Fos Expression after Mating in Noradrenergic Cells of the A1 and A2 Areas of the Medulla is Altered by Adrenalectomy

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In the female rat, the integrity of the ventral noradrenergic bundle (VNAB) is necessary to carry stimuli from the uterine cervix and vagina to brain areas involved in mating-induced pseudopregnancy. Because adrenal hormones are known to alter noradrenergic function, we examined whether adrenalectomy altered mating-induced Fos expression in the A1 and A2 noradrenergic cell groups that project through the VNAB. Ovariectomized females were adrenalectomized (ADX) or sham-operated (Sham) and, 2 weeks after surgery, were given oestrogen and progesterone and mated. They received 15 intromissions, five intromissions or 15 mounts-without-intromission (mounts-only) from a male. Two hours after mating, rats were perfused and brains were collected; controls were perfused after being taken directly from their home cage. After immunocytochemical staining, Fos-immunoreactive (Fos-IR) and dopamine-β-hydroxylase-immunoreactive (DBH-IR) cells and the percentage of DBH cells that were labelled with Fos (% DBH/Fos) were counted. In the A1 area, Fos-IR and percentage DBH/Fos were not affected by adrenalectomy. Although an overall effect of mating treatment was found for both measures, no specific mating treatment increased labelled cells above home cage levels. In the caudal, middle and rostral A2, 15 intromissions induced a significant increase in Fos-IR in Sham females above all other groups and a higher percentage of DBH/Fos in the middle and rostral A2 areas. ADX females showed no rise in either Fos-IR or percentage DBH/Fos after 15 intromissions. However, in the middle and rostral A2, ADX females showed significantly increased Fos-IR and percentage DBH/Fos after mounts-only treatment above Sham mounts-only females and all other ADX groups. These results demonstrate that adrenal hormones suppress activation of A2 cells to mounts-only stimuli but contribute to A2 activation in response to intromissions from males. The latter effect may result from stress associated with receipt of vaginocervical stimulation during mating.

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