Intrapulmonary receptors in the garter snake (Thamnophis sirtalis).

Receptors in the respiratory system of anesthetized, unidirectionally ventilated garter snakes were analyzed from single-unit vagal recordings. Three types of receptors were found: rapidly adapting mechanoreceptors (RARs), slowly adapting pulmonary stretch receptors (SARs) and intrapulmonary chemoreceptors (IPCs). RARs gave a burst of activity when the lung was inflated or deflated. Discharge frequency of SARs increased during a sustained elevation of intrapulmonary pressure (PIP); a step increase in PIP usually caused an overshoot in receptor activity that slowly adapted to a new tonic level during the sustained inflation. The activity of intrapulmonary chemoreceptors (IPCs) decreased when airway CO2 was raised. A sudden removal of CO2 caused a striking overshoot in activity which slowly adapted. Receptor discharge of SARs and IPCs was studied at 20, 25 and 30 degrees C. Discharge frequency increased with increasing temperature. The Q10 of discharge frequency averaged 3.0 for IPCs and 1.5 for SARs. Temperature clearly had a profound effect on pulmonary receptor activity; however, the relative change of activity of IPCs or SARs to a given stimulus was similar regardless of body temperature, and since the body temperature of snakes varies considerably, this may have important implications regarding the control of breathing in these animals.