脊髄運動ノイロンに対するCO2並びにpHの影響

EFFECT OF CO2 AND pH ON THE RESPONES OF SPINAL MOTONEURONS

Ⅰ．緒言

　脊髄反射に及ぼすCO₂の影響に関しては，ネコについてはMathison^2），Porter^24），Brooks　＆　Eccles^5），Bradley, Schlapp　＆　Spaccarelli^3），Kirstein^15）；犬についてはGlazer^10），King, Gar-rey＆Bryan^14）等の報告があり，高濃度のCO₂を吸入させた時の反射活動の変化が論じられている。脊髄反射に対するpHの影響に関しても前記のMathison, Bradley et al．やKoenig＆Groat^16）等が血中に乳酸などを投与し血液pHを変化させたときに反射活動に現われる変化を追求している。

　本論文においては以上の諸家の報告を考慮の上，脊髄反射に及ぼすCO₂の影響，並びにpHとの関連につき単一前角運動ノイロンについて研究した結果を述べる。

1. Changes in responses of toad's spinal motoneurons associated with modified conce-ntration of CO₂ (5-100% in O₂) were studied by means of intracellular potential recording.CO₂ was applied introducing the gas mixture into the chamber in which the excised spinal cord was placed.

2. By increasing CO₂ concentration ( <ca. 30%), action potentials were increased in si-ze and orthodromically evoked action poten-tials became larger than those evoked anti-dromically.

3. The excitability of motoneuron was lo-wered with the increased action potential size.

4. The reflex activity was enhanced initia-lly, but depressed eventually by increasing CO₂ concentration.

5. Within limits, lowering of pH of Rin-ger's solution had similar effects as those of CO₂. It was suggested that the effects of CO₂ were mainly due to lowering of pH, so far as examined in this report.