Mating-activated brainstem catecholaminergic neurons in the female rat

Central catecholaminergic systems play an important role in the control of reproductive activities including sexual behavior, luteinizing hormone (LH) and prolactin secretion. It has been reported that catecholaminergic neuro ns in the locus coeruleus (A6) are activated by mating in rabbits and ferre ts, animals known as reflex ovulators. This study used Fos as a marker of n euronal activity to examine whether brainstem catecholaminergic neurons are activated by mating in the spontaneous ovulator, the female rat. Proestrou s rats receiving intromissions (mated group) from males or mounts-without-i ntromission (mounted group) were sacrificed along with rats taken directly from their home cage (control group) 90 min after the beginning of mating o r mounting. Double-label immunocytochemistry was used to examine the expres sion of c-Fos in catecholaminergic neurons labeled by tyrosine hydroxylase (TH) antibody, or adrenergic neurons labeled by phenylethanolamine-N-methyl transferase (PNMT) antibody. Double label immunofluorescent immunohistoche mistry was used to determine the number of neurons containing the estrogen receptor (ER alpha) that were activated by mating in these brain areas. The results showed that mating-with-intromissions induced a significant increa se in the percentage of TK/Fos colabeled neurons in both A1 and A2 cells co mpared to mounting-without-intromission or control. In both these areas, ov er 50% ER alpha -ir neurons were activated after mating while mounting-with out-intromission did not affect the percentage of colabeled Fos/ER alpha ne urons. In A6 region, neither the expression of Fos nor the percentage of TH /Fos colabeled cells was influenced by either mating or mounting compared t o controls. The percentage of PNMT-containing neurons colabeled with Fos wa s not different in C1 and C2 among the three experimental groups. The resul ts indicate that catecholaminergic neurons were activated by mating in A1 a nd A2 but not in adjoining adrenergic C1 and C2 cells. In contrast to the f indings that catecholaminergic neurons in A6 are activated by mating in ind uced ovulators, mating did not affect neuronal activity in 126 neurons in t he female rat. In A1 and A2 areas, a high percentage of neurons containing ER alpha were activated by mating suggesting both tactile and hormonal info rmation may converge on these populations of neurons. The activated catecho laminergic neurons in A1 and A2 may be an important pathway by which sensor y information generated during sexual interaction modulates both behavior a nd pituitary function. (C) 2001 Elsevier Science B.V. All rights reserved.