Kask A, Harro J, Tuomaine P, Rägo L, Männistö P T
Department of Pharmacology University of Tartu, Estonia.
Naunyn Schmiedebergs Arch Pharmacol. 1997 Feb;355(2):267-72. doi: 10.1007/pl00004942.
The changes in the extracellular concentration of endogenous noradrenaline and dopamine in the frontal cortex following pretreatment with noradrenergic neurotoxin DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine] were studied by in vivo microdialysis in rats anaesthetized with chloral hydrate. Noradrenaline and dopamine levels in frontal cortex were detected only when the uptake inhibitor, nomifensine (10 microM) was present in dialysis fluid. Under those conditions, the Na+ channel agonist veratridine and a depolarising concentration of potassium chloride (60 mM), applied locally through the microdialysis probe, increased the overflow of noradrenaline. Tetrodotoxin had an opposite effect. These results indicate that most of the noradrenaline probably arose from exocytotic release. Noradrenaline efflux in the frontal cortex of DSP-4 pretreated rats (52 +/- 6.1 fmol/sample) did not differ significantly from that of the control animals (69 +/- 4.9 fmol/sample). Dopamine efflux was not changed either (64 +/- 9.6 and 62 +/- 3.9 fmol/sample, respectively). The alpha 2-adrenoceptor antagonist, atipamezole (3 mg/kg i.p.), increased the overflow of noradrenaline in the frontal cortex of saline-treated rats by 100%, whereas in DSP-4 treated rats the increase was only around 30%. The overflow of dopamine was not changed under the conditions described. The effect of atipamezole in DSP-4 treated rats may be of smaller magnitude due to the diminished pool of releasable noradrenaline or due to a downregulation of presynaptic alpha 2-adrenoceptors in the frontal cortex. The perfusion of 60 mM KCl at the end of the experiment unexpectedly produced equivalent increases in noradrenaline and dopamine content in dialysates of both vehicle and DSP-4 treated rats. We conclude that the uptake inhibitor, nomifensine, and atipamezole, which had a stronger effect in vehicle-treated animals, reduced the effect of KCl-stimulation and masked the true difference in changes of noradrenaline efflux. Post-mortem tissue concentrations of noradrenaline 7 days after DSP-4 administration (50 mg/kg) were significantly reduced in the frontal cortex (54%), hippocampus (62.5%) and to lesser extent in the hypothalamus (27%) as compared to vehicle-treated rats. Dopamine and 3,4-dihydroxyphenylacetic acid concentrations were not changed confirming the efficacy and selectivity of the DSP-4 lesion. These results demonstrate that one week after DSP-4 treatment the extracellular levels of noradrenaline and dopamine as assessed by in vivo microdialysis are not changed in the frontal cortex, but atipamezole-stimulated release of noradrenaline is decreased in DSP-4 treated rats.
采用水合氯醛麻醉大鼠，运用体内微透析技术研究了用去甲肾上腺素能神经毒素DSP - 4 [N - (2 - 氯乙基)-N - 乙基 - 2 - 溴苄胺]预处理后额叶皮质内源性去甲肾上腺素和多巴胺细胞外浓度的变化。仅当透析液中存在摄取抑制剂诺米芬辛（10微摩尔）时，才能检测到额叶皮质中的去甲肾上腺素和多巴胺水平。在这些条件下，通过微透析探针局部施加的Na⁺通道激动剂藜芦碱和去极化浓度的氯化钾（60毫摩尔）可增加去甲肾上腺素的溢出量。河豚毒素则产生相反的作用。这些结果表明，大部分去甲肾上腺素可能源自胞吐释放。经DSP - 4预处理的大鼠额叶皮质中的去甲肾上腺素流出量（52±6.1飞摩尔/样本）与对照动物（69±4.9飞摩尔/样本）相比无显著差异。多巴胺流出量也未改变（分别为64±9.6和62±3.9飞摩尔/样本）。α₂ - 肾上腺素能受体拮抗剂阿替美唑（3毫克/千克，腹腔注射）使生理盐水处理大鼠额叶皮质中的去甲肾上腺素溢出量增加了100%，而在DSP - 4处理的大鼠中，增加量仅约为30%。在上述条件下，多巴胺溢出量未改变。阿替美唑对DSP - 4处理大鼠的作用可能较小，这是由于可释放去甲肾上腺素的储备减少或额叶皮质中突触前α₂ - 肾上腺素能受体下调所致。实验结束时灌注60毫摩尔氯化钾意外地使溶剂处理组和DSP - 4处理组大鼠的透析液中去甲肾上腺素和多巴胺含量均等量增加。我们得出结论，摄取抑制剂诺米芬辛和阿替美唑在溶剂处理动物中作用更强，它们降低了氯化钾刺激的效应并掩盖了去甲肾上腺素流出量变化的真正差异。与溶剂处理的大鼠相比，给予DSP - 4（50毫克/千克）7天后，额叶皮质（54%）、海马体（62.5%）中的去甲肾上腺素死后组织浓度显著降低，下丘脑（27%）中的降低程度较小。多巴胺和3,4 - 二羟基苯乙酸浓度未改变，证实了DSP - 4损伤的有效性和选择性。这些结果表明，DSP - 4处理一周后，通过体内微透析评估的额叶皮质中去甲肾上腺素和多巴胺的细胞外水平未改变，但阿替美唑刺激的DSP - 4处理大鼠去甲肾上腺素释放减少。
