Differing from other subtypes of inhibitory interneuron, chandelier or axo-axonic cells form depolarizing GABAergic synapses exclusively onto the axon initial segment (AIS) of targeted pyramidal cells (PCs). However, the debate whether these AIS-GABAergic inputs produce excitation or inhibition in neuronal processing is not resolved. Using realistic NEURON modeling and electrophysiological recording of cortical layer-5 PCs, we quantitatively demonstrate that the onset-timing of AIS-GABAergic input, relative to dendritic excitatory glutamatergic inputs, determines its bi-directional regulation of the efficacy of synaptic integration and spike generation in a PC. More specifically, AIS-GABAergic inputs promote the boosting effect of voltage-activated Na⁺ channels on summed synaptic excitation when they precede glutamatergic inputs by >15 ms, while for nearly concurrent excitatory inputs, they primarily produce a shunting inhibition at the AIS. Thus, our findings offer an integrative mechanism by which AIS-targeting interneurons exert sophisticated regulation of the input-output function in targeted PCs.
Axon Initial Segment ; Axons/physiology* ; Neurons ; Synapses/physiology* ; Pyramidal Cells/physiology* ; Interneurons/physiology* ; Action Potentials/physiology*

The anterior auditory field (AAF) is a core region of the auditory cortex and plays a vital role in discrimination tasks. However, the role of the AAF corticostriatal neurons in frequency discrimination remains unclear. Here, we used c-Fos staining, fiber photometry recording, and pharmacogenetic manipulation to investigate the function of the AAF corticostriatal neurons in a frequency discrimination task. c-Fos staining and fiber photometry recording revealed that the activity of AAF pyramidal neurons was significantly elevated during the frequency discrimination task. Pharmacogenetic inhibition of AAF pyramidal neurons significantly impaired frequency discrimination. In addition, histological results revealed that AAF pyramidal neurons send strong projections to the striatum. Moreover, pharmacogenetic suppression of the striatal projections from pyramidal neurons in the AAF significantly disrupted the frequency discrimination. Collectively, our findings show that AAF pyramidal neurons, particularly the AAF-striatum projections, play a crucial role in frequency discrimination behavior.
Acoustic Stimulation/methods* ; Neurons/physiology* ; Auditory Cortex/physiology* ; Auditory Perception ; Pyramidal Cells

The axon initial segment (AIS) is a highly specialized axonal compartment where the action potential is initiated. The heterogeneity of AISs has been suggested to occur between interneurons and pyramidal neurons (PyNs), which likely contributes to their unique spiking properties. However, whether the various characteristics of AISs can be linked to specific PyN subtypes remains unknown. Here, we report that in the prelimbic cortex (PL) of the mouse, two types of PyNs with axon projections either to the contralateral PL or to the ipsilateral basal lateral amygdala, possess distinct AIS properties reflected by morphology, ion channel expression, action potential initiation, and axo-axonic synaptic inputs from chandelier cells. Furthermore, projection-specific AIS diversity is more prominent in the superficial layer than in the deep layer. Thus, our study reveals the cortical layer- and axon projection-specific heterogeneity of PyN AISs, which may endow the spiking of various PyN types with exquisite modulation.
Mice ; Animals ; Axon Initial Segment ; Synapses/physiology* ; Pyramidal Cells/physiology* ; Cerebral Cortex ; Axons/physiology*

The family of voltage-gated potassium Kv2 channels consists of the Kv2.1 and Kv2.2 subtypes. Kv2.1 is constitutively highly phosphorylated in neurons and its function relies on its phosphorylation state. Whether the function of Kv2.2 is also dependent on its phosphorylation state remains unknown. Here, we investigated whether Kv2.2 channels can be phosphorylated by protein kinase C (PKC) and examined the effects of PKC-induced phosphorylation on their activity and function. Activation of PKC inhibited Kv2.2 currents and altered their steady-state activation in HEK293 cells. Point mutations and specific antibodies against phosphorylated S481 or S488 demonstrated the importance of these residues for the PKC-dependent modulation of Kv2.2. In layer II pyramidal neurons in cortical slices, activation of PKC similarly regulated native Kv2.2 channels and simultaneously reduced the frequency of action potentials. In conclusion, this study provides the first evidence to our knowledge that PKC-induced phosphorylation of the Kv2.2 channel controls the excitability of cortical pyramidal neurons.
Action Potentials ; HEK293 Cells ; Humans ; Protein Kinase C/metabolism* ; Pyramidal Cells/enzymology* ; Shab Potassium Channels/genetics*

Diverse types of GABAergic interneurons tend to specialize in their inhibitory control of various aspects of cortical circuit operations. Among the most distinctive interneuron types, chandelier cells (i.e., axo-axonic cells) are a bona fide cell type that specifically innervates pyramidal cells at the axon initial segment, the site of action potential initiation. Chandelier cells have been speculated to exert ultimate inhibitory control over pyramidal cell spiking. Thus, chandelier cells appear to share multiple similarities with basket cells, not only in firing pattern (fast spiking) and molecular components, but also in potentially perisomatic inhibitory control. Unlike basket cells, however, synaptic recruitment of chandelier cells is little known yet. Here, we examined the mediodorsal thalamocortical input to both chandelier cells and basket cells in medial prefrontal cortex, through combining mouse genetic, optogenetic and electrophysiological approaches. We demonstrated that this thalamocortical input produced initially weak, but facilitated synaptic responses at chandelier cells, which enabled chandelier cells to spike persistently. In contrast, this thalamocortical input evoked initially strong, but rapidly depressed synaptic responses at basket cells, and basket cells only fired at the initiation of input. Overall, the distinct synaptic recruitment dynamics further underscores the differences between chandelier cells and basket cells, suggesting that these two types of fast spiking interneurons play different roles in cortical circuit processