Nrxn3 Expression in the Amygdala Alters GABA Release to the PBN of Adult Rats

Abstract

The parabrachial nucleus (PBN) modulates the affective-motivational component of the orofacial pain pathway, as the trigeminal region projects to the PBN and the amygdala. Central amygdala (CeA) inhibitory GABAergic neurons project to and inhibit the lateral PBN. Neurexin 3 (nrxn3), a synaptic adhesion molecule, has a role in GABA signaling, and nrxn3 depletion results in a decrease in inhibitory GABAergic response. Our lab uses a post herpetic neuralgia (PHN) model, in which rats are injected with human varicella zoster virus (VZV) into their vibrissal pad resulting in herpes zoster-associated pain (HZ; shingles) that lasts for at least 3 months. In humans, the prevalence of HZ increases with age and immunosuppression. The most common complication of HZ is post herpetic neuralgia, which is observed more following HZ of the orofacial region. VZV-induced pain in rodents results in a hypersensitivity like PHN in humans. Previously, we reported that VZV alters the expression of nrxn3 in the CeA of rats. Therefore, we hypothesized that nrxn3 knockdown in the CeA would result in an increase in VZV-induced affective-motivational pain behaviors and a reduction of GABA released to the PBN of adult rats. Adult Long Evans rats were infused with nrxn3 shRNA to the CeA. PBN neurons were infused with an iGABA SnFR construct followed by implantation of a fiber photometry filament to visualize fluorescent signal in-vivo using the Tucker and Davis RZ10X fiber photometry station. Four weeks later, VZV was injected to the whisker pad. Affective-motivational pain behavior was measured and iGABA SnFR activity recorded simultaneously before and after VZV injection. Fluorescent signal for GABA SnFR increased after VZV injection. Knockdown of nrxn3 in CeA reduced fluorescent signal in the PBN and increased VZV-induced affective motivational behavior. In conclusion, nrxn3 alters GABA release to the PBN and affective-motivational pain behaviors in VZV injected rats. Grant support from NIDCR R01DE026749 (PR Kramer) NINDS R01NS064022 (PR Kinchington).