Methamphetamine-Induced Brain Injury and Alcohol Drinking

Abstract

A majority of methamphetamine (Meth) abusers also abuse alcohol but the neurochemical consequences of this co-abuse are unknown. Individually, alcohol and Meth cause inflammation and long-term alterations in dopamine and serotonin signaling within the brain. Experiments were conducted to identify if serial exposure to alcohol and Meth has neurochemical consequences that are greater than after either drug alone. Male Sprague Dawley rats voluntarily drank 10% ethanol (EtOH) every other day for 4 weeks and were then exposed to a binge injection regimen of Meth (10 mg/kg injected every 2 h, for a total of 4 injections). EtOH drinking and preference increased over the 4 weeks and caused inflammation evidenced by increases in serum and brain lipopolysaccharide (LPS) and brain cyclooxygenase-2 (COX-2) 24 h after the last day of drinking. Meth alone depleted dopamine and serotonin in the striatum, as well as serotonin in the prefrontal cortex when measured 1 week later. In contrast, EtOH drinking alone did not affect dopamine and serotonin content in the striatum and prefrontal cortex, but prior EtOH drinking followed by injections of Meth enhanced Meth-induced depletions of dopamine, serotonin, as well as dopamine and serotonin transporter immunoreactivities in a manner that was correlated with the degree of EtOH consumption. Cyclooxygenase inhibition by ketoprofen during EtOH drinking blocked the increases in LPS and COX-2 and the enhanced decreases in dopamine and serotonin produced by Meth. Therefore, prior EtOH drinking causes an increase in inflammatory mediators that mediate a synergistic interaction with Meth to cause an enhanced neurotoxicity.

Keywords: Alcohol; Cyclooxygenase-2; Lipopolysaccharide; Methamphetamine; Monoamines.

Figure 1. EtOH intake and preference are increased over 28 days

EtOH drinking was on odd numbered days and alternated with water drinking only on even number days (not shown). a) Escalated intake of 10% EtOH (g/kg/day) over 14 24-hr exposures (p<0.001; n=43). b) Preference for 10% EtOH (% total fluid intake (EtOH+Water)) follows a similar trend over 14 24-hr exposures as compared to water intake (p<0.001; n=43).

Figure 2. EtOH drinking increases markers of inflammation

Twenty four hr after the last day of drinking, a) serum lipopolysaccharide (LPS), b) striatal LPS, c) striatal cyclooxygenase-2 (COX-2), and d) prefrontal cortex COX-2 in EtOH-drinking rats was significantly higher compared to water-drinking rats (*p<0.05; n=5–7/group).

Figure 3. Previous EtOH drinking does not increase Methamphetamine-induced hyperthermia

Rats receiving Meth displayed higher body temperatures compared to saline-treated rats over time (*p<0.01; n=12/group) but there were no significant differences between Water+Meth and EtOH+Meth groups. Arrows denote injection times.

Figure 4. Previous EtOH drinking or gavage enhances Methamphetamine-induced depletions of dopamine and serotonin in striatum and prefrontal cortex

Seven days after Meth, there was a significant Meth-induced decrease in a) striatal dopamine, b) striatal serotonin, and c) prefrontal cortex serotonin compared to Water+Saline rats (*p<0.05; n=5–7/group, 2-way ANOVA). There were greater decreases in a) striatal dopamine and b) striatal serotonin, and c) prefrontal cortex serotonin compared to Water+Meth rats (#p<0.05; n=5–7/group, Tukey post hoc).

Figure 5. Previous EtOH drinking or gavage enhances Methamphetamine-induced depletions of dopamine transporter (DAT) and serotonin transporter (SERT) immunoreactivities

Seven days after Meth, there was a significant Meth-induced decrease in a) striatal DAT, b) striatal SERT, and c) prefrontal cortex SERT compared to Water+Saline rats (*p<0.05; n=5–7/group, 2-way ANOVA). There were greater decreases in a) striatal DAT, b) striatal SERT and c) prefrontal cortex SERT compared to Water+Meth rats (#p<0.05; n=5–7/group, Tukey post hoc).

Figure 6. Methamphetamine-induced dopamine and serotonin depletions are dose-dependently affected by previous amount of EtOH consumed

Linear regression showed a significant correlation between total EtOH intake over 28 days and degree of a) dopamine (r²=−0.89; p<0.001) and b) serotonin (r²=−0.58; p<0.05) depletions in the striatum, as well as c) serotonin (r²=−0.75; p<0.05) depletions in the prefrontal cortex (n=10).

Figure 7. Markers of inflammation are blocked by ketoprofen during EtOH drinking

COX-2 inhibitor ketoprofen (Keto) during EtOH only blocked EtOH-induced increases in a) LPS and b) striatal COX-2 (*p<0.01; n=4–7/group; 1-way ANOVA).

Figure 8. Enhanced monoamine depletions are blocked by ketoprofen during EtOH drinking

Meth alone resulted in significant depletions of dopamine in a) striatum, and 5-HT in b) striatum and c) prefrontal cortex (#p<0.05 vs. Water+Saline+Vehicle; 3-way ANOVA and post hoc Tukey tests; n=5–12/group). Previous exposure to EtOH significantly enhanced DA depletions in a) striatum, and 5-HT depletions in b) striatum and c) prefrontal cortex (&p<0.05 vs. Water+Meth+Vehicle). Treatment with Keto during EtOH drinking attenuated dopamine depletions in a) striatum, and 5-HT depletions in b) striatum and c) prefrontal cortex (*p<0.05 vs. EtOH+Meth+Vehicle).