Inspiratory neurons with decrementing firing pattern in raphe nuclei of feline medulla.

Extracellular spikes of single inspiratory (I) neurons with decrementing firing pattern were recorded in the medullary raphe nuclei in decerebrated or Nembutal anesthetized cats. A total of 23 neurons with decrementing firing patterns during the I phase were recorded in the raphe obscurus and pallidus at the levels of 2.0-4.0 mm rostral to the obex. The respiratory neurons fired in the I phase during a brief stop of the ventilator, indicating that their respiratory-related activities were central in origin. The effect of electrical stimulation of the recording site of the respiratory neuron on diaphragm EMG was examined: both the diaphragm EMG activity and the respiratory frequency were increased. None of six neurons tested for projections to the cervical spinal cord was antidromically activated by electrical stimulation. The present results suggest that cat I-decrementing neurons in the medullary raphe nuclei receive inputs from the central respiratory rhythm generator and may modify the respiratory activity of supraspinal neural structures.