On the role of noradrenaline in psychostimulant-induced psychomotor activity and sensitization.
BACKGROUND
Psychostimulant drugs exert their behavioral effects primarily through enhancement of monoaminergic neurotransmission. Augmented dopamine activity is thought to play a critical role in the psychomotor stimulant effects of amphetamine and cocaine, as well as in the development of long-term behavioral sensitization evoked by repeated exposure to amphetamine. However, despite the fact that brain dopamine and noradrenaline systems are closely interconnected, the extent to which noradrenergic transmission contributes to these behavioral effects of psychostimulants is a relatively unexplored issue.


OBJECTIVE
By inhibiting noradrenergic neurotransmission with the alpha2-adrenoceptor agonist clonidine, the alpha1-antagonist prazosin and the beta-antagonist propranolol, we investigated the involvement of noradrenaline neurotransmission in the psychomotor stimulant and long-term sensitizing effects of d-amphetamine and cocaine in rats.


METHODS
Clonidine (0.003-0.1 mg/kg), prazosin (0.1-3.0 mg/kg) and propranolol (1.0-3.0 mg/kg) were administered prior to d-amphetamine (1.0 mg/kg), cocaine (15 mg/kg) or apomorphine (1.0 mg/kg) and psychomotor activity was measured. In separate studies, clonidine (0.03 mg/kg), prazosin (1.0 mg/kg) or propranolol (3.0 mg/kg) were co-administered with d-amphetamine (2.5 mg/kg) or cocaine (30 mg/kg) for 5 days, and locomotor sensitization was assessed 3 weeks post-treatment.


RESULTS
The psychomotor stimulant effect of d-amphetamine, but not that of cocaine or apomorphine, was dose-dependently inhibited by clonidine and prazosin, and enhanced by propranolol. Clonidine, prazosin, and propranolol did not influence the induction of sensitization by amphetamine or cocaine.


CONCLUSIONS
Enhancement of synaptic noradrenaline concentrations contributes to the psychomotor stimulant effect of d-amphetamine, but not cocaine or apomorphine. In addition, noradrenergic neurotransmission is not critically involved in the induction of psychostimulant sensitization.
Vanderschuren
Louk J M J
LJ
Drug Abuse Program, Department of Medical Pharmacology, Research Institute Neurosciences VU, VU Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands. ljmj.vanderschuren.pharm@med.vu.nl
Beemster
Patricia
P
Schoffelmeer
Anton N M
AN
D019969:Amphetamine-Related Disorders / Q000150:complications / Q000517:prevention & control; D000818:Animals; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003000:Clonidine / Q000008:administration & dosage / Q000493:pharmacokinetics; D003042:Cocaine / Q000009:adverse effects / Q000037:antagonists & inhibitors; D019970:Cocaine-Related Disorders / Q000150:complications / Q000517:prevention & control; D003913:Dextroamphetamine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006948:Hyperkinesis / Q000139:chemically induced* / Q000150:complications / Q000517:prevention & control*; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D009638:Norepinephrine / Q000378:metabolism* / Q000494:pharmacology*; D011224:Prazosin / Q000008:administration & dosage / Q000493:pharmacokinetics; D011433:Propranolol / Q000008:administration & dosage / Q000493:pharmacokinetics; D011595:Psychomotor Agitation / Q000378:metabolism* / Q000517:prevention & control; D051381:Rats; D017208:Rats, Wistar
D000697:Central Nervous System Stimulants; D011433:Propranolol; D003042:Cocaine; D003000:Clonidine; D003913:Dextroamphetamine; D009638:Norepinephrine; D011224:Prazosin