Postsynaptic potentials of bulbar respiratory neurons of the turtle

Membrane potentials of bulbar respiratory neurons of Pseudemys scripta were recorded from unanesthetized, decerebrate animals. Efferent neurograms were recorded from the serratus magnus (inspiratory) and pectoralis (expiratory) nerves. The animals were paralyzed and ventilated by a servo-respirator driven by the pectoralis neurogram to mimic the spontaneous turtle respiratory cycle. Neurons, comparable to mammalian medullary respiratory neurons, were observed, namely: augmenting inspiratory, augmenting expiratory and postinspiratory neurons. In addition, two types of phase-spanning neurons, postinspiratory-expiratory and expiratory-inspiratory, were encountered. The pattern of appearance of inhibitory postsynaptic potentials generally resembled that observed in the cat. The neurons observed correspond to the activity pattern of known respiratory muscles of the turtle. The results suggest that the three phase respiratory cycle of the turtle corresponds to the ternary neural cycle postulated for mammals.