Effect of a neurotoxic dose regimen of (+)-methamphetamine on behavior, plasma corticosterone, and brain monoamines in adult C57BL/6 mice

Abstract

Rationale: In rats, neurotoxic doses of methamphetamine (MA) induce astrogliosis, long lasting monoamine reductions, reuptake transporter down-regulation, and learning impairments.

Objective: We tested whether comparable effects occur in C57BL/6 mice.

Method: C57BL/6 mice were treated with 10mg/kgs.c.x4 MA on a single day and evaluated at various intervals thereafter.

Results: The neurotoxic dose regimen of MA caused the predicted acute hyperthermia and increased striatal glial fibrillary acidic protein and reduced neostriatal dopamine. The MA-treated mice were hypoactive 24h later but not 48h later. MA-treated mice also showed exaggerated initial hyperactivity after a pharmacological dose of MA used to stimulate locomotion followed by a later phase of hypoactivity compared to saline-treated mice. No differences were observed on learning or memory tests (novel object recognition, egocentric, or spatial learning/memory). MA-treated mice showed a trend toward increased prepulse inhibition but not baseline acoustic startle reactivity. After testing, MA-treated mice showed reduced neostriatal dopamine and increased basal plasma corticosterone.

Conclusions: A neurotoxic/binge regimen of MA in mice that produces the typical pattern of neurotoxic changes to those seen in rats, results in few behavioral changes. This may limit the utility of C57BL/6 mice for modeling the cognitive and behavioral effects described in human MA users who show such changes even after prolonged abstinence.

Fig. 1

Core body temperatures of mice treated with MA (10 mg/kg) or SAL 4 times on a single day. Beginning 60 min and lasting for at least 12 h after the first dose, animals treated with MA showed increased core body temperatures compared to SAL controls. Arrows indicate when injections were given. There were main effects of treatment, F(1, 114) = 60.01, p<0.0001, time, F(16, 1824) = 87.01, p<0.0001, and treatment × time, F(16, 1824) = 40.49, p<0.0001. ***p < 0.001

Fig. 2

Locomotor activity: Locomotion was measured as distance traveled on day 1 (A) and day 2 (B) after treatment. Main effects of treatment, F(1, 36) = 7.00, p<0.05, day, F(1, 36) = 29.58, p<0.0001, and treatment × day, F(1, 36) = 13.35, p<0.001, were observed for total distance. The treatment × day interaction showed that animals treated with MA were hypoactive on day 1. Effects of treatment, F(1, 36) = 4.08, p<0.05, interval, F(11, 396) = 8.12, p<0.0001, and treatment × interval, F(11, 396) = 3.32, p< 0.001, were observed for center distance on day 1. For the treatment × interval interaction, decreased center distance was observed in MA-treated animals compared to SAL-treated animals (not shown). There was a main effect of interval for center distance on day 2, F(11, 396) = 6.48, p< 0.0001, only. Effects of treatment, F(1, 36) = 10.21, p<0.01, day, F(1, 36) = 56.26, p<0.0001, and treatment × day, F(1, 36) = 12.88, p<0.001, were observed for peripheral distance. The treatment × day interaction showed that MA-treated animals on day-1 were less active than SAL-treated animals (p<0.0001; not shown). ***p< 0.001

Fig. 3

Acoustic startle/pre-pulse inhibition: Mice treated with 10 mg/kg MA or SAL all showed prepulse inhibition as a function of prepulse intensity but no significant group differences were obtained. A trend toward a treatment × prepulse interaction was observed, F(1, 35) = 3.94, p< 0.06. NS = no stimulus, †p< 0.06

Fig. 4

Morris water maze cued platform trials. Animals administered MA had increased latencies to reach the platform on day 1, F(1, 36) = 4.26, p<0.05. On the remaining days, there were main effects of treatment, F(1, 36) = 12.27, p<0.01, day, F(4, 144) = 31.80, p<0.0001, and treatment × day F(4, 144) = 5.05, p<0.001, for latency. The treatment × day interaction was due to increased latency in MA-treated animals on day 2 (p<0.0001) and 3 (p< 0.001). On days 4–6, latencies were similar to controls. **p< 0.01, ***p< 0.001

Fig. 5

Morris water maze hidden platform trials. Learning curves for latency to reach the platform during each phase of testing: acquisition (A), reversal (B), and shift (C). No differences were observed between treatment groups in any phase of the test.

Fig. 6

Locomotor activity with MA challenge: The challenge (1 mg/kg MA) was administered following 30 min of baseline activity. Total distance showed a main effect of interval, F(23, 727) = 8.31, p<0.0001, and treatment × interval, F(23, 727) = 6.74, p<0.0001. The interaction showed both groups were initially hyperactive following drug challenge and then gradually showed reduced locomotion 85 min later (distance traveled (A)), although the MA-treated animals were even less active at 120 min compared to SAL-treated animals. Focused movements showed effects of treatment, F(1, 35) = 4.24, p<0.05, interval, F(23, 828) = 11.44, p<0.0001, and treatment × interval, F(23, 828) = 13.73, p<0.0001. The treatment × interval interaction showed MA-treated groups had increased focused movements (B) compared to controls that lasted approximately 60 min after acute MA challenge. For vertical activity (C), there were main effects of treatment, F(1, 35.2) = 4.30, p<0.05, interval, F(23, 748) = 7.53, p<0.0001, and treatment × interval, F(23, 748) = 2.73, p<0.0001. MA animals had increased vertical activity compared to controls. ***p< 0.001, **p< 0.01, *p< 0.05, †p< 0.06

Fig. 7

Neostriatal monoamine levels: Monoamine concentrations in SAL- and MA-treated animals 3 days following behavioral experiments (day 47). MA caused reductions in DA (t(18) = 6.08, p< 0.0001) and its primary metabolite, DOPAC, (t(18) = 2.97, p< 0.01), compared to SAL controls. 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) were unaffected. *p< 0.01, ***p< 0.001

Fig. 8

Cincinnati water maze: Egocentric learning was assessed by latency to escape (A) and number of errors (B) in animals treated with MA or SAL. MA animals had similar latencies and errors as SAL controls. There was only an effect of day for latency to the platform, F(14, 597) = 3.92, p< 0.0001. There was a main effect of day, F(14, 666) = 5.89, p< 0.0001, and treatment × day interaction, F(14, 666) = 1.77, p< 0.04 for errors. The treatment × day interaction showed no significant effect of treatment by slice ANOVA for any day. *p< 0.05