Long non-coding RNA Carip loss alters parabrachial synapses and drives pain hyposensitivity.

Pain is an unpleasant sensory and emotional experience that can lead to anxiety and attention deficit. To date, effective therapies for pain have remained limited. Although multiple factors have been reported to modulate pain, few studies have explored the neural mechanisms of long non-coding RNA in pain. Here, we identified a high expression level of Carip in the lateral parabrachial nucleus (LPBN), which participates in modulating pain-like behaviours. Thermal stimulation can induce the significant upregulation of long non-coding RNA Carip in LPBN neurons. The knockout of Carip elevates pain thresholds. Electrophysiological assays in the LPBN-central nucleus of the amygdala (CeA) neurocircuit demonstrated that Carip knockout simultaneously increased the amplitude of evoked AMPA receptor excitatory postsynaptic currents and evoked GABAA receptor inhibitory postsynaptic currents, disrupting the neuronal excitation and inhibition balance due to the enhanced phosphorylation of synapsin 1 Ser9 via a protein kinase A-dependent signalling cascade in LPBN neurons, which is determined to be the crucial reason for abnormal pain-like behaviours. Importantly, blocking the Carip-mediated intracellular signalling cascade by specific knockdown of synapsin 1 or protein kinase A in LPBN neurons of Carip knockout mice not only restores the excitation/inhibition balance but also ameliorates abnormal pain-like behaviours. Together, our results demonstrate the important roles of Carip in pain-like behaviours and suggest that modulating excitation/inhibition balance via the Carip-mediated intracellular signalling pathway could effectively alleviate pain. Our study provides synaptic and molecular explanations for how Carip modulates pain-like behaviours.