Induction of Galanin Gene Expression in Gonadotropin- Releasing Hormone Neurons with Puberty in the Rat*

The onset of puberty reflects the developmental activation of GnRH neurons whose secretory activity awakens the reproductive axis; how-ever, the cellular mechanisms involved in this activational process remain poorly understood. GnRH neurons coexpress the neuropeptide galanin, and we have previously shown that galanin’s level of coexpres-sion is linked to the activity state of GnRH neurons. We theorized that altered expression of galanin by GnRH neurons may be an important mechanism related to activation of GnRH neurons at puberty. We examined two hypotheses related to this idea. First, we tested the hypothesis that expression of galanin messenger RNA (mRNA) in GnRH neurons is induced across the transition from prepubertal to adult life in the rat. To accomplish this, we used double label in situ hybridization and image analysis to compare cellular levels of galanin mRNA in GnRH neurons between groups of prepubertal and adul