Avanzi V, Castilho V M, de Andrade T G, Brandão M L
Laboratório de Psicobiologia, FFCLRP, Campus USP, Av. Bandeirantes 3900, 14049-901, Ribeirão Preto, SP, Brazil.
Brain Res. 1998 Apr 20;790(1-2):178-84. doi: 10.1016/s0006-8993(97)01538-2.
The median raphe nucleus (MRN) has been suggested as the origin of a behavioral inhibition system that projects to the septum and hippocampus. Electrical stimulation of this mesencephalic area causes behavioral and autonomic manifestations characteristic of fear such as, freezing, defecation and micturition. In this study we extend these observations by analyzing the behavioral and autonomic responses of rats with lesions in the MRN submitted to a contextual conditioning paradigm. The animals underwent electrolytic or sham lesions of the median raphe nucleus. One day (acute) or 7 days (chronic) later they were tested in an experimental chamber where they received 10 foot-shocks (0.7 mA, 1 s with 20-s interval). The next day, sham and MRN-lesioned animals were tested again either in the same or in a different experimental chamber. During this, the duration of freezing, rearings, bouts of micturition and number of fecal boli were recorded. Sham-operated rats placed in the same chamber showed more freezing than rats exposed to a different context. This freezing behavior was clearly suppressed in rats with acute or chronic lesions in the MRN. MRN lesions also reduced the bouts of micturition and number of fecal boli. These rats showed a reduced number of rearings than sham-lesioned rats. This effect is probably the result of the displacement effect provoked by freezing since no significant differences in the number of rearings could be observed between these animals and the NMR-lesioned rats tested in an open field. This lesion produced higher horizontal locomotor activity in this test than the controls (sham-lesioned rats). These results point to the importance of the median raphe nucleus in the processing of fear conditioning with freezing being the most salient feature of it. Behavioral inhibition is also under control of MRN but its neural substrate seems to be dissociated from that of contextual fear.
中缝正中核（MRN）被认为是投射到隔区和海马的行为抑制系统的起源。对该中脑区域进行电刺激会引发恐惧的行为和自主神经表现，如僵住、排便和排尿。在本研究中，我们通过分析接受情境条件范式的中缝正中核损伤大鼠的行为和自主神经反应来扩展这些观察结果。动物接受中缝正中核的电解损伤或假损伤。一天（急性）或7天（慢性）后，它们在一个实验箱中接受测试，在那里它们接受10次足部电击（0.7毫安，持续1秒，间隔20秒）。第二天，假手术和中缝正中核损伤的动物在同一个或不同的实验箱中再次接受测试。在此期间，记录僵住的持续时间、直立次数、排尿次数和粪便颗粒数。置于同一实验箱中的假手术大鼠比暴露于不同环境的大鼠表现出更多的僵住行为。在中缝正中核急性或慢性损伤的大鼠中，这种僵住行为明显受到抑制。中缝正中核损伤还减少了排尿次数和粪便颗粒数。这些大鼠的直立次数比假损伤大鼠少。这种效应可能是由僵住所引发的替代效应的结果，因为在这些动物与在旷场中测试的中缝正中核损伤大鼠之间，直立次数没有观察到显著差异。在该测试中，这种损伤比对照组（假损伤大鼠）产生了更高的水平运动活动。这些结果表明中缝正中核在恐惧条件反射过程中的重要性，僵住是其中最显著的特征。行为抑制也受中缝正中核的控制，但其神经基质似乎与情境恐惧的神经基质不同。
