Endocrine Abstracts

Glucagon like peptide-1 (GLP-1) is derived from selective cleavage of the preproglucagon (PPG) molecule synthesised in intestinal L-cells. The physiological action of GLP-1 is most commonly recognised as a peripherally released incretin, but a subset of neurons in the lower brainstem, the PPG neurons, also express GLP-1. The majority of PPG neuronal cell bodies are located in the nucleus of the solitary tract and their axons project to numerous sites throughout the CNS. Many of these are located in regions of the forebrain associated with food intake. We have combined the use of a CRE recombinase-dependent adeno-associated virus, a transgenic mouse line, which expresses tdRFP and CRE under control of the PPG promoter and precise stereotaxic injection to target these neurons using optogenetics. We demonstrate successful and high-level expression of Channelrhodopsin2-eYFP (ChR2) selectively in tdRFP expressing PPG neurons located in the caudal brain stem but also in axons projecting from these neurons to the forebrain. Electrical activity of PPG neurons in acute slices, expressing ChR2, was analysed with whole-cell patch-clamp recordings. In current clamp, laser light stimuli at 455 nm of 20 ms duration reliably elicited action potentials in PPG neurons, with shorter light pulses (10–2 ms) causing smaller depolarisations and decreased probability of eliciting action potentials. In voltage clamp at a holding potential of −60 mV, inward currents of ~ 70 pA amplitude were elicited by light pulses of 10 ms or longer and were sustained for the duration of the light pulse. Shorter light pulses did not reach full amplitude. These results demonstrate that selective optogenetic stimulation of the PPG neurons can be achieved by targeting these neurons with Cre-dependent virally-encoded ChR2 expression, and will allow investigation of their involvement in feeding and cardiovascular function.