Synergistic regulation of itch behaviors by corticotropin-releasing hormone neurons in the medial prefrontal cortex.

The medial prefrontal cortex (mPFC), which abundantly expresses corticotropin-releasing hormone (CRH) and its receptors, is a key region for integrating somatosensory, cognitive, and emotional information. Although CRH has been implicated in itch modulation, the cellular and local-circuit roles of CRH-positive neurons in the mPFC remain poorly defined. Here, we combined behavioral assays, in vivo fiber photometry, chemogenetics, optogenetics, immunofluorescence, and ex vivo whole-cell patch-clamp recordings to determine how mPFC CRH neurons regulate itch-related scratching in mice. mPFC CRH neurons were predominantly vasoactive intestinal polypeptide (VIP)-expressing inhibitory interneurons and responded rapidly to both histaminergic and non-histaminergic pruritic stimuli. Chemogenetic activation increased spontaneous and pruritogen-evoked scratching, whereas chemogenetic inhibition reduced pruritogen-evoked scratching. Consistent with this observation, histamine stimulation elevated c-Fos expression in layer 5 pyramidal (PYR) neurons. Optogenetic activation of mPFC CRH neurons elevated spontaneous excitatory postsynaptic current (sEPSC) frequency, reduced rheobase, and depolarized the resting membrane potential in PYR neurons. Bath-applied CRH similarly increased sEPSC frequency and reduced rheobase. Pharmacological experiments further showed that both CRHR1- and GABAA receptor-dependent signaling contribute to the regulation of PYR-neuron excitability. Collectively, mPFC CRH neurons promote itch-related scratching through the coordinated actions of CRH and GABA, which together enhance the activity of downstream layer 5 PYR neurons. These findings identify a local prefrontal microcircuit involved in itch regulation and suggest potential targets for treating intractable pruritus.