In the paraventricular nucleus (PVN) of the hypothalamus, corticosteroids reduce CRH expression, but in some extrahypothalamic sites, such as the amygdala, they produce opposite effects 29, 46–49. We find that plasma levels of ACTH are increased, whereas, in CSF, levels of CRH are decreased. The lower CSF CRH levels can be accounted for based on the likelihood of a low or nonexistent contribution of PVN-median eminence CRH to the CSF pool relative to other sources, such as the amygdala. 33 Our finding is consistent with what have been previously reported in human and non-human primates, which indicate opposing rhythms of CSF levels of CRH and HPA axis output. 33,43 In rodents, some exploratory/novelty-seeking strains have higher levels of Crh expression in the hypothalamus, but lower levels in the amygdala 50 and others find that bold/aggressive rat strains have higher baseline levels of ACTH 10. We examined behavioral dimensions during infancy and found that carriers of the -2232 G allele were more “Exploratory/bold,” exhibiting relatively high levels of environmental exploration and aggression. We also employed a challenge that has been developed
