Somatostatin production by rat cerebral neurones in dissociated cell culture

Abstract

Somatostatin (somatotropin release inhibiting factor, SRIF) is the 14-amino acid polypeptide found to be the active growth hormone-release inhibiting factor in extracts of sheep hypothalamus^1,2. Although found in highest concentrations in the hypothalamus, it is widely distributed in the gastrointestinal tract and extra-hypothalamic nervous system. In fact, the cerebral cortex contains a larger total amount of Somatostatin than any other brain region or visceral organ³. The source of somatostatin in extra-hypothalamic brain has been unclear. Initially, the hypothalamus was considered the only source, but elegant immunohistochemical demonstrations of positively staining neuronal perikarya in amygdala, hippocampus and neocortex suggested that these areas might be independent sources of Somatostatin⁴. In addition, bilateral anterior hypothalamic periventricular lesions reduced Somatostatin content in the median eminence to less than 10% of control levels, but did not affect its concentration in the preoptic area, amygdala or cortex⁵. Our laboratory has previously shown that dissociated rat cortical neurones in culture exhibit structural and electro-physiological properties similar to those of adult neurones in situ⁶. In conjunction with studies being carried out on the physiological effects of Somatostatin on these neurones, we investigated the occurrence of endogeneous IR-somatostatin. We show here that dissociated cell cultures from rat cerebral hemispheres in the absence of any hypothalamic tissue produce immunoreactive (IR)-somatostatin. This IR-somatostatin is demonstrable histochemically in an exclusively neuronal population within the cultures.