SAT-422 Galanin-Like Peptide Neurons Are Required for Correctly-Timed Puberty Onset in Mice

The timing of puberty requires exquisite coordination of hormones and brain circuitry. Numerous neuronal pathways have been identified as being involved, but exactly how they affect puberty onset is poorly understood. Galanin-like peptide (GALP)-expressing neurons are located in the arcuate nucleus of the hypothalamus, and their fibers make apparent contacts with GnRH neurons. Many GALP neurons express receptors for estrogens (ERα) and leptin, so they are good candidates for estrogenic and metabolic regulation of puberty onset and adult fertility. Prior experiments involving central GALP antiserum infusion suggest a stimulatory role for GALP, but the animal models for elucidating this role have been lacking to date. We therefore generated a GALP-Cre recombinase mouse to enable GALP neuronal ablation and activity modulation. To test if GALP neurons are required for male and female puberty onset, in experiment 1 we used GALP-Cre mice crossed with Cre-dependant diphtheria toxin (DT) receptor mice to produce mice with DT-inducible GALP neuronal ablation. In males treated with DT on day 18 of age, preputial separation was delayed in DT receptor-expressing mice vs controls (27.9 ± 0.6 vs 26.2 ± 0.5 days old (P<0.05, n=6-11). There was no significant difference in age of vaginal opening in DT receptor-expressing females compared to controls. To test if activation of GALP neurons advances male and female puberty onset, in experiment 2 we used GALP-Cre mice crossed with Cre-dependant hM3Dq excitatory designer receptor mice to produce mice with clozapine-n-oxide (CNO; hM3Dq receptor ligand)-inducible GALP neuron activation. In females receiving chronic CNO in drinking water from day 26 to day 30 of age, there was a non-significant trend towards advanced vaginal opening age in hM3Dq receptor-expressing mice vs controls (31.9 ± 0.7 vs 33.3 ± 0.6 days old (P=0.2, n=4-8). There was no significant difference in preputial separation age in DT receptor-expressing males compared to controls. These results support a stimulatory role for GALP neurons in puberty onset. One possible explanation for the sex differences in this study is that males may have higher GALP neuronal activity at the time of treatment compared to females, making them more responsive to neuronal ablation. Follow-up studies will use earlier ablation and activation protocols.