Seasonal morphological changes in the neuro-glial interaction between gonadotropin-releasing hormone nerve terminals and glial endfeet in Japanese quail

In a previous study we showed that photoperiodically generated T-3 in the hypothalamus is critical for the photoperiodic response of gonads in Japanese quail. The expression of thyroid hormone receptors in the median eminence (ME) suggested that photoperiodically generated T-3 acts on the ME. Because thyroid hormone is known to play a critical role in the development and plasticity of the central nervous system, in the present study we have examined ultrastructure of the ME in Japanese quail kept in short-day and long-day environments. Immunoelectron microscopy revealed that GnRH nerve terminals are in close proximity to the basal lamina under long-day conditions, and conventional transmission electron microscopy demonstrated the encasement of the terminals by the endfeet of glia under short-day conditions. These morphological changes may regulate photoperiodic GnRH secretion.