大脳半球摘除ラット神経組織の生化学的変化—中枢神経の可塑性に関連して

NEUROCHEMICAL FINDINGS OF HEMISPHERECTOMIZED RATS

I．はじめに

　前回われわれは，成熟ラットに大脳半球摘除を行い，術後，経時的にシナプス関連物質である，noradrenaline（NA），serotonin （5HT），acetylcholine分解酵素であるacetylcholine esterase （AchE）活性を計測することにより，生化学的な面から，中枢神経組織に変性→再生機構が働いている可能性を報告した^35,36）。

　中枢神経が損傷を受けた時，幼若動物は成熟動物に比べ，あまり大きな欠陥を残さず回復することをわれわれはよく経験する。これは幼若な中枢神経組織では，成熟した巾枢神経組織にはすでに失われたか，または少ししか残されていない代償機構がより多く働いていると考えられる^10）。幼若ラットの大脳半球摘除および幼若ハムスターでの上丘，視皮質の損傷で，成熟動物にはないかまたは少ない新たな解剖学的結合が証明^12,28）されている。

It has been generally observed that the central nervous system injury given to immature mammals usually produces less damage than does similar injury given at their maturity. The immature brain seems to be endowed with compensatory mechanisms which lack partly or totally in the adult brain.

The purpose of the present study is to clarify the biochemical basis of the neural plasticity in young animals.

Several regions of the central nervous tissue ofadult rats whose hemisphere was extirpated soon after the birth were analyzed on acetylcholine esterase activity, content of noradrenaline and serotonin, uptake of noradrenaline and serotonin into the crude synaptosomes. Catecholamine con-taining neurons were demonstrated histochemically by the use of the glyoxylic acid induced fluorescence. Following results were obtained:

1. Content of noradrenaline increased nearly 2-fold in the brain stem and in the cerebellum at the 2nd and the 3rd month after the operation. Synap-tosomal uptake of ³H-noradrenaline also increased in the brain stem and V_max elevated remarkably, through K_m stayed unchanged. Concomitant in-creases in the content of noradrenaline and V_max of synaptosomal uptake of ³H-noradrenaline may in-dicate an increased number of noradrenergic nerve terminals.

2. The glyoxylic acid induced histofluorescence increased in some pontine nuclei and in the molecular layer of the cerebellar cortex.

3. Above mentioned results probably indicate axonal sprouting of noradrenergic neurons after the neonatal hemispherectomy.