CRHR1 and Anxiety: Anxiety may be modulated by photoperiod-mediated changes in HPA axis activity: glucocorticoid metabolites are lower in SD-housed voles and neural receptor densities of corticotropin releasing factor receptors (CRF1 and CRF2) change with day length in opposing directions, consistent with seasonal decline in anxiety (Beery et al., 2014; Anacker et al., 2016b).