Female rats are only aggressive towards intruders during lactation. The complex neuroendocrine mechanisms controlling this behavioural switch require elucidation. Here we sought to identify the brain regions involved using immunohistochemistry for the immediate early gene, c-fos, as an indicator of neuronal activation. Lactating, Sprague-Dawley residents (250-300g) with pups (lactation day 4-6) were exposed for 30 min to a conspecific female intruder (weight matched; n=8) or left unchallenged (control; n=7; cage disturbance controlled for) and behavioural measurements were recorded. The rats were then left undisturbed for a further 60 min before being deeply anaesthetized (Pentobarbitone, Sagatal, 50mg/kg i.p.) and then transcardially perfused with 4% paraformaldehyde. Brains were removed and coronal, free-floating sections were cut at 52 μm and processed for Fos immunohistochemistry. Intruders elicited aggressive behaviour in all residents. In these aggressive rats, the numbers of Fos-immunoreactive cell nuclei per section (mean±SEM) were significantly higher in the lateral septal nucleus (228.3±10.2 vs. 163.6±19.2), bed nucleus of the stria terminalis (BnST; 70.6±6.5 vs. 40.7±9.8), supraoptic nucleus (36.1±8.9 vs. 9.3±2.2), parvocellular paraventricular nucleus (pPVN; 59.7±10.2 vs. 26.2±4.2) amygdala (medial amygdala, 83.7±10.4 vs. 46.3±9.8; central amygdala, 63.8±11.1 vs. 32.6±7.5; cortical amygdala, 40.9±4.2 vs. 27.7±3.3) and ventromedial hypothalamus (31.2±3.1 vs. 20.3±1.6), as compared to controls (Student’s t test, P<0.05). Double immunocytochemistry revealed activation of corticotropin-releasing factor (CRF) immunoreactive neurones (double-labelled cells per section; mean±SEM; Student’s t test, P<0.05) in the central amygdala (8.07±1.49 vs. 2.14±0.46) and BnST (12.86±2.82 vs. 4.64±1.27). There was no significant increase in CRF cell activation within the pPVN (7.61±2.33 vs. 3.11±0.60). In the supraoptic and paraventricular nuclei, both vasopressin and oxytocin neurones were double-immunostained for Fos (Student’s t test; P<0.05). Thus, we have identified several populations of neurones, including those in the limbic system, which appear to be involved in maternal aggression. Moreover the present results provide evidence for the participation of the central CRF, oxytocin and vasopressin systems in the regulation of maternal aggressive behaviour in the rat.
|Journal||Proceedings of The Physiological Society|
|Publication status||Published - 2007|