Fos expression in hypocretinergic neurons in C57B1/6 male and female mice after long-term consumption of high fat diet.

Objective: It is generally known that hypocretin (Hcrt) neurons in lateral hypothalamus (LH) are involved in feeding behaviour. The aim of this study was to reveal the activity response of Hcrt neurons, as measured by Fos protein incidence, to prolonged high fat (HF) diet in the LH of both genders of C57B1/6 mice.

Methods: Standard (St) and high fat (HF) diets were available to mice for 16 weeks and thereafter the animals were perfused transcardially with fixative. Then the brains were removed, soaked with 15 % sucrose in 0.1 M phosphate buffer (PB), and cryo-sectioned throughout the hypothalamus into 35 microm thick coronal sections. Fos/Hcrt co-localizations were processed by employing avidin-biotin-peroxidase (ABC) complex and diaminobenzidine chromogen for Hcrt labeling. Fos immunoproduct was intensified by nickel chloride as a black color inducer. Evaluation of the incidence of Fos/Hcrt co-labeled perikarya was performed using a computerized Leica light microscopy.

Results: The effect of of mice gender, applied diet, and gender plus applied diet on the activation of Hcrt neurons was found. Turkey s test revealed significant (p<0.05) rise in Fos labeled Hcrt neurons in male vs. female mice after consumption of both types of diets: St (44.64 +/- 2.28 % vs. 1.47 +/- 0.195 %, resp.) and HF (44.15 +/- 3.77 % vs. 24.32 +/- 0.7 %, resp.). This showed that HF diet significantly elevated the number of activated Hcrt neurons only in female mice (24.32 +/- 0.7 % in HF fed vs. 1.47 +/- 0.195 % in St fed, p<0.05). The body weight and accumulation of body fat in animals (body fat weight expressed as % of body weight) were influenced by gender and applied diet, although the body fat weight was influenced by HF diet (more noticeably in females).

Conclusion: The data indicated a positive correlation between body weight, fat gain, and Hcrt activities in females but not in males, thus accentuating the importance of the gender impact.