The pharmacology of impulsive behaviour in rats V: the effects of drugs on responding under a discrimination task using unreliable visual stimuli.
Impulsivity is widely considered to be multifactorial. One factor, frequently termed "reflection-impulsivity", refers to the need to give time to information analysis and reflection before making a response. In most reaction time tasks employed for non-human subjects, responding is expected immediately after a specific stimulus has been presented. In the present experiment, the need to wait before responding was made explicit by using a signal which increased in predictive value the longer the subject (a rat) waited before responding. First, the rats learned that a light signal indicated the availability of a food reinforcer if one of two levers was pressed. In the test procedure, on each trial, when the light was turned on it was only 50% likely to indicate the "correct" lever. After a brief interval it was turned off and on again, this time with a slightly higher probability (>50%) of indicating the correct lever. Over a period of a few seconds the probability that the light indicated the correct lever increased to almost 100%. Thus a quick response to the light would result in many errors, whereas a slow response could always result in food delivery. Once trained the rats were treated with a series of drugs: haloperidol (0.01-0.1 mg/kg), chlordiazepoxide (1-10mg/kg), ethanol (100-1000 mg/kg), d-amphetamine (0.4-1.2 mg/kg), metergoline (0.3-3.0 mg/kg), imipramine, desipramine and clomipramine (all 1, 3 and 10 mg/kg), as well as being given additional food just prior to testing. Ethanol and clomipramine had no effects on behaviour in the dose range tested. Amphetamine did not affect accuracy and had no effect on reaction time. The other drugs all reduced the number of short reaction times and thereby increased overall accuracy. Additional feeding, chlordiazepoxide and haloperidol also increased selectively the accuracy of responses made with short reaction times. These results can be interpreted by supposing that desipramine and imipramine specifically reduced impulsivity whereas additional feeding, chlordiazepoxide, haloperidol increased the response criterion. The pharmacological specificity of the tricyclics suggests that stimulation principally of the noradrenergic system (via desipramine), but not necessarily the serotonergic (clomipramine) or dopaminergic (amphetamine) improves performance in this procedure.
D000818:Animals; D004193:Discrimination Learning / Q000187:drug effects; D004192:Discrimination, Psychological / Q000187:drug effects*; D007175:Impulsive Behavior / Q000139:chemically induced*; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000187:drug effects; D011619:Psychotropic Drugs / Q000494:pharmacology*; D051381:Rats; D011930:Reaction Time / Q000187:drug effects