[The effects of hyperventilation upon the spinal pain modulating system]

The purpose of this study is to investigate the effects of hyperventilation on the wide dynamic range (WDR) cell of the dorsal horn of the feline lumbar spinal cord. Cats received midcollicular decerebration and lumbar laminectomy. The spinal cord was transected at T12-L1. WDR cells were sampled with microelectrode at the depth of 2,000 microns from the cord dorsum. Following the control period with PaCO2 of 35-45 mmHg, respiratory rate and tidal volume were adjusted to make a level of hypocapnia as low as 20-25 mmHg. The recovery of cell activity was followed when normocapnia was restored. Hypocapnia with PaCO2 of 25-30 mmHg and 20-25 mmHg suppressed the activity of WDR cell significantly. At PaCO2 of 25-30 mmHg, the spontaneous activity was suppressed for about 20% and evoked activity for 27%. At PaCO2 of 20-25 mmHg, the spontaneous activity was suppressed for about 50% and evoked activity for 33%. The results suggest that the hyperventilation has suppressive effects on single-unit activity of WDR cell.