Fig. 7. Intravenous morphine administered to awake rats significantly decreased acetylcholine (ACh) release and altered power in the prefrontal cortex (PFC) electroencephalogram (EEG). Morphine ( A ) but not saline ( C ) injected via a jugular cannula significantly decreased acetylcholine release in PFC of these unanesthetized animals ( t = 4.15; df = 34; P < 0.0001). Quantification of electroencephalogram power before (Pre) and after (Post) morphine injection (B) showed that morphine caused a significant slowing of the electroencephalogram (F = 256; df = 1, 13; P < 0.0001). In contrast, there was no change in electroencephalogram power before (Pre) and after (Post) intravenous injection of saline ( D ). Insets in B and D show 10-s recordings of representative electroencephalogram before and after administration of morphine ( B ) or saline ( D ).