Sensorimotor gating changes across the estrous cycle in female rats

Sensorimotor gating deficits are considered to be among the factors that cause schizophrenic symptoms in humans, a fact that has fostered the research interest into sensorimotor gating phenomena in experimental animals. A measure for sensorimotor gating deficits in humans and animals is the disruption of prepulse inhibition (PPI) of the acoustic startle response (ASR). PPI is the reduction of the ASR that is normally observed when the startling pulse is preceded by a weak prepulse. In humans PPI is lower in women than in men and varies across the menstrual cycle in women. The present study assessed PPI in female and male rats to possibly provide an animal model for the investigation of the neuronal basis of sex differences in sensorimotor gating in humans. No differences in PPI between males and females (diestrous or estrous) were observed. However, PPI was significantly reduced in female rats during proestrous compared to diestrous or estrous or compared with male rats. No significant effect of 1 mg/kg of apomorphine on PPI was found in either sex. The magnitude of the ASR in the absence of prepulses was not affected by the gender, the drug, or the phase of the estrous cycle. Because a prominent role for dopamine and serotonin in the regulation of PPI in rats has been shown, and because there is evidence for a strong interaction between estrogen and the monoaminergic systems, the present data are consistent with the hypothesis that estrogen regulates PPI through an interaction with the dopaminergic and/or serotonergic systems.