Distribution of respiratory and seizure-like neurons in cervical spinal cord

Hideki Shimomura1, Ayae Nishiyama2, YasuhiroTakeshima1, Akiko Arata2

Department of Pediatrics, Hyogo College of Medicine1
Division of Physiome, Department of Physiology, Hyogo College of Medicine2

The inspiratory activity drives phrenic motoneurons then contracts diaphragm. Phrenic motoneurons are located in cervical 4th (C4) -5th ventral horn. Our previous results suggested that respiratory activity and fetal movement like activity were recorded in C4 nerve root of isolated rat brainstem-spinal cord preparation during embryonic day (E) 16 to 19. After E20, strychnine-induced seizure-like activity was recorded in C4 nerve root. Our previous results of electrophysiological and pharmacological studies showed that seizure-like activity after E20 was nearly identical to fetal movement-like activity.
The purpose of this study is to clarify the functional correlation between fetal movement-like activity and respiratory activity. We examined distribution of the strychnine-induced seizure-like neurons instead of fetal movement neurons in ventral horn area.
Isolated brainstem-spinal cord preparations from postnatal day 0 to 4 Wistar rats were used. C4 nerve root activity was monitored by suction electrode using one side of the preparation; and the respiratory activities and the strychnine induced seizure-like activities were recorded by extra-cellular electrode in contralateral C4 level. We found respiratory activities, seizure-like activities and combination of them in C4 ventral horn area under strychnine. The respiratory neurons were located in one third position from the lateral edge of spinal cord. The seizure-like neurons were located in one third position from the midline of spinal cord. Furthermore we detected the neuron which showed both respiratory and seizure-like activities in an area between them. These results suggested that the neurons received both respiratory and seizure-like activities were found in C4 level; respiratory activity might be highly influenced by seizure-like activity. Fetal movement-like neuron, phrenic motoneuron, and the neuron which has both activities showed column structure of spinal cord.