Premenstrual dysphoric disorder (PMDD) shows comorbidity with other psychiatric conditions such as panic disorder (PD). The symptoms of both conditions are exacerbated during the late luteal phase of the menstrual cycle, when progesterone levels fall sharply. The present study investigated the effect of withdrawal from progesterone (PWD) on expression of alpha4, beta1, and delta GABA(A) receptor subunits in neurons within the panic circuitry of the midbrain periaqueductal gray matter (PAG) in adult female Wistar rats. Immunostaining for alpha4, beta1, and delta GABA(A) receptor subunits was present in neurons throughout the PAG in vehicle-treated animals (VEH), in rats after 24 hours withdrawal from a progesterone dosing regime (PWD, 5 mg kg(-1) i.p. twice daily for 6 days), and in animals maintained on progesterone for 7 days (HP). Compared to HP and VEH animals, which did not differ significantly from each other, the number of immunostained neurons present in the PAG of PWD rats was significantly higher. The effect was most pronounced in the dorsolateral column of the PAG. The parallel changes in the three GABA(A) receptor subunits suggests that falling progesterone levels may be associated with expression of new receptors of the alpha4beta1delta subtype. This could lead to functional changes in GABAergic transmission within the PAG. We suggest that changes in GABA(A) receptor-mediated inhibitory tone in the PAG consequent to withdrawal from progesterone may contribute to the increased anxiety and susceptibility to panic seen during the late luteal phase of the menstrual cycle in PMDD and PD patients.
(c) 2005 Wiley-Liss, Inc.