The Role Of Calretinin In L5a Pyramidal Neuron Development And Barrel Cortex Circuit Formation

Background:The rodent whisker-barrel cortex system has been established as an ideal model for studying sensory information integration.The barrel cortex consists of barrel and septa columns that receive information input from the lemniscal and paralemniscal pathways,respectively.The lemniscal pathway transmits whisker-specific signals to homologous barrel columns,and the paralemniscal pathway transmits multiwhisker signals.As the main target of the paralemniscal pathway,layer 5a(L5a)is involved in both barrel and septa circuits and play a key role in information integration.However,the role of L5a in the development of the barrel cortex remains unclear.Calcium ions(Ca²⁺)participate in a series of physiological functions,including gene transcription,enzyme activity,and neurotransmitter release.The precise control of Ca²⁺concentration and spatial location is a prerequisite for accomplishing these tasks.These regulations are achieved by calcium-binding protein.Calretinin(CR)is a well-known Ca²⁺buffer influencing spatiotemporal Ca²⁺transients within the cytosol.Previously,we found that calretinin is dynamically expressed in L5a.Thus,this study aims to explore the role of calretinin in the development of L5a pyramidal neurons and the formation of the barrel cortex.Methods:(1)Morphological studies:We used immunostaining,Nissl staining and sholl analysis to explore the effect of Cr deletion on morphology and development of L5a pyramidal neurons and barrel cortex.(2)The function of L5a pyramidal neurons:We performed whole-cell patch-clamp recording on Cr deletion neurons using acute brain slices.The rest membrane potential,action potential threshold,input resistance,and action potential frequency were recorded through current-clamp recordings.The spontaneous miniature excitatory postsynaptic current(m EPSC)was recorded through voltage-clamp recordings,and the mean amplitude and frequency were analyzed.(3)Behavioral test:To evaluate the spontaneous spatial exploration ability,we conducted an open-field test.To examine the level of anxiety,we conducted elevated O-maze and elevated plus maze tests.To examine the whisker?associated tactile sensation behavior,we conducted the gap crossing test.Results:In this study,we analyzed calretinin KO mice and found that the dendritic complexity and length of L5a pyramidal neurons were significantly decreased after calretinin ablation.The membrane excitability and excitatory synaptic transmission of L5a neurons were increased.Consequently,the organization of the barrels was impaired.Moreover,layer 4(L4)spiny stellate cells were not able to properly gather,leading to abnormal formation of barrel walls as the ratio of barrel/septum size obviously decreased.Calretinin KO mice exhibited exploratory behavior deficits and were unable to estimate gap distance accurately.And the texture discrimination of KO mice was also impaired.Besides,deletion of calretinin impaired the social novelty preference.Conclusion:Our results demonstrate that calretinin can affect the formation of the barrel and septa columns by regulating the development and function of L5a pyramidal neurons,and then affect the whisker?associated tactile sensation behavior.