Hormonal Control of Sexual Behavior in the Female Rat: Molecular, Cellular and Neurochemical Studies1

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Abstract
The present era of molecular research on steroid hormone action originates from the demonstration that there are intracellular protein receptors that bind steroid hormones and carry them to sites in cell nuclei where they regulate gene expression (Jensen and Jacobson, 1962; Toft and Gorski, 1966; Jensen et al., 1968; O''Malley and Means, 1974). Researchers of steroid hormone action in brain tissue have taken advantage of this revolution in biochemistry and cell biology and have found a way to understand the actions of gonadal and adrenal steroids on neural cells in cellular and molecular terms. However, the road has not been an easy one. The difficulties stem from the extreme complexity and anatomical heterogeneity of the brain, and the precise and highly localized neural networks involved in governing behavior. There also have been conceptual problems caused by a common tendency to regard the hormone as a stimulus and the behavior it regulates as a response, a relationship that implies temporal immediacy. However, because a hallmark of steroid hormone-regulated behaviors is their long latency and duration in relation to hormone priming, it has been necessary to look at the role of hormones in a different light. More than 40 year ago, the preeminent pioneer in elucidating hormones'' effects on behavior, Frank Beach, anticipated the current view of steroid hormone action by writing: "The sex hormones are best regarded not as stimuli... but as chemical sensitizers which alter the stimulability of critical mechanisms within the central nervous system" (Beach, 1945). In particular, because neurons commuicate by means of neurotransmitters released at synaptic endings, it is necessary to relate the long-term and frequently delayed actions of steroid hormones to neurochemical processes governing synaptic transmission, and to show how these processes are modified by the actions of steroid hormones. This has been our goal for more than 15 years (McEwen and Pfaff, 1973), and we have been aided in our studies by the existence of an excellent system in which to explore both temporal and spatial (McEwen et al., 1979) aspects of steroid hormone action, namely, lordotic behavior in the female rat. This chapter is a progress report on our attempts to flesh out the concept embodies in Beach''s statement and to relate it to emerging concepts in molecular endocrinology.