Release of immunoreactive somatostatin from hypothalamic cells in culture: inhibition by gamma-aminobutyric acid.

Abstract

Primary cultures of dispersed hypothalamic cells were prepared from embryonic rats to study the release of immunoreactive somatostatin. The immunoreactive somatostatin content of these cultures increased during the first 2 weeks after plating and was readily measurable for several weeks thereafter; this material was characterized by gel permeation and reverse-phase chromatography. Depolarization of the cells with 60 mM K+ or with veratridine resulted in a calcium-dependent release of immunoreactive somatostatin which cochromatographed with synthetic somatostatin on reverse-phase chromatography. Tetrodotoxin blocked the veratridine-evoked release. However, even in the absence of exogenous stimuli, immunoreactive somatostatin was released by the cells into the medium. More than 70% of this tonic release was found to be calcium dependent and to be inhibited by tetrodotoxin, indicating that spontaneous electrical activity in the cultures leads to a release of immunoreactive somatostatin. gamma-Aminobutyric acid inhibited the tonic release of immunoreactive somatostatin and this was reversed by bicuculline. These findings support the hypothesis that gamma-aminobutyric acid inhibits somatostatin release in vivo.

Biosynthesis of immunoreactive somatostatin by hypothalamic neurons in culture.

“…For elucidation of the biosynthetic relationships between 15,000-mol-wt SLI, S-28, and S-14, the hypothalamus offers the distinct advantage of containing substantial quantities of all three molecular forms as opposed to tissues such as the pancreas, which have been studied previously (5). Primary cultures of dispersed hypothalamic and cerebrocortical cells derived from fetal rat brain and containing SLI have recently been described from two laboratories (25,26). the cultured neonatal hypothalamic cells in the present study are comparable to those reported for the two fetal tissues.…”

GABAergic dysfunction in mood disorders

“…158,159 Baclofen, a GABA B receptor agonist, stimulates GH secretion in healthy individuals, [160][161][162] and is considered to be an in vivo index of human hypothalamic GABA B receptor function. The GH response to baclofen has been found to be significantly lower in depressed patients 163,164 and significantly higher in manic patients than healthy subjects.…”

Somatostatin selectively enhances acetylcholine-induced excitations in rat hippocampus and cortex.

“…Subsequently, it has become evident that this peptide has a widespread distribution throughout the central, peripheral, and gastrointestinal nervous systems and the endocrine pancreas (2-6). Its role as a neurotransmitter in the central nervous system is supported by its presence in neuronal cell bodies and terminals in several regions (2,(7)(8)(9), its calcium-dependent release upon depolarization (10)(11)(12), and its ability to affect neuronal activity (13)(14)(15)(16)(17)(18)(19)(20). Subsequent chemical (5,6) and cytochemical (8,21) studies revealed that the cellular localization and the major biological actions of somatostatin are shared with a larger 28 amino acid form, of which the original somatostatin is the C-terminal tetradecapeptide (SS-14).…”