Distribution of substance P‐immunoreactive elements in the preoptic area and the hypothalamus of the rat

Abstract

The localization and morphology of neurons, processes, and neuronal groups in the rat preoptic area and hypothalamus containing substance P-like immunoreactivity were studied with a highly selective antiserum raised against synthetic substance P. The antiserum was thoroughly characterized by immunoblotting; only substance P was recognized by the antiserum. Absorption of the antiserum with synthetic substance P abolished immunostaining while addition of other hypothalamic neuropeptides had no effect on the immunostaining. The specificity of the observed immunohistochemical staining pattern was further confirmed with a monoclonal substance P antiserum. The distribution of substance P immunoreactive perikarya was investigated in colchicine-treated animals, whereas the distribution of immunoreactive nerve fibers and terminals was described in brains from untreated animals. In colchicine-treated rats, immunoreactive cells were reliably detected throughout the preoptic area and the hypothalamus. In the preoptic region, labeled cells were found in the anteroventral periventricular and the anteroventral preoptic nuclei and the medial and lateral preoptic areas. Within the hypothalamus, immunoreactive cells were found in the suprachiasmatic, paraventricular, supraoptic, ventromedial, dorsomedial, supramammillary, and premammillary nuclei, the retrochiasmatic, medial hypothalamic, and lateral hypothalamic areas, and the tuber cinereum. The immunoreactive cell groups were usually continuous with adjacent cell groups. Because of the highly variable effect of the colchicine treatment, it was not possible to determine the actual number of immunoreactive cells. Mean soma size varied considerably from one cell group to another. Cells in the magnocellular subnuclei of the paraventricular and supraoptic nuclei were among the largest, with a diameter of about 25 microns, while cells in the supramammillary and suprachiasmatic nuclei were among the smallest, with a diameter of about 12 microns. Immunoreactive nerve fibers were found in all areas of the preoptic area and the hypothalamus. The morphology, size, density, and number of terminals varied considerably from region to region. Thus, some areas contained single immunoreactive fibers, while others were innervated with such a density that individual nerve fibers were hardly discernible. During the last decade, knowledge about neural organization of rodent hypothalamic areas and mammalian tachykinin biochemistry has increased substantially. In the light of these new insights, the present study gives comprehensive morphological evidence that substance P may be centrally involved in a wide variety of hypothalamic functions. Among these could be sexual behavior, pituitary hormone release, and water homeostasis.

Distribution of mRNA for vanilloid receptor subtype 1 (VR1), and VR1-like immunoreactivity, in the central nervous system of the rat and human

“…The vanilloid-sensitive terminals in the hypothalamus may be glutamatergic because capsaicin was shown to evoke glutamate release from slices of hypothalamus (15). A subpopulation of hypothalamus neurons, like primary sensory neurons, expresses SP (33). Capsaicin was shown to deplete SP from primary sensory neurons by Jessell and coworkers in 1978 (34).…”

The suprachiasmatic nucleus and intergeniculate leaflet ofArvicanthis niloticus, a diurnal murid rodent from East Africa

“…Immunohistochemical methods have revealed SP-IR fibers within the SCN of all mammals examined to date, including various rodents (Cuello and Kanazawa, 1978;Smale et al, 1991Smale et al, , 1993Larsen, 1992;Morin et al, 1992) and primates (Mick et al, 1992). In A. niloticus, SP-IR fibers were distributed across the SCN, where their density was lower than in surrounding hypothalamic tissue, and their caliber was finer.…”

Review: Central non-glucocorticoid inhibitors of the hypothalamo-pituitary-adrenal axis

“…Observations that axonal terminals in the ME of the rat and primate stained strongly for SP (Hökfelt et al 1978, Larsen 1992) raised the possibility that significant amounts of SP are released into hypophysial portal blood to act as an ACTH inhibitor directly on corticotrophs of the anterior pituitary. However, concentrations of SP are very low in hypophysial portal blood of sheep (Clarke et al 1993), rat (Lim et al 1990) and monkey (Eckstein et al 1980), and SP in physiological doses had no effect on ACTH release from dispersed anterior pituitary cells in vitro (Chowdrey et al 1990).…”