Low catechol-O-methyltransferase and stress potentiate functional pain and depressive behavior, especially in female mice

Abstract

Low levels of catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, and stress, which potentiates catecholamine release from sympathetic nerves, are fundamental to chronic functional pain syndromes and comorbid depression, which predominantly affect females. Here, we sought to examine the independent and joint contributions of low COMT and stress to chronic functional pain and depression at the behavioral and molecular level. Male and female C57BL/6 mice received sustained systemic delivery of the COMT inhibitor OR486 over 14 days and underwent a swim stress paradigm on days 8 to 10. Pain and depressive-like behavior were measured over 14 days, and brain-derived neurotrophic factor (BDNF; a factor involved in nociception and depression) and glucocorticoid receptor (GR; a stress-related receptor) expression were measured on day 14. We found that stress potentiates the effect of low COMT on functional pain and low COMT potentiates the effect of stress on depressive-like behavior. The joint effects of low COMT and stress on functional pain and depressive-like behavior were significantly greater in females vs males. Consistent with behavioral data, we found that stress potentiates COMT-dependent increases in spinal BDNF and low COMT potentiates stress-dependent decreases in hippocampal BDNF in females, but not males. Although low COMT increases spinal GR and stress increases hippocampal GR expression, these increases are not potentiated in the OR486 + stress group and are not sex-specific. These results suggest that genetic and environmental factors that enhance catecholamine bioavailability cause abnormalities in BDNF signaling and increase risk of comorbid functional pain and depression, especially among females.

Figure 1.. Stress exacerbates COMT-dependent functional pain, especially among females.

Sustained systemic delivery of the COMT inhibitor OR486 or 3 days of swim stress each produce pronounced (A, B) mechanical allodynia, (C, D) mechanical hyperalgesia, and (E, F) thermal heat hyperalgesia in both males and females. OR486 and swim stress together lead to significantly greater mechanical allodynia and mechanical hyperalgesia in males and females and greater thermal hyperalgesia only in females. Data are shown as Mean ± SD, N=6–9 per group. ***P < 0.001 different from the Vehicle+Sham group; ^##P < 0.01, ^###P < 0.001 different from the OR486+Sham group.

Figure 2.. Stress exacerbates COMT-dependent increases in spinal BDNF expression in females, but not males.

Immunohistochemical staining shows expression of spinal BDNF on day 14 in (A) males and (B) females receiving the COMT inhibitor OR486 or vehicle in the absence or presence of swim stress. Quantitative analysis of immunofluorescence intensity demonstrates that sustained OR486 delivery results in increased expression of BDNF in spinal dorsal horn in both (C) males and (D) females, and that swim stress potentiates COMT-dependent increases in spinal BDNF expression in females, but not males. (E) The potentiation of COMT-dependent increases in spinal BDNF expression by stress in females vs males is confirmed by analysis of between-subjects factors in the same ANOVA. Data are shown as Mean ± SD, N=6–8 per group, *P < 0.1, **P < 0.01, ***P < 0.001 different from the Vehicle+Sham group; ^##P < 0.01, different from the OR486+Sham group. Scale bar = 100 μm.

Figure 3.. COMT inhibition leads to increases in spinal GR expression in a stress- and sex-independent manner.

Immunohistochemical staining shows expression of spinal GR on day 14 in (A) males and (B) females receiving the COMT inhibitor OR486 or vehicle in the absence or presence of swim stress. Quantitative analysis of immunofluorescence intensity demonstrates that sustained OR486 delivery leads to increased expression of GR in spinal dorsal horn in both (C) males and (D) females, and that swim stress does not alter COMT-dependent increases in spinal GR expression. (E) No sexually dimorphic effects were observed following analysis of between-subjects factors in the same ANOVA. Data are shown as Mean ± SD, N=6–8 per group, ***P < 0.001 different from the Vehicle+Sham group. Scale bar = 100 μm.

Figure 4.. COMT inhibition exacerbates stress-induced depressive-like behavior, especially in females.

(A) Swim stress leads to increased immobility time during the tail suspension test, which is potentiated by sustained OR486 delivery, in males and females. Data are shown as Mean ± SD, N=8–13 per group, *P < 0.05, **P < 0.01, ***P < 0.001 different from the Vehicle+Sham group; ^##P < 0.01, different from the Vehicle+Stress group. (B) Compared to males, female mice in the OR486+Stress group exhibit a 4-fold greater increase in immobility time during the swim task on day 3. Data are shown as Mean ± SD, N=8–13 per group, *P < 0.05.

Figure 5.. COMT inhibition exacerbates stress-dependent decreases in expression of hippocampal BDNF in females, but not males.

(A) A gross hippocampal image stained with NeuN (Green) depicts the CA1 area where we focused our analyses. The pyramidal layer (CA1sp) is shown as the transverse dot line in the middle, the area below CA1sp is stratum radiatum (CA1sr), and the area above CA1sp is stratum oriens (CA1so). Immunohistochemical staining shows expression of BDNF in the hippocampal CA1 area on day 14 in (B) males and (C) females receiving the COMT inhibitor OR486 or vehicle in the absence or presence of swim stress. Quantitative analysis of immunofluorescence intensity demonstrates that swim stress leads to decreased expression of hippocampal BDNF in both (D) male and (E) female mice, and that sustained OR486 delivery potentiates stress-induced decreases in hippocampal BDNF expression in females, but not males. (F) The potentiation of stress-dependent increases in spinal BDNF expression by OR486 in females vs males is confirmed by analysis of between-subjects factors in the same ANOVA. Data are shown as Mean ± SD, N=6–8 per group, **P < 0.01, ***P < 0.001 different from the Vehicle+Sham group; ^##P < 0.01 different from the Vehicle+Stress group. Scale bar = 100 μm.

Figure 6.. Stress leads to increases in hippocampal GR expression in a COMT- and sex-independent manner.

Immunohistochemical staining shows expression of GR in the hippocampal CA1 area on day 14 in (A) males and (B) females receiving the COMT inhibitor OR486 or vehicle in the absence or presence of swim stress. Quantitative analysis of immunofluorescence intensity demonstrates that swim stress leads to increased expression of hippocampal GR in both (C) male and (D) female mice, and that sustained OR486 delivery does not alter stress-dependent increases in hippocampal GR expression. (E) No sexually dimorphic effects were observed following analysis of between-subjects factors in the same ANOVA. Data are shown as Mean ± SD, N=7 per group, *P < 0.1, **P < 0.01, ***P < 0.001 different from the Vehicle+Sham group. Scale bar = 100 μm.