In the following two sentences the authors acknowledge an apparent paradox, where an increased GC-secretion following handling has two (opposing) effects on hippocampal neuron number.  One such effect is an increased sensitization of the hippocampus to GCs, due to the presence of excess GC.  The second effect is a decreased lifetime GC-secretion due to a sensitized negative-feedback mechanism.  Although the second effect is indirect as opposed to direct, it seems that the increased negative feedback associated with neonatal handling has the greater effect, and thus the senescent loss of hippocampal neurons is lessened in handled animals.

We proposed to Dr. Sapolsky the idea that adult hippocampal neurogenesis might in fact account for the above-explained paradox, rather than it simply being an uneven balance between two opposing trends.  Seeing as hippocampal neurons are continually produced throughout one's life, the presence of new neurons could actually account for the diminished rate of hippocampal neuron loss seen in adulthood.  Dr. Sapolsky agreed that had they known of adult hippocampal neurogenesis at the time of the study, the possibility would have been explored.

Click here to watch Dr. Sapolsky address the possibility of adult neurogenesis playing a role in the effect of GCs on hippocampal neuron loss.  (26:10-27:01)