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The primate dorsolateral prefrontal cortex (DLPFC) displays unique in vivo activity patterns, but how in vivo activity regulates DLPFC pyramidal neuron (PN) properties remains unclear. We assessed the effects of in vivo Kir2.1 overexpression, a genetic silencing tool, on synapses in monkey DLPFC PNs. We show for the first time that recombinant ion channel expression successfully modifies the excitability of primate cortex neurons, producing effects on synaptic properties apparently different from those in the rodent cortex. 

ImportanceThe risk of mental disorders is consistently associated with variants inCACNA1C(L-type calcium channel Cav1.2) but it is not known why these channels are critical to cognition, and whether they affect the layer III pyramidal cells in the dorsolateral prefrontal cortex that are especially vulnerable in cognitive disorders. ObjectiveTo examine the molecular mechanisms expressed in layer III pyramidal cells in primate dorsolateral prefrontal cortices. Design, Setting, and ParticipantsThe design included transcriptomic analyses from human and macaque dorsolateral prefrontal cortex, and connectivity, protein expression, physiology, and cognitive behavior in macaques. The research was performed in academic laboratories at Yale, Harvard, Princeton, and the University of Pittsburgh. As dorsolateral prefrontal cortex only exists in primates, the work evaluated humans and macaques. Main Outcomes and MeasuresOutcome measures included transcriptomic signatures of human and macaque pyramidal cells, protein expression and interactions in layer III macaque pyramidal cells using light and electron microscopy, changes in neuronal firing during spatial working memory, and working memory performance following pharmacological treatments. ResultsLayer III pyramidal cells in dorsolateral prefrontal cortex coexpress a constellation of calcium-related proteins, delineated byCALB1(calbindin), and high levels ofCACNA1C(Cav1.2),GRIN2B(NMDA receptor GluN2B), andKCNN3(SK3 potassium channel), concentrated in dendritic spines near the calcium-storing smooth endoplasmic reticulum. L-type calcium channels influenced neuronal firing needed for working memory, where either blockade or increased drive by β1-adrenoceptors, reduced neuronal firing by a mean (SD) 37.3% (5.5%) or 40% (6.3%), respectively, the latter via SK potassium channel opening. An L-type calcium channel blocker or β1-adrenoceptor antagonist protected working memory from stress. Conclusions and RelevanceThe layer III pyramidal cells in the dorsolateral prefrontal cortex especially vulnerable in cognitive disorders differentially express calbindin and a constellation of calcium-related proteins including L-type calcium channels Cav1.2 (CACNA1C), GluN2B-NMDA receptors (GRIN2B), and SK3 potassium channels (KCNN3), which influence memory-related neuronal firing. The finding that either inadequate or excessive L-type calcium channel activation reduced neuronal firing explains why either loss- or gain-of-function variants inCACNA1Cwere associated with increased risk of cognitive disorders. The selective expression of calbindin in these pyramidal cells highlights the importance of regulatory mechanisms in neurons with high calcium signaling, consistent with Alzheimer tau pathology emerging when calbindin is lost with age and/or inflammation. 

Abstract Reciprocal connections between primate dorsolateral prefrontal (DLPFC) and posterior parietal (PPC) cortices, furnished by subsets of layer 3 pyramidal neurons (PNs), contribute to cognitive processes including working memory (WM). A different subset of layer 3 PNs in each region projects to the homotopic region of the contralateral hemisphere. These ipsilateral (IP) and callosal (CP) projections, respectively, appear to be essential for the maintenance and transfer of information during WM. To determine if IP and CP layer 3 PNs in each region differ in their transcriptomes, fluorescent retrograde tracers were used to label IP and CP layer 3 PNs in the DLPFC and PPC from macaque monkeys. Retrogradely-labeled PNs were captured by laser microdissection and analyzed by RNAseq. Numerous differentially expressed genes (DEGs) were detected between IP and CP neurons in each region and the functional pathways containing many of these DEGs were shared across regions. However, DLPFC and PPC displayed opposite patterns of DEG enrichment between IP and CP neurons. Cross-region analyses indicated that the cortical area targeted by IP or CP layer 3 PNs was a strong correlate of their transcriptome profile. These findings suggest that the transcriptomes of layer 3 PNs reflect regional, projection type and target region specificity.