PAQR8 and PAQR9 expression is altered in the ventral tegmental area of aged rats infected with varicella zoster virus

Abstract

Infection with varicella zoster virus (VZV) results in chicken pox and reactivation of VZV results in herpes zoster (HZ) or what is often referred to as shingles. Patients with HZ experience decreased motivation and increased emotional distress consistent with functions of the ventral tegmental area (VTA) of the brain. In addition, activity within the ventral tegmental area is altered in patients with HZ. HZ primarily affects individuals that are older and the VTA changes with age. To begin to determine if the VTA has a role in HZ symptoms, a screen of 10,000 genes within the VTA in young and old male rats was completed after injecting the whisker pad with VZV. The two genes that had maximal change were membrane progesterone receptors PAQR8 (mPRβ) and PAQR9 (mPRε). Neurons and non-neuronal cells expressed both PAQR8 and PAQR9. PAQR8 and PAQR9 protein expression was significantly reduced after VZV injection of young males. In old rats PAQR9 protein expression was significantly increased after VZV injection and PAQR9 protein expression was reduced in aged male rats versus young rats. Consistent with previous results, pain significantly increased after VZV injection of the whisker pad and aged animals showed significantly more pain than young animals. Our data suggests that PAQR8 and PAQR9 expression is altered by VZV injection and that these changes are affected by age.

Keywords: Aging; herpes zoster; membrane progesterone receptors; orofacial pain; ventral tegmental area.

Figure 1.

Behavioral pain response in young and aged rats after control or VZV injection of the whisker pad (a) 1 week after injection and (b) 2 weeks after injection. Two-way ANOVA and Tukey’s post-hoc test was performed to compare groups and an asterisk indicates a significant difference (p < .05) between young VZV group and the aged VZV group. A hashtag indicates a significant difference between the young control group and the young VZV group. A hashtag also indicates a significant difference between the aged control group and the aged VZV group. Six animals were in each treatment group.

Figure 2.

Histograms of PAQR8 and PAQR9 protein content within the VTA for young and aged male rats. In panel (a) PAQR8 was measured in young and aged rats after injecting the whisker pad with either MeWo control or VZV. In panel (b) shows a histogram of PAQR9 protein content within the VTA for young and aged rats after injecting the whisker pad with either MeWo control or VZV. Two-way ANOVA and Tukey’s post-hoc test was performed to compare groups and an asterisk indicates a significant difference (p < .05). Each point represents an individual animal.

Figure 3.

PAQR8 expression in neurons within the VTA. (a) Low magnification image of a coronal brain slice from a representative young male rat injected with MeWo control. Hoechst 33,342 nuclear stain is blue, NeuN staining is red and PAQR8 staining is green. (b) A high magnification image of cells positive for NeuN. (c) Cells staining positive for PAQR8. (d) Cells that colocalize for NeuN and PAQR8 are shown with black (arrows). (e) Staining for Hoechst 33,342, NeuN and PAQR8. Arrows point to the same cells in panels (b), (c), (d) and (e) cross section images through the z plane of the brain slice was completed at the green line in panels (b) through (e) cross sections of cell (open arrow) are shown in panels (f) through (h); NeuN and PAQR8 colocalized for the cell on the left and PAQR8 positive cell without NeuN is shown on the right. Bar = 50 µM.

Figure 4.

PAQR9 expression in neurons within the VTA. (a) Hoechst 33,342 nuclear stain (blue) from cells within the VTA from a coronal brain slice from a representative young male rat injected with VZV control. (b) Image of NeuN positive cells (red). (c) Cells staining positive for PAQR9 (green). (d) Image of overlay for Hoechst 33,342, NeuN and PAQR9 staining. Cross section images through the z plane of the brain slice were completed at the green line in panels (a) through (d) panels (e) through (h) are the cross section of the cell indicated by the open arrow. Panel (i) is the cross section through the cell indicated by the arrow. Colocalized NeuN and PAQR9 were observed in the cell in panels (e) through (h) PAQR9 was not colocalized with NeuN in the cell in panel (i) Bar = 20 µM.

Figure 5.

Histogram for cell counts colocalizing with the PAQRs positive signal and the neuronal marker NeuN in the entire VTA. For the histogram in panel (a) the counts for cells colocalizing for PAQR8 and NeuN in the VTA are shown and panel (b) shows cells colocalizing for PAQR9 and NeuN. Four animals were counted for each treatment group.