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Notes: In the rat, vaginocervical stimulation (VCS) received during mating is required for the subsequent expression of 10–12 days of twice-daily prolactin surges that are necessary for pregnancy or pseudopregnancy (PSP). This temporal separation of sensory stimulus and neuroendocrine response suggests that a mnemonic of the vaginocervical stimulation is created in the brain that triggers and sustains the daily prolactin surges. We investigated the possible involvement of the medial preoptic area (mPOA) and the medial amygdala (mAMYG) as potential neural sites involved in the processing of this neuroendocrine arc. Cycling female rats were bilaterally implanted with intracerebral cannulae in either the mPOA or mAMYG. On proestrus, females were manually palpated to confirm sexual receptivity and then received bilateral infusions of either the local anesthetic lidocaine, the Ca++ channel blocker, verapamil, or phosphate-buffered saline (PBS) into either brain site before or both before and after receipt of 15 intromissions from an experienced male. Unmated control females received comparable infusions of lidocaine or verapamil, and were placed in the empty test arena for 10 min. Infusions consisted of either a single bilateral infusion 15 min before mating (Expt. 1), bilateral infusions both 15 min before and after mating (Expt. 2) or eight bilateral infusions separated by 30 min intervals spanning a period beginning 45 min before and ending 2 h 45 min after mating (Expt. 3). None of the lidocaine infusions into the mPOA prevented the establishment of PSP, and neither verapamil infusions into the mAMYG nor the shorter-term neural block (i.e. single or double lidocaine infusions) of the mAMYG prevented mating-induced PSP. However, the longer-term neural block (i.e. multiple lidocaine infusions) of the mAMYG significantly reduced the incidence of PSP. These data support previous findings that the mAMYG receives sensory input from VCS, and suggest that the mAMYG is a site at which a mnemonic of VCS is established.

Notes: The present experiments sought to characterize the particular stimuli received during mating in the female rat which induce acute increases in luteinizing hormone (LH) and prolactin (PRL) following copulation. Comparisons were made between cycling females mated on the evening of proestrus in partitioned chambers in which spontaneous patterns of approach/withdrawal toward the male served to pace copulatory stimulation (paced), in non-partitioned chambers in which female regulation of intervals between copulatory mounts was prevented (non-paced), or under conditions in which they received mounts-without-intromission (mounts-only). Frequent blood samples were withdrawn via surgically implanted intra-atrial catheters. In experiment 1, blood samples for LH determinations were taken at 15-min intervals for 1 h prior to and for 2 h after mating on the evening of proestrus. In experiment 2, samples for PRL determinations were taken at 10-min intervals for 30 min prior to and for 90 min after mating on proestrus and at 0300, 0400 and 0500 h on the day of estrus (reported times corrected for reversed light cycle). LH levels were significantly higher in paced animals 15 min after initiation of mating than in non-paced and mounts-only females; no differences in LH were seen between females who subsequently became or did not become pregnant/pseudopregnant (P/PSP). PRL values were not different between groups receiving the different mating treatments at any time; however, P/PSP animals showed significantly higher levels of PRL between 20 to 60 min after mating than did non-P/PSP females. No differences in PRL were seen between mating treatments or pseudopregnancy condition at 0300 to 0500 h on estrus. Paced females in both experiments received intromissions at a significantly slower rate than did non-paced females. There was a significant positive correlation (r = 0.619, P〈0.001) between LH concentration at 15 min and the inter-intromission interval (in seconds) in paced and non-paced groups of females. These data suggest that an LH response to mating is dependent upon the particular characteristics of mating stimulation received. In addition, they demonstrate that PRL increases acutely after mating stimulation in animals destined to become P/PSP but does not increase in response to those characteristics of mating stimulation which induced increases in LH.

Notes: When estrous female rats control or pace (P) their sexual contacts with males, several neuroendocrine and behavioral responses to mating occur that are not observed or are greatly attenuated after nonpaced mating. The present study examined whether the distribution and amount of FOS immunoreactivity (FOS-IR) induced in brain by mating would be altered in females receiving paced rather than nonpaced mating stimulation. In the first experiment, females received 5 or 15 intromissions during paced mating tests (5P and 15P), 5 or 15 intromissions during nonpaced mating tests (5NP and 15NP), 15 mounts-without-intromission (MO) or remained in their homecages (HC). Selective increases 1 h after paced mating stimulation were observed in the posterodorsal medial amygdala (MePD), where significantly more FOS-IR cells were present in the 5P and 15P groups than in the respective NP groups. The 5P, 5NP and 15NP had significantly more FOS-IR than the HC, MO, and 5NP groups, and the 5P group had levels of FOS-IR which were equivalent to that seen in the 15NP group. In the posteromedial portion of the bed nucleus of the stria terminalis (BNSTpm) and the ventrolateral portion of the ventromedial nucleus of the hypothalamus (VMHvl), paced mating induced significantly greater numbers of FOS-IR cells than did either MO or HC treatments; increases induced by nonpaced mating were not statistically greater than HC controls. No differences between groups were seen in the medial preoptic area (mPOA). In the second experiment, experimentally lengthening the interintromission interval (III) as well as increasing the intromission duration to mimic the characteristics of paced mating, resulted in significant increases in FOS-IR in the MePD but not in the other three brain regions. These results demonstrate that paced mating is more effective in inducing c-fos expression than nonpaced mating, and that the MePD is particularly sensitive to differing characteristics of the mating stimuli received.