Polyethylene glycol-induced hypovolemia affects the expression of MCH mRNA, but not dynorphin or secretogranin II mRNAs, in the rat lateral hypothalamus

Two prominent neuron populations of the rat lateral hypothalamus express genes encoding respectively the prepromelanin-concentrating hormone (MCH) or dynorphin (DYN) and secretogranin II (SGII). Their roles remain hypothetical in mammals. In the present study, we examined the changes in MCH, DYN and SGII gene expression in dehydrated rats compared to controls. Dehydration was obtained by subcutaneous injection of polyethylene glycol (PEG) resulting in a large reduction of the extracellular fluid volume. Using competitive semi-quantitative RT-PCR and in situ hybridization methods, PEG-injected animals showed a significant increase of MCH mRNA level but no variation of DYN and SGII mRNA levels. These results confirm previous observations suggesting that intra- and extracellular dehydration challenges affect different regulation circuits; they indicate that both neuron populations could be involved in the maintenance of body fluid homeostasis, directly, or indirectly, as integrators of various information leading to goal-oriented behaviour.