Stenkamp K, Palva J M, Uusisaari M, Schuchmann S, Schmitz D, Heinemann U, Kaila K
Johannes-Müller-Institut für Physiologie, Humboldt Universität Berlin, 10117 Berlin, Germany.
J Neurophysiol. 2001 May;85(5):2063-9. doi: 10.1152/jn.2001.85.5.2063.
The decrease in brain CO(2) partial pressure (pCO(2)) that takes place both during voluntary and during pathological hyperventilation is known to induce gross alterations in cortical functions that lead to subjective sensations and altered states of consciousness. The mechanisms that mediate the effects of the decrease in pCO(2) at the neuronal network level are largely unexplored. In the present work, the modulation of gamma oscillations by hypocapnia was studied in rat hippocampal slices. Field potential oscillations were induced by the cholinergic agonist carbachol under an N-methyl-D-aspartate (NMDA)-receptor blockade and were recorded in the dendritic layer of the CA3 region with parallel measurements of changes in interstitial and intraneuronal pH (pH(o) and pH(i), respectively). Hypocapnia from 5 to 1% CO(2) led to a stable monophasic increase of 0.5 and 0.2 units in pH(o) and pH(i), respectively. The mean oscillation frequency increased slightly but significantly from 32 to 34 Hz and the mean gamma-band amplitude (20 to 80 Hz) decreased by 20%. Hypocapnia induced a dramatic enhancement of the temporal stability of the oscillations, as was indicated by a two-fold increase in the exponential decay time constant fitted to the autocorrelogram. A rise in pH(i) evoked by the weak base trimethylamine (TriMA) was associated with a slight increase in oscillation frequency (37 to 39 Hz) and a decrease in amplitude (30%). Temporal stability, on the other hand, was decreased by TriMA, which suggests that its enhancement in 1% CO(2) was related to the rise in pH(o). In 1% CO(2), the decay-time constant of the evoked monosynaptic pyramidal inhibitory postsynaptic current (IPSC) was unaltered but its amplitude was enhanced. This increase in IPSC amplitude seems to significantly contribute to the enhancement of temporal stability because the enhancement was almost fully reversed by a low concentration of bicuculline. These results suggest that changes in brain pCO(2) can have a strong influence on the temporal modulation of gamma rhythms.
无论是在自主过度通气还是病理性过度通气期间，脑二氧化碳分压（pCO₂）的降低都会引起皮质功能的显著改变，进而导致主观感觉和意识状态的改变。在神经网络水平上介导pCO₂降低效应的机制在很大程度上尚未得到探索。在本研究中，我们在大鼠海马切片中研究了低碳酸血症对γ振荡的调节作用。在N-甲基-D-天冬氨酸（NMDA）受体阻断的情况下，由胆碱能激动剂卡巴胆碱诱导场电位振荡，并在CA3区的树突层进行记录，同时并行测量细胞外和细胞内pH值（分别为pHₒ和pHᵢ）的变化。二氧化碳浓度从5%降至1%导致pHₒ和pHᵢ分别稳定单相升高0.5和0.2个单位。平均振荡频率从32赫兹略有但显著地增加到34赫兹，平均γ频段振幅（20至80赫兹）降低了20%。低碳酸血症使振荡的时间稳定性显著增强，这通过拟合自相关图的指数衰减时间常数增加了两倍得以体现。弱碱三甲胺（TriMA）引起的pHᵢ升高与振荡频率略有增加（37至39赫兹）和振幅降低（30%）相关。另一方面，TriMA降低了时间稳定性，这表明在1%二氧化碳条件下其增强与pHₒ升高有关。在1%二氧化碳条件下，诱发的单突触锥体抑制性突触后电流（IPSC）的衰减时间常数未改变，但其振幅增强。IPSC振幅的这种增加似乎对时间稳定性的增强有显著贡献，因为低浓度荷包牡丹碱几乎完全逆转了这种增强。这些结果表明，脑pCO₂的变化可对γ节律的时间调制产生强烈影响。
