Stimulating fastigial nucleus alters central mechanisms regulating phrenic activity

In paralyzed, mechanically ventilated, anesthetized cats, 30-sec trains of electrical stimulation in the rostral fastigial nucleus caused either respiratory excitation or inhibition (apnea) of respiration. The response elicited by stimulation was dependent on the frequency of stimulation: the duration of apnea decreased and respiratory excitation occurred more frequently at lower frequencies of stimulation. Excitation was characterized by increases of f and the rate of rise and peak (TNA) integrated activity of the phrenic nerve. TI and TE decreased. TNA and f remained elevated for at least three minutes after excitatory respiratory responses. Also, respiration was frequently elevated after an inhibitory response. Brief stimulation (100-200 ms) administered during expiration or inspiration altered either TE or TI and TNA, respectively. In addition, brief stimulation elicited short-latency inhibition or excitation of phrenic nerve activity. These effects were often unassociated with other phase changes. We conclude that activation of neurons or axons within the rostral fastigial nucleus can modulate activity of the phrenic nerve by altering the activity of at least three separate central mechanisms.