da Silva Luis Felipe Souza, Menescal-de-Oliveira Leda
Department of Physiology, Faculty of Medicine of Ribeirão Preto, University of São Paulo, 14049-900 Ribeirão Preto, SP, Brazil.
Physiol Behav. 2006 Apr 15;87(4):821-7. doi: 10.1016/j.physbeh.2006.01.019. Epub 2006 Mar 20.
Tonic immobility (TI) is an inborn defensive behavior characterized by a temporary state of profound and reversible motor inhibition elicited by some forms of physical restraint. It is known that endogenous antinociceptive systems are activated during the emission of defensive behaviors including TI. The nucleus raphe magnus (NRM) is related to the modulation of nociceptive and behavioral responses. In the present study, we investigated the role of the cholinergic system of the NRM in the modulation of TI and nociception in guinea pigs. Microinjection of the cholinergic agonist carbachol (0.5 microg/0.2 microl) into the NRM promoted a reduction in the duration of TI episodes and nociception, the latter measured by the vocalization test in guinea pigs. The effect of microinjection of carbachol on TI reduction and antinociception was blocked by the previous microinjection of the cholinergic antagonist atropine (0.5 microg/0.2 microl and 1 microg/0.2 microl, respectively), demonstrating the participation of muscarinic receptors in the modulation of these responses. Microinjection of atropine per se did not interfere with the duration of TI episodes. In summary, the present results demonstrate that cholinergic stimulation of the NRM promoted analgesia and a reduction in the duration of TI in guinea pigs. These data indicate that the NRM possibly contributes to the modulation of defensive and nociceptive behavioral responses, probably by modulating the activity of neurons in the ventral and dorsal horn of the spinal cord, respectively.
紧张性不动（TI）是一种先天性防御行为，其特征是由某些形式的身体束缚引发的深度且可逆的运动抑制的暂时状态。已知内源性抗伤害感受系统在包括TI在内的防御行为发出过程中被激活。中缝大核（NRM）与伤害感受和行为反应的调节有关。在本研究中，我们调查了NRM胆碱能系统在豚鼠TI和伤害感受调节中的作用。向NRM微量注射胆碱能激动剂卡巴胆碱（0.5微克/0.2微升）可使TI发作持续时间和伤害感受降低，后者通过豚鼠发声试验来测量。预先微量注射胆碱能拮抗剂阿托品（分别为0.5微克/0.2微升和1微克/0.2微升）可阻断卡巴胆碱微量注射对TI降低和抗伤害感受的作用，这表明毒蕈碱受体参与了这些反应的调节。单独微量注射阿托品并不干扰TI发作的持续时间。总之，本研究结果表明，对NRM的胆碱能刺激可促进豚鼠的镇痛作用并缩短TI的持续时间。这些数据表明，NRM可能分别通过调节脊髓腹角和背角神经元的活动，对防御和伤害感受行为反应的调节有贡献。
