CELLULAR-DISTRIBUTION OF IMMUNOREACTIVE SOMATOSTATIN IN THE BASAL FOREBRAIN OF HORSES AND PONIES

In other experimental models, somatostatin (SRIF) helps coordinate cen tral nervous system (CNS) activity associated with the response to str ess. It also plays an important role in the effects of exercise, stres s and bacterial infections on growth hormone (GH) release and it may i nteract with specific SRIF receptors found on lymphocytes. Pituitary G H is a potent immunomodulatory hormone which is important to normal fu nction of the thymus and a wide range of immune defense mechanisms. Th is experiment mapped the distribution of immunoreactive (ir) SRIF in t he basal forebrain of horses and ponies. Results are compared to those for other species in order to determine if the anatomical substrate f or stress-dependant SRIF effects may be similar to that described for other animal models. Immersion fixed brain tissues were obtained from animals submitted for euthanasia and/or necropsy. Alternate sections w ere stained for ir-SRIF using characterized polyclonal SRIF antibody a nd the peroxidase-anti-peroxidase technique, as previously described. Distribution of SRIF cells and fibers was mapped on projection drawing s following light microscopic examination. Tissues in this analysis in cluded cell groups at the border between the telencephalon and the ros tral diencephalon, the hypothalamus, caudate nucleus (n) subthalamus a nd thalamus. At rostral levels, ir-SRIF was widely dispersed throughou t medial tissues. Caudally, pronounced immunoreactivity was found in v entromedial tissues. Reactive perikarya were localized in the caudate n, olfactory tuberculum, n of the lamina terminalis, rostral preoptic n, suprachiasmatic n, periventricular n, supraoptic n, paraventricular n, arcuate n and ventromedial n. Numerous SRIF fibers extended into t he lateral septum, all preoptic n, paraventricular n, rostral hypothal amic n, dorsomedial n, ventromedial n and mammillary n. Reactive fiber s were also found in midline thalamic n, perifornical areas, the zona incerta and the habenular n, This distribution is similar to that desc ribed in most vertebrates. It reflects the role of SRIF in multiple ne urocrine interactions as well as its neuroendocrine activity. Results from this experiment suggest that equine SRIF is likely to participate in neural and endocrine pathways similar to that for other mammalian species. Similar localization patterns also suggest that the coordinat ion of SRIF cell functions within the equine CNS may be comparable to that in other species. This suggests that studies in other species are likely to facilitate the characterization of control mechanisms for S RIF secretion in the equine species.