Generation and characterization of mice harboring a conditional CXCL12 allele.

The chemokine CXCL12 has important functions in immune and central nervous systems. Moreover, a global disruption of CXCL12 in mice results in perinatal lethality. To circumvent this impediment and provide a tool for analyzing CXCL12 functions in specific organ systems, we have generated a mouse line harboring a loxP-site flanked exon 2 of CXCL12. A germ line deleter, ß-actin::cre was used to remove a CXCL12 exon 2 and subsequently systemic CXCL12 exon 2 deficient embryos were generated. These mutant embryos showed a marked depletion of CXCL12 transcript. As expected from the global mutant phenotype, our mutants were also characterized by highly irregular cerebellar cytoarchitecture of the external granule layer as well as altered radial migration of midbrain dopaminergic neurons. Importantly, migration of the pontine grey nucleus (PGN) was derailed and remarkably resembled the global mutant phenotype of the CXCL12 receptor - CXCR4 in this system. Despite the fact that CXCL12 signaling can be mediated through receptors other than CXCR4, our results indicate a monogamous relationship between the CXCL12 ligand and CXCR4 receptor in controlling PGN migration. Our findings further expand on the understanding of CXCL12 function in PGN development. Moreover, phenotypic similarities between our mutants and mice harboring a global CXCL12 disruption support the validity of our line. Importantly, these results strongly suggest that our conditional CXCL12 line can be used as a powerful tool to manipulate CXCL12 signaling and function in vivo.

Stimulation of the hypothalamic ventromedial nuclei by pituitary adenylate cyclase-activating polypeptide induces hypophagia and thermogenesis.

Numerous studies have demonstrated that the hypothalamic ventromedial nuclei (VMN) regulate energy homeostasis by integrating and utilizing behavioral and metabolic mechanisms. The VMN heavily express pituitary adenylate cyclase-activating polypeptide (PACAP) type I receptors (PAC1R). Despite the receptor distribution, most PACAP experiments investigating affects on feeding have focused on intracerebroventricular administration or global knockout mice. To identify the specific contribution of PACAP signaling in the VMN, we injected PACAP directly into the VMN and measured feeding behavior and indices of energy expenditure. Following an acute injection of PACAP, nocturnal food intake was significantly reduced for 6 h after injections without evidence of malaise. In addition, PACAP-induced suppression of feeding also occurred following an overnight fast and could be blocked by a specific PAC1R antagonist. Metabolically, VMN-specific injections of PACAP significantly increased both core body temperature and spontaneous locomotor activity with a concurrent increase in brown adipose uncoupling protein 1 mRNA expression. To determine which signaling pathways were responsive to PACAP administration into the VMN, we measured mRNA expression of well-characterized hypothalamic neuropeptide regulators of feeding. One hour after PACAP administration, expression of pro-opiomelanocortin mRNA was significantly increased in the arcuate nuclei (ARC), with no changes in neuropeptide Y and agouti-related polypeptide mRNA levels. This suggests that PAC1R expressing VMN neurons projecting to pro-opiomelanocortin neurons contribute to hypophagia by involving melanocortin signaling. While the VMN also abundantly express PACAP protein, the present study demonstrates that PACAP input to the VMN can influence the control of energy homeostasis.

Serotonin mediated changes in corticotropin releasing factor mRNA expression and feeding behavior isolated to the hypothalamic paraventricular nuclei.

Fenfluramine reduces hunger and promotes body weight loss by increasing central serotonin (5-HT) signaling. More recently, neuropeptides have been linked to the regulation of feeding behavior, metabolism and body weight. To examine possible interactions between 5-HT and neuropeptides in appetite control, fenfluramine (200 nmol/0.5 µl/side) was administered directly into the hypothalamic paraventricular nuclei (PVN) of male rats. Bilateral fenfluramine produced significant hypophagia and increased expression of PVN corticotropin releasing factor (CRF) mRNA and neuropeptide Y (NPY) mRNA in the arcuate nucleus within the first hour after drug administration. Fenfluramine's effects on feeding behavior and mRNA expression were blocked by PVN injections of a 5-HT(1-2) receptor antagonist, metergoline (15 nmol/0.5 µl/side). These data suggest that 5-HT neurons targeting hypothalamic paraventricular CRF neurons may participate in an appetite control circuit for reducing food intake.