SOMATOSTATIN SYSTEM OF THE BRAIN AND HIBERNATION IN THE EUROPEAN HAMSTER (CRICETUS-CRICETUS)

The depression of physiological processes characteristic of mammalian hibernation is precisely regulated by the central nervous system, espe cially by the neuropeptidergic apparatus of the hypothalamus. Because of inhibitory influences on neuronal circuits within the brain and sup pressive effects on the metabolism via the endocrine axis, somatostati n has been implicated in the regulation of hibernation. The somatostat in system of the brain was investigated with immunocytochemistry, in s itu hybridization, and radioimmunoassays in euthermic summer, euthermi c winter, and hibernating European hamsters (Cricetus cricetus). Numer ous somatostatin-immunorenctive perikarya were observed in the periven tricular hypothalamic nucleus. The striatum, amygdala, and cortex cont ained only scattered immunoreactive perikarya. These entities also con tained immunoreactive fiber profiles, although the highest density of immunoreactive fibers was found in the median eminence. Immunocytochem istry and radioimmunoassays showed that the number of somatostatin-imm unoreactive perikarya and fibers and the content of somatostatin in th e hypothalamus and the median eminence was conspicuously lower in euth ermic winter animals than in euthermic summer animals. This decrease w as more pronounced in hibernating specimens. In situ hybridization als o demonstrated a decrease in the expression and synthesis rate of soma tostatin in euthermic winter animals; again, this was even more dramat ic in hibernating hamsters. These changes were less pronounced or non- significant in the extrahypothalamic somatostatin-immunoreactive perik arya and fiber systems, as shown by immunocytochemistry and radioimmun oassay, respectively.