Neonatal maternal separation up-regulates protein signalling for cell survival in rat hypothalamus

Abstract

We have previously reported that in response to early life stress, such as maternal hyperthyroidism and maternal separation (MS), the rat hypothalamic vasopressinergic system becomes up-regulated, showing enlarged nuclear volume and cell number, with stress hyperresponsivity and high anxiety during adulthood. The detailed signaling pathways involving cell death/survival, modified by adverse experiences in this developmental window remains unknown. Here, we report the effects of MS on cellular density and time-dependent fluctuations of the expression of pro- and anti-apoptotic factors during the development of the hypothalamus. Neonatal male rats were exposed to 3 h-daily MS from postnatal days 2 to 15 (PND 2-15). Cellular density was assessed in the hypothalamus at PND 21 using methylene blue staining, and neuronal nuclear specific protein and glial fibrillary acidic protein immunostaining at PND 36. Expression of factors related to apoptosis and cell survival in the hypothalamus was examined at PND 1, 3, 6, 9, 12, 15, 20 and 43 by Western blot. Rats subjected to MS exhibited greater cell-density and increased neuronal density in all hypothalamic regions assessed. The time course of protein expression in the postnatal brain showed: (1) decreased expression of active caspase 3; (2) increased Bcl-2/Bax ratio; (3) increased activation of ERK1/2, Akt and inactivation of Bad; PND 15 and PND 20 were the most prominent time-points. These data indicate that MS can induce hypothalamic structural reorganization by promoting survival, suppressing cell death pathways, increasing cellular density which may alter the contribution of these modified regions to homeostasis.

Modulation of the Hypothalamic-Pituitary-Adrenal Axis by Early Life Stress Exposure

“…Understandably, the exposure to a novel environment might cause additional stress in either the dam or pups, causing variable stress levels between studies. Amongst ESD studies similar variations arise, as they either allow the mother to keep part of her litter by her side (Barna et al, 2003) or separate her from all her pups (Irles et al, 2014), which is evidently more stressful. Potentially depending on the amount of stress experienced by the dam, temporary compensatory increases in nurturing behavior following the reunion with her pups are also observed (Macrì et al, 2008), which might modulate the impact of the stressful separation on the offspring.…”

“…Although MS was not found to affect local neuronal density during the SHRP, it increased neuronal density afterwards, which was joined by decreased levels of apoptosis-stimulating proteins and enzymes, whilst cell survival-stimulating protein levels were increased (Irles et al, 2014). These data indicate that ELS influences the structural reorganization of the PVN throughout development, and thereby likely alters its role in HPA-axis regulation.…”

Stress and the social brain: behavioural effects and neurobiological mechanisms

“…However, neural plasticity markers, neuron numbers and basal metabolic activities were not altered in the limbic brain after early social subjugation in rats and hamsters [104][105][106] , suggesting that structural changes are minimal following this stressor. Interestingly, early deprivation increased neuron numbers and decreased apoptosis throughout the hypothalamus 107 , whereas it had mixed effects in different hippocampal fields 108 . Taking into consideration the important role of the hypothalamus in aggression control 81,109 , this suggests that adult consequences of early stressors may be attributed to both structural brain deficits and structural "gains".…”

Regulating effect of TongXie-YaoFang on colonic epithelial secretion via Cl- and HCO3- channel

“…On days 50-59, NMS + RS rats were placed in transparent plastic restraint cylinders (4 cm × 4 cm × 18 cm), in which they could move forward and backward but could not turn around[14]. The rats remained in the restraint cylinders for 3 h, with access to food and water ad libitum, in the morning and in the afternoon of each day.…”