Nowicky A V, Christofi G, Bindman L J
Department of Physiology, University College London, UK.
Neurosci Lett. 1992 Mar 30;137(2):270-3. doi: 10.1016/0304-3940(92)90420-c.
Long-term potentiation (LTP) of synaptic transmission is considered to be a neuronal model of learning. Recently, the probability of induction of associative LTP in layer V cells in sensorimotor neocortex was shown to be much higher in the awake cat than in the slice preparation. We hypothesised that the loss of extrinsic noradrenergic activity in the slice might account for this difference, particularly since a beta-adrenergic enhancement of field potentials has been seen in this preparation. We therefore bath-applied noradrenaline (NA) or the beta 1-adrenergic agonist, isoprenaline (ISO) to elucidate the cellular basis of the enhancement of field potentials, and to see if the drugs increased the probability of induction of associative LTP in slices. We found that NA and ISO produced a dose-dependent, reversible reduction of spike accommodation and an increase in excitability but had no effect on the depolarizing slope or peak amplitude of sub-threshold EPSPs, and that drug application did not increase the probability of induction of LTP. We conclude that: (1) the enhancement of field potentials and late components of EPSPs (7) can be explained by the known actions of beta-adrenergic drugs on membrane currents in layer V cells, and (2) the lower probability of induction of associative LTP in slices cf. the awake cat cannot be due solely to the loss of noradrenergic activity.
突触传递的长时程增强（LTP）被认为是学习的神经元模型。最近研究表明，在清醒猫的感觉运动新皮质V层细胞中，联合LTP的诱导概率比脑片标本中的高得多。我们推测，脑片中去甲肾上腺素能外部活性的丧失可能是造成这种差异的原因，特别是因为在该标本中已观察到β-肾上腺素能对场电位的增强作用。因此，我们通过浸浴应用去甲肾上腺素（NA）或β1-肾上腺素能激动剂异丙肾上腺素（ISO），来阐明场电位增强的细胞基础，并观察这些药物是否会增加脑片中联合LTP的诱导概率。我们发现，NA和ISO可剂量依赖性、可逆地减少动作电位适应并增加兴奋性，但对阈下兴奋性突触后电位（EPSP）的去极化斜率或峰值幅度没有影响，且应用药物并未增加LTP的诱导概率。我们得出以下结论：（1）场电位和EPSP晚期成分（7）的增强可以用β-肾上腺素能药物对V层细胞膜电流的已知作用来解释；（2）与清醒猫相比，脑片中联合LTP诱导概率较低不能仅仅归因于去甲肾上腺素能活性的丧失。
