GALANIN-BINDING SITES IN THE FEMALE RAT-BRAIN ARE REGULATED ACROSS PUBERTY YET SIMILAR TO THE MALE PATTERN IN ADULTHOOD

The neuropeptide galanin (GAL) has been implicated in a variety of neuroendocrine functions and has been shown to be regulated by gonadal hormones in several brain regions. We have used slice binding and quantitative autoradiography techniques to determine whether the activation of GAL pathways across puberty in female rats is associated with changes in the density of GAL binding in telencephalic and diencephalic regions as we previously observed in male rats. We have also asked whether sex differences in GAL immunoreactivity and GAL gene expression detected in some brain regions would be paralleled by sex differences in I-125-GAL-binding density in adult male and female rat brains. To control for intrinsic differences in the level of endogenous GAL synthesis and release, brain slices from prepubertal female and adult male and female rats were treated with guanosine 5'-triphosphate (GTP) to induce dissociation of endogenous GAL from its binding sites prior to incubation with radiolabeled ligand. I-125-GAL binding was significantly reduced in seven brain regions of adult compared with prepubertal female rats. These regions included the islands of Calleja (p less than or equal to 0.03), the medial amygdaloid nucleus, posterodorsal division (p less than or equal to 0.05), median eminence (p less than or equal to 0.02), medial habenular nucleus (p less than or equal to 0.05), rhomboid thalamic nucleus (p less than or equal to 0.05), and paraventricular (p less than or equal to 0.05) and intermediodorsal (p less than or equal to 0.02) thalamic nuclei. Only one region, the lateral preoptic area, exhibited significantly enhanced I-125-GAL binding in adult female (p less than or equal to 0.04) compared with prepubertal animals. The distribution and density of I-125-GAL-binding sites were similar in adult male and female rat brains and no statistically significant effect of sex or interaction of sex with brain region were detected by ANOVA. These results suggest that gonadal hormones and/or some other factors associated with puberty may regulate central GAL receptor number and/or affinity in discrete regions of the female rat brain. The regional diversity of this regulation suggests that multiple factors are involved.