Effects of acute and chronic cocaine on breathing and chemosensitivity in awake rats

Abstract

The barometric method was used to study effects of acute (AC) and chronic cocaine (CC) on breathing and chemosensitivity in awake rats. Effects of AC were evaluated 15 min after daily intraperitoneal injections, and effects of CC were measured at each week of the 4-wk treatment. Sham rats (group 1, n = 10) were injected with NaCl (0.2 ml). Cocaine HCl was given daily in groups 2 (20 mg/kg, n = 5) and 3 (40 mg/kg, n = 10). Effects of AC on the respiratory responses to 10% O2 in N2 and 5% CO2 in 21% O2 were studied 15 min after the first injection of cocaine. Effects of CC on chemosensitivity were studied at weekly intervals. NaCl had no effects on the breathing pattern or chemosensitivity. During normoxia, AC caused an increase in respiratory rate in group 2 and rapid and shallow respiration in group 3. The effects were similar from the first to the last injection at week 4. Haloperidol, a dopamine (DA) receptor blocker, abolished (group 4, n = 8) or prevented (group 5, n = 9) effects of AC. CC had no effects in all normoxic rats. During exposure to either low O2 or high CO2 the AC-induced polypnea was replaced by deep and slow respiration. CC had no effects on CO2 response in all rats. In contrast, 10% O2 response of tidal volume in group 2 and minute ventilation in group 3 were attenuated at weeks 3 and 4 compared with control.(ABSTRACT TRUNCATED AT 250 WORDS)