Dissociation of active from immobility components of sexual behavior in female rats by central 6-hydroxydopamine: implications for CA involvement in sexual behavior and sensorimotor responsiveness.

Ovariectomized female rats were given a hormone treatment (2 X 8 micrograms/kg estradiol benzoate) that normally supports only low levels of lordosis responding and no soliciting behavior in tests with sexually active males. When subjected to an intraventricular 6-hydroxydopamine (6-OHDA) procedure (with pargyline pretreatment) that produced 85% and 95% depletions of caudate dopamine and cortical norepinephrine respectively, these females exhibited a dramatic increase in the intensity and frequency of lordotic responding but no soliciting behavior over 3 weekly tests. The increase in lordosis was not due to a drug- or stress-induced release of adrenal progesterone, since dexamethasone suppressed the progesterone levels, as documented by radioimmunoassay, but not the higher receptivity of 6-OHDA treated females. In other ovariectomized females given a hormone regimen (2 X 50 micrograms/kg estradiol benzoate plus 500 micrograms progesterone) that supported maximal levels of lordosis and soliciting, the same 6-OHDA treatment prolonged the average duration of lordosis while actually decreasing the incidence and duration of soliciting. The hypothesis is put forward that the differential effects of interfering with catecholamine, and more likely dopamine function on the soliciting and lordosis components of female sexual behavior might best be understood as a dissociation between mutually antagonistic behavior patterns such that responsiveness involving active orientation and forward locomotion is suppressed, whereas responses requiring immobility are augmented.