Trace amine-associated receptor 1 regulation of methamphetamine-induced neurotoxicity

Abstract

Trace amine-associated receptor 1 (TAAR1) is activated by methamphetamine (MA) and modulates dopaminergic (DA) function. Although DA dysregulation is the hallmark of MA-induced neurotoxicity leading to behavioral and cognitive deficits, the intermediary role of TAAR1 has yet to be characterized. To investigate TAAR1 regulation of MA-induced neurotoxicity, Taar1 transgenic knock-out (KO) and wildtype (WT) mice were administered saline or a neurotoxic regimen of 4 i.p. injections, 2h apart, of MA (2.5, 5, or 10mg/kg). Temperature data were recorded during the treatment day. Additionally, striatal tissue was collected 2 or 7days following MA administration for analysis of DA, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and tyrosine hydroxylase (TH) levels, as well as glial fibrillary acidic protein (GFAP) expression. MA elicited an acute hypothermic drop in body temperature in Taar1-WT mice, but not in Taar1-KO mice. Two days following treatment, DA and TH levels were lower in Taar1-KO mice compared to Taar1-WT mice, regardless of treatment, and were dose-dependently decreased by MA. GFAP expression was significantly increased by all doses of MA at both time points and greater in Taar1-KO compared to Taar1-WT mice receiving MA 2.5 or 5mg/kg. Seven days later, DA levels were decreased in a similar pattern: DA was significantly lower in Taar1-KO compared to Taar1-WT mice receiving MA 2.5 or 5mg/kg. TH levels were uniformly decreased by MA, regardless of genotype. These results indicate that activation of TAAR1 potentiates MA-induced hypothermia and TAAR1 confers sustained neuroprotection dependent on its thermoregulatory effects.

Keywords: Dopamine; GFAP; Methamphetamine; Neurotoxicity; TAAR1; Temperature.

Figure 1

Effects of repeated saline or MA injections on core body temperature. Taar1-WT and -KO mice received 4 i.p. injections (indicated by arrows) of saline or MA (2.5, 5, or 10 mg/kg), spaced 2 hr apart. Body temperature was measured every 15 min via telemetry over 8 hr in an ambient temperature of 23 ± 1°C. Data represent temperature for each genotype and treatment group (mean ± SEM) at specified time points, n = 11–21 mice per group. Time points selected for detailed analysis were 30 min after each injection. *: p < 0.05, **: p < 0.01, ***: p < 0.001, ****: p < 0.0001 compared between genotypes.

Figure 2

Striatal levels of DA, DOPAC, HVA and DA turnover measured 2 and 7 days following saline or MA treatment. Taar1-WT and -KO mice received 4 i.p. injections of saline or MA (2.5, 5, or 10 mg/kg), spaced 2 hr apart and were euthanized either 2 or 7 days following the final injection for striatal tissue collection. Values were normalized to the amount of protein in each tissue sample. Data represent means ± SEM of 7–11 mice per group. *: p < 0.05, **: p < 0.01, ***: p < 0.001 compared to saline-treated controls; +: p < 0.001, ++: p < 0.0001 between genotypes; #: p < 0.05, ##: p < 0.01, ###: p < 0.001 for main effect of genotype; †: p < 0.01, ††: p < 0.0001 for main effect of dose; ∘: p < 0.05, ∘∘: p < 0.01, ∘∘∘: p < 0.001, ∘∘∘∘: p < 0.0001 compared to saline-treated controls, regardless of genotype.

Figure 3

Striatal levels of 5HT, 5HIAA, 5HT turnover, and NE measured 2 and 7 days following saline or MA treatment. Taar1-WT and -KO mice received 4 i.p. injections of saline or MA (2.5, 5, or 10 mg/kg), spaced 2 hr apart and were euthanized either 2 or 7 days following the final injection for striatal tissue collection. Values were normalized to the amount of protein in each tissue sample. Data represent means ± SEM of 7–11 mice per group. †: p < 0.05, ††: p < 0.01, †††: p < 0.01, ††††: p < 0.0001 for main effect of dose; ∘: p < 0.05, ∘∘: p < 0.01, ∘∘∘: p < 0.001 compared to saline-treated controls, regardless of genotype.

Figure 4

Striatal TH levels measured via sandwich ELISA 2 and 7 days following saline or MA treatment. Taar1-WT and -KO mice received 4 i.p. injections of saline or MA (2.5, 5, or 10 mg/kg), spaced 2 hr apart. Animals were euthanized either 2 (A.) or 7 (B.) days following the final injection for striatal tissue collection. TH values were normalized to the amount of protein in each tissue sample. Data represent means ± SEM of 7–11 mice per group. #: p < 0.001 for main effect of genotype, †: p < 0.0001 for main effect of dose; ∘: p < 0.001 compared to saline-treated controls, regardless of genotype.

Figure 5

Striatal GFAP levels measured via sandwich ELISA 2 and 7 days following saline or MA treatment. Taar1-WT and -KO mice received 4 i.p. injections of saline or MA (2.5, 5, or 10 mg/kg), spaced 2 hr apart. Animals were euthanized either 2 (A.) or 7 (B.) days following the final injection for striatal tissue collection. GFAP values were normalized to the amount of protein in each tissue sample. Data represent means ± SEM of 7–11 mice per group. *: p < 0.05, **: p < 0.001 compared to saline-treated controls; +: p < 0.001 between genotypes.