McLean D L, McDearmid J R, Sillar K T
School of Biology, Division of Biomedical Sciences, Bute Medical Buildings, University of St Andrews, St Andrews, Fife KY16 9TS, Scotland.
J Exp Biol. 2001 Apr;204(Pt 7):1307-17. doi: 10.1242/jeb.204.7.1307.
Nitric oxide (NO) is a ubiquitous neuromodulator with a diverse array of functions in a variety of brain regions, but a role for NO in the generation of locomotor activity has yet to be demonstrated. The possibility that NO is involved in the generation of motor activity in embryos of the frog Rana temporaria was investigated using the NO donors S-nitroso-n-acetylpenicillamine (SNAP; 100--500 micromol l(-1)) and diethylamine nitric oxide complex sodium (DEANO; 25--100 micromol l(-1)). Immobilised Rana temporaria embryos generate a non-rhythmic 'lashing' motor pattern either spontaneously or in response to dimming of the experimental bath illumination. Bath-applied NO donors triggered a qualitatively similar motor pattern in which non-rhythmic motor bursts were generated contra- and ipsilaterally down the length of the body. The inactive precursor of SNAP, n-acetyl-penicillamine (NAP), at equivalent concentrations did not trigger motor activity. NO donors failed to initiate swimming and had no measurable effects on the parameters of swimming induced by electrical stimulation. Intracellular recordings with potassium-acetate-filled electrodes revealed that the bursts of ventral root discharge induced by NO donors were accompanied by phasic depolarisations in motor neurons. During the inter-burst intervals, periods of substantial membrane hyperpolarization below the normal resting potential were observed, presumably coincident with contralateral ventral root activity. With KCl-filled electrodes, inhibitory potentials were strongly depolarising, suggesting that inhibition was Cl(-)-dependent. The synaptic drive seen in motor neurons after dimming of the illumination was very similar to that induced by the NO donors. NADPH-diaphorase histochemistry identified putative endogenous sources of NO in the central nervous system and the skin. Three populations of bilaterally symmetrical neurons were identified within the brainstem. Some of these neurons had contralateral projections and many had axonal processes that projected to and entered the marginal zones of the spinal cord, suggesting that they were reticulospinal.
一氧化氮（NO）是一种普遍存在的神经调节剂，在多种脑区具有多种功能，但NO在运动活动产生中的作用尚未得到证实。本研究使用NO供体S-亚硝基-N-乙酰青霉胺（SNAP；100 - 500 μmol l(-1)）和二乙胺一氧化氮络合物钠（DEANO；25 - 100 μmol l(-1)），研究了NO是否参与青蛙林蛙胚胎运动活动的产生。固定的林蛙胚胎会自发地或在实验浴光照变暗时产生非节律性的“甩动”运动模式。浴加NO供体引发了定性相似的运动模式，其中非节律性运动爆发沿身体长度向对侧和同侧产生。同等浓度的SNAP无活性前体N-乙酰青霉胺（NAP）不会引发运动活动。NO供体未能引发游泳，对电刺激诱导的游泳参数也没有可测量的影响。用醋酸钾填充电极进行的细胞内记录显示，NO供体诱导的腹根放电爆发伴随着运动神经元的相位去极化。在爆发间期，观察到膜电位大幅超极化至低于正常静息电位的时期，推测与对侧腹根活动一致。使用氯化钾填充电极时，抑制性电位强烈去极化，表明抑制是Cl(-)依赖性的。光照变暗后在运动神经元中看到的突触驱动与NO供体诱导的非常相似。NADPH-黄递酶组织化学鉴定了中枢神经系统和皮肤中假定的内源性NO来源。在脑干内鉴定出三群双侧对称的神经元。其中一些神经元有对侧投射，许多神经元有轴突伸向并进入脊髓边缘区，表明它们是网状脊髓神经元。
