The neuropeptide, melanin concentrating hormone (MCH), and its G protein-coupled receptor, melanin concentrating hormone receptor 1 (Mchr1), are expressed centrally in adult rodents. MCH signaling has been implicated in diverse behaviors such as feeding, sleep, anxiety, as well as addiction and reward. While a model utilizing the Mchr1 promoter to drive constitutive expression of Cre recombinase (Mchr1-Cre) exists, there is a need for an inducible Mchr1-Cre to determine the roles for this signaling pathway in neural development and adult neuronal function. Here, we generated a BAC transgenic mouse where the Mchr1 promotor drives expression of tamoxifen inducible CreER recombinase. Many aspects of the Mchr1-Cre expression pattern are recapitulated by the Mchr1-CreER model, though there are also notable differences. Most strikingly, compared to the constitutive model, the new Mchr1-CreER model shows strong expression in adult animals in hypothalamic brain regions involved in feeding behavior but diminished expression in regions involved in reward, such as the nucleus accumbens. The inducible Mchr1-CreER allele will help reveal the potential for Mchr1 signaling to impact neural development and subsequent behavioral phenotypes, as well as contribute to the understanding of the MCH signaling pathway in terminally differentiated adult neurons and the diverse behaviors that it influences.

Primary cilia dysfunction has been associated with hyperphagia and obesity in both ciliopathy patients and mouse models of cilia perturbation. Neurons throughout the brain possess these solitary cellular appendages, including in the feeding centers of the hypothalamus. Several cell biology questions associated with primary neuronal cilia signaling are challenging to address in vivo . Here we utilize primary hypothalamic neuronal cultures to study ciliary signaling in relevant cell types. Importantly, these cultures contain neuronal populations critical for appetite and satiety such as pro-opiomelanocortin (POMC) and agouti related peptide (AgRP) expressing neurons and are thus useful for studying signaling involved in feeding behavior. Correspondingly, these cultured neurons also display electrophysiological activity and respond to both local and peripheral signals that act on the hypothalamus to influence feeding behaviors, such as leptin and melanin concentrating hormone (MCH). Interestingly, we found that cilia mediated hedgehog signaling, generally associated with developmental processes, can influence ciliary GPCR signaling (Mchr1) in terminally differentiated neurons. Specifically, pharmacological activation of the hedgehog-signaling pathway using the smoothened agonist, SAG, attenuated the ability of neurons to respond to ligands (MCH) of ciliary GPCRs. Understanding how the hedgehog pathway influences cilia GPCR signaling in terminally differentiated neurons could reveal the molecular mechanisms associated with clinical features of ciliopathies, such as hyperphagia-associated obesity.

Maintenance of homeostatic cerebrospinal fluid (CSF) secretion and absorption is essential for basic neurologic function. The choroid plexus epithelia, which is thought to produce the majority of the CSF, are among the most secretory of all epithelia. However, the control of this secretory process is poorly described. In diseased states such as hydrocephalus, where this homeostasis is disrupted, patients often experience symptoms such as cognitive impairment, motor/stability issues, and incontinence, among others. Current treatment for hydrocephalus is limited to surgically invasive shunting procedures which often fail and need revising – particularly in pediatric cases. In order to study the mechanism of this disease, a knock out mouse line of the Growth Arrest Specific 8 (Gas8) allele was generated. Loss of function of the Gas8 allele induces ciliopathy similar to Primary Ciliary Dyskinesia (PCD) in humans, with one of the symptoms being severe perinatal hydrocephalus. The disease progression in the mutant (−/−) mice is from postnatal day 0 (P0) to postnatal day 12–16 (P12–16), which makes this an excellent model to study pediatric/juvenile hydrocephalus. It is believed that one of the mechanisms of pediatric hydrocephalus is the overproduction of CSF by the choroid plexus (CP) epithelial cells that line the ventricles of the brain. The protein of interest to this research is the non‐specific cation channel, Transient Receptor Potential Vanilloid 4 (TRPV4), which has been shown to be activated by multiple stimuli including osmotic and pressure changes as well as by prostanoid metabolites. Activation of TRPV4 results in Ca2+ influx through the channel resulting in changes in intracellular signaling including the secondary activation of Ca2+‐stimulated ion transporters. Consistent with other studies, TRPV4 is localized to the apical membrane of the CP epithelial tissue in the Wild Type Gas8 mice. Preliminary data on the juvenile Gas8 mice indicate that TRPV4 is overexpressed in CP epithelia, ependymal cells and in the sub‐ventricular zone in the mutants as their hydrocephalus progresses as compared to the wild type (+/+) and heterozygous (+/−) animals. This suggests that antagonistic compounds of the TRPV4 channel have the potential to reduce hydrocephalus in the Gas8 model. Successfully targeting the molecular mechanisms for hydrocephalus in rodent models can provide a promising base for preclinical studies aimed at developing pharmaceutical agents to treat this disease.Support or Funding InformationFunding: Grants from the Hydrocephalus Association and the Department of Defense Office of the Congressionally Directed Medical Research Programs (CDMRP).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.