Excitotoxic lesions of the medial amygdala differentially disrupt prolactin secretory responses in cycling and mated female rats

This study examined the role of the posterodorsal medial amygdala (MePD) in the control of prolactin secretion in gonadally intact female rats 20 min after mating, during the oestrous cycle, and during early pregnancy/pseudop regnancy (P/PSP). Cycling females received bilateral infusions of an excito toxic dose of N-methyl-d-aspartate (NMDA) or vehicle into the MePD. Two to 4 weeks later, they were surgically implanted with intra-atrial catheters f or repeated blood sampling and were mated on the evening of proestrus until receiving 5, 10, 15 or 20 intromissions or 15 mounts-without-intromission (MO) from males. The percentages of rats becoming P/PSP increased as a func tion of numbers of intromissions received. All groups receiving intromissio ns showed similar approximately four-fold increases in plasma prolactin con centrations 20 min after mating, while MO rats showed no increase at this t ime. There was no effect of NMDA lesion on this acute secretory response. A mong rats that continued cycling, bilateral MePD lesion completely abolishe d the diurnal preovulatory prolactin surge, while incomplete and sham lesio ns did not. In rats that subsequently became P/PSP, bilateral lesion of the MePD resulted in dampening of prolactin concentrations at all sampling tim es 6-7 days after mating, while incomplete or sham lesions did not alter pr olactin secretion at these times. These results demonstrate that the MePD i s selectively important for the secretion of prolactin on the afternoon of proestrus and that this structure may also modulate prolactin release in P/ PSP rats. Activity within MePD neurones does not appear to be required for the acute prolactin response to vaginocervical stimulation which occurs wit hin minutes after mating.