Pierce R C, Rebec G V
Department of Psychology, Indiana University, Bloomington 47405, USA.
Neuroscience. 1995 Jul;67(2):313-24. doi: 10.1016/0306-4522(95)00012-8.
The neostriatum and its major afferent transmitters, dopamine and glutamate, play a critical role in behavior, but relatively little information is available on their postsynaptic effects in behaving animals. As a first step in addressing this shortcoming, single-unit electrophysiology was combined with iontophoresis in the neostriatum of awake, unrestrained rats. Relative to periods of quiet rest, most neurons (58 of 77) changed discharge rate in close temporal association with movement, while the remainder showed no such relationship. When animals resumed a resting posture, iontophoretic current-response curves were established for dopamine and glutamate as well as for ascorbate, a modulator of neostriatal function released from glutamatergic terminals. Application of either glutamate or ascorbate produced current-dependent increases in activity in all neurons, although this effect was somewhat less pronounced for nonmotor cells. In both types of neurons, the excitatory effect of ascorbate either diminished or shifted to an inhibition at high ejection currents. Dopamine, on the other hand, routinely excited motor-related, but inhibited nonmotor-related neurons. Further assessment of motor-related neurons revealed that in most cases the excitatory effects of either glutamate or dopamine alone were supra-additive when these compounds were either administered together or co-administered with ascorbate. Our results suggest that the response of neostriatal neurons to glutamate or dopamine depends, at least in part, on the motor responsiveness of these cells. Motor-related neurons, moreover, respond to the co-administration of glutamate and dopamine with synergistic increases in firing rate. Ascorbate also influences neostriatal activity, but the postsynaptic action of this substance cannot be explained as a simple interaction with either glutamatergic or dopaminergic mechanisms.
新纹状体及其主要传入递质多巴胺和谷氨酸在行为中起关键作用，但关于它们在行为动物中的突触后效应的信息相对较少。作为解决这一缺陷的第一步，将单单位电生理学与离子电泳相结合，应用于清醒、不受约束大鼠的新纹状体。相对于安静休息期，大多数神经元（77个中的58个）的放电率在与运动密切的时间关联中发生变化，而其余神经元则没有这种关系。当动物恢复休息姿势时，建立了多巴胺、谷氨酸以及抗坏血酸（一种从谷氨酸能终末释放的新纹状体功能调节剂）的离子电泳电流-反应曲线。应用谷氨酸或抗坏血酸均可使所有神经元的活动呈电流依赖性增加，尽管这种效应在非运动细胞中不太明显。在这两种类型的神经元中，抗坏血酸的兴奋作用在高喷射电流时减弱或转变为抑制作用。另一方面，多巴胺通常兴奋与运动相关的神经元，但抑制与非运动相关的神经元。对与运动相关的神经元的进一步评估表明，在大多数情况下，当这些化合物一起给药或与抗坏血酸共同给药时，单独使用谷氨酸或多巴胺的兴奋作用是超加性的。我们的结果表明，新纹状体神经元对谷氨酸或多巴胺的反应至少部分取决于这些细胞的运动反应性。此外，与运动相关的神经元对谷氨酸和多巴胺的共同给药反应为放电率协同增加。抗坏血酸也影响新纹状体活动，但这种物质的突触后作用不能解释为与谷氨酸能或多巴胺能机制的简单相互作用。
