PATTERNS OF INDUCTION OF THE IMMEDIATE-EARLY GENES C-FOS AND EGR-1 INTHE FEMALE RAT-BRAIN FOLLOWING DIFFERENTIAL AMOUNTS OF MATING STIMULATION

Vaginocervical stimulation received either during mating or by artific ial mechanical means has been shown to induce FOS expression in medial amygdala, preoptic area, hypothalamus, and midbrain of female rats, W hile mating-induced increases in FOS-like immunoreactivity (FOS-IR) ha ve been shown to require intromissive stimulation from males, the patt ern of FOS-IR in animals receiving numbers of intromissions across a r ange relevant to the induction of the prolactin surges of early pregna ncy has not been explored. Experiment 1 examined brain FOS-IR followin g 15 mounts without intromission or 5, 10, or 15 intromissions in ovar iectomized females treated with estrogen and progesterone; these treat ments are known to be less than or more than sufficient to trigger pro lactin surges in cycling females, FOS was expressed in a graded fashio n in the medial amygdala with respect to the numbers of intromissions received and in an all-or-nothing manner in preoptic area, bed nucleus of the stria terminalis, and ventromedial nucleus of the hypothalamus , In experiment 2, 15 intromissions induced expression of another imme diate-early gene, egr-1, in each of these same areas as well as in a s econd division of the bed nucleus of the stria terminalis and in the p araventricular nucleus of the hypothalamus, These studies demonstrate that mating is differentially effective in inducing FOS expression in responsive brain areas and point to the medial amygdala as a site in w hich summation of intromissive stimulation may occur. Furthermore, the induction of EGR-1 may be a more sensitive marker for mating-induced neural activation in these areas than is FOS.