Emotional perception modulated by an opioid and a cholecystokinin agonist

Rationale The cholecystokinin (CCK) and opioid neuromodulatory systems work in an antagonistic fashion and can modulate emotional states and noxious input in opposite directions. In this behavioral study, we generalize this idea and suggest that CCK and opioids can modulate the processing of other external signals, e.g., visual stimuli rather than only noxious input. Objectives The objective of this study was to determine whether CCK and an opioid agonist could modulate the emotional experience of visual stimuli. Materials and methods Thirteen healthy male volunteers viewed standardized pictures with either neutral or unpleasant content. Simultaneously, one of three treatments was administered in a randomized, double-blind crossover design: the CCKb receptor agonist pentagastrin (0.1 mu g/kg), the mu-opioid receptor agonist remifentanil (0.0625 mu g/kg), or saline. Self-ratings of the emotional experience of pictures and drugs were sampled together with psychological tests and recording of heart rate. Results Pentagastrin treatment increased the rating of unpleasantness for both neutral and unpleasant pictures, while it decreased the rating of pleasantness for the neutral pictures. These effects did not correlate with the degree of general unpleasantness induced by the drug. Remifentanil treatment increased the pleasantness for the neutral pictures. While pentagastrin treatment induced a heart rate increase, unpleasant pictures induced a heart rate decrease, and the magnitude of change in heart rate correlated positively for these conditions. Conclusions This study shows that the CCK and the opioid system modulate how external stimuli are emotionally perceived, suggesting a possible involvement in affective disorders.