Inhibitory effect of A10 dopaminergic neurons of the ventral tegmental area on the orienting response evoked by acoustic stimulation in the cat.

The effect of bilateral electric stimulation of A10 dopaminergic neurons of the ventral tegmental area (80-300 microA, 20-50 Hz, 0.1-0.5 ms, 2 s duration) on latency and duration of the orienting response, evoked by acoustic stimuli (4500-8000 Hz, 2 s), was studied in the cat. A10 neuron stimulation, simultaneous with the acoustic one, was performed with threshold parameters inducing minimal behavioral signs (head searching movement, sniffing, increase in alertness). By means of a videoanalysis system, a statistically significant increase, both of latency and duration of the response, was observed. The possible role of dopamine was studied administrating sulpiride (20 mg/kg i.p.), a dopaminergic antagonist prevalently acting on the mesolimbic-mesocortical system. In this condition, the disappearance of A10 neuron effect occurred. Sulpiride injection did not affect the parameters of the orienting response to acoustic stimulus alone, suggesting a direct effect on A10 dopaminergic neurons. Moreover, when saline administration was carried out, no significant modification of the effects, obtained following A10 neuron activation, was observed. The data suggest that A10 dopaminergic neurons, origin of the mesolimbic-mesocortical system, may be involved in the control of the response to sensory stimuli, likely by influencing sensorimotor integration processes. An involvement in the inhibitory regulation of the switching of attention is also discussed.