HYPOTHALAMIC GALANIN-LIKE IMMUNOREACTIVITY AND ITS GENE-EXPRESSION INRELATION TO CIRCULATING CORTICOSTERONE

The neuropeptide galanin (GAL), which exists in dense concentrations w ithin the hypothalamus, has physiological actions which are neuroendoc rine in nature. In light of evidence showing GAL to alter the release of the adrenal steroid, corticosterone (CORT), a possible effect of th is steroid on GAL gene expression and peptide production in discrete h ypothalamic and brainstem sites was investigated. Using radioimmunoass ay and in situ hybridization techniques, this peptide was examined in rats that had received SHAM surgery, adrenalectomy (ADX) and ADX + COR T replacement. The results showed a clear, site-specific change in GAL in relation to circulating CORT. A loss of CORT after ADX caused a dr amatic decline in GAL peptide and mRNA levels in the arcuate nucleus a nd peptide levels in the median eminence, with no change occurring in other hypothalamic areas. In the brainstem, a similar change was detec ted in the dorsal raphe nucleus but not the locus coeruleus. The GAL p eptide and mRNA levels in these specific brain areas of ADX rats was r estored by CORT replacement, which had no impact on GAL in other brain sites. These findings demonstrate that CORT's impact on brain GAL is highly site specific, possibly determined by local concentrations of s teroid receptors.