Functional involvement of catecholamines in reward-related neuronal activity of the monkey amygdala.

Abstract

Neuronal activity was studied in the behaving active monkey to elucidate the functional significance of catecholamines (CA) in the amygdala during reward-related behavior, and the effects of noradrenaline (NA), dopamine (DA), and their antagonists, electrophoretically applied, were examined using multibarreled electrode techniques. The operant food intake task had four phases: 1) cue light on to signal the start of bar pressing, 2) execution of high fixed-ratio bar pressing (FR 20), 3) short cue tone triggered by the last bar press to signal the presentation of food, and 4) ingestion, reward. More than half of the 292 cells tested (198, 68%) changed activity during the task. Most changes occurred during the bar press and/or reward periods (164/198, 83%), the former affecting neuronal activity more (127/198, 64%) than the latter (70/198, 35%). Phasic responses to the cue light and cue tone were observed in 62 cells (31%) and 19 cells (10%), respectively. The effects of NA and DA were studied in 199 and 177 cells, respectively. Of these, 90 cells (46%) responded to NA, 87 (97%) with a decrease of firing, and only 3 (3%) with an increase, whereas 40 (26%) responded to DA by increasing (28 cells, 70%) or decreasing (18 cells, 30%) activity. The inhibitory effect of NA was blocked by alpha- and/or beta-adrenoceptive antagonists. Task-related activity changes occurred significantly more often among DA sensitive cells than among DA insensitive cells. CA sensitivity and task-related neuronal activity were functionally correlated only in the reward period. Activity of NA sensitive cells decreased in this period more frequently than insensitive cells, and DA sensitive cells increased more often than insensitive cells. Application of a beta-adrenoceptive antagonist or a DA antagonist attenuated the activity changes during the reward period. Application of a alpha-adrenoceptive antagonist had no effect on the reward-related neuronal activity changes. When grouped according to recording site, centromedial cells had a significantly higher occurrence of task-related activity changes than those in the basolateral parts of the amygdala. The bar-press responsive and reward-related cells, the firing of which decreased, were found more often in the centromedial than in the basolateral division, although the numbers of cells that responded to sensory cues were not different in the two parts. Catecholaminergic involvement in the task-related activity changes was also different.(ABSTRACT TRUNCATED AT 400 WORDS)