Amphetamine- type reinforcement by dopaminergic agonists in the rat

Area of Science:

• Neuroscience
• Pharmacology
• Behavioral Science

Background:

• D-amphetamine is a widely abused stimulant drug with significant reinforcing properties.
• The reinforcing effects of amphetamines are thought to be mediated, in part, by actions within the dopaminergic system.
• Understanding the neurobiological mechanisms underlying amphetamine reinforcement is crucial for developing effective treatments for addiction.

Purpose of the Study:

• To investigate the effects of dopaminergic agonists (apomorphine, piribedil) and an alpha noradrenergic agonist (clonidine) on intravenous d-amphetamine self-administration in rats.
• To determine if dopaminergic agonists alter amphetamine metabolism or directly substitute for amphetamine's reinforcing effects.
• To examine the role of dopamine receptor blockade in disrupting responding for dopaminergic agonists.

Main Methods:

• Rats were trained to self-administer d-amphetamine intravenously.
• The effects of systemic injections of apomorphine, piribedil, and clonidine on d-amphetamine intake were assessed.
• Brain levels of 14C-amphetamine were measured after administration of dopaminergic agonists.
• Drug substitution and blockade studies using (+)-butaclamol were conducted.

Main Results:

• Dopaminergic agonists apomorphine and piribedil decreased d-amphetamine self-administration in a dose-dependent manner, mimicking the effects of amphetamine itself.
• Clonidine did not produce similar suppressive effects on amphetamine intake.
• Apomorphine and piribedil did not alter amphetamine metabolism, and rats readily self-administered these agonists when substituted for amphetamine.
• (+)-Butaclamol disrupted responding for apomorphine and piribedil, confirming the involvement of dopaminergic pathways.

Conclusions:

• Dopaminergic agonists suppress amphetamine intake by extending drug satiation, suggesting a shared mechanism with amphetamine.
• The reinforcing properties of amphetamine are strongly linked to its actions within the dopaminergic synapse.
• These findings provide further evidence for the critical role of the dopamine system in mediating the rewarding effects of psychostimulants.