Vianna D M L, Allen C, Carrive P
School of Medical Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
Neuroscience. 2008 Jun 2;153(4):1344-53. doi: 10.1016/j.neuroscience.2008.03.033. Epub 2008 Mar 22.
Conditioned fear to context in the rat leads to a host of sympathetically mediated physiological changes, including a marked rise in mean arterial pressure, a delayed rise in heart rate and a marked cutaneous vasoconstriction, along with the behavioral responses of freezing and ultrasonic vocalization. In this study we examine the role of the rostral ventromedial medulla (RVM), which includes raphe nuclei pallidus and magnus, in the expression of these changes. RVM is a major premotor sympathetic and somatic center and an important integrating center in the descending emotional motor system. To evaluate its role, conditioned fear was tested after temporary blockade with microinjections (0.4 microl) of the GABA-A receptor agonist muscimol (0.2 mM) or the glutamate receptor antagonist kynurenic acid (0.1 M). Changes in mean arterial pressure, heart rate and activity were recorded by radio-telemetry. Cutaneous vasoconstriction in the tail was recorded indirectly by infrared thermography. Muscimol and kynurenic acid had different, almost complementary effects. Muscimol abolished the skin vasoconstrictor response and significantly reduced the tachycardic response, but did not reduce the pressor response significantly and had little effect on the somatic motor components, freezing and ultrasonic vocalization. In contrast, kynurenic acid abolished ultrasonic vocalization and significantly reduced freezing but had no effect on the cardiovascular components. The results show that neurons in the rostral ventromedial medulla are implicated in the expression of some of the cardiac, vascular and somatic motor components of conditioned fear. Most importantly, these cardiovascular components are not under local glutamatergic control whereas the somatic motor components are.
大鼠对环境的条件性恐惧会引发一系列由交感神经介导的生理变化，包括平均动脉压显著升高、心率延迟上升以及明显的皮肤血管收缩，同时还伴有僵住不动和超声发声等行为反应。在本研究中，我们探究了延髓头端腹内侧区（RVM），其中包括中缝苍白核和中缝大核，在这些变化的表现中所起的作用。RVM是一个主要的运动前交感神经和躯体中枢，也是下行情绪运动系统中的一个重要整合中枢。为了评估其作用，在用微量注射（0.4微升）GABA - A受体激动剂蝇蕈醇（0.2毫摩尔）或谷氨酸受体拮抗剂犬尿氨酸（0.1摩尔）进行临时阻断后，测试条件性恐惧。通过无线电遥测记录平均动脉压、心率和活动的变化。通过红外热成像间接记录尾部的皮肤血管收缩情况。蝇蕈醇和犬尿氨酸具有不同的、几乎互补的作用。蝇蕈醇消除了皮肤血管收缩反应并显著降低了心动过速反应，但没有显著降低升压反应，并且对躯体运动成分（僵住不动和超声发声）影响很小。相比之下，犬尿氨酸消除了超声发声并显著减少了僵住不动，但对心血管成分没有影响。结果表明，延髓头端腹内侧区的神经元参与了条件性恐惧的一些心脏、血管和躯体运动成分的表现。最重要的是，这些心血管成分不受局部谷氨酸能控制，而躯体运动成分则受其控制。
