Decrease of food intake by MC4-R agonist MTII in Siberian hamsters in long and short photoperiods

Area of Science:

• Neuroendocrinology
• Seasonal biology
• Behavioral neuroscience

Background:

• The Siberian hamster exhibits significant seasonal changes in food intake and body weight, particularly in response to photoperiod.
• The hypothalamic melanocortin system is implicated in appetite regulation.

Purpose of the Study:

• To investigate the role of the hypothalamic melanocortin system in regulating food intake in Siberian hamsters under different photoperiod conditions.
• To determine if the melanocortin system's sensitivity changes between long photoperiod (obese) and short photoperiod (lean) states.

Main Methods:

• Intracerebroventricular injections of melanotan II (MTII) or vehicle were administered to male Siberian hamsters.
• Food intake and body weight were monitored in hamsters housed in long photoperiod (LP) and short photoperiod (SP) conditions.
• Dose-response effects of MTII on food intake were assessed.

Main Results:

• Melanotan II significantly reduced food intake in both LP and SP hamsters.
• No significant differences in MTII efficacy or sensitivity were observed between LP and SP states.
• MTII increased grooming behavior in both photoperiod conditions.

Conclusions:

• The melanocortin system acts as a potent regulator of short-term food intake.
• The findings do not support the hypothesis that alterations in the melanocortin pathway mediate the long-term seasonal reduction in food intake in Siberian hamsters.
• Seasonal changes in feeding behavior may involve other regulatory mechanisms beyond the melanocortin system.