Anderson R M, Fatigati M D, Rompré P P
Centre de recherche, Hôpital du Sacré-Coeur, Université de Montréal, Qué, Canada.
Brain Res. 1996 Apr 29;718(1-2):83-8. doi: 10.1016/0006-8993(96)00038-8.
Psychophysical studies have shown that the directly activated neurons subserving the rewarding effect produced by electrical stimulation of the medial forebrain bundle (MFB) have refractory periods (RPs) shorter than those of dopaminergic (DA) neurons: this suggests that the directly stimulated substrate for the rewarding effect does not include DA neurons. Comparison of RP estimates. however, is difficult since those of DA neurons were obtained with the standard electrophysiological technique that characterizes cell body/initial segment rather than the directly stimulated axonal segment. Using electrophysiological recording techniques in urethane anesthetized rats, we re-estimated and compared the RP of DA neurons that project to the MFB and the ventral striatum (VST) with two stimulation procedures: one that characterizes the axonal segment near the stimulation electrode and the standard one that characterizes the cell body/initial segment near the recording electrode. Results showed that DA axonal RPs range from 1.0 to 2.2 ms, whereas cell body/initial segment RPs range from 1.0 to 3.0 ms. The axonal RP was equal to or shorter (mean difference = 0.22 ms, n = 15) than the cell body/initial segment RP. Axonal RP estimates for MFB sites range from 1.3 to 2.1 ms. values that slightly overlap with the late recovery from refractoriness reported in psychophysical studies for reward-relevant neurons. Axonal RP estimates obtained for VST sites were very similar (mean = 1.66, LH and 1.62 ms, VST) suggesting that the excitability of DA axons does not differ along their path. These results further support the hypothesis that DA axons are unlikely to constitute a major component of the directly-stimulated reward-relevant axons in the MFB. They also suggest that the direct contribution of DA axons to reward produced by VST stimulation is more important than by the MFB.
心理物理学研究表明，介导内侧前脑束（MFB）电刺激产生的奖赏效应的直接激活神经元的不应期（RPs）比多巴胺能（DA）神经元的不应期短：这表明奖赏效应的直接刺激底物不包括DA神经元。然而，比较不应期估计值很困难，因为DA神经元的不应期是通过表征细胞体/起始段而非直接刺激的轴突段的标准电生理技术获得的。在乌拉坦麻醉的大鼠中使用电生理记录技术，我们通过两种刺激程序重新估计并比较了投射到MFB和腹侧纹状体（VST）的DA神经元的不应期：一种表征刺激电极附近的轴突段，另一种是表征记录电极附近的细胞体/起始段的标准程序。结果表明，DA轴突不应期范围为1.0至2.2毫秒，而细胞体/起始段不应期范围为1.0至3.0毫秒。轴突不应期等于或短于（平均差异=0.22毫秒，n=15）细胞体/起始段不应期。MFB部位的轴突不应期估计值范围为1.3至2.1毫秒，这些值与心理物理学研究中报道的奖赏相关神经元不应期的晚期恢复略有重叠。VST部位获得的轴突不应期估计值非常相似（左侧平均为1.66毫秒，VST平均为1.62毫秒），表明DA轴突的兴奋性沿其路径没有差异。这些结果进一步支持了DA轴突不太可能构成MFB中直接刺激的奖赏相关轴突主要成分的假设。它们还表明，DA轴突对VST刺激产生的奖赏的直接贡献比MFB刺激更重要。
