Nitric oxide and ERK/MAPK mediation of estrous behavior induced by GnRH, PGE2 and db-cAMP in rats

We tested the hypothesis that GnRH, PGE2 and db-cAMP act via the nitric oxide (NO)-cGMP and MAPK pathways to facilitate estrous behavior (lordosis and proceptivity) in estradiol-primed female rats. Estradiol-primed rats received intracerebroventricular (icv) infusions of pharmacological antagonists of NO synthase (L-NAME), NO-dependent soluble guanylyl cyclase (ODQ), protein kinase G (KT5823), or the ERK1/2 inhibitor PD98059 15 min before icv administration of 50 ng of GnRH, 1 μg of PGE2 or 1 μg of db-cAMP. Icv infusions of GnRH, PGE2 and db-cAMP enhanced estrous behavior at 1 and 2 h after drug administration. Both L-NAME and ODQ blocked the estrous behavior induced by GnRH, PGE2 and db-cAMP at some of the times tested. The protein kinase G inhibitor KT5823 reduced PGE2 and db-cAMP facilitation of estrous behavior but did not affect the behavioral response to GnRH. In contrast, PD98059 blocked the estrous behavior induced by all three compounds. These data support the hypothesis that the NO-cGMP and ERK/MAPK pathways are involved in the lordosis and proceptive behaviors induced by GnRH, PGE2 and db-cAMP. However, cGMP mediation of GnRH-facilitated estrous behavior is independent of protein kinase G.