Ras-GRF1 in CRF Cells Controls the Early Adolescent Female Response to Repeated Stress

Ras-GRF1 (GRF1) is a calcium-stimulated guanine-nucleotide exchange factor that activates Ras and Rac GTPases. In hippocampal neurons, it mediates the action of NMDA and calcium-permeable AMPA glutamate receptors on specific forms of synaptic plasticity, learning, and memory in both male and female mice. Recently, we showed that GRF1 also regulates the HPA axis response to restraint stress, but only in female mice before puberty. In particular, we found that after exposure to 7-days of restraint-stress (7DRS) (30 min/day) elevation of serum CORT levels are suppressed in early adolescent (EA) female, but not EA male or adult female GRF1 knockdown mice. Here, we show that this phenotype is due, at least in part, to the loss of GRF1 expression in CRF cells of the paraventricular nucleus of the hypothalamus, as GRF1 knockdown specifically in these cells also reduces serum CORT response to 7DRS in EA females, but not EA males or adult females. Moreover, it reduces females CORT levels to those to found in comparably stressed control male mice. GRF1 knockdown in CRF cells also blocks the anxiolytic phenotype normally found in EA females 24 hrs after 7DRS. Interestingly, loss of GRF1 in these cells has no effect after only 3 exposures to restraint stress, revealing a role for GRF1 in repeated stress-induced CRF cell plasticity that appears to be specific to EA female mice. Overall, these findings indicate that GRF1 in CRF cells makes a key contribution to the distinct response early-adolescent female display to repeated stress.