GABA-B-mediated Leptin's Effect On Food Intake In Fasted Mice

Feeding behavior is one of the most basic physiological activities of humans and animals.Overeating and energy metabolism imbalance can induce obesity and other metabolic diseases.Abnormal central regulation of feeding behavior can lead to eating disorders,including neurological bulimia and anorexia,which could bring serious harm to patients and their family.Leptin,secreted by white fat cells,can transport across the blood-brain barrier and reach the “feeding center” of hypothalamus to depress appetite,reduce food intake and regulate energy metabolism of the organism.GABA is one of the most important inhibitory neurotransmitters in the central nervous system.Recently,it was found that GABA could regulate feeding behavior via activating the GABA-A and GABA-B receptor.There's lack of studies which focus on the GABA-mediated leptin regulation in feeding behaviors.Objective:Recently,a large number of neurobiological and medical studies focused on the signal pathways and regulatory molecules involved in feeding behavior regulation.In this research,we used fasting-induced overeat mice and tend to investigate the mechanisms of leptin's feeding regulation and the role of GABA played in this regulation,which provide theoretical basis for the prevention and treatment of neurological diseases and obesity.Methods:40 healthy ICR male mice were randomly divided into 4 groups,including control group,fasting group,leptin group,leptin +baclofen group and baclofen group(n=8).Except the control group mice,the left mice were fasted 16 h.Then,the baclofen group and leptin+baclofen group mice received 8mg/kg baclofen intraperitoneally injection.30 min later,the leptin group and leptin+baclofen group mice received 1mg/kg leptin intraperitoneally injection.After administration,the cumulative food intakes were recorded at 0.5,1 and 1.5h.5mice of each group were randomly selected and decapitated.The trunk blood was collected in plastic tubes and for serum GABA,leptin,insulin and POMC levels analyses.The hypothalamus was quickly removed from the brain and we used western blot analysis to test the GAD67,TH,POMC and STAT3 expression in hypothalamus.The left 3mice of each group were anesthetized and then decapitated.Brains were removed to make frozen sections.The c-Fos expression of DM,VMH,PALM,PAMM and AHP in hypothalamus was tested via immunohistochemistry and the locations of nucleus in hypothalamus were confirmed by staining and a mouse brain atlas.Results:1.Food deprivation significantly increased the food intake during 0-0.5h.The cumulative food intakes of baclofen group were lower than the fasting group.During the 0.5-1h,the cumulative food intakes of leptin group were lower than that of fasting group.Administration of baclofen can reverse the inhibitory effects of leptin on food intake.Also,it was detected that the cumulative food intakes of baclofen group were lower than the fasting group.2.The c-Fos expression of LH,DM,VMH,PALM,PAMM and AHP of hypothalamus in fasting group were significantly enhanced than that of control group.3.The c-Fos expression of LH,DM,PAMM and AHP of hypothalamus in leptin group were reduced than that of fasting group.Administration of baclofen to fasted mice significantly reduced the c-Fos expression in DM,VMH,PAMM and AHP of hypothalamus.baclofen can reverse the inhibitory effects of leptin on c-Fos expression of PAMM in fasted mice.4.The GAD67 expression of hypothalamus in fasted mice was significantly increased compared to the non-fated mice.Administration of leptin inhibited the GAD67 expression of the fasted mice.Furthermore,the GAD67 expression was also reduced in fasted mice treated with baclofen.5.The TH expression of hypothalamus in fasted mice was significantly decreased compared to the non-fated mice.6.The STAT3 expression of hypothalamus in fasted mice was significantly increased compared to the non-fated mice.7.The serum insulin levels of baclofen group mice were significant higher than the fasting group.The serum POMC levels of baclofen group mice were enhanced compared to the fasting group mice.Food deprivation significantly promoted the serum leptin levels compared to the non-fasted mice.Conclusion:1.Leptin can suppress the fasting-induced overfeeding in mice.Administration of baclofen can reverse the inhibitory effects of leptin on food intake.2.baclofen's effect on leptin-dependent feeding regulation might relate to the c-Fos expression in PAMM of hypothalamus.3.Leptin might inhibit the fasting-induced overfeeding via inhibiting the GAD67 and STAT3 expression in hypothalamus.