Visceral and somatic reflexes produced by J pulmonary receptors in newborn kittens

The functional efficiency of J pulmonary receptor reflexes was studied in 28 newborn anesthetized kittens. J receptor stimulation was achieved by injecting phenyl diguanide (PDG) solution into the right atrium using a technique established earlier for cats. Control injections of PDG into the aorta were made. Respiration, aortic blood presure, and knee jerk were recorded. The Hering-Breuer reflex was routinely tested in each kitten by inflating the lungs through the tracheal cannula. In the newborn kitten (1-6 days old), it was not possible to elicit any effect on injection of PDG into the right atrium. At 1 wk, the visceral reflexes--apnea, rapid shallow breathing, bradycardia--could be produced by doses much higher (six times) than the adult dose. By the 10th day, the visceral reflexes were fully developed. The motor reflex, i.e., inhibition of EMG and reduction of knee jerk, was elicited after 3 wk. The earliest response was seen in a 3-wk-old kitten. All these reflexes were abolished by bilateral cervical vagotomy. These results suggest that the J receptor reflexes are poorly developed in the newborn kitten and that the motor reflexes develop much later than the visceral reflexes.