Subchronic methamphetamine treatment selectively attenuates apomorphine-induced decrease in 3,4-dihydroxyphenylacetic acid level in mesolimbic dopaminergic regions

Attenuation of the inhibitory effect of dynorphin on dopamine release in the rat nucleus accumbens by repeated treatment with methamphetamine

Dynorphin (1-100 nM) dose dependently inhibited both spontaneous and electrically evoked endogenous dopamine (DA) release from slices of the nucleus accumbens of untreated rats. When this inhibitory effect was compared, it was significantly reduced in rats pretreated (for 9 days) with methamphetamine (6 mg/kg per day i.p.) relative to rats treated with saline. These findings indicate that dynorphin inhibits DA release from the nucleus accumbens, and that treatment with methamphetamine reduces the modulatory action of dynorphin on DA release. It is possible that repeated administration of methamphetamine leads to attenuation of the inhibition of DA release from the nucleus accumbens via presynaptic dynorphin-sensitive receptors.

Changes in sensitivity of dopamine autoreceptors in rat striatum after subchronic treatment with methamphetamine

To determine the functional alterations of the release modulating striatal dopamine (DA) autoreceptors that might be associated with the behavioral sensitization to methamphetamine after pretreatment with methamphetamine, we investigated the effect of apomorphine and sulpiride on electrically evoked DA release from striatal slices of rats pretreated with methamphetamine. Apomorphine induced a dose-dependent inhibition of the DA release evoked from the striatal slices. Pretreatment with methamphetamine (6 mg/kg per day for 9 days) significantly reduced the inhibitory effect of apomorphine. On the other hand, sulpiride caused a dose-dependent increase in the DA release evoked from the striatal slices. The enhancement by sulpiride of the evoked DA release was diminished by pretreatment with methamphetamine. These results show that pretreatment with methamphetamine blunts the responsiveness of evoked DA release to the DA antagonists as well as to the DA agonists, indicating that DA autoreceptor subsensitivity is produced by pretreatment with methamphetamine.

Cholecystokinin binding sites in the rat forebrain: effects of acute and chronic methamphetamine administration

Using the in vitro quantitative receptor autoradiographical technique, changes in the binding parameters of [propionyl-3H] propionylated CCK-8 [( 3H]pCCK-8) binding sites in the rat forebrain were investigated following acute and chronic administration of methamphetamine (MAP). The (Kd)app values of [3H]pCCK-8 binding sites in the frontal medial cortex and anterior cingulate cortex were significantly reduced after a single injection of 4mg/kg MAP. On the other hand, chronic treatment (14 days) with MAP at this dose significantly decreased the Bmax value of [3H]pCCK-8 binding sites in the anterior cingulate cortex accompanied by supersensitivity of locomotor effects to MAP. These findings suggest that dopamine (DA) neurons in these two regions are functionally related to intrinsic CCK-containing cortical neurons, and that CCK subsensitivity, perhaps due to an alteration in DA transmission, is involved in MAP sensitization. These findings may be relevant to the DA hypothesis of schizophrenia.

Subchronic methamphetamine treatment enhances methamphetamine- or cocaine-induced dopamine efflux in vivo

Intracerebral dialysis was used to study the mechanism underlying behavioral sensitization. Rats were divided into two groups: a control group that received intraperitoneal injections of saline and an experimental group that was given methamphetamine (MAP) (4 mg/kg) once a day for 14 days. Seven days after the last injection, dopamine (DA) and its metabolites were measured in striatal dialysates obtained from awake freely moving rats. A challenge injection of MAP (4 mg/kg) caused a marked increase in the extracellular concentrations of DA, and the extent of the increase was significantly greater in MAP-pretreated rats than in the saline-pretreated controls. A challenge injection of cocaine (20 mg/kg) also caused a significantly greater increase in extracellular DA levels in MAP-pretreated rats than in saline-pretreated rats. These results suggest that an enhancement in striatal DA efflux may play an important role in MAP-induced behavioral sensitization and cross-sensitization to cocaine.

