Contribution of Corticotropin-Releasing Factor Receptor 1 (CRF1) to Serotonin Receptor 5-HT(2C)R Function in Amygdala Neurons in a Neuropathic Pain Model

The amygdala plays a key role in emotional-affective aspects of pain and in pain modulation. The central nucleus (CeA) serves major amygdala output functions related to emotional-affective behaviors and pain modulation. Our previous studies implicated the corticotropin-releasing factor (CRF) system in amygdala plasticity and pain behaviors in an arthritis model. We also showed that serotonin (5-HT) receptor subtype 5-HT(2C)R in the basolateral amygdala (BLA) contributes to increased CeA output and neuropathic pain-like behaviors. Here, we tested the novel hypothesis that 5-HT(2C)R in the BLA drives CRF1 receptor activation to increase CeA neuronal activity in neuropathic pain. Extracellular single-unit recordings of CeA neurons in anesthetized adult male rats detected increased activity in neuropathic rats (spinal nerve ligation model) compared to sham controls. Increased CeA activity was blocked by local knockdown or pharmacological blockade of 5-HT(2C)R in the BLA, using stereotaxic administration of 5-HT(2C)R short hairpin RNA (shRNA) viral vector or a 5-HT(2C)R antagonist (SB242084), respectively. Stereotaxic administration of a CRF1 receptor antagonist (NBI27914) into the BLA also decreased CeA activity in neuropathic rats and blocked the facilitatory effects of a 5-HT(2C)R agonist (WAY161503) administered stereotaxically into the BLA. Conversely, local (BLA) knockdown of 5-HT(2C)R eliminated the inhibitory effect of NBI27914 and the facilitatory effect of WAY161503 in neuropathic rats. The data suggest that 5-HT(2C)R activation in the BLA contributes to neuropathic pain-related amygdala (CeA) activity by engaging CRF1 receptor signaling.