CM156, a high affinity sigma ligand, attenuates the stimulant and neurotoxic effects of methamphetamine in mice

Abstract

Methamphetamine (METH) is a highly addictive psychostimulant drug of abuse. Low and high dose administration of METH leads to locomotor stimulation, and dopaminergic and serotonergic neurotoxicity, respectively. The behavioral stimulant and neurotoxic effects of METH can contribute to addiction and other neuropsychiatric disorders, thus necessitating the identification of potential pharmacotherapeutics against these effects produced by METH. METH binds to σ receptors at physiologically relevant concentrations. Also, σ receptors are present on and can modulate dopaminergic and serotonergic neurons. Therefore, σ receptors provide a viable target for the development of pharmacotherapeutics against the adverse effects of METH. In the present study, CM156, a σ receptor ligand with high affinity and selectivity for σ receptors over 80 other non-σ binding sites, was evaluated against METH-induced stimulant, hyperthermic, and neurotoxic effects. Pretreatment of male, Swiss Webster mice with CM156 dose dependently attenuated the locomotor stimulation, hyperthermia, striatal dopamine and serotonin depletions, and striatal dopamine and serotonin transporter reductions produced by METH, without significant effects of CM156 on its own. These results demonstrate the ability of a highly selective σ ligand to mitigate the effects of METH.

Figure 1

(A) Dose dependent effects of METH on locomotor activity. Male, Swiss Webster mice (n = 6–11 per group) were injected with saline or METH (0.1, 0.5, 1.0, 5 mg/kg, i.p.). (B) Effects of CM156 on locomotor activity following METH treatment. Male, Swiss Webster mice (n = 6–8 per group) were pretreated with saline or CM156 (0.1, 1, 10, 20 mg/kg, i.p.) prior to saline or METH (1 mg/kg, i.p.). (C) Effect of CM156 on the time course of METH treatment. Male, Swiss Webster mice (n = 6 per group) were pretreated with saline or CM156 (20 mg/kg, i.p.) followed 15 min later by saline or METH (1 mg/kg, i.p.). Locomotor activity was recorded for a total of 135 min starting at the pretreatment injection. (D) Effect of CM156 pretreatment on the shift in the dose response curve for METH. Male, Swiss Webster mice (n = 6–11 per group) were pretreated with saline or CM156 (20 mg/kg, i.p.) followed by saline or METH (0.1, 0.5, 1, 5, 10, 30, 50 mg/kg, i.p.). Locomotor activity was recorded for 30 min after saline or METH treatment. Data are reported as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001 vs. saline; #p < 0.05, ###p < 0.001 vs. METH.

Figure 2

Dose response effects of METH on dopamine (DA) levels in the striatum. Male, Swiss Webster mice (n = 7–9 per group) were injected (i.p.) with METH (1.25– 5.0 mg/kg, i.p.) or saline (0 mg/kg, i.p.) at 2 h intervals for a total of four times. DA levels in the striatum were measured one week later. (B) Effects of CM156 on METH-induced depletion of dopamine (DA) levels in striatum of mouse brain tissue. Male, Swiss Webster mice (n = 5 per group) were pretreated with saline or CM156 (5, 10, 20 mg/kg, i.p.). Mice were then treated with saline (−METH 0 mg/kg, i.p.) or METH (+METH 5 mg/kg, i.p.) after 15min. This treatment regimen was repeated at 2 h intervals for a total of four times. Tissue samples from mouse striatum were collected and DA concentration was measured one week later. Data was reported as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001 vs. saline, ###p < 0.001 vs. METH.

Figure 3

Effects of METH and CM156 on DAT immunoreactivity in the mouse striatum. Male, Swiss Webster mice (n = 4 per group) were pretreated with saline (SAL) or CM156 (CM, 20 mg/kg, i.p.). After 15 min, the mice were then treated with saline (SAL) or METH (5 mg/kg, i.p.). This treatment schedule was repeated 4 times at 2 h intervals. One week later, the brain was removed and stained for DAT immunoreactivity. A representative section from each treatment group is shown, along with average optical density readings (mean ± SEM). ***p < 0.001 vs. saline, ###p < 0001 vs. METH.

Figure 4

(A) Dose response effects of METH on 5-HT levels in the striatum. Male, Swiss Webster mice (n = 5–10 per group) were injected with saline or METH (1.25–10.0 mg/kg, i.p.) at 2 h intervals for a total of four times. Striatal tissue samples were collected one week later and measured for 5-HT concentration. (B) Effect of CM156 pretreatment on METH-induced alteration of 5-HT levels in the striatum of mouse brain. Male, Swiss Webster mice (n = 5–10 per group) were pretreated with saline or CM156 (5, 10, 20 mg/kg, i.p.), and 15 min later, the mice were treated with saline (−METH 0 mg/kg, i.p.) or METH (+METH 10 mg/kg, i.p.). These treatment combinations were repeated at 2 h intervals a total of four times. One week later, mouse striatum were collected and 5-HT concentration was measured. Data was reported as mean ± SEM. **p < 0.01, ***p < 0.001 vs. saline, #p < 0.05 vs. METH.

Figure 5

(A) Dose response effects of METH on SERT immunoreactivity in striatum. Male, Swiss Webster mice (n = 4 per group) were injected with METH (5, 10 mg/kg, i.p.) or saline at 2 h intervals for a total of four times. One week later, the brain was removed and stained for SERT immunoreactivity. (B) Effect of pretreatment of CM156 on METH-induced decreases in SERT immunoreactivity. Male, Swiss Webster mice (n = 4 per group) were pretreated with saline (SAL) or CM156 (CM, 20 mg/kg, i.p.), and 15 min later, injected (i.p.) with saline or METH (5 mg/kg, i.p.). These treatment combinations were repeated at 2 h intervals for a total of four times. One week later, the brain was removed and evaluated for SERT immunoreactivity. A representative section from each treatment group is shown, along with average optical density readings (mean ± SEM). ***p < 0.001 vs. saline, ###p < 0.001 vs. METH.

Figure 6

Dose response effects of (A) METH and (B) CM156 on core body temperature. Male, Swiss Webster mice (n = 5–10 per group) were injected with saline or CM156 (5–10 mg/kg, i.p.) followed by saline or METH (1.25–10 mg/kg, i.p.) at 2 h intervals for a total of four times. Core body temperature was measured via rectal thermometer 1 h after each injection and data was reported as mean ± SEM. *p < 0.05, **p < 0.01 vs. saline. No significant difference was observed with CM156.

Figure 7

Effects of CM156 on (A) METH (5 mg/kg, i.p.) or (B) METH (10 mg/kg, i.p.) induced hyperthermia. Male, Swiss Webster mice (n = 5–10 per group) were pretreated with saline or CM156 (5, 10, 20 mg/kg, i.p.), and after 15 min, the mice were treated with saline or METH (5, 10 mg/kg, i.p.). Core body temperature was measured 1 h after each injection combination. This regimen was repeated four times at 2 h intervals. Data was reported as mean ± SEM. *p < 0.05, **p < 0.01 vs. saline.