Susceptibility to sensitization. II. The influence of gonadal hormones on enduring changes in brain monoamines and behavior produced by the repeated administration of D-amphetamine or restraint stress

Repeated amphetamine use produces an enduring sensitization of brain dopamine (DA) systems and behavior. Repeated exposure to stress can also produce sensitization, and amphetamine and stress may be interchangeable in this regard. There is, however, enormous individual variation in the susceptibility to sensitization by either stimulants or stress. The purpose of the present study was to determine if endogenous gonadal hormones contribute to individual variation in the sensitization of stereotyped behaviors, locomotion or regional brain monoamine metabolism. It was found that removal of testicular hormones by castration of male rats facilitated the behavioral sensitization produced by either repeated amphetamine treatment or repeated restraint stress, but ovariectomy of female rats was without effect. Prior exposure to amphetamine enhanced striatal homovanillic acid (HVA) levels and dihydroxyphenylacetic acid to DA and HVA to DA ratios in intact female, ovariectomized female and castrated male rats, but not gonadally-intact male rats. As a group, intact males were particularly heterogeneous because they were divisible into two neurochemically distinct subgroups based on their degree of behavioral sensitization, and the other groups were not. It is suggested that individual differences in the sensitization of brain DA systems and behavior produced by repeated exposure to amphetamine or stress may be due in part to individual differences in the concentration of a testicular hormone.

Susceptibility to sensitization. I. Sex differences in the enduring effects of chronic D-amphetamine treatment on locomotion, stereotyped behavior and brain monoamines

There are sex differences in a number of behavior elicited by amphetamine (AMPH). The purpose of the present experiment was to determine if there are also sex differences in the sensitization of the locomotor activity and stereotypy produced by repeated intermittent AMPH treatment, and whether this is accompanied by sex differences in dopamine (DA) metabolism. It was found that female rats showed greater and more rapid sensitization of locomotor activity and stereotyped behavior than males. In addition, prior exposure to AMPH was associated with an elevation in resting striatal dihydroxyphenlacetic acid (DOPAC) to DA ratios in female, but not male rats, suggesting a sex difference in one neurochemical correlate of sensitization. As a group, males were more variable and heterogeneous in their response to repeated AMPH treatment, because they were divisible into two neurochemically distinct subgroups on the basis of their change in behavior and females were not. This heterogeneity may make it more difficult to identify neurochemical correlates of sensitization in males. It is suggested that there is a sex difference in the responsiveness of brain DA systems to repetitive activation, and this contributes to individual variation in the susceptibility to sensitization.

Enhancement of dopamine release from striatal slices of rats that were subchronically treated with methamphetamine

The effect of dopamine (DA) uptake inhibitors (methamphetamine, nomifensine, and phenylethylamine) on the release of endogenous DA from striatal slices of rats pretreated with methamphetamine (6 mg/kg/day for 9 days) was investigated. The exposure of methamphetamine-pretreated rat striatal slices to a low concentration (10(-7) M, 5 X 10(-7) M) of methamphetamine caused a greater increase in DA efflux than that of saline-treated rat striatal slices. The drug-treated rats displayed an enhanced stereotyped behavioral response to a small dose of methamphetamine (1 mg/kg). Removal of Ca2+ from the superfusion medium did not affect the difference in the rates of methamphetamine (10(-7) M) induced DA release between methamphetamine-treated and saline-treated rat striatal slices. Nomifensine- and phenylethylamine-induced DA release from striatal slices was also enhanced by repeated administration of methamphetamine. On the other hand, there was no difference in K+-induced DA release between the two groups. Moreover, repeated administration of methamphetamine caused a significant increase in 3H-dopamine uptake in rat striatal synaptosomes. These results suggest that the behavioral sensitization produced by the repeated administration of methamphetamine is accompanied by an enhancement in the release of DA induced by methamphetamine, nomifensine, and phenylethylamine in vitro and is also accompanied by increased DA uptake into striatal synaptosomes.