Central nervous system responses to cigarette smoke inhalation in the cat

Intact, pentobarbital anesthetized cats (with and without brainstem stimulating electrode implants) and unanesthetized Sherrington (gamma-driven) decerebrate cats "smoked" cigarettes of varying nicotine content (0.2-2.5 mg). Nicotine free lettuce leaf cigarettes were used as controls. "Smoking doses" of nicotine base (10-25 micrograms/kg) were administered i.v. for comparison. Smoke inhalation produced motor reflex depression which paralleled the nicotine content of the cigarettes "smoked". Patellar reflex facilitation due to mesencephalic reticular stimulation was reduced by doses of nicotine and cigarette smoke. Cigarettes (2.5 mg nicotine) and doses of nicotine (25-50 micrograms/kg, i.v.) significantly reduced rigidity and patellar reflex amplitude in the gamma-decerebrate cat. Dihydro-beta-erythroidine reduced the nicotine and cigarette smoke induced patellar reflex depression but not the diminution in the rigidity. Smoking doses of nicotine suppressed pentobarbital-induced EEG spindles in acutely prepared cats. Nicotine (10-25 micrograms/kg) produced EEG and behavioral arousal in cats with chronic deep electrodes. It was concluded that cigarette smoke produces its pharmacological effects via its nicotine content.