Differential effects of chloral hydrate and pentobarbital sodium on a cocaine level and its catecholamine response in the medial prefrontal cortex: a comparison with conscious rats.

Adult male Sprague-Dawley rats anesthetized with chloral hydrate and pentobarbital sodium were used as two different treatment groups. Conscious 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 microdialysis collection period (20 min) in the medial prefrontal cortex was 299 +/- 46% for the chloral hydrate group, 168 +/- 12% for the pentobarbital 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 of DA and NA in the chloral hydrate group and in the control group were both significantly higher than that in the pentobarbital sodium group. Meanwhile, the cocaine concentration was higher over a 100-min period of time in the chloral hydrate group when compared with the pentobarbital group and the control group. The peak cocaine concentration in dialysate occurred in the same time slot of maximal DA and NA responses, which were 0.65 +/- 0.08, 0.30 +/- 0.02, and 0.41 +/- 0.05 microM, respectively. Anesthetics suppress the pharmacologic response of neurons, which may explain the difference in catecholamine response between the pentobarbital sodium and the conscious groups. Conversely, because there was no significant difference in DA and NA response between the chloral hydrate group and the conscious group, it may possible be due to the balancing effect between the higher existing cocaine concentration and the anesthetic suppression on pharmacological response of neurons in the chloral hydrate group. The effect of guide cannula implantation on the cocaine-induced catecholamine response was also evaluated.