micro波加熱前処理法によるラット脳内biogenic aminesとその代謝産物のレベル

LEVELS OF BIOGENIC AMINES AND THEIR METABOLITES IN RAT WHOLE BRAIN AFTER RAPID TISSUE FIXATION WITH MICROWAVE IRRADIATION

Ⅰ．はじめに

　最近，脳内biogenic amines （norepinephrine；NE，dopamine：DA,serotonin：5—HT）の生合成や代謝のturn-over rateがこれまで考えられていたよりはるかに迅速であることを示唆する報告がいくつか行なわれている。すなわち，断頭後in situのまま脳を放置しておくと，数分後にはDAのO-methylated metaboliteの3—methoxytyramine （3—MT）量の増加が^2），また，insituのままで，あるいは切り出してice cooled plateの上に5-10分間放置されたラット線状体におけるDAがoxidative deaminationを受けた3,4—dihydroxy-phenyl—acetic acid （DOPAC）レベルに著明な減少や増加が認められたという^12）。さらに，NEやDAのO-methy—lated deaminated metaboliteである3—methoxy 4—hy—droxy-phenylglycol sulphate　（MOPEG SO₄）^18）やhomovanillic acid （HVA）^20）が脳を取り出して空気に晒らされると，急速に増加することが報告されている。一方，脳内NE,DA,5—HT含有量そのものに関しては，4℃の条件下でin situの状態でおかれた場合にはあまり低下しないが，頭蓋より取り出し，さらに脳を各部位に分けるといつた操作を加えると，その減少率が著しく高まるともいわれている^16）。

Levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3, 4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxy-indoleacetic acid were measured fluorometrically in the whole brain of rats killed either by decapitation or by 5 kW microwave irradiation for 1.6 sec. which inactivates the relevant brain enzymes rapidly and irreversibly. There were statistically no differ-ences in the levels of NE, DA, 5-HT and 5-HIAA between the two methods of sacrifice, while the level of DA increased slightly in the irradiated brains. On the other hand, the level of DOPAC,an oxidative deaminated metabolite of DA, increased significantly and the level of HVA, a final metabolite of DA, reduced markedly in the irradiated brains compared to that in the decapitated brains, re-spectively. These findings suggest that the turnover rates for metabolism of DA at synaptic nerve terminals and synaptic clefts may be relatively rapid. Therefore, it may be concluded that rapid inactivation of the brain enzymes involved in metabolism of DA is necessary prior to analysis of DA and its metabolites and microwave irradiation is the most suitable method available at the present time.