An examination of avian hippocampal neurogenesis in relationship to photoperiod

More neurons are recruited into the hippocampus of adult black-capped chickadees in the fall than at other times of year. To determine whether declining photoperiod and photorefractoriness are cues stimulating this neuronal recruitment; we examined three groups of chickadees receiving bromodeoxyuridine injections 10 days before being killed: one group was photostimulated with long days (15L), a second group was held on 15L until photorefractory and another group was held on 15L until photorefractory, then moved to short days (8L). Measures of neurogenesis revealed no significant differences in hippocampal neuronal recruitment. However, neuronal recruitment was increased in the hyperpallium apicale of photostimulated birds. These results suggest that declining photoperiod per se is not a major factor regulating enhanced neuronal recruitment to the hippocampus in the fall. (c) Lippincott Williams & Wilkins.