Dopamine and complex sensorimotor integration: further studies in a conditioned motor task in the rat.

Full Abstract

Rats were trained to depress a lever and wait for the onset of a light stimulus, occurring after four equiprobable and variable intervals. At the stimulus onset, they had to release the lever within a reaction time limit for food reinforcement. This paradigm required time estimation of the various intervals and high attentional load for correct performance. Following activation of the dopaminergic transmission after systemic injection of d-amphetamine (0.6 and 0.8 mg/kg) or intrastriatal injection of dopamine (2.5 microgram/microliters), the rat's performance was impaired. Compared with control animals, the performance deficits were expressed as an increased number of premature lever releases before the conditional stimulus onset ("premature responses") and decreased reaction times. Indeed, the reaction times distribution was shifted to the left towards shortened reaction times. Although the number of premature responses was increased, the time estimation of the four different equiprobable intervals was not disturbed after stimulation of dopaminergic activity. A delay-dependent shortening of reaction times as a result of the conditional probability of the stimulus occurrence (i.e. reaction times are shorter as the duration of the delay increases) was found in control and drug sessions, indicating that the animals were still able to prepare their motor response (lever release) even after overstimulation of the dopaminergic transmission. In contrast, blocking dopamine receptors with the selective D2 antagonist raclopride was found to induce opposite effects on the reaction time performance. The number of delayed responses (i.e. occurring with a latency > 600 ms) was found to be significantly enhanced. Furthermore, the reaction times distribution showed a shift of the values to the right revealing a general tendency to lengthened reaction times. These results indicate that a "critical level" of dopamine activity (neither too low nor too high) in the striatum is necessary for a correct execution of the movement in a conditioned motor task with temporal constraint. Moreover, while delayed responses might reflect a motor impairment, anticipatory responses might reflect a "motor facilitation" revealed by a higher level of motor readiness, without disturbing time estimation nor attentional processes.

Author information

Author/s: Baunez, C (C); Nieoullon, A (A); Amalric, M (M);

Affiliation: Laboratoire de Neurobiologie Cellulaire et Fonctionnelle, C.N.R.S. 31, Marseille, France.

Journal and publication information

Publication Type: Journal Article; Research Support, Non-U.S. Gov't

Journal: Neuroscience (Neuroscience), published in ENGLAND. (Language: eng)

Reference: 1995-Mar; vol 65 (issue 2) : pp 375-84

Dates: Created 1995/07/10; Completed 1995/07/10; Revised 2006/11/15;

PMID: 7777155, status: MEDLINE (last retrieved date: 2/18/2009)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MeSH Headings (categories) shown below.

Animals
Behavior, Animal - drug effects
Conditioning, Operant - drug effects; physiology
Dextroamphetamine - pharmacology
Dopamine - administration & dosage; pharmacology; physiology
Dopamine Agonists - pharmacology
Dose-Response Relationship, Drug
Injections
Male
Motor Cortex - cytology; physiology

Motor Cortex - cytology; physiology
Neostriatum
Raclopride
Rats
Rats, Wistar
Reaction Time - drug effects
Receptors, Dopamine D2 - antagonists & inhibitors
Salicylamides - pharmacology
Somatosensory Cortex - cytology; physiology
Time Perception - drug effects

Note: Bold headings indicate primary MeSH headings or qualifiers.

Associated Chemicals: Dopamine Agonists (0) ; Receptors, Dopamine D2 (0) ; Salicylamides (0) ; Dopamine (51-61-6) ; Dextroamphetamine (51-64-9) ; Raclopride (84225-95-6)

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