Changes in respiratory-modulated neural activities, consistent with obstructive and central apnea, during fictive seizures in an in situ anaesthetized rat preparation
St-John WM, Rudkin AH, Homes GL, and Leiter JC (2006) Changes in respiratory-modulated neural activities, consistent with obstructive and central apnea, during fictive seizures in an in situ anaesthetized rat preparation. Epilepsy Res 70:2-3 218–28.
Abstract: Sudden unexplained death in epilepsy (SUDEP) has been proposed to result from seizure-induced changes in respiratory and cardiac function. Our purpose was to characterize changes in respiration during seizures. We used a preparation of the anaesthetized, perfused in situ rat. This preparation has the advantage over in vivo preparations in that delivery of oxygen to the brain does not depend upon the lungs or cardiovascular system. Electroencephalographic activity was recorded as were activities of the hypoglossal, vagus and phrenic nerves. The hypoglossal and vagus nerves innervate muscles of the upper airway and larynx while the phrenic nerve innervates the diaphragm. Fictive seizures were elicited by injections of penicillin into the parietal cortex or the carotid artery. Following elicitation of the fictive seizures, activities of the hypoglossal and vagal nerves declined greatly while phrenic activity was little altered. Such a differential depression of activities of nerves to the upper airway and larynx, compared to that to the diaphragm, would predispose to obstructive apnea in intact preparations. With more time, activity of the phrenic nerve also declined or ceased. These changes characterize central apnea. The major conclusion is that seizures may result in recurrent periods of obstructive and central apnea. Thus, seizures can adversely alter respiratory function in a profound manner.
Keywords: Apnea; Seizures; Respiration; Upper airway
- Animal study in rats who were anesthetized and placed on cardiopulmonary bypass to provide continuous oxygenation to tissues independent of heart and brain function. During fictive seizures induced by penicillin, activities of hypoglossal and vagal nerves declined, though phrenic activity was largely unchanged. The authors contend that this pattern of altered neural activity would lead to obstructive apnea. The extent to which alterations in the function of cranial and spinal nerves in this seizure model recapitulate those that occur during seizures in patients is not clear. Later in experiments, activity in the phrenic nerve also declined, which the authors take as a correlate of central apnea, but this late change could reflect an overall loss of viability.