Andre P, Fascetti F, Pompeiano O, White S R
Dipartimento di Fisiologia e Biochimica, Universita di Pisa, Italy.
Brain Res. 1994 Feb 21;637(1-2):1-9. doi: 10.1016/0006-8993(94)91210-6.
An important function of cholinergic projections to the cerebellar cortex may be to modulate the effects of classical afferent inputs to the cerebellar cortex. This hypothesis is supported by the recent observation that cholinergic agonists act at muscarinic receptors in the cerebellar cortex to facilitate Purkinje cell responses to glutamate, the excitatory neurotransmitter of parallel fibers [Brain Res., 617 (1993) 28-36]. Since Purkinje cell excitability is influenced by inhibitory input from basket and stellate cells as well as by excitatory input from granule cells and climbing fibers, the present study investigated whether muscarinic agonists could also modify the Purkinje cell responses to GABA, the putative inhibitory transmitter of basket and stellate neurons. In anesthetized rats, microiontophoretic application of bethanechol produced a long-lasting enhancement of GABA-evoked inhibition of firing of Purkinje cells in the cerebellar vermis (22/25 cells) regardless of whether bethanechol increased, decreased or failed to alter the basal firing rate of the cell. The muscarinic antagonist scopolamine prevented the bethanechol-induced increase in the GABA response. It appears, therefore, that cholinergic activation of muscarinic receptors enhances not only the excitatory but also the inhibitory component of cerebellar cortex circuitry. Further experiments are required to investigate whether this combination of effects may potentiate the signal processing capabilities of the cerebellar cortex.
胆碱能投射至小脑皮质的一个重要功能可能是调节经典传入输入对小脑皮质的影响。这一假说得到了最近一项观察结果的支持，即胆碱能激动剂作用于小脑皮质的毒蕈碱受体，以促进浦肯野细胞对谷氨酸（平行纤维的兴奋性神经递质）的反应[《脑研究》，617(1993)28 - 36]。由于浦肯野细胞的兴奋性受篮状细胞和星状细胞的抑制性输入以及颗粒细胞和攀缘纤维的兴奋性输入的影响，本研究调查了毒蕈碱激动剂是否也能改变浦肯野细胞对GABA（篮状神经元和星状神经元的假定抑制性递质）的反应。在麻醉大鼠中，微量离子电泳应用氨甲酰甲胆碱可使小脑蚓部浦肯野细胞的GABA诱发的放电抑制产生持久增强(22/25个细胞)，无论氨甲酰甲胆碱是增加、降低还是未能改变细胞的基础放电率。毒蕈碱拮抗剂东莨菪碱可阻止氨甲酰甲胆碱诱导的GABA反应增加。因此，似乎毒蕈碱受体的胆碱能激活不仅增强了小脑皮质回路的兴奋性成分，也增强了抑制性成分。需要进一步的实验来研究这种效应组合是否可能增强小脑皮质的信号处理能力。
