Epigenetic regulation of the hypothalamic-pituitary-adrenal stress axis and its effects on social behaviour
Activity of the hypothalamic-pituitary-adrenal (HPA) stress axis is influenced thru enhancement of the corpus amygdala and inhibition thru the hippocampus. Glucocorticoid receptor (GCR) density in the hippocampus is likely to affect its inhibitory effect on this system. Epigenetic input is known to impact regulation of GCR expression. Factors described include down-regulation of GCR expression by enhanced methylation of GRexon1;7promotorbloc as a consequence of increased methionine ingestion. Psychosocial factors like licking and grooming enhance GCR expression via increased serotonin and subsequently increased NGF levels binding on GRexon1;7promotorbloc.GCR density and thereby activity of the stress axis and with its characteristics of the individual are determined in the childhood but stay variable during adolescence and adulthood. This model has been evaluated to establish a new theory of active social domestication from the wolf to the dog, considering that the change of the HPA-axis via epigenetic induced GCR expression is the main aspect for decrease the flightdistance of a wild wolf to domesticated dog. In this way active social interaction between human and wolf resp. dog grows, influenced due to the evolutionary continuity of same neural structures. So even human social learning ability could be improved. It may, however, also provide a new insight in the biochemical mechanisms of known phenomenons like infantile imprinting and psychotherapy exspecially concerning post-traumtic syndrome.