Paroxetine, a selective 5-hydroxytryptamine uptake inhibitor with antidepressant properties, lacks amphetamine-like stimulus properties in an operant drug discrimination bioassay in rodents

Evaluation of the discriminative stimulus and reinforcing effects of sertraline in rhesus monkeys

Rhesus monkeys (N = 4) were allowed to self-administer cocaine (0.03 mg/kg/injection) under a fixed-ratio 10 (FR 10) schedule during daily 2-h experimental sessions. When responding was stable, a variety of doses of sertraline, a serotonin reuptake blocker under development as an antidepressant, were made available for self-administration. Baseline conditions were reinstated between doses of sertraline. Cocaine 0.03 mg/kg/injection maintained high rates of injection, while total saline injections decreased to low levels within four to seven sessions. Sertraline (0.05-0.4 mg/kg/injection) did not maintain self-administration above saline levels in three of the four monkeys. In the fourth, responding was marginally above saline levels at two doses but was not systematically related to dose. In a second experiment, rhesus monkeys (N = 6) were trained to discriminate either d-amphetamine (0.56-1.0 mg/kg, IG) or pentobarbital (10 mg/kg, IG) from saline in a discrete-trials shock avoidance/escape paradigm. Sertraline (4.0-32 mg/kg) failed to substitute for either d-amphetamine or pentobarbital as a discriminative stimulus. These results suggest that sertraline is unlikely to have abuse potential in humans and is unlikely to have either d-amphetamine-like or pentobarbital-like subjective effects.

An overview of the animal pharmacology of paroxetine

Animal studies show that paroxetine is a potent and selective inhibitor of 5-hydroxytryptamine (5-HT) neuronal uptake. It shows excellent activity after oral administration, and pharmacological studies on its principal metabolites indicate that they are much less active than the parent compound. Paroxetine possesses no overt sedative or antihistaminergic properties and it does not potentiate the effects of alcohol. Weak activating properties are observed in EEG studies in animals at doses generally greater than those required to inhibit 5-HT uptake in the CNS, and the activated EEG in rats is associated with slight locomotor stimulation. However, specific studies indicate that this activation is not amphetamine-like. Paroxetine does not inhibit monoamine oxidase in vitro. Paroxetine is well tolerated by the cardiovascular system, being qualitatively and quantitatively less cardiotoxic than amitriptyline. The weak affinity of paroxetine for muscarinic cholinergic receptors in vitro is associated with mydriasis in vivo, but only at doses well in excess of those required to potentiate the effects of 5-HT in the CNS. It is therefore concluded that paroxetine should be an effective antidepressant with a reduced propensity to induce the adverse events that are characteristic of the tricyclic class of antidepressants.