Hickling Y M, Cheung N S, Larm J A, Cowen M S, Shulkes A, Beart P M
Department of Pharmacology, Monash University, Clayton, Victoria, Australia.
Neurochem Int. 1997 Feb;30(2):171-9. doi: 10.1016/s0197-0186(96)00051-4.
Neurones of the cerebral cortex immunoreactive for the neuropeptide, cholecystokinin (CCK), also invariably contain GABA. Hence CCK is believed to modulate some aspect of GABAergic synaptic activity. The present study therefore investigated the effects of CCK on basal, K(+)- and L-glutamate-induced release of [3H]GABA from slices of rat neocortex and cultured murine neocortical neurones. Rat neocortical prisms loaded with [3H]GABA (10 nM) were superfused with Krebs-Henseleit buffer and stimulated twice (S1 and S2, 2 min) with K+ (30 mM). Release associated with each stimulus was measured and expressed relative to basal release (R1 and R2). The effects of non-selective and CCKB selective agonists, CCK-8S and CCK-4, respectively, on basal and K(+)-induced release of [3H]GABA were subsequently assessed by alternately including the peptides in S2 and comparing R2/R1 and S2/S1 ratios to control experiments. Contrary to previous findings, CCK-8S (30 nM-1 microM) and CCK-4 (0.3 nM-1 microM) failed to influence basal or K(+)-induced release. In similar experiments, murine cortical neurones superfused with HEPES balanced salt buffer, released exogenous [3H]GABA upon stimulation (1 min) with either K+ (55 mM) or L-glutamate (30 microM). However, CCK-8S, CCK-4 (both 300 nM-1 microM) and the CCKB selective antagonist, L365,260 (1 microM), failed to influence basal, K(+)- or L-glutamate-induced release of [3H]GABA from these neurones when included in S2. These data therefore do not support the postulate that CCK acting via CCKA or CCKB receptors modulates release of GABA under the present experimental conditions. GABA-CCK interactions were not specifically studied because only L-glutamate (30 microM) significantly elevated release of CCK-like immunoreactivity (115% above basal) in murine cortical neurones: basal release of CCK was estimated to be 7 and 11 pM from neurones and slices, respectively. Further studies employing more rigorous stimulation and perhaps examining endogenous GABA release are necessary to fully investigate the co-release of CCK and GABA.
大脑皮层中对神经肽胆囊收缩素（CCK）呈免疫反应性的神经元也总是含有γ-氨基丁酸（GABA）。因此，人们认为CCK可调节GABA能突触活动的某些方面。因此，本研究调查了CCK对大鼠新皮层切片和培养的小鼠新皮层神经元中基础的、钾离子（K⁺）和L-谷氨酸诱导的[³H]GABA释放的影响。用[³H]GABA（10 nM）装载的大鼠新皮层棱柱体用Krebs-Henseleit缓冲液进行灌流，并用钾离子（30 mM）刺激两次（S1和S2，各2分钟）。测量与每次刺激相关的释放量，并相对于基础释放量（R1和R2）进行表达。随后，分别通过在S2中交替加入非选择性激动剂CCK-8S和CCK B选择性激动剂CCK-4，并将R2/R1和S2/S1比值与对照实验进行比较，来评估它们对基础的和钾离子诱导的[³H]GABA释放的影响。与先前的研究结果相反，CCK-8S（30 nM - 1 μM）和CCK-4（0.3 nM - 1 μM）未能影响基础的或钾离子诱导的释放。在类似的实验中，用HEPES平衡盐缓冲液灌流的小鼠皮层神经元在受到钾离子（55 mM）或L-谷氨酸（30 μM）刺激（1分钟）时会释放外源性[³H]GABA。然而，当在S2中加入时，CCK-8S、CCK-4（均为300 nM - 1 μM）以及CCK B选择性拮抗剂L365,260（1 μM）均未能影响这些神经元中基础的、钾离子或L-谷氨酸诱导的[³H]GABA释放。因此，这些数据不支持在当前实验条件下CCK通过CCK A或CCK B受体调节GABA释放的假设。未对GABA - CCK相互作用进行专门研究，因为只有L-谷氨酸（30 μM）能显著提高小鼠皮层神经元中CCK样免疫反应性的释放（比基础水平高115%）：据估计，神经元和切片中CCK的基础释放量分别为7 pM和11 pM。需要采用更严格的刺激并可能检查内源性GABA释放的进一步研究，以充分研究CCK和GABA的共同释放。
