海馬切片におけるペニシリン誘発てんかん様発作波—CA 3錐体細胞と顆粒細胞の比較

PENICILLIN INDUCED EPILEPTIFORM ACTIVITY IN HIPPOCAMPAL, SLICE:COMPARISON BETWEEN CA 3 PYRAMIDAL CELL AND GRANULE CELL

　抄録　神経細胞の種類により，てんかん様発作波の発生の難易度に差があるかどうかを検討するため，海馬にある2種類の神経細胞（CA3錐体細胞と頼粒細胞）のペニシリン誘発てんかん様発作波について，モルモットの脳切片を用いて調べた。切片を標準メディウムで灌流して，細胞層に入力する神経線維を電気刺激した時に発生する外界電位の記録で，2つの神経絹胞層は発作波を生じなかった。しかし，ペニシリンを含むメディウム（濃度500I．U．／ml）で10分以上灌流して，同様の刺激を加えると，　CA3錐体細胞層では，閾値の電気刺激で約20msecの潜時の後に発作波が出現した。刺激を強くすると，潜時は短くなったが，発作波の振幅，持続時間はほぼ一定であった。顆粒細胞層では，弱い電気刺激では発作波は出現しなかった。しかし，ペニシリン濃度を高くして（濃度1000〜2000I．U．／ml），強い刺激を加えると，短潜時の発作波様の多和性の電位が出現した。2つの神経細胞層の反応の違いは，神経細胞の性質や局所の神経回路の違いによるものと考えられた。

To investigate whether a different type of neu-rons has a different susceptibility to a drug in producing epileptiform activity, we compared penicillin induced epileptiform activities of the two types of neurons in the hippocampal forma-tion of guinea pigs, i. e. the CA 3 pyramidal cells in the hippocampus proper and the granule cells in the dentate gyrus, using slice preparations.

The thin slice of 0.4 mm thickness was cut nearly perpendicularly to the longitudinal axis of the hippocampus and was transferred to a nylon mesh in an observation chamber which was per-fused with the oxygenated and warmed medium at a rate of 2 ml/min. Under tenfold magnification stimuli were delivered to the nerve fiber layer through bipolar electrodes and evoked field poten-tials were recorded from the cell body layer with glass micropipettes of 10u tip diameter filled with normal medium.

In both cell body layers no epileptiform field potentials could be induced during perfusion of normal medium even if stimulus strength was in-creased. The CA 3 pyramidal cell body layer showed a delayed multipeaked field potential in response to threshold stimulus applied to the mossy fiber in penicillin-containing medium (Pc concentration =500, 1000, 2000I. U./ml). When the strength of stimulation increased, the latency short-ened, but the amplitude and the duration of epi-leptiform activity did not change. The granule cell body layer generated no epileptiform activity in response to weak electrical stimulus applied to the perforant path in penicillin-containing medium (Pc concentration =500, 1000, 2000 I. U./ml). How-ever, at high penicillin concentrations (1000, 2000 I. U./ml) multiple population spikes having a short latency appeared on intense stimulation.

The result that the CA 3 pyramidal cell gene-rated epileptiform activity far more easily than the granule cell suggested that a different type of neurons has a different susceptibility to epilep-tiform activity. The difference between the two types of the neurons seemed to derive from the intrinsic cell properties and their local circuits.