Sites of Estrogen and Progesterone Facilitation of Lordosis Behavior in the Spayed Rat

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Abstract
To elucidate the neural sites of hormonal facilitation of lordosis behavior in the ovariectomized rat, estradiol benzoate (EB) was implanted into the preoptic-diagonal band area (POA) through an indwelling cannula. Three days later, progesterone (P) was inserted into the mesencephalic reticular formation (MRF) or caudate-putamen (CPU), again by means of an indwelling cannula. The lordosis quotient (LQ) in 20 mount tests was obtained before and after P exposure. P in the MRF or CPU significantly increased the LQ, whereas cholesterol (C) implants in either area had no effect. The LQ was also obtained daily for 9 days in ovariectomized animals in which EB was implanted in the POA, MRF or CPU, or in which 2 .mu.g EB was injected s.c. daily. Although P was not administered, s.c. EB or implants in the POA markedly facilitated lordosis behavior. In other rats, P was injected s.c. 1 or 3 days after EB was implanted in the POA, MRF or CPU. The marked facilitation of the LQ in the first 2 groups, particularly 1 day after EB implantation (i.e., before the appearance of vaginal cornification), suggests that EB can act either at the level of the POA or MRF to facilitate behavioral responsiveness to systemic P. However, when the anti-estrogen CI-628 was implanted in the MRF during a 3 day period of exposure of the POA to EB, subsequent substitution of P for the MRF implant failed to facilitate lordosis. Thus, the MRF and CPU appear both to be sites of P action; EB alone is effective only when given systemically or implanted in the POA. Finally, although exposure of either the POA or MRF to EB facilitates the response to systemic P, prior exposure of the MRF to estrogen may be required for the action of locally implanted P.