SUN-473 The Contribution of Bmal1 Expression in the Suprachiasmatic Nucleus to Female Fertility

The preovulatory gonadotropin-releasing hormone (GnRH) and resulting luteinizing hormone (LH) surge is gated to the onset of the active period in mice by a circadian and steroid signal. The temporal signal that initiates this process is believed to arrive from the suprachiasmatic nucleus (SCN), the hypothalamic circadian pacemaker. The SCN may contribute to reproduction through two discrete projections: vasoactive inhibitory peptide (VIP) neurons in the SCN project to gonadotropin-releasing hormone (GnRH) neurons in the preoptic area, and arginine vasopressin (AVP) neurons in the SCN project to kisspeptin (Kiss1) neurons in the anteroventral periventricular (AVPV). Genomic deletion of the critical circadian clock component, Bmal1, results in infertility in females. We sought to determine whether Bmal1 was critical in the SCN VIP and AVP neurons by using cre/lox technology to create three lines of mutant mice: AVP-Bmal1(-/-), VIP-Bmal1(-/-), and AVP-VIP-Bmal1(-/-). We found no significant difference in LH levels following a kisspeptin challenge (2 mg/kg) between AVP-Bmal1(-/-) and Bmal1(flox/flox) (617.4 ± 216.9 vs 629.6 ± 110.6 pg/mL) or GnRH challenge (10 μg/kg) (1029.0 ± 246.2 vs 712.7 ± 142.6 pg/mL). Preliminary findings of an induced LH surge found AVP-Bmal1(-/-) and VIP-Bmal1(-/-) mice are able to mount a surge at the time of lights off (Bmal1(flox/flox): 3 of 5; AVP-Bmal1(-/-): 1 of 2, VIP-Bmal1:(-/-) 4 of 4; AVP-VIP-Bmal1(-/-) 0 of 2). Additionally, we were able to detect an endogenous surge at the time of lights off in both AVP-Bmal1(-/-), VIP-Bmal1(-/-) mice, but not AVP-VIP-Bmal1(-/-). However, AVP-Bmal1(-/-), VIP-Bmal1(-/-), and AVP-VIP-Bmal1(-/-) females carried litters to term and show no differences in the time to first litter compared to Bmal1(flox/flox) control (AVP-Bmal1(-/-): 48 ± 4.8 vs 44.3 ± 0.3 days; VIP-Bmal1(-/-): 29.6 ± 7.7 vs 31.0 ± 4.2 days; AVP-VIP-Bmal1(-/-);27.7 ± 7 vs 23 ± 0 days); number of litters in 100 days (AVP-Bmal1(-/-): 3.7 ±0.6 vs 4 ± 0.6; VIP-Bmal1(-/-): 3.0 ± 1.0 vs 3.0 ± 0.0; AVP-VIP-Bmal1(-/-) 3.5 ± 0.7 vs 3.5 ± 0.7 days); or pups per litter (AVP-Bmal1(-/-): 7.2 ± 0.7 vs 7.3 ± 0.7; VIP-Bmal1(-/-): 6.2 ± 1.6 vs 7.6 ± 2.9; AVP-VIP-Bmal1(-/-) 8.1 ± 0.9 vs 9 ± 1.4 pups). Overall, these findings suggest that Bmal1 expression in the SCN AVP or VIP neurons is not required for fertility in a 12:12 light:dark cycle.