Yasmin Farhana, Marwick Katie F M, Hunter Daniel W, Nawaz Sarfaraz, Marshall Grant F, Booker Sam A, Hardingham Giles E, Kind Peter C, Wyllie David J A
Centre for Discovery Brain Sciences, University of Edinburgh, Hugh Robson Building, Edinburgh EH8 9XD, UK.
Simons Initiative for the Developing Brain, University of Edinburgh, Hugh Robson Building, Edinburgh EH8 9XD, UK.
Brain Commun. 2025 Mar 26;7(2):fcaf124. doi: 10.1093/braincomms/fcaf124. eCollection 2025.
GluN2A is a NMDA receptor subunit postulated as important for learning and memory. In humans, heterozygous loss of function variants in the gene encoding it () increase the risk of epilepsy, intellectual disability and schizophrenia. Haploinsufficient mouse models show electrophysiological abnormalities and thus to improve and widen understanding of the pathogenesis of -associated disorders in humans, this study aimed to assess the impact of absence and haploinsufficiency on core neuronal and synaptic properties in genetically modified rats. Electrophysiological whole-cell current- and voltage-clamp recordings were made from CA1 pyramidal neurons in acute hippocampal slices from wild-type and heterozygous ( ) and homozygous ( ) knock out rats aged postnatal day 27-34. While reduced levels or absence of GluN2A did not affect neuronal excitability or intrinsic membrane properties in both and rats, we found a reduced frequency of miniature excitatory post synaptic currents and a reduced density of proximal dendrites suggestive of a reduced number of excitatory synapses. Recordings from CA1 neurons in slices prepared from and rats revealed there was a reduced ratio of the current mediated by NMDA receptors compared to AMPA receptors, while in recordings, there was a slowing of the decay time-constant of the NMDA receptor-mediated excitatory postsynaptic currents. Moreover, neither summation of sub-threshold excitatory postsynaptic potentials nor summation of supra-threshold excitatory postsynaptic potentials to initiate action potential firing in CA1 pyramidal neurons indicated any dependence on GluN2A. We conclude that reduced levels of GluN2A alters the kinetics of NMDA receptor-mediated synaptic events and dendritic structure of CA1 neurons, but do not affect several other core neuronal functions. These relatively subtle changes are consistent with the largely intact neural functioning of the majority of humans carrying loss of function variants. Further research could explore whether the changes in synaptic properties we observed contribute to alterations in higher level circuit dynamics and computation, which may manifest as disorders of cognition and excitability in humans.
GluN2A是一种NMDA受体亚基，被认为对学习和记忆很重要。在人类中，编码它的基因中的杂合功能丧失变异会增加癫痫、智力残疾和精神分裂症的风险。单倍体不足的小鼠模型显示出电生理异常，因此，为了增进和拓宽对人类相关疾病发病机制的理解，本研究旨在评估基因敲除和单倍体不足对转基因大鼠核心神经元和突触特性的影响。采用全细胞膜片钳电流钳和电压钳记录技术，对出生后第27 - 34天的野生型、GluN2A杂合（）和纯合（）基因敲除大鼠急性海马脑片中的CA1锥体神经元进行记录。虽然GluN2A水平降低或缺失在杂合和纯合大鼠中均不影响神经元兴奋性或内在膜特性，但我们发现微小兴奋性突触后电流频率降低，近端树突密度降低，提示兴奋性突触数量减少。从杂合和纯合大鼠制备的脑片中CA1神经元的记录显示，与AMPA受体介导的电流相比，NMDA受体介导的电流比例降低，而在纯合记录中，NMDA受体介导的兴奋性突触后电流的衰减时间常数减慢。此外，在CA1锥体神经元中，阈下兴奋性突触后电位的总和以及阈上兴奋性突触后电位的总和以引发动作电位发放均未显示对GluN2A有任何依赖性。我们得出结论，GluN2A水平降低会改变NMDA受体介导的突触事件的动力学以及CA1神经元的树突结构，但不影响其他几个核心神经元功能。这些相对细微的变化与大多数携带功能丧失变异的人类神经功能基本完整是一致的。进一步的研究可以探索我们观察到的突触特性变化是否有助于更高水平的电路动力学和计算的改变，这可能表现为人类认知和兴奋性障碍。
