TIMING OF MEDULLARY LATE-INSPIRATORY NEURON DISCHARGES - VAGAL AFFERENT EFFECTS INDICATE POSSIBLE OFF-SWITCH FUNCTION

1. In decerebrate paralyzed cats, we observed the responses of ventral and dorsal medullary inspiratory (I) neurons to two types of vagal af ferent input that shorten neural I: lung inflation and vagal electrica l stimulation. 2. A study population of 15 I neurons whose firing patt erns suggested involvement in the inspiratory OFF-switch (IOS) was sel ected on the basis of two criteria: late onset of firing and excitatio n by vagal inputs. 3. Firing in relation to the end of I showed two ty pes of response to vagal inputs. The pre-expiratory onset time (time f rom initial spike to end of I) was either unchanged (type 1 response i n 5/15 neurons) or significantly changed (type 2 response in 10/15 neu rons). 4. It is suggested that type 1 neurons, whose firing patterns r emain closely locked to the end of I despite considerable changes of I duration, are involved in promoting the IOS, whereas type 2 neurons a re either not involved (e.g., late-onset premotor neurons) or are invo lved at an earlier temporal processing stage.