An additional, but not mutually exclusive, possibility is that neurogenesis is affected indirectly through adrenal steroid actions on granule cell afferents. Lesion of the entorhinal cortex, one of the main afferent populations to the dentate gyrus, stimulates the production of new neurons (Cameron et al., 1995). Likewise, blockade of NMDA receptors, glutamate receptors involved in perforant path-granule cell synapses, increases adult neurogenesis (Cameron et al., 1995; Maekawa et al., 2009). Moreover, manipulation of cholinergic inputs, via either neurotoxin or pharmacological intervention, alters the rate of adult neurogenesis (Kotani et al., 2006; Frechette et al., 2009). Although not directly explored in the context of adrenal steroids, these afferent populations contain adrenal steroid receptors and may be one of the intermediate steps between alterations in hormone levels and changes in the production of new neurons.
