Opioid modulation of hypothalamic arcuate agRP neurons in transgenic mice

Agouti-related peptide (AgRP) neurons, localized in the arcuate nucleus (ARC) of the hypothalamus, have a central role in the regulation of appetite, metabolism, and energy. Manipulations of this neuron group have been proved to be effective in the acute regulation of feeding behavior. AgRP neurons send dense axonal projections to the paraventricular nucleus (PVH) and establish synaptic connections with other neurons found in PVH. Since ARCAgRPPVH synaptic connections play important roles in the regulation of energy balance, metabolism and, more importantly, feeding, it is possible that the drugs that modulate these connections will also play an important role in the regulation appetite. In this study, we aimed to characterize the possible functional changes of µ opioid receptor antagonism on AgRP neurons by ex vivo and in vivo methods. Both female and male AgRP-Cre mice were used in our study. While the effects of µ opioid receptor agonist DAMGO on AgRP neurons were examined ex vivo by electrophysiological activity experiments, the in vivo effects of µ opioid receptor inhibition were examined by using feeding behavior, locomotor activity and fiber photometry Ca+2 imaging methods. In ex vivo experiments, DAMGO significantly reduced the firing frequency of AgRP neurons and hyperpolarized the resting membrane potential of them. In addition, DAMGO significantly decreased the frequency excitatory post-synaptic currents to these neurons decreased significantly without altering the frequency of inhibitory post-synaptic currents. In ARCAgRPPVH synaptic connection experiments using the optogenetic technique, it was observed that the synaptic peak amplitude decreased significantly after drug administration. After five days of intraperitoneal administration of DAMGO, it was observed that the amount of food consumption in mice increased, although not significantly. As a result of DAMGO administration, the distance traveled by the animals significantly decreased, however, there was no change in their velocity. We used fiber photometry Ca+2 imaging technique to record in vivo electrophysiological activity of AgRP neurons after systemic DAMGO administration. When the drug was administered to mice that were fasted for 16 hours, it was observed that the in vivo AgRP neuron activity decreased, but not significantly. In conclusion, when the available data was considered, it can be suggested that the µ opioid agonism strongly stimulates hedonic nutrition and plays a role in the regulation of activity AgRP neurons in homeostatic nutrition.