Cyclooxygenase activity contributes to the monoaminergic damage caused by serial exposure to stress and methamphetamine

Abstract

Methamphetamine (Meth) is a widely abused psychostimulant that causes long-term dopamine (DA) and serotonin (5-HT) depletions. Stress and Meth abuse are comorbid events in society and stress exacerbates Meth-induced monoaminergic terminal damage. Stress is also known to produce neuroinflammation. This study examined the role of the neuroinflammatory mediator, cyclooxygenase (COX), in the depletions of monoamines caused by serial exposure to chronic unpredictable stress (CUS) and Meth. CUS produced an increase in COX-2 protein expression and enhanced Meth-induced monoaminergic depletions in the striatum and hippocampus. The enhanced DA and 5-HT depletions in the striatum, but not the hippocampus, were prevented by pretreatment with COX inhibitor, ketoprofen, during stress or during Meth; however, ketoprofen did not attenuate the monoaminergic damage caused by Meth alone. The COX-dependent enhancement by stress of Meth-induced monoaminergic depletions was independent of hyperthermia, as ketoprofen did not attenuate Meth-induced hyperthermia. In addition, the EP1 receptor antagonist, SC-51089, did not attenuate DA or 5-HT depletions caused by stress and Meth. These findings illustrate that COX activity, but not activation of the EP1 receptor, is responsible for the potentiation of Meth-induced damage to striatal monoamine terminals by stress and suggests the use of anti-inflammatory drugs for mitigating the neurotoxic effects associated with the combination of stress and Meth.

Figure 1

Effects of CUS on COX-2 protein expression. Rats were exposed to 10 days of CUS or daily handling. On the day after the last stressor, A) hippocampal COX-2 and B) striatal COX-2 immunoreactivity were quantified via Western Blot. CUS significantly increased COX-2 protein expression in the A) hippocampus (*, p<0.05) and B) striatum (*, p<0.05), compared to No Stress, as indicated by a t-test (n=5–6 for each group). Representative Western Blot images of C) hippocampal and D) striatal COX-2 (~72 kDa) and the α tubulin (50 kDa) loading control.

Figure 2

Effects of ketoprofen pretreatment during stress on stress and Meth-induced hyperthermia. Meth (7.5 mg/kg q 2hrs, ×4 ip) or saline (1 mL/kg q 2hrs, ×4 ip) was administered to previously stressed or control rats. Some rats received ketoprofen (5 mg/kg, sc) 1 hr before each stressor or handling. Body temperatures were measured before and every hr after each Meth or saline injection (indicated by the arrows on the x-axis). Meth significantly increased body temperature over time (*, p<0.001) and prior exposure to 10 days of CUS significantly enhanced Meth-induced hyperthermia (#, p<0.001), as revealed by a two-way repeated measures ANOVA. Ketoprofen had no significant effect on stress or Meth-induced hyperthermia. (n=6–9 for each group)

Figure 3

Effect of ketoprofen pretreatment during stress on stress and Meth-induced hippocampal and striatal monoamine depletions, 7 days after treatment. Meth (7.5 mg/kg q 2hrs, ×4 ip) or saline (1 mL/kg q 2hrs, ×4 ip) was administered to previously stressed or control rats. Some rats received ketoprofen (5 mg/kg, sc) 1 hr before each stressor or handling. A) Hippocampal 5-HT: Stress+Meth produced a significant hippocampal 5-HT depletion (#, p<0.05, Tukey post hoc test) compared to No Stress+Meth treatments. Ketoprofen pretreatment did not attenuate Stress+Meth-induced hippocampal 5-HT depletions. Striatal B) DA & C) 5-HT: Three-way ANOVA revealed a significant effect of Meth on DA and 5-HT content compared to No Stress+Saline groups (*, p<0.001). Stress+Meth produced a significant DA and 5-HT depletion (#, DA: p<0.001; 5-HT: p<0.001, 2-way ANOVA and Tukey’s post hoc test) compared to No Stress+Meth. Ketoprofen pretreatment attenuated Stress+Meth-induced striatal DA and 5-HT depletions (&, DA: p<0.01; 5-HT: p<0.01, Tukey’s post hoc test). (n=6–12 for each group)

