A role for MCH neuron firing in hippocampal plasticity and learning

It has been revealed that melanin-concentrating hormone (MCH) neurons in the hypothalamus can influence learning (Liu et al., 2022) and memory formation (Kosse & Burdakov, 2019), but the cellular mechanisms by which they perform this function are not understood. Here, we examine the role of MCH neural input to the hippocampus, and show in vitro that optogenetically increasing MCH axon activity facilitates hippocampal plasticity by lowering the threshold for synaptic potentiation. In vivo, we find that MCH neurons are naturally active in response to reinforcing cues during a spatial learning task, and that this activity is correlated with the speed of learning. Together, our results align with increasing evidence that MCH neurons play an ‘on-line’ regulatory role in learning, and reveal that this could be achieved through modulation of synaptic plasticity in the hippocampus.