Use of a rapid brain-sampling technique in a physiologic preparation: effects of morphine, ketamine, and halothane on tissue energy intermediates.

A new method of rapid sampling of brain tissue, "freeze-blowing," has been used to compare the neurochemistry of the brain during anesthesia with that in the awake state. The method avoids anoxia associated with the sampling process. Physiologic variables, including body temperature, blood-gas tensions and blood pressure, were carefully monitored and controlled in the experimental animals. None of the agents tested (halothane, morphine, and ketamine) reduced the brain tissue high-energy phosphate reserved. All three drugs doubled glucose levels. Morphine lowered both lactate and the lactate/pyruvate ratio. Uniformly, the three anesthetic agents led to twofold increases of brain cyclic 3'-5' adenosine monophosphate concentrations. These changes suggest a possible role for cyclic nucleotides in central neurotransmission.