ALPHA-2-ADRENERGIC MODULATION OF PREFRONTAL CORTICAL NEURONAL-ACTIVITY RELATED TO A VISUAL-DISCRIMINATION TASK WITH GO AND NO-GO PERFORMANCES IN MONKEYS

The effects of clonidine (a selective agonist for alpha-2 receptor) an d B-HT920 (an agonist for both alpha-2 and D2 receptors) were examined iontophoretically on neurons in the prefrontal cortex of three monkey s performing a visual discrimination task with GO and NO-GO responses. A total of 212 task-related neurons were sampled, of which 120 neuron s were related to the visual signals (visually-related neurons; 32 neu rons were related to the warning signal, 45 to the GO signal and 43 to the NO-GO signal), 34 neurons were related to both the GO signal and GO response ('intermediate'-related neurons), and 58 neurons were rela ted to GO response (movement-related neurons). Clonidine and B-HT920 w ere tested in 137 and 115 neurons, respectively, and showed mainly a f acilitatory effect on the neurons. Clonidine enhanced the visually-rel ated activity in 83.0% of modulated neurons, the intermediate-related activity in 81.0% neurons and the movement-related activity in 85.0% n eurons. Similarly, B-HT920 enhanced the visually-related activity in 8 0.0% of modulated neurons, the intermediate-related activity in 77.8% neurons and the movement-related activity in 81.0% neurons. The facili tatory effect of clonidine or B-HT920 on the visually-related activity was stronger than that on the movement-related activity. In 22 visual ly-related neurons enhanced by clonidine and-or B-HT920 (6 WS-, 7 GS- and 9 NS-related neurons), the alpha-2 antagonist yohimbine suppressed the visually-related activities. In 13 neurons enhanced by B-HT920, t he facilitatory effect of B-HT920 was blocked by yohimbine, but not by the D2 antagonist sulpiride. The present results suggest that alpha-2 adrenoceptors in the monkey prefrontal cortex an involved in neural p rocessing related to visual discrimination and selection of GO and NO- GO responses, and that the facilitatory effect of B-HT920 may be media ted via alpha-2 adrenoceptors instead of D2-receptors. (C) 1998 Elsevi er Science Ireland Ltd. All rights reserved.