Lactation alters gamma-aminobutyric acid neuronal activity in the hypothalamus and cerebral cortex in the rat

gamma -Aminobutyric acid (GABA) neurons terminating in the hypothalamus hav e been implicated in the neuroendocrine regulation of reproductive hormones , particularly luteinizing hormone (LH) and prolactin. The aim of this stud y was to examine whether GABAergic neuronal activity in the hypothalamus wa s modified during lactation, and whether any observed changes correlated wi th changes in secretion of these hormones. Animals were divided into three experimental groups: diestrous controls, lactating with pups present (with pups), and lactating with pups removed for 4 h (without pups). Animals were decapitated either without treatment, or 60 min after inhibition of GABA d egradation by aminooxyacetic acid (AOAA) (100 mg/kg, i.p.). The rate of GAB A accumulation in the tissue after AOAA is a measure of GABA turnover. GABA turnover was estimated in 13 microdissected brain regions, and serum prola ctin and LH measured by radioimmunoassay. Suckling was associated with sign ificantly increased prolactin and significantly decreased LH compared with diestrous rats. In lactating rats with pups, GABA turnover was significantl y increased in the cingulate cortex compared with diestrous rats. GABA turn over was significantly increased in the ventrolateral preoptic nucleus of l actating rats with pups compared with diestrous rats or lactating rats with out pups. There was significantly lower GABA turnover in the anterior hypot halamic area, ventromedial and dorsomedial hypothalamic nuclei in lactating rats without pups compared with diestrous rats. There were no significant changes in other brain regions examined. The results demonstrate that activ ity of GABAergic neurons in specific parts of the hypothalamus and cerebral cortex is altered during lactation. Copyright (C) 2001 S. Karger AG, Basel .