大脳皮質誘発反応におよぼすGABOBおよびGABA溶液塗布の影響

INFLUENCE OF GABOB AND GABA SOLUTIONS ON THE CORTICAL EVOKED POTENTIALS AFTER THALAMIC STIMULATIONS OF CATS AND HUMAN

緒言

　1953年Floreyは，脊椎動物の脳内にニューロン活動を抑制する物質すなわちFactor I—を発見し，1956年これがγ—aminobutyric acid （以後GABAと略す）であると同定した^1）。また同年，Hayashi，Nagai^2）は，中枢神経系の抑制物質としてはむしろγ—amino—β—hydroxybutyricacid （以後GABOBと略す）がGABAよりより強い作用をもつことを指摘している。その後，GABAおよびGABOBの中枢抑制のメカニズムにつき，多くの研究がなされてきたが，未だ明らかとはいえない。Iwama，Jasper^3）は，GABA液を皮質内に注入してみても，その効果のみられないことからGABAの作用は，皮質表層のみに限局され，この意味でGABAは，"selective blo—cking action"をもつものと考えている。これに対してBindman，Lippoldら^10）は，皮質表層に高濃度のGABA溶液を長時間作用させると，その影響は，皮質深層にも達し得ることを証明し，この意味でGABAは"non—selective blocking action"をもつものと考えている。そこでわれわれは，各種濃度のGABAおよびGABOB液を作成し，それらをネコおよびヒトの皮質上に塗布し視床核刺激による皮質誘発反応におよぼす影響について実験的検討を加えたので報告する。

Influence of GABOB and GABA solutions with various concentrations on the cortical evoked poten-tials of cats and human was investigated.

1) Cortical evoked potentials after stimulations of the ventrobasal nucleus of the cat thalamus almost completely reversed their polarity after the applica-tion of 5% GABOB or GABA solution on the cortex.

2) Diluted GABOB or GABA solutions of various concentrations (0.05%, 0.1%, 1%, 5%) were applied on the sensori-motor cortex of cats, and the influence on the cortical evoked potentials after the stimula-tion of the ventrolateral nucleus of cats was in-vestigated. As the results, stronger inhibitory in-fluence on the evoked potentials was noted in the case of longer time of application. High concentrated GABOB or GABA solution (5% solution) had in-hibitory influences on the evoked potentials in the deeper layers of the cortex.

3) Spiky after-discharges, which were evoked by local cortical electrical stimulations at the site of cortical scar in a traumatic epileptic patient, were markedly depressed after the application of 5% GABOB or GABA solution on the cortex.

4) No significant discrepancy was found between the action of GABOB and GABA solutions in the evoked cortical potentials after thalamic atimulation.

5) As a conclusion, it is supposed that GABOB and GABA solutions have "Nonselective blocking action" to the cortical activities.