fos, permits identification of populations of neurons that are activated in response to a variety of stimuli. This study examined the distribution of Fos-like immunoreactive (FLI) neurons in the spinal cord and the nucleus tractus solitarii (NTS) of the caudal medulla evoked by a noxious visceral stimulus in the unanesthetized rat. It also compared the inhibition of pain behavior and Fos expression by a mu-selective opioid agonist, morphine, and a kappa-selective opioid agonist, U-50,488. ⋯ Both morphine (1-10 mg/kg s.c.) and U-50,488 (3-30 mg/kg s.c.) produced a dose-dependent inhibition of the pain behavior in these animals and a dose-dependent suppression of the number of FLI neurons in both the spinal cord and in the NTS; complete suppression of FLI neurons was, however, not necessary for the production of antinociception. Furthermore, although equianalgesic doses of morphine and U-50,488 reduced the number of labelled neurons in the spinal cord to a comparable extent, morphine reduced the number of immunoreactive neurons in the NTS to a greater extent than did U-50,488. These results suggest that morphine and U-50,488 have comparable effects on the transmission of visceral nociceptive messages by spinal neurons, but differentially affect the autonomic response to noxious visceral stimuli.
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Physiological and pharmacological studies have suggested that catecholamines modulate cholinergic neurons in the medial septal and diagonal band nuclei (i.e., the septal complex). Thus, the ultrastructural morphology of neurons containing choline acetyltransferase (ChAT), the biosynthetic enzyme for acetylcholine, and their relation to catecholaminergic terminals exhibiting immunoreactivity for the catecholamine synthesizing enzyme tyrosine hydroxylase (TH) were examined in the rat septal complex. Dual immunoautoradiographic and peroxidase anti-peroxidase labeling methods were used to simultaneously localize antibodies raised in rabbits against TH and from rat-mouse hybridomas against ChAT in single sections. ⋯ Moreover, most of the associations formed were either symmetric synapses or appositions not separated by astrocytes in the plane of section analyzed. These findings provide cellular substrates in the septal complex (1) for sparse synaptic input relative to astrocytic investment of cholinergic neurons and (2) for direct synaptic modulation of cholinergic and non-cholinergic neurons by catecholamines and/or acetylcholine. These findings have direct relevance to catecholaminergic-cholinergic interactions and to the neuropathological basis for Alzheimer's disease.