People with herpes zoster (HZ) or ?shingles? can suffer from orofacial pain. Orofacial HZ is caused by the reactivation of latent varicella zoster virus (VZV) in the trigeminal ganglia. Importantly, women report HZ pain three times more often than men, but the mechanism for this sex disparity is unknown. A screen by our lab of over 20,000 genes in five different regions of the orofacial pain pathway revealed that the greatest change in gene expression occurred in the thalamus, such that glutamate decarboxylase 2 (GAD2) and vesicular GABA transporter (VGAT) were elevated at proestrus (high 17 ?-estradiol, E2) but not diestrus (low E2). In preliminary studies we showed that female rats have a greater VZV induced orofacial nociceptive response in comparison to males; mirroring the human sex difference. We also showed that reducing E2 production in male and female rats increases their nociceptive response and lastly, knock-down of VGAT expression in the thalamus increased the nociceptive response. Based on these studies we hypothesized that E2 attenuates orofacial nociception by increasing GAD2 or VGAT, enhancing GABAergic neural inhibition within the thalamus to reduce pain. To test this hypothesis, Aim 1 will characterize thalamic control of the VZV induced orofacial nociceptive response. The working hypothesis for Aim 1 is that GABA interneurons inhibit neurons in the thalamus to reduce VZV induced nociception. To test this hypothesis first, VZV induced nociception and neuronal activity will be recorded after attenuating inhibitory interneurons. Second, nociception and neuronal activity will be determined after modulating GAD2 and VGAT expression in these interneurons.
Aim 2 will determine the role of sex steroids in modulating the VZV induced nociceptive response. Our working hypothesis is that E2 will increase expression of VGAT and GAD2 in the thalamus causing attenuation of neuronal activity and the nociceptive response. To test this hypothesis first, the nociceptive response and neuronal activity will be measured in female and male rats after administering E2 or reducing E2 production. Second, nociception and neuronal activity will be measured after knock-down of GAD2 and VGAT expression in rats with varied E2 levels.
Aim 3 will characterize the mechanism by which sex steroids modulate VGAT and GAD2 to affect the VZV induced orofacial nociceptive response. Our working hypothesis is that E2 binds to estrogen receptor alpha (ER?) causing increased expression of VGAT and GAD2 in the thalamus resulting in attenuation of nociception. To test this idea, the nociceptive response and neuronal activity will be quantitated in rats after mutating ER? promoter sites using CRISPR/Cas9 technology. From these three aims we expect to determine 1) that GABA interneurons inhibit thalamic signaling to reduce orofacial pain, 2) that GAD2 and VGAT increases in these neurons through an ER? dependent mechanism, and 3) that GAD2 and VGAT are responsible, in part, for the sex difference observed in HZ pain. Identifying a mechanism by which E2 affects HZ-associated pain will provide new targets for treating people suffering from this chronic disorder.
These studies will evaluate the role of two neuron inhibitory genes, glutamate decarboxylase 2 (GAD2) and vesicular GABA transporter (VGAT). Thalamic expression of these two genes was regulated by estrogen and the role of these genes in the underlying molecular pathogenesis of Zoster associated nociception will be evaluated in this application. These experiments will provide valuable insights into an area of Herpes Zoster pain biology and pathology that are poorly understood and highly prioritized by the NIDCR. PUBLIC HEALTH RELEVANCE: Novel genes by which 17?-estradiol affects orofacial hypersensitivity will be identified, providing a greater understanding of why females suffer greater pain and allow for targeted control of their expression to reduce orofacial pain.
| Strand, Jennifer; Stinson, Crystal; Bellinger, Larry L et al. (2018) Gi protein functions in thalamic neurons to decrease orofacial nociceptive response. Brain Res 1694:63-72 |