Figure 4

Effects of ketoprofen pretreatment during drug treatment on stress and Meth-induced hyperthermia. Meth (7.5 mg/kg q 2hrs, ×4 ip) or saline (1 mL/kg q 2hrs, ×4 ip) was administered to previously stressed or control rats. Some rats received ketoprofen (5 mg/kg, sc) 1 hr before each Meth or saline injection. Body temperatures were measured before and every hr after a Meth or saline injection. Larger arrows on the x-axis indicate the time of Meth or saline injections, while the smaller arrows indicate ketoprofen or vehicle injections. Meth significantly increased body temperature over time (*, p<0.001, two-way RM ANOVA) and prior exposure to 10 days of CUS significantly enhanced Meth-induced hyperthermia (#, p<0.001, Tukey’s post hoc test). Ketoprofen pretreatment had no significant effect on stress or Meth-induced hyperthermia. (n=6–10 for each group)

Figure 5

Effects of ketoprofen pretreatment during drug treatment on stress and Meth-induced hippocampal and striatal monoamine depletions, 7 days after treatment. Meth (7.5 mg/kg q 2hrs, ×4 ip) or saline (1 mL/kg q 2hrs, ×4 ip) was administered to previously stressed or control rats. Some rats received ketoprofen (5 mg/kg, sc) 1 hr before each Meth or saline injection. A) Hippocampal 5-HT: Stress+Meth produced a significant hippocampal 5-HT depletion (#, p<0.005, Tukey’s post hoc test) compared to No Stress+Meth treatments. Ketoprofen pretreatment did not significantly attenuate Stress+Meth-induced hippocampal 5-HT depletions. Striatal B) DA and C) 5-HT: Three-way ANOVA revealed a significant effect of Meth on DA and 5-HT content compared to No Stress+Saline groups (*, p<0.001). Stress+Meth produced a significant DA and 5-HT depletion (#, DA: p<0.01; 5-HT: p<0.05, two-way ANOVA and Tukey post hoc test) compared to No Stress+Meth. Ketoprofen pretreatment attenuated the Stress+Meth-induced DA and 5-HT depletions (&, DA: p<0.005; 5-HT: p<0.005, Tukey’s post hoc test). (n=6–10 for each group)

Figure 6

Effects of the EP1 receptor antagonist, SC-51089, pretreatment during drug treatment on stress and Meth-induced hyperthermia. Meth (7.5 mg/kg q 2hrs, ×4 ip) or saline (1 mL/kg q 2hrs, ×4 ip) was administered to previously stressed or control rats. Some rats received SC-51089 (5, 10 or 20 μg/kg, ip) 1 hr before each Meth or saline injection. Body temperatures were measured before and every hr after a Meth or saline injection. Larger arrows on the x-axis indicate the time of Meth or saline injections, while the smaller arrows indicate SC-51089 or vehicle injections. Stress+Meth significantly increased body temperature over time (*, p<0.001, two-way RM ANOVA). Pretreatment with SC-51089, at any dose, did not alter No Stress+Saline or Stress+Meth-induced hyperthermia. (n=5–7 for each group)

Figure 7

Effects of EP1R antagonist, SC-51089, on Stress+Meth-induced hippocampal and striatal monoamine depletions, 7 days after treatment. Meth (7.5 mg/kg q 2hrs, ×4 ip) or saline (1 mL/kg q 2hrs, ×4 ip) was administered to previously stressed or control rats. Some rats received the EP1R antagonist, SC-51089 (5, 10 or 20 μg/kg, ip) 1 hr before each Meth or saline injection. Stress+Meth treatment resulted in a significant depletion of A) hippocampal 5-HT, B) striatal DA and C) striatal 5-HT (*, p<0.001, two-way ANOVA) compared to No Stress+Saline treatments. SC-50189 treatments did not attenuate Stress+Meth-induced monoamine depletions. (n=5–7 for each group)