García-Vallejo P, Gómez F M, Infante C, Ginestal E, Giralt M T
Department of Stomatology, Faculty of Medicine and Odontology, University of the Basque Country, Leioa, Apdo. 699-48080, Bilbao, Vizcaya, Spain.
Brain Res. 1998 Aug 10;801(1-2):72-7. doi: 10.1016/s0006-8993(98)00547-2.
In a previous study, we found that the sensitivity of central postsynaptic alpha2-adrenoceptors which modulate, in an inhibitory way, the activity of the jaw-opening reflex (JOR) is reduced after chronic repeated stress (tail pinch) in the rat. The aim of this study was to assess the effects of exposure to a chronic variable stress regime on these adrenoceptors. To do this, the digastric electromyographic responses elicited by orofacial electrical stimulation after the intravenous administration of cumulative doses (x3.3) of the alpha2-adrenoceptor agonist, clonidine (0.1-10000 microgram/kg), were recorded. As expected, in unmanipulated control rats, clonidine inhibited the reflex, in a dose-dependent manner, until abolition (ED50 = 17.3 +/- 2.2 microgram/kg). Single tail pinch did not significantly alter the ability of clonidine to abolish the reflex. However, chronic variable stress led to an enhancement of the inhibitory effect of clonidine on the amplitude of JOR, resulting in a shift to the left of the dose-response curve in comparison with that of the control group (ED50 was reduced by 37%, P = 0.032), without affecting either the estimated maximum effect for the agonist or the slope of the inhibitory function. This in vivo result indicates that chronic variable stress leads to an increased sensitivity of central alpha2-adrenoceptors which modulate JOR, in contrast to the desensitization of these adrenoceptors found after repeated exposure to the same stressor.
在先前的一项研究中，我们发现，大鼠经慢性重复应激（夹尾）后，以抑制方式调节张口反射（JOR）活动的中枢突触后α2-肾上腺素能受体的敏感性降低。本研究的目的是评估暴露于慢性可变应激方案对这些肾上腺素能受体的影响。为此，在静脉注射累积剂量（x3.3）的α2-肾上腺素能受体激动剂可乐定（0.1 - 10000微克/千克）后，记录口面部电刺激引发的二腹肌肌电图反应。正如预期的那样，在未处理的对照大鼠中，可乐定以剂量依赖性方式抑制反射，直至反射消失（半数有效剂量[ED50] = 17.3±2.2微克/千克）。单次夹尾并未显著改变可乐定消除反射的能力。然而，慢性可变应激导致可乐定对JOR幅度的抑制作用增强，与对照组相比，剂量反应曲线向左移动（ED50降低了37%，P = 0.032），而既不影响激动剂的估计最大效应，也不影响抑制功能的斜率。这一体内结果表明，慢性可变应激导致调节JOR的中枢α2-肾上腺素能受体敏感性增加，这与重复暴露于同一应激源后这些肾上腺素能受体的脱敏情况相反。
