PHOTOPERIOD AFFECTS THE EXPRESSION OF NEURAL CELL-ADHESION MOLECULE AND POLYSIALIC ACID IN THE HYPOTHALAMUS OF THE SIBERIAN HAMSTER

Immunohistochemical and immunoblot procedures were used to examine the effects of inhibitory short day (SD) photoperiod on the expression of neural cell adhesion molecule (NCAM) and its polysialylated form (PSA -NCAM) in the hypothalamus and preoptic area (POA) of the adult male S iberian hamster. In animals that had undergone SD-induced gonadal regr ession, immunoblot analyses revealed significant reductions in the con tent of immunoreactive PSA in anterior hypothalamic (AH) and mediobasa l hypothalamic (MBH) regions. These changes were accompanied by increa sed contents of the 180 kDa NCAM isoform in the POA and AH, and decrea sed content in the MBH. The 140 kDa NCAM isoform also was elevated in the AH. Light microscopic analysis revealed a marked reduction in the density of NCAM-immunoreactive tanycyte-like processes in the MBH of a nimals exposed to SD. This effect was not blocked by castration, indic ating that this may be a primary (sex steroid-independent) effect of a ltered photoperiod in the hypothalamus. Also, photoperiod-induced alte rations in NCAM expression were not evident in non-responsive hamsters that maintained active testes under SD exposure. Collectively, these results are evidence that seasonal changes in photoperiod affect the e xpression of NCAM and PSA in the hypothalamus. Such changes could help promote plastic morphological rearrangements related to the regulatio n of seasonal reproductive and/or metabolic cycles.