EFFECT OF TEMPERATURE AND PHOTOPERIOD ON PROLACTIN TRANSCRIPTION IN CYPRINUS-CARPIO

We studied the effect of temperature and photoperiod on prolactin (PRL ) gene expression in the pituitaries of summer-aclimatized carp (C. ca rpio). To assess the level of PRL gene transcription, we used a 24mer synthetic oligonucleotide probe derived from the known carp PRL gene s equence. Employing in situ hybridization assays, we observed high expr ession of PRL mRNA in the rostral pars distalis of summer-acclimatized carp in contrast to the almost negligible PRL transcription which occ urs in the winter-acclimatized fish. When experimental combinations of long and short photoperiods with 10 degrees C and 20 degrees C enviro nmental temperatures were studied, only a short photoperiod (8L-16D) i n summer-acclimatized carp acclimated to a winter temperature (10 degr ees C) markedly depressed PRL gene expression. Our observations indica te that photoperiod constitutes a particularly relevant modulator in t he neuroendocrine cascade that activates PRL transcription in the carp .