<em>In Vivo</em> Whole-cell Patch-clamp Recording of Hypothalamic Peptidergic Neurons in Larval Zebrafish

The hypothalamus is an ancient brain region that regulates diverse aspects of physiology and behavior, including sleep and wakefulness, appetite, energy homeostasis, anxiety, depression, and social interaction. Specific neuronal populations in the hypothalamus exert their effects via the release of neurotransmitters and neuropeptides. Whole-cell patch-clamp recording is an indispensable approach for studying the roles of these factors in synaptic transmission and brain function. However, it is challenging to access hypothalamic neurons for electrophysiological recordings in intact mammals due to their location deep within the brain. As a result, our understanding of the intrinsic properties and physiological functions of hypothalamic neurons is limited. The larval zebrafish is a useful alternative model to study hypothalamic neurons due to its transparent and small, but well-conserved, vertebrate brain. Here, we present a protocol for in vivo whole-cell patch clamp recordings of hypothalamic neurons in intact larval zebrafish. Using this technique, we can record from peptidergic neurons in the hypothalamus, examine the responses of these neurons to sensory stimuli, and explore their effects on downstream neurons. This experimental technique thus provides a useful approach to study the physiological functions of hypothalamic neuropeptidergic neurons in intact animals.