Changes in limbic neuronal function during hormonal induction of lordosis in behaving hamsters

Several limbic structures influence copulatory behavior and contain receptors for estradiol and progesterone. In the present study, single neuron activity was recorded from septal, amygdaloid, and other limbic regions during the hormonal induction of lordosis in behaving golden hamsters. Limbic neurons had low firing rates and a small number showed firing associated with orienting, sniffing, and rearing. Progesterone administration to estradiol-primed hamsters produced the following neuronal effects: a reduction in the number of active neurons and narrowing of dynamic activity range; enhanced neuronal responsiveness to face stimulation; and lordosis-correlated firing, consisting of depressed activity during lordosis and increased firing at response onset or offset. Unlike previously studied midbrain and hypothalamic neurons, control progesterone injections that didn't produce lordosis were about as effective in altering limbic neuronal activity levels and sensory responsiveness as behaviorally effective injections. The progesterone effects on limbic neurons are consistent with previous evidence suggesting that these neurons tend to suppress lordosis. The significance of these results to hormone influences on epilepsy is discussed.