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The localization and brain stem projections of neurons innervating the carotid sinus of the dog were studied by horseradish peroxidase histochemistry following microinjection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) under the adventitia of the carotid sinus. Within the brain stem, labeled afferent fibers and presumptive terminals were found bilaterally in the caudal nucleus tractus solitarius (nTS), the area postrema (AP), and the lateral tegmental field (LTF), reaching the area of the nucleus ambiguus (nA). Sparse labeling was also seen in the ipsilateral spinal trigeminal nucleus (SpV) and lateral cuneatus nucleus (LCn). These findings suggest the existence of multiple pathways by which peripheral baroreceptor inputs may influence central cardiovascular-related neurons. In addition to classically defined relay in the nTS, carotid sinus afferents may also interact more directly with these neurons in other brain stem regions.

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The localization of neurons innervating the carotid sinus of the dog was studied by horseradish peroxidase histochemistry following microinjection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) under the adventitia of the carotid sinus. Labeled cell bodies were found in the petrosal (198 +/- 108; mean +/- S.D.) and superior cervical ganglia (SCG) (890 +/- 354 mean +/- S.D.) supporting the existence of both a sensory afferent and a sympathetic efferent innervation of the carotid sinus. Labeled neurons in the petrosal ganglion were round pseudounipolar neurons of variable size. Labeled neurons in the SCG were multipolar and appeared distributed over the whole ganglion, but with a higher density toward its caudal half. No labeled perikarya appeared either in the brainstem or in the nodose or jugular ganglia, suggesting that in the dog a vagal pathway for carotid sinus baroreceptor afferents does not exist.

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The coexistence of serotonin and cholecystokinin was studied in foetal sheep lungs at pseudoglandular stage of development by light microscopic immunohistochemistry. The coexistence was examined by staining consecutive sections with the different antibodies. Serotonin and cholecystokinin immunoreactivity was found within consecutive sections of most bronchopulmonary neuroepithelial bodies and in consecutive sections of the same intrapulmonary autonomic ganglia.

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The lower respiratory tract of the sheep was studied by light-microscopical immunocytochemistry for serotonin, cholecystokinin, somatostatin, bombesin and calcitonin during different periods of lung development; embryonic, foetal and postnatal. At embryonic period only intraepithelial serotonin-containing cells as solitary neuroendocrine cells (NEC) and neuroepithelial bodies (NEB) were found. At foetal stages, immunoreactive cells to serotonin, cholecystokinin and somatostatin were observed in airway epithelium, as solitary NEC and NEBs, and in autonomic intrapulmonary ganglia as single or clusters of small intensely-fluorescent (SIF) cells. In postnatal sheep, serotonin- and cholecystokinin-containing cells were found within airway mucosa as solitary NECs and NEBs. No immunoreactive cells were observed with antiserum to bombesin and calcitonin. Quantitative studies showed that serotonin was the predominant substance, and that solitary neuroendocrine cells were more numerous in distal conducting airways and at foetal stages.

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Using light microscopic immunohistochemistry, serotonin immunoreactivity was found in paraganglionic cells within pulmonary autonomic ganglia of fetal sheep at pseudoglandular and canalicular stages of lung development. Serotonin immunoreactive cells appeared individually or in clusters, and were occasionally seen around or in close contact with blood vessels.

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The neuronal and fibrous architecture of the nucleus of the tractus solitarius (NTS) of the dog has been studied in transversely cut Nissl, myelin and reduced silver stained serial sections. Eight distinct subdivisions, clearly delimited both by their cytoarchitectonic and fibrous characteristics, have been identified. They are: the commissural, gelatinous, lateral, interstitial, dorsolateral, ventrolateral, intermediate and medial subdivisions. Their rostrocaudal extensions and locations in relation to the obex are summarised in Table 1. A morphometric analysis was additionally done. The frequency distributions of cell areas and cell form factor of each subdivision are represented by histograms in Figures 8 and 9 respectively.

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In this article we have studied the topography, relationship and projection of the hippocampus in the dog by means of 1 mm thick transverse, horizontal and parasagital sections stained with Mulligan's reagent and 50 microns transverse sections (Nissl). The macroscopical disposition of this part of the CNS was completed by means of a gross dissection. Horizontal sections of 10 microns through the middle or limbic part were used to determine the general microscopic anatomy and to define the morphometry of its cells. From this point of view the Hippocampus of the dog appears to be intermediate between the rat and primates, species better studied.

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The organization of the thalamus varies considerably from species to species. This article reports a tridimensional study of the canine thalamus in which 18 nuclei were distinguished on the basis of their delimitation in sections and their differing cytoarchitectonic characteristics, the latter having been objectively quantified by means of an image analyser. On the basis of their location and/or mutual similarities, these 18 nuclei are classified in 5 groups. The thalamus of the dog is similar to that the cat, but differs considerably from those of other well-studied species.

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The basal ganglia are very similarly disposed in superior animal, but their way of grouping is different in human species and domestic mammals. We have studied them in the dog, except for the Nucleus accumbens, from macroscopic and microscopic points of view, with the help of 25 and 50 pm thick transverse serial sections, stained by Nissl's technique. Each of these nuclei presents its own characteristics, as well topographically and extended as of shape, size and neuron density.

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