Behavioral effects of serotonergic and dopaminergic drugs in cats following chronic amphetamine administration

Long-lasting decrease in dopamine uptake sites following repeated administration of methamphetamine in the rat striatum

We investigated the effects of repeated administration of methamphetamine on dopamine (DA) uptake sites in the rat striatum by using an increasing dose paradigm of methamphetamine (2.5 mg/kg on day 1; 5 on day 3; 7.5 on day 5 and 10 on day 7), each being given twice on the indicated day by s.c. injection. It has been established that this administration paradigm produces distinct sensitization in methamphetamine-induced behavior. A 36% reduction in specific [3H]DA uptake, and a 29% reduction in specific [3H]GBR12935 binding in the striatum were demonstrated in rats sacrificed 7 days after the last methamphetamine administration. A similar reduction in striatal [3H]GBR12935 binding sites was observed even 30 days after discontinuation of the drug. These data indicate that this treatment regimen of gradually escalating doses of methamphetamine induces a long-lasting decrease of DA uptake sites in rat striatum.

Time-dependent changes in the sensitivity of dopamine neurons to low doses of apomorphine following amphetamine infusion

Changes in dopamine autoregulatory mechanisms following a chronic infusion of amphetamine were studied. Rats were infused with D-amphetamine (4.8 mg/day) for 7 days by osmotic minipumps, and were studied at various times after withdrawal. In contrast to no changes in the spontaneous firing rate of single dopamine cells, the potency of apomorphine in the substantia nigra was markedly decreased soon after withdrawal, followed by an increase 7 days later. The ventral tegmental area showed no changes in either spontaneous firing rate or sensitivity to apomorphine following a 7-day withdrawal. Moderate decreases in striatal and tubercle dopamine concentrations were not accompanied by any significant decrease in basal dopamine synthesis. Under intact impulse-flow, the sensitivity of terminal dopamine synthesis to low doses of apomorphine was decreased immediately following withdrawal; by Day 7 supersensitivity was observed. Direct assessment of terminal autoreceptors following a 7-day withdrawal revealed normo- and supersensitivity of these receptors in the striatum and olfactory tubercle, respectively. Possible mediating mechanisms as well as implications of these findings for the development of characteristic behavioral syndromes during and after amphetamine infusion are discussed.

Persistent sensitization of dopamine neurotransmission in ventral striatum (nucleus accumbens) produced by prior experience with (+)-amphetamine: a microdialysis study in freely moving rats

In humans the repeated use of amphetamine (AMPH) produces a hypersensitivity to the psychotogenic effects of AMPH that persists for months to years after the cessation of drug use. To explore the neurobiological basis of this phenomenon the long-term effects of dextroamphetamine [+)-AMPH) on brain monoamines and behavior were studied in an animal model of AMPH psychosis. An escalating dose pretreatment regimen (from 1 to 10 mg/kg over 5 weeks) was used to mimic the pattern of drug use associated with the development of addiction and AMPH psychosis. The effect of pretreatment with AMPH on dopamine (DA) release in the ventral striatum (nucleus accumbens) was determined by measuring the extracellular concentrations of DA and DA metabolites using in vivo microdialysis, both before and after an AMPH challenge. The postmortem tissue concentrations of DA, serotonin and their metabolites were measured to determine if this treatment was neurotoxic. Escalating doses of (+)-AMPH were not neurotoxic, and 25-30 days after the cessation of drug treatment animals showed relatively normal levels of spontaneous motor activity across the day-night cycle. However, AMPH pretreatment produced robust behavioral sensitization. Animals showed a marked hypersensitivity to the motor stimulant effects of an AMPH challenge, even after 15-20 days of withdrawal. Most importantly, this hyperdopaminergic behavioral syndrome was accompanied by significantly elevated DA release in the ventral striatum. In contrast, AMPH pretreatment had no effect on the basal extracellular concentrations of DA.(ABSTRACT TRUNCATED AT 250 WORDS)

Ketotifen can antagonise changes in sensitivity of cerebral dopamine receptors: behavioural correlates in rodent and primate

Rats preselected as "low responders" to the hyperactivity-inducing action of (-)N-n-propylnorapomorphine [(-)NPA] responded to an infusion of dopamine into the nucleus accumbens (25 micrograms/24 hr for 13 days) with hyperactivity during the infusion and long-term increased sensitivity to (-)NPA administered after the infusion. Both effects were antagonised by ketotifen (intraperitoneal infusion, 1 mg/kg/day), administered during the period of infusion of dopamine. Animals subject to infusion of dopamine also showed enhanced hyperactivity to L-DOPA (plus benserazide): this enhanced response was also antagonised by ketotifen, given acutely as a single dose (1 mg/kg i.p.). When haloperidol was given concurrently with the infusion of dopamine, spontaneous locomotor activity was markedly increased after the infusion for a period of at least 7 weeks: this long-term change was antagonised by ketotifen (1 mg/kg/24 hr), given during the period of treatment with dopamine/haloperidol or by a single acute injection of ketotifen (0.1-1.0 mg/kg i.p.) on an established response. Ketotifen, in doses up to 20 mg/kg (i.p.) did not reduce spontaneous locomotor activity, cause catalepsy or antagonise amphetamine-induced stereotypy in normal rats. In the marmoset, an enhanced sensitivity to the locomotor-stimulant effects of L-DOPA was induced 5 to 8 weeks after a treatment for 4 days with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which led to the development of akinesia and severe depletion of dopamine in the striatum. Treatment with a single dose of ketotifen (1 mg/kg i.p.) 60 min before L-DOPA antagonised the enhanced locomotor responsiveness to the L-DOPA/benserazide regimen.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic administration of dextroamphetamine on enzymes of energy metabolism in regions of the rat brain

