1. ¹Department of Biomedical Sciences, Tufts University Cummings School of Veterinary Medicine, North Grafton, MA, USA
2. ²Department of Neuroscience, Tufts University School of Medicine, Center for Neuroscience Research, Boston, MA, USA

Correspondence: Dr EM Byrnes, Department of Biomedical Sciences, Tufts University Cummings School of Veterinary Medicine, 200 Westboro Road, North Grafton, MA 01536, USA. Tel: +1 508 839 7986; Fax: +1 508 839 7091; E-mail: elizabeth.byrnes@tufts.edu

Received 26 January 2006; Revised 22 August 2006; Accepted 24 August 2006; Published online 18 October 2006.

Abstract

There is much speculation regarding the effects of estrogen withdrawal at the end of pregnancy on forebrain dopamine, however, few studies have directly examine changes in this system postpartum. The present work sought to determine what changes in forebrain dopamine function occur in the postpartum rat. Specifically, prepulse inhibition of the acoustic startle response (PPI) was measured in primiparous female rats on postpartum day 2 (PPD2) or 14 (PPD14) following treatment with saline or the dopamine D2 agonist, quinpirole. Diestrus (DI) females served as controls. Dopamine content and turnover as well as cyclic AMP (cAMP) accumulation were determined within the nucleus accumbens and dorsal striatum in these same females. In addition, circulating levels of plasma corticosterone, estradiol and progesterone were measured. PPI was significantly disrupted in both postpartum groups. This effect was associated with decreased cAMP content within the nucleus accumbens. Quinpirole treatment (0.1 and 0.5 mg/kg) dose-dependently disrupted PPI in DI controls while PPD2 and PPD14 animals demonstrated reduced sensitivity to the D2 agonist. PPD14 animals demonstrated increased startle amplitude, an effect that was attenuated by quinpirole treatment. PPD14 females were also less sensitive to quinpirole-mediated reductions in DA turnover within the nucleus accumbens and both PPD2 and PPD14 females had an attenuated response to the stimulatory effects of quinpirole on corticosterone secretion. Collectively these findings suggest that the postpartum period is associated with reduced sensorimotor gating and altered forebrain DA systems, which may be related to shifts in circulating hormones.