Respiratory motor nerve activities during experimental seizures in cats

We evaluated respiratory motor nerve activities during experimental seizures induced with subcortical penicillin. The activities of the phrenic (PH), nasolabial (NL), and hypoglossal (HG) nerves and the recurrent laryngeal motor branches to the thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles were analyzed in 13 anesthetized, vagotomized, paralyzed, and ventilated cats. During ictal and interictal phases of seizures, nerve activities became irregular and peak integrated nerve activities increased, particularly in the case of the PH nerve. The ictal phase of seizures was associated with increased tonic activity and decreased phasic respiratory discharges, particularly in the cases of the HG, NL, and PCA nerves. During some prolonged ictal discharges, entrainment of nerve activities by cortical spiking was associated with irregular uncoordinated activation, particularly in the TA nerve. These studies help explain respiratory impairment during seizures by providing evidence of impaired coordination between activation of muscles that regulate upper airway patency and activation of the diaphragm.