DIFFERENTIAL-EFFECTS OF CHLORAL HYDRATE AND PENTOBARBITAL SODIUM ON ACOCAINE LEVEL AND ITS CATECHOLAMINE RESPONSE IN THE MEDIAL PREFRONTALCORTEX - A COMPARISON WITH CONSCIOUS RATS

Adult male Sprague-Dawley rats anesthetized with chloral hydrate and p entobarbital sodium were used as two different treatment groups. Consc ious rats were used as a control group. By using baseline (precocaine) concentration as 100%, after cocaine administration (3.0 mg/kg i.v,), the maximal dopamine (DA) increase occurring at the first microdialys is collection period (20 min) in the medial prefrontal cortex was 299 +/- 46% for the chloral hydrate group, 168 +/- 12% for the pentobarbit al sodium group, and 325 +/- 23% for the conscious group. At the same time, norepinephrine (NA) increases reached a maximum and were 162 +/- 20%, 100 +/- 5%, and 141 +/- 17%, respectively. The maximal changes o f DA and NA in the chloral hydrate group and in the control group were both significantly higher than that in the pentobarbital tal sodium g roup, Meanwhile, the cocaine concentration was higher over a 100-min p eriod of time in the chloral hydrate group when compared with the pent obarbital group and the control group. The peak cocaine concentration in dialysate occurred in the same time slot of maximal DA and NA respo nses, which were 0.65 +/- 0.08, 0.30 +/- 0.02, and 0.41 +/- 0.05 mu M, respectively. Anesthetics suppress the pharmacologic response of neur ons, which may explain the difference in catecholamine response betwee n the pentobarbital sodium and the conscious groups. Conversely, becau se there was no significant difference in DA and NA response between t he chloral hydrate group and the conscious group, it may possibly be d ue to the balancing effect between the higher existing cocaine concent ration and the anesthetic suppression on pharmacological response of n eurons in the chloral hydrate group, The effect of guide cannula impla ntation on the cocaine-induced catecholamine response was also evaluat ed.