Amphetamine-induced prolonged disturbances in tissue levels of dopamine and serotonin in the rat brain

Abstract

Background: A hallmark of psychostimulants is the persistence of neurobiological changes they produce. The difficulty in reversing long-time effects of psychostimulants use is why addiction therapy is so ineffective. This study aimed to look for such drug-induced changes that can be detected even after many weeks of abstinence.

Methods: Rats were given 12 doses of amphetamine (Amph) at 1.5 mg/kg. The rewarding effect of Amph was assessed using ultrasonic vocalization. After 14 and 28 days of abstinence, tissue levels of dopamine (DA), serotonin (5-HT), and their metabolites were measured in the prefrontal cortex (PFC), nucleus accumbens (Acb), dorsomedial (CPuM), and dorsolateral (CPuL) striatum.

Results: After 28 days of abstinence, DA levels were increased in the dorsal striatum while 5-HT levels were decreased in all brain regions studied. The opposite direction of changes in DA and 5-HT tissue levels observed in the dorsal striatum may be related to the changes in the emotional state during abstinence and may contribute to the incubation of craving and relapses. Tissue levels of 5-HT and DA showed intra- and inter-structural correlations, most pronounced after 14 days of abstinence. Most of them were absent in the control group (ctrl), which may indicate that their appearance was related to the changes induced by earlier Amph administration. We did not find any associations between reward sensitivity and the persistence of Amph-induced neurochemical disturbances.

Conclusions: Administration of 12 moderate doses of Amph causes prolonged changes in DA and 5-HT tissue levels. The direction and severity of the changes are dependent on the brain region and the neurotransmitter studied.

Keywords: Addiction; Dopamine–serotonin interaction; Long-term withdrawal; Psychostimulants ultrasonic vocalization.

Fig. 1

General scheme of experiment. Amph1–Amph12 indicates consecutive intraperitoneal injections of Amph (1.5 mg/kg). The control group received NaCl. USV was recorded for Amph1, Amph2 and Amph12. Amph amphetamine

Fig. 2

A The rate of FM 50-kHz USV during the 20-min sessions preceding the injection of 1st, 2nd, and 12th injection of Amph (test group, total n = 28) or NaCl (control group, n = 8); Two-way repeated measures ANOVA followed by post hoc Tukey’s test. ^xxxp < 0.0001 vs the USV prior 1st Amph dose, ^^p < 0.001 vs the USV prior 12th Amph dose. B Effect of repeated Amph (test group, total n = 28) or NaCl (control group, n = 8) treatment on FM 50-kHz USV rate response after 1st, 2nd, and 12th injection; Two-way repeated measures ANOVA followed by post-hoc Tukey’s test. ^#p < 0.05, ^##p < 0.01 Amph vs. relevant NaCl group, *p 0.05, ***p < 0.001 vs. the USV post 1st Amph dose. The data are shown as the means + SEM. FM 50-kHz USV frequency-modulated ultrasonic vocalization, Amph amphetamine

Fig. 3

Tissue levels of DA, DOPAC, and HVA, in the rat PFC, Acb, CPuM, and CPuL after 12 injections of Amph (1.5 mg/kg) measured by HPLC 14 and 28 days following the last dose. Test groups received Amph with 14 (n = 14) or 28 (n = 14) days of withdrawal. The control group received NaCl (n = 8). One-way ANOVA followed by Post hoc Tukey’s test. *p < 0.05, ***p < 0.001 vs. the control group; ^#p < 0.05, ^###p < 0.001 vs. the group with 14 days withdrawal. The data are shown as the means + SEM. DA dopamine, DOPAC 3,4-dihydroxyphenylacetic acid, HVA homovanillic acid, PFC prefrontal cortex, Acb nucleus accumbens, CPuM dorsomedial striatum, CPuL dorsolateral striatum, Amph amphetamine

Fig. 4

Tissue levels of 5-HT and 5-HIAA in the rat PFC, Acb, CPuM and CPuL after 12 injections of Amph (1.5 mg/kg) measured by HPLC 14 and 28 days following the last dose. Test groups received Amph with 14 (n = 14) or 28 (n = 14) days of withdrawal. The control group receiving NaCl (n = 8). One-way ANOVA followed by Post-hoc Tukey’s test. *p < 0.05, **p < 0.01, ***p < 0.001 vs. the control group; ^#p < 0.05, ^###p < 0.001 vs. the group with 14 days withdrawal. The data are shown as the means + SEM. 5-HT serotonin, 5-HIAA 5-hydroxyindoleacetic acid, PFC prefrontal cortex, Acb nucleus accumbens, CPuM dorsomedial striatum, CPuL dorsolateral striatum, Amph amphetamine

Fig. 5

Pearson’s correlations with Bonferroni–Holm correction between DA and 5-HT levels measured by HPLC, in the control group (n = 8) and at 14 (n = 14) and 28 (n = 14) days after completion of 12 doses of Amph (1.5 mg/kg). p < 0.05 in all cases. 5-HT serotonin, DA dopamine, Amph amphetamine

Fig. 6

Comparison of 5-HT and DA changes in CPuM and CPuL 14 (n = 14) and 28 (n = 14) days after administration of 12 injections of Amph (1.5 mg/kg) measured by HPLC. 5-HT serotonin, DA dopamine, CPuM dorsomedial striatum, CPuL dorsolateral striatum, Amph amphetamine