Opioid modulation of working memory: intraseptal, but not intraamygdaloid, infusions of beta-endorphin impair performance in spatial alternation.

The effect of beta-endorphin on spatial working memory was examined following microinfusions of beta-endorphin into the medial septal area and central amygdaloid nucleus in Long-Evans male rats. Working memory was assessed by spatial alternation in a T-maze. beta-Endorphin, 250 and 1000 ng/site, respectively, and muscimol, 20 ng/site, were infused into the medial septal area or central amygdaloid nucleus prior to behavioral testing. The hippocampal theta rhythm was examined following intraseptal infusions of beta-endorphin and muscimol. In the medial septal area, beta-endorphin and muscimol impaired choice accuracy and reduced the power of hippocampal theta rhythm. The degree of reduction in the power of hippocampal theta rhythm was correlated with the magnitude of behavioral impairment of choice accuracy in spatial alternation. In the central amygdaloid nucleus, beta-endorphin (1000 ng) and muscimol (20 ng) did not affect choice accuracy. The results suggest that septal, but not amygdaloid, opioid, and GABAergic activity modulate spatial working memory and hippocampal physiology.