PHASIC INCREASE OF MONOAMINE-RELATED ELECTROCHEMICAL SIGNAL IN THE RAT CAUDATE-NUCLEUS FOLLOWING CONDITIONED AUDITORY-STIMULATION DURING THE REACTION-TIME-TASK

Monoamine-related electrochemical signal was measured by in vivo chron oamperometry at a sampling rate of 5 Hz with a Nafion-coated carbon fi ber placed in the caudate nucleus of the rat (n = 5) performing an aud itory reaction-time task. During the task, the rat pressed a lever in response to a tone stimulus to get food reward. An averaging technique was employed to extract event-related changes in monoamine concentrat ion with respect to the tone stimulus, lever pressing or feeding. It w as found that the oxidation current increased phasically for several s econds following the tone presentation with the mean onset latency bei ng 0.4 +/- 0.2 s. Level-pressing was preceded by the onset of increase in two rats. Prominent increase was not observed following the tone p resentation during the resting state, passive feeding, and lever press ing unrelated to the task. The results indicate that phasic increase i n monoamine concentration occurs at the caudate nucleus in response to conditioned auditory stimulation in the reaction-time task. This resp onse is not simply the consequence of sensory stimulation, motor react ion, or feeding, but is possibly influenced by integrative processes. The present electrochemical findings are consistent with the previous electrophysiological data on dopamine neuronal activity. However, phar macological researches will be necessary in order to determine the sub stance involved in the phasic response. (C) 1998 Elsevier Science B.V.