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

Abstract

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-beta-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.

Noradrenergic Nuclei that Receive Sensory Input During Mating and Project to the Ventromedial Hypothalamus Play a Role in Mating‐Induced Pseudopregnancy in the Female Rat

“…PSP block was associated with reduced numbers of mating‐activated noradrenaline cells in A1 and A2, but not in A5 or A6 (LC). Previous studies in which VCS induced Fos expression in noradrenergic neurones in A1 and A2, but not in A6, are in accordance with this finding (22,23). Anatomical reports also support this interpretation, demonstrating that noradrenergic inputs to the VMHvl are derived primarily from lateral tegmental and dorsal medullary cell groups, such as A1 and A2, which send ascending projections through the VNAB (17,47).…”

“…Electrolytic lesioning of the VNAB reduces PSP by 80% (20,21), suggesting that inputs to one or both of these areas from A1 and A2 noradrenergic cell groups are important for PSP induction. This premise is further confirmed by studies examining the expression of Fos, a marker for neuronal activation, in which VCS specifically activated neurones in the A1 and A2 nuclei, but not in A5 or A6 (locus coeruleus; LC) noradrenergic nuclei (22,23).…”

Measurement of Immediate‐Early Gene Activation‐ c‐fos and Beyond

“…It is generally held that c‐fos and its protein product c‐Fos are reliable markers for identifying activated cells and central nervous system circuits that respond to physiological [daily rhythm (12–15), sleep/wake cycle (16), oestrus (17, 18), mating (19–21), lactation (22–24)]; environmental (light noise (25), predator odour (26, 27)]; pharmacological (28) and various stress challenges (Table 1; see also below). It is important to bear in mind, however, that the lack of a Fos response does not necessarily preclude the involvement of a cell group in a functional circuit (29, 30).…”

“…sleep ⁄ wake cycle (16), oestrus (17,18), mating (19)(20)(21), lactation (22)(23)(24)]; environmental (light noise (25), predator odour (26,27)]; pharmacological (28) and various stress challenges (Table 1; see also below). It is important to bear in mind, however, that the lack of a Fos response does not necessarily preclude the involvement of a cell group in a functional circuit (29,30).…”

AMPA receptors in the medial amygdala are critical for establishing a neuroendocrine memory in the female rat

“…Increased norepinephrine release into the MePD was observed between 60 and 160 min after mating (Cameron et al. , 2004a), presumably from the activated ventral noradrenergic bundle following receipt of VCS (Cameron et al. , 2004b).…”