Maternal separation changes maternal care, anxiety‐like behaviour and expression of paraventricular oxytocin and corticotrophin‐releasing factor immunoreactivity in lactating rats

• Published in: Journal of neuroendocrinology Vol. 32; no. 6; pp. e12861 - n/a
• Main Authors: Baracz, Sarah J., Everett, Nicholas A., Robinson, Katherine J., Campbell, Gemma R., Cornish, Jennifer L.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.06.2020
• Subjects: Animal behavior; Animals; Animals, Newborn; Anxiety; Anxiety - etiology; Anxiety - metabolism; Anxiety - pathology; Anxiety - psychology; Behavior, Animal - physiology; corticotrophin‐releasing factor; Corticotropin-Releasing Hormone - metabolism; Female; Hypothalamus; Immunofluorescence; Immunoreactivity; Lactation; Lactation - metabolism; maternal anxiety; Maternal behavior; Maternal Behavior - physiology; Maternal Behavior - psychology; maternal care; Maternal Deprivation; maternal separation; Neuroendocrine system; Neuropeptides; Oxytocin; Oxytocin - metabolism; Paraventricular Hypothalamic Nucleus - metabolism; Paraventricular nucleus; Postpartum; Rats; Rats, Long-Evans; maternal separation; corticotrophin-releasing factor; oxytocin; maternal care; maternal anxiety
• ISSN: 0953-8194; 1365-2826; 1365-2826
• DOI: 10.1111/jne.12861

The early postnatal period is a time of tremendous change for the dam and her offspring. During this time, environmental insults such as repeated stress exposure can have detrimental effects. In research that has focused on the effect of postnatal stress exposure on the dams, conflicting changes in maternal care and anxiety‐like behaviour have been reported. Additionally, changes to hypothalamic neuropeptides that are crucially involved in the transition to motherhood and stress regulation, namely oxytocin and corticotrophin‐releasing factor (CRF), have not been examined. Accordingly, the present study aimed to determine (i) whether repeated postpartum stress increases engagement in maternal care behaviours and anxiety‐like behaviour and (ii) whether these behavioural changes correspond with changes to CRF‐ or oxytocin‐immunoreactive (‐IR) cells in the paraventricular nucleus (PVN) of the hypothalamus. A non‐lactating group was also included to control for the effects of lactation on anxiety and the hypothalamic neuroendocrine system. Following the birth of their litters, Long‐Evans dams were separated from their pups from postnatal day (PND) 1 to PND21 for either 15 minutes (maternal separation [MS]15) or 6 hours (MS360). Maternal behaviours were recorded for 30 minutes on select PNDs following the separation. On PND22, dams were exposed to the elevated plus maze, brains were collected, and immunofluorescence analysis of PVN oxytocin‐ and CRF‐IR cells was conducted. Our findings demonstrate that prolonged maternal separation altered typical maternal behaviours and reduced anxiety relative to MS15 dams. At the cellular level, oxytocin‐IR cells in the caudal PVN were reduced in MS360 dams to a level similar to that in non‐lactating controls, and PVN CRF‐IR cells were reduced relative to both MS15 and non‐lactating controls. Taken together, these data reveal the behavioural and neuronal changes that occur in the mother dam following repeated postnatal stress exposure. Little of the early life stress literature has focused on how the dams are detrimentally impacted by postnatal stress exposure. We sought to investigate whether repeated maternal separation stress impacts maternal care, anxiety‐like behaviour and paraventricular oxytocin and corticotropin‐releasing factor immunoreactivity in lactating dams. We showed that dams repeatedly separated from their litters engaged in more nursing behaviours and less self‐care behaviours, displayed reduced maternal motivation and anxiety‐like behaviour, and had fewer oxytocin immunoreactive cells in the caudal paraventricular nucleus and fewer paraventricular corticotropin‐releasing factor cells relative to the briefly separated controls.