Photoperiod and Gonadal Feedback on CCK in Sticklebacks
This study investigates cholecystokinin (CCK) within the brain-pituitary-gonadal (BPG) axis of the three-spined stickleback. By comparing castrated and sham-operated males under varying photoperiods, results showed that hypothalamic ccka and cckb expressions are sensitive to gonadal hormones. Specifically, castration upregulated both genes under inhibitory short days, paralleling pituitary fshβ and suggesting negative feedback. Conversely, a decrease in ccka under stimulatory long days suggests a shift toward positive feedback required to maintain reproductive status. While these findings support CCK's role in feedback regulation, its inconsistent correlation with gonadotropin fluctuations indicates that photoperiodic maturation is likely governed by additional factors beyond the CCK system.
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