In the present study the effects of chronic administration of dextroamphetamine on energy metabolism in the brain of the rat were examined. The enzymes studied were: hexokinase (soluble and particulate forms), phosphofructokinase, pyruvate kinase, lactate dehydrogenase, citrate synthase, NAD+ and NADP+-dependent isocitrate dehydrogenases, succinate dehydrogenase and malate dehydrogenase. All the activities of the enzymes were assayed in four regions of the brain of the rat (cerebellum, medulla oblongata and pons, cererbral cortex and diencephalon). Rats were injected intaperitoneally once daily with dextroamphetamine for 20 consecutive days. The initial dose was 5 mg/kg/day and the dose was then increased by 1 mg/kg/every 5 days up to a total of 8 mg/kg/day on days 16-20. In the glycolytic enzymes a reduction of the activity of phosphofructokinase was found in the diencephalon and an increase of the activity of pyruvate kinase and lactate dehydrogenase in the diencephalon and medulla oblongata and pons, respectively. Citrate synthase was the only enzyme in the Krebs' cycle affected by chronic administration of dextroamphetamine. The results presented here show that chronic administration of dextroamphetamine produced important changes in some enzymes of glycolysis and the Krebs' cycle in the brain of the rat.

Tyrosine hydroxylase immunochemistry and quantitative light microscopic studies of the mesolimbic dopamine system in rat brain: effects of chronic methamphetamine administration

Long-term treatment of rats with methamphetamine (20 mg/kg, IP, every 12 hours for 10 days) resulted in a large decrease in tyrosine hydroxylase staining axons and terminal boutons in the nucleus accumbens and frontal cortex, as well as the ventral tegmental area of the midbrain, when examined 60 days following termination of the drug treatment regimen. Quantitative analysis showed a 71 and 78% decrease in tyrosine hydroxylase staining processes in the nucleus accumbens and frontal cortex, respectively, and a 90% decrease in tyrosine hydroxylase positive material in the ventral tegmental area. Thus, tyrosine hydroxylase enzyme in both the cell bodies of the midbrain ventral tegmental area as well as in the nerve terminals in post-synaptic target regions of the forebrain is depleted by chronic methamphetamine administration.

Differential behavioral effects of tryptophan and 5-hydroxytryptophan in vervet monkeys: influence of catecholaminergic systems

In previous studies tryptophan and 5-hydroxy-tryptophan (5-HTP) treatments produced opposite effects on aggression and vigilance and differing effects on eating and locomoting in vervet monkeys. This study examined the effects of the serotonin reuptake inhibitor fluoxetine, and the catecholamine reuptake inhibitor desmethylimipramine (DMI) on tryptophan and 5-HTP induced behavioral changes. Thirty-two adult males from 16 different social groups were studied. Tryptophan (10, 20, and 40 mg/kg/day) produced dose-dependent reductions in aggression, vigilance, and locomotion and increases in eating. In contrast, 5-HTP (20, 40, and 80 mg/kg/day) increased aggression and vigilance and did not affect locomotion or eating. Fluoxetine (0.5, 1.0, and 2.0 mg/kg/day) produced effects identical to tryptophan while DMI (1.5, 3.0, and 6.0 mg/kg/day) resulted in dose-dependent increases in aggression, vigilance, and locomotion, and decrements in eating. When combined with tryptophan, fluoxetine augmented and DMI diminished the effects of tryptophan on all behaviors. Fluoxetine decreased and DMI increased the effects of 5-HTP on aggression and vigilance. Thus concurrent DMI enhanced and concurrent fluoxetine reduced the differences between 5-HTP and tryptophan. These results suggest that 5-HTP's effects on catecholaminergic systems may underlie the differing behavioral effects of tryptophan and 5-HTP on behavior in a species closely related to humans.

Chronic administration of D-amphetamine increases [3H]spiroperidol binding in cat brain

Administration of D-amphetamine sulfate twice daily for 10 consecutive days, in doses increasing from 10 mg/kg per day (i.p.) to 30 mg/kg per day resulted in significant increases in the Bmax for [3H]spiroperidol receptor binding in the striatum (+44.7%) and limbic forebrain (+40.3%) in cats. There were no significant changes in the KD value for either brain region. A single dose of amphetamine (15 mg/kg i.p.) produced no significant changes in [3H]spiroperidol binding in either brain region. These data are in contrast with previous studies which reported a significant decrease in dopamine receptor binding following chronic amphetamine treatment in rats.