Sexually dimorphic activation of midbrain tyrosine hydroxylase neurons after mating or exposure to chemosensory cues in the ferret.

Mating with intromission induces a prolonged preovulatory LH surge in the estrous female ferret but inhibits LH secretion in the male. We used the dual immunocytochemical localization of Fos (as a marker of neural activation) and tyrosine hydroxylase (TH) to determine whether neurons containing norepinephrine or other catecholamines are activated after mating. Breeding male ferrets were allowed to intromit with estrous females; both animals were perfused 90 min after the onset of intromission. Other male and female ferrets were perfused 90 min after being placed in a cage in which an opposite-sex ferret in breeding condition had previously been housed for 48 h. Control ferrets of each sex were perfused 90 min after being placed alone in a clean testing cage. Mating with intromission significantly augmented the percentage of TH-immunoreactive (TH-IR) neurons colabeled with nuclear Fos-like immunoreactivity (Fos-IR) in both the A6 and the rostral A2 midbrain catecholamine cell groups in females, but not males. Exposure to chemosensory cues alone also increased the percentage of Fos-IR TH neurons in the rostral A2, but not the A6, cell group in females. Chemosensory cues alone did not affect the percentage of double-labeled neurons in either cell group in males. These activated midbrain TH-IR neurons are most likely noradrenergic, and their activation in estrous females may facilitate the mediobasal hypothalamic release of LHRH required for the preovulatory LH surge. In both sexes, mating with intromission, but not chemosensory cues alone, augmented the percentage of periglomerular TH-IR neurons in the main olfactory bulb (MOB) that were colabeled with Fos-IR. These activated TH-IR neurons in the MOB are most likely dopaminergic. Their role in the neural response to mating is currently unknown.