Hand G A, Potts J T, Treuhaft B S, Wilson L B, Petty F, Mitchell J H
Department of Psychiatry, University of Texas Southwestern Medical Center at Dallas, USA.
Brain Res. 1997 Feb 14;748(1-2):211-8. doi: 10.1016/s0006-8993(96)01303-0.
In anesthetized cats, static contraction of the hindlimb reflexly increases mean arterial pressure (MAP). This cardiovascular adjustment is reduced by the arterial baroreflex. Both of these reflex responses are mediated through activation of ventrolateral medullary (VLM) regions. We tested the hypothesis that the concentration of glutamate (Glu) increases in the caudal ventrolateral medulla (cVLM) during static hindlimb contractions in anesthetized cats, and that barodenervation reduces this elevation in Glu levels. Static contractions of the triceps surae muscle of one hindlimb were evoked by electrical stimulation of the peripheral ends of cut L7 and S1 ventral roots. After the insertion of the microdialysis probes and a 3-h recovery period, a 2-min static contraction increased MAP by 47 +/- 7 mmHg. The concentration of Glu increased from 606 +/- 189 to 1042 +/- 228 nM. These results were repeatable in that Glu, as well as MAP, rose by a similar amount in two subsequent contractions. By contrast, in a subset of cats paralyzed prior to the third contraction, neither MAP nor Glu were significantly increased over baseline levels during the third stimulation period. In a third group of cats, hindlimb contraction increased MAP and Glu levels. However, the Glu release was attenuated in subsequent contractions after these cats were barodenervated. During the same periods of stimulation, the denervation accentuated the rise in MAP. These data demonstrate that static contraction of the hindlimb increases the extracellular concentration of Glu in the cVLM. Further, our study implicates this neurotransmitter in the baroreflex mediated reduction of the pressor reflex response to static muscle contraction.
在麻醉猫中，后肢的静态收缩会反射性地增加平均动脉压（MAP）。这种心血管调节会被动脉压力感受性反射减弱。这两种反射反应都是通过激活延髓腹外侧（VLM）区域介导的。我们测试了这样的假设：在麻醉猫后肢静态收缩期间，尾侧延髓腹外侧（cVLM）中的谷氨酸（Glu）浓度会增加，并且压力感受性神经去传入会降低Glu水平的这种升高。通过电刺激切断的L7和S1腹侧神经根的外周端，诱发一侧后肢腓肠三头肌的静态收缩。插入微透析探针并经过3小时恢复期后，2分钟的静态收缩使MAP增加了47±7 mmHg。Glu浓度从606±189 nM增加到1042±228 nM。这些结果是可重复的，因为在随后的两次收缩中，Glu以及MAP都以相似的幅度升高。相比之下，在第三次收缩前瘫痪的一部分猫中，在第三次刺激期间，MAP和Glu均未比基线水平显著升高。在第三组猫中，后肢收缩增加了MAP和Glu水平。然而，在这些猫进行压力感受性神经去传入后，随后的收缩中Glu释放减弱。在相同的刺激期间，去传入加重了MAP的升高。这些数据表明，后肢的静态收缩会增加cVLM中Glu的细胞外浓度。此外，我们的研究表明这种神经递质参与了压力感受性反射介导的对静态肌肉收缩的升压反射反应的减弱。
