Effect of catecholamine-receptor antagonists on feeding-related neuronal activity in the central amygdaloid nucleus of the monkey: a microiontophoretic study

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Abstract
1. Neuronal activity in the central amygdaloid nucleus (ACE) was recorded during a visually guided bar-press feeding task, and the modulatory effects of catecholaminergic blockers were investigated. 2. The feeding task had the following four phases: 1) a cue light to signal the start of bar press, 2) bar press, 3) a short cue tone followed by food delivery, and 4) ingestion reward. Of 278 cells observed, 176 (63%) increased or decreased their discharge rates in one or more phases of the feeding task. Of these, 60 (34%) responded to the cue light, 81 (46%) to the bar press, 66 (37%) to the cue tone, and 176 (100%) during the reward period. In the ingestion reward phase, firing of 128 (73%) increased and firing of 48 (27%) decreased. The reward-related response depended on the nature of food. In the trials with aversion food, some neurons increased firing (n = 6), whereas others showed opposite firing changes (n = 10). 3. The decreased firing rate during the reward period was greatly attenuated in the no-reward tasks (n = 29) and was blocked by electrophoretic application of a beta-adrenoceptive antagonist [sotalol (SOT), n = 26]. Noradrenaline (NA) application mimicked the inhibitory effect on the reward-related activity during extinction trial (n = 4). These results suggest that the decreased firing rate observed during the reward period was modulated by beta-adrenoreceptors. 4. Of 32 neurons tested, the activity of 8 (25%) and 14 (44%) were enhanced by the cue light or bar press, respectively. These effects were attenuated by electrophoretic application of a dopamine (DA) antagonist [spiperone (SPP)] but not by SOT. This indicates that dopaminergic inputs may be related to recognition of visual signals and to motor initiation during the monkey feeding paradigm.

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