Galanin-like immunoreactivity and galanin messenger RNA levels increase across puberty in neurons of gonadal steroid-dependent brain nuclei. We hypothesized that this activation and the associated increase in endogenous galanin release would result in changes across puberty in both galanin binding density and the level of receptor occupancy. Here we have assessed the density of galanin binding sites in several brain regions of prepubertal and adult male rats with or without GTP to induce dissociation of endogenous galanin from its binding sites. The developmental changes in the level of receptor occupancy were used as an indirect measure of changes in neuropeptide release from galanin expressing neurons. In standard binding conditions (buffer preincubation), 125I-labeled galanin binding showed a generalized decline in adult brains (34-68%) compared with prepubertal levels in most regions of the telencephalon and diencephalon. Following preincubation with 10(-5) M GTP, galanin binding showed a dramatic increase in most regions of the adult (152-504%) and several regions of the prepubertal brain (132-245%) over their standard binding levels. However, this increase was greatest in adult animals. Finally, although preincubation of brain slices with GTP eliminated most of the apparent age-related differences observed in standard binding conditions, several brain regions of the adult brain continued to show a significant reduction (38-76%) in 125I-labeled galanin binding compared with prepubertal animals. Only one region, the lateral preoptic area, exhibited enhanced 125I-labeled galanin binding in adult (160%) compared with prepubertal brain after GTP preincubation.(ABSTRACT TRUNCATED AT 250 WORDS)