Interaction Between HCN and Slack Channels Regulates mPFC Pyramidal Cell Excitability and Working Memory

Abstract

The ability of monkeys and rats to carry out spatial working memory tasks has been shown to depend on the persistent firing of pyramidal cells in the prefrontal cortex (PFC), arising from recurrent excitatory connections on dendritic spines. These spines express hyperpolarization-activated cyclic nucleotide-gated (HCN) channels whose open state is increased by cAMP signaling, and which markedly alter PFC network connectivity and neuronal firing. In traditional neural circuits, activation of these non-selective cation channels leads to neuronal depolarization and increased firing rate. Paradoxically, cAMP activation of HCN channels in PFC pyramidal cells reduces working memory-related neuronal firing. This suggests that activation of HCN channels may hyperpolarize rather than depolarize these neurons. The current study tested the hypothesis that Na+influx through HCN channels activates Na+-activated K+(KNaor Slack) channels to hyperpolarize the membrane. We have found that HCN and Slack KNachannels co-immunoprecipitate in cortical extracts and that, by immunoelectron microscopy, they colocalize at postsynaptic spines of PFC pyramidal neurons. A specific blocker of HCN channels, ZD7288, reduces KNacurrent in pyramidal cells that express both HCN and Slack channels, indicating that blockade of HCN channels reduced K+current indirectly by lowering Na+influx. In contrast, ZD7288 has no effect on KNacurrents in an HEK cell line stably expressing this Slack channels but no HCN channels, demonstrating that ZD7288 does not block Slack channels directly. Activation of HCN channels by cAMP in a cell line expressing a Ca2+reporter results in elevation of cytoplasmic Ca2+, but the effect of cAMP is completely reversed if the HCN channels are co-expressed with Slack channels. Finally, we have used a novel pharmacological blocker of Slack channels to show that inhibition of either Slack or HCN channels in rat PFC improves working memory performance, and that the actions of Slack and HCN channel blockers occlude each other in the memory task. Our results suggest that the regulation of working memory by HCN channels in PFC pyramidal neurons is mediated by an HCN-Slack channel complex that links activation HCN channels to suppression of neuronal excitability.

Key Roles of CACNA1C/Cav1.2 and CALB1/Calbindin in Prefrontal Neurons Altered in Cognitive Disorders

“…These channels are expressed in CALB1 -expressing pyramidal cells (Figure 1), and localize on layer III dlPFC spines . They are opened by cyclic adenosine monophosphate signaling and can couple with slack potassium channels, consistent with feedforward calcium–cyclic adenosine monophosphate signaling in layer III spines.…”

HCN channels regulate excitability and gate synaptic amplification via NMDA in mouse L2/3 pyramidal neurons

“…As L2/3 PCs are one of the most abundant cell populations of the neocortex, HCN channels in these cells may exert overwhelming control over cortical excitability and thus cognition and memory. Cell non-autonomous HCN channel dysregulation manifests in clear behavioral changes, such as altered spatial learning (57) or impaired working memory (58). Curiously, higher HCN1 protein levels in the postmortem brain also correlate with cognitive resilience in aging humans (59).…”

“…Cell non-autonomous HCN channel dysregulation manifests in clear behavioral changes, such as altered spatial learning (57) or impaired working memory (58). Curiously, higher HCN1 protein levels in the postmortem brain also correlate with cognitive resilience in aging humans (59).…”

Dynamic Network Connectivity: from monkeys to humans

“…For instance, there are dopamine D1Rs on the spine membrane near these channels, at a distance from the synapse, and they likely activate cAMP-PKA-calcium signaling to refine network inputs to a cell, narrowing its tuning properties ( Vijayraghavan et al, 2007 ; Paspalas et al, 2013 ; Gamo et al, 2015 ). For example, KCNQ2 potassium channels are opened by PKA signaling ( Galvin et al, 2020 ), and HCN channels are opened by cAMP, and appear to couple with Slack K + channels to ultimately increase K + efflux ( Wu et al, 2023 ). In this way, moderate levels of dopamine D1R stimulation can sculpt away non-preferred inputs to create more precise mental representations ( Vijayraghavan et al, 2007 ), while high levels of dopamine D1R and norepinephrine α1-AR activation, as occurs with uncontrollable stress exposure, can markedly reduce Delay cell firing, likely by cAMP-calcium opening of nearby K + channels ( Birnbaum et al, 2004 ; Gamo et al, 2015 ; Datta et al, 2019 ).…”