BEHAVIORAL AND PHARMACOLOGICAL MODULATION OF RESPIRATION IN RHESUS MONKEYS

Changes in respiration associated with schedule‐controlled behavior were determined in seated rhesus monkeys prepared with a pressure‐displacement head plethysmograph for monitoring ventilation continuously during behavioral experiments. Subjects were trained to press a lever under fixed‐ratio 40 and fixed‐interval 300‐s schedules of stimulus termination. Episodic increases in ventilation were closely associated with periods of responding under both schedules. Recurring episodes of increased ventilation occurred during fixed‐ratio responding, and were separated by brief 10‐s timeouts during which ventilation decreased. Under the fixed‐interval schedule, both ventilation and response rate typically increased as the 300‐s interval elapsed. The effects of cocaine, caffeine, and two adenosine agonists, 5′‐N‐ethylcarboxamidadenosine (NECA) and 2‐(carboxyethylphenylamino)adenosine‐5′‐carboxamide (CGS 21680), on behavior and respiration were determined using a cumulative‐dosing procedure. Drug‐induced suppression of behavior eliminated the episodic increases in ventilation during the performance components of both schedules. Schedule‐related increases in ventilation were compared to those produced by elevated levels of CO2 in inspired air. Exposure to 4% CO2 mixed in air increased ventilation in all subjects, and the combined effects of CO2 exposure and schedule‐controlled responding on respiration appeared to be additive. The results suggest that behavioral activities may increase ventilation through increased metabolic demand and increased CO2 production.