Maternal Care and Stress Reactivity in Rats System theories consider the interaction of biology, environment and behavior. (Sigelman & Rider, 2009, p. 53; Woolf, 1998) Corticotropin-releasing hormone (CRH) stimulates ACTH release which in turn stimulates secretion of glucocorticoids which feedback to inhibit ACTH. ACTH is released in response to stress. A glucocorticoid is a stress hormone which stimulates the body’s response to the increased metabolic demands of stress. GABA inhibits the effect of acetylcholine (a cholinergic agonist) on CRH release. (Cecil, 1927/1992) A rat mother’s behavior of frequently licking and grooming her pups produces offspring that show milder hypothalamic-pituitary-adrenal (HPA) response to stress. Increased maternal care affects the development of the central nucleus of the amygdala locus coeruleus, resulting in less corticotropin-releasing factor (CRF) gene expression. Decreased CRF mRNA expression and CFR peptide content in the locus coeruleus means less ACTH which is necessary in the response to stress. (Meaney, 2001) Offspring of mothers giving high levels of care show increased levels of mRNA for ∂1 and ∂2 subunits of the GABA/CBZ receptor. These subunits provide affinity for GABA. Offspring mothers giving low levels of care show increase levels of mRNA for α3 and α4 subunits which cause a decreased affinity for GABA. Increased affinity for GABA increases inhibition of CRH release thus dampening the stress response. The reverse is true for decreased affinity. (Meaney, 2001) If offspring are separated from their mothers for longer than in normal mother-pup bonding, for example if the nest is far from food or water sources, they show an increased response to stress as seen in offspring receiving low levels of care. Separation of offspring causes methylation (deactivation) of the glucocorticoid receptor gene thus less glucocorticoid binding, resulting in more circulating glucocorticoid, increasing the stress response. (Meaney, 2001) In conclusion we see the impact of maternal care (environmental) influence on gene expression (biology) and resulting behavior. It is important to appreciate our role of how we interact with our environment and its consequences on development. References 1) Cecil, R. L. (1992). Neuroendocrine regulation and its disorders. In J. B. Wyngaarden, L. H. Smith, & J. C. Bennett (Eds.), Textbook of medicine (19th ed., Vol. 2, pp. 1215-1224). Philadelphia: W. B. Saunders Company. (Original work published 1927) 2) Meaney, M. J. (2001). Maternal care, gene expression and the transmission of individual differences in stress reactivity across generations. Annual Review of Neuroscience, 24(1), 1161-1192. 3) Sigelman, C. K. & Rider, E. A. (2009). Life-span human development (7th ed.) Belmont, CA: Wadsworth Cengage Learning
Posted on: Wed, 12 Jun 2013 21:16:52 +0000
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