ICV vs. VMH injection of leptin: comparative effects on hypothalamic gene expression

Leptin regulates feeding behavior and body weight by binding to its receptors localized in specific areas of the hypothalamus. Leptin injected twice daily for 4 days either into the right ventromedial hypothalamus (VMH) or into the right lateral cerebral ventricle (ICV) and using Real-Time Taqman RT-PCR, mRNA expression levels of selected genes in the arcuate nucleus-median eminence (ARC-ME) complex were quantitatively measured. Expression of selected genes from the ipsi- vs. contralateral VMH areas in rats injected with leptin into the VMH was also compared. VMH injections of leptin increased ARC-ME mRNAs of proopiomelanocortin (POMC), 27.3% (p<0.05); gamma-aminobutyric acid A receptor (GABRD), 89.3% (p<0.01); and thyrotropin-releasing hormone (TRH), 57.7% (p<0.01); and decreased janus kinase 2 (JAK2), 44.4% (p<0.001); suppressor of cytokine signaling 3 (SOCS3), 86.6% (p<0.001); signal transducer and activator of transcription 3 (STAT3), 46.8% (p<0.01); tyrosine hydroxylase (TH), 51.1% (p<0.001); prostaglandin E synthase (PTGES), 96.5% (p<0.001); tumor necrosis factor-alpha (TNF-alpha), 47% (p<0.01); and secretin, 55.4% (p<0.001). Only GABRD, 76.6% (p<0.01) and SCT, 64.9% (p<0.01) were up-regulated in the hypothalamic ARC-ME of rats with ICV leptin injections. VMH injections of leptin induced identical reductions in expression levels of CART, SOCS3, PTGES, and TNF-alpha in both VMH areas; except TH mRNA, whose expression was lowered ipsilaterally. Food intake, body and fat pad weights and serum insulin and leptin were also decreased in rats given leptin through VMH. This study suggests that leptin either unilateral exposure through VMH or bilateral exposure through ICV injections induces divergent ARC-ME gene profiles.