Sensitization of methamphetamine-induced disorganization of daily locomotor activity rhythm in male rats

Acute and chronic continuous methamphetamine have different long-term behavioral and neurochemical consequences

We compared two different methamphetamine dosing regimens and found distinct long-term behavioral and neurochemical changes. Adult rats were treated with 1-day methamphetamine injection (3x5 mg/kg s.c., 3 h apart) or 7-day methamphetamine minipump (20 mg/kg/day s.c.). The minipump regimen models the sustained methamphetamine plasma levels in some human bingers whereas the 1-day regimen models a naive user overdose. On withdrawal days 7 and 28, rats were acutely challenged with cocaine to test for behavioral sensitization and subsequently sacrificed for caudate and accumbens dopamine tissue content. Other rats were analyzed on withdrawal days 3, 7 or 28 using voltammetry in caudate slices. On withdrawal days 7 and 28, the methamphetamine injection but not the minipump rats showed behavioral cross-sensitization to cocaine. There was no change in baseline dopamine release, reuptake or sensitivity to quinpirole in any treatment group on either withdrawal day. However, consistent with the behavioral sensitization, cocaine had a greater effect in potentiating dopamine release and in blocking dopamine reuptake in methamphetamine injection versus saline irrespective of withdrawal day. The minipump group showed tolerance to the dopamine releasing effect of cocaine on withdrawal day 28 and had lower dopamine tissue content in the caudate versus the methamphetamine injection group. Dopamine turnover as measured by the DOPAC/dopamine ratio tended to be higher in the minipump-treated rats. These data suggest that the behavioral cross-sensitization seen in the methamphetamine injection rats could be in part due to the increased potency of cocaine in blocking dopamine reuptake and in increasing dopamine release. The decreased potency of cocaine in the caudate slices from the minipump-treated group may be related to decreased dopamine tissue content.

Invertebrate models of drug abuse

Susceptibility to drug addiction depends on genetic and environmental factors and their complex interactions. Studies with mammalian models have identified molecular targets, neurochemical systems, and brain regions that mediate some of the addictive properties of abused drugs. Yet, our understanding of how the primary effects of drugs lead to addiction remains incomplete. Recently, researchers have turned to the invertebrate model systems Drosophila melanogaster and Caenorhabditis elegans to dissect the mechanisms by which abused drugs modulate behavior. Due to their sophisticated genetics, relatively simple anatomy, and their remarkable molecular similarity to mammals, these invertebrate models should provide useful insights into the mechanisms of drug action. Here we review recent behavioral and genetic studies in flies and worms on the effects of ethanol, cocaine, and nicotine, three of the most widely abused drugs in the world.

Drugs, flies, and videotape: the effects of ethanol and cocaine on Drosophila locomotion

Drosophila melanogaster has been introduced recently as a model organism in which to study the mechanisms by which drugs of abuse change behavior and by which the nervous system changes upon repeated drug exposure. Surprising similarities between flies and mammals have begun to emerge at the behavioral, neurochemical and molecular levels.

Methamphetamine-induced, suprachiasmatic nucleus-independent circadian rhythms of activity and mPer gene expression in the striatum of the mouse

While the suprachiasmatic nucleus (SCN) coordinates the majority of daily rhythms, some circadian patterns of expression are controlled from outside of the SCN. These include responses to daily methamphetamine (MAP) injection, or daily restricted feeding. The mechanisms underlying these SCN-independent circadian rhythms are unknown. A circadian oscillation in the expression of mPer1 and/or mPer2, mouse period, in the SCN is considered necessary to generate an SCN-dependent circadian rhythm. Therefore, in this experiment, we examined the association between mPer gene expression and the MAP-induced, SCN-independent circadian rhythm. Acute injection of MAP caused an elevation of mPer1, mBmal1, and mNpas2 gene expression in the striatum and mPer1 in the liver. Daily MAP injection at a fixed time for 6 days shifted the rhythmic mPer1 and mPer2 expression in the striatum from a nocturnal to a diurnal rhythm, but failed to affect that in the SCN. Although lesion of the SCN 'flattened'mPer gene oscillation in the striatum and liver, daily MAP injection caused both behavioural and mPer gene expression rhythms. Daily MAP injection at variable injection intervals (12-36 h) for 6 days, however, failed to produce mPer gene rhythm in the striatum. Daily repeated MAP signals may strengthen the oscillatory force of SCN-independent circadian behavioural and molecular rhythms. The present results suggest that daily oscillation of mPer genes outside the SCN is closely associated with the regulation of SCN-independent rhythms. Thus, the present experiment highlights strongly the important role of clock gene expression, in the brain, that underlies the circadian behavioural rhythm.

Sensitized increase of period gene expression in the mouse caudate/putamen caused by repeated injection of methamphetamine

Methamphetamine (MAP) causes the sensitization phenomena not only in MAP-induced locomotor activity, dopamine release, and Fos expression, but also in MAP-induced circadian rhythm. Cocaine-induced sensitization is reportedly impaired in Drosophila melanogaster mutant for the Period (Per) gene. Thus, sensitization may be related to induction of the Per gene. A rapid induction of mPer1 and/or mPer2 in the suprachiasmatic nucleus after light exposure is believed to be necessary for light-induced behavioral phase shifting. Although the caudate/putamen (CPu) expresses mPer1 and/or mPer2 mRNA, the function of these genes in this nucleus has not yet been elucidated. Therefore, we examined whether MAP affects the expression of mPer1 and/or mPer2 mRNA in the mouse CPu. Injection of MAP augmented the expression of mPer1 but not mPer2 or mPer3 in the CPu, and this MAP-induced increase in mPer1 expression lasted for 2 h. Also, the MAP-induced increase of mPer1 mRNA was strongly antagonized by pretreatment with a dopamine D1 receptor and N-methyl-D-aspartate (NMDA) receptor antagonist, but not by a D2 receptor antagonist. Interestingly, application of either the D1 or the D2 agonist alone did not cause mPer1 expression. The present results demonstrate that activation of both NMDA and D1 receptors is necessary to produce MAP-induced mPer1 expression in the CPu. Repeated injection of MAP caused a sensitization in not only the locomotor activity but also mPer1 expression in the CPu without affecting the level of mPer2, mPer3, or mTim mRNA. Thus, these results suggest that MAP-induced mPer1 gene expression may be related to the mechanism for MAP-induced sensitization in the mouse.