Yeomans J S, Maidment N T, Bunney B S
Department of Psychology, University of Toronto, Ont., Canada.
Brain Res. 1988 May 31;450(1-2):86-93. doi: 10.1016/0006-8993(88)91547-8.
A9 and A10 units identified as dopaminergic were recorded with extracellular micropipettes. The units were antidromically activated by electrical stimulation at the level of the preoptic area. The absolute refractory periods ranged from 1.2 to 2.5 ms. During the 2-8 ms of the relative refractory period, conduction was slower than normal by up to 1.5 ms. The time constant, C, of the strength-duration curve ranged from 0.4 to 0.6 ms. The current (I)-distance (D) relationship, tested by moving the stimulating electrode past the axon, was approximately parabolic (I = K D exp 2), with the constant of the equation, K, ranging from 900 to 2000 microA/mm exp 2, for 0.5 ms pulses. This relationship allows calculation of the radius of the field of dopamine axon excitation at any current. These high K values show that axons of dopamine cells cannot be activated unless high current densities are delivered, even when electrodes are placed near the axons. These data allow determination of the extent to which dopamine axons can be the directly activated substrates for behaviors, such as self-stimulation and circling, which are evoked by electrical stimulation of the medial forebrain bundle or internal capsule.
用细胞外微电极记录被确定为多巴胺能的A9和A10单位。这些单位通过视前区水平的电刺激进行逆向激活。绝对不应期为1.2至2.5毫秒。在相对不应期的2至8毫秒内，传导速度比正常情况慢达1.5毫秒。强度 - 时间曲线的时间常数C为0.4至0.6毫秒。通过将刺激电极移过轴突来测试的电流（I） - 距离（D）关系近似为抛物线形（I = K D²），对于0.5毫秒的脉冲，该方程的常数K为900至2000微安/毫米²。这种关系允许计算在任何电流下多巴胺轴突兴奋场的半径。这些高K值表明，除非施加高电流密度，否则即使电极放置在轴突附近，多巴胺细胞的轴突也无法被激活。这些数据有助于确定多巴胺轴突在多大程度上可以成为诸如自我刺激和转圈等行为的直接激活底物，这些行为是由内侧前脑束或内囊的电刺激所诱发的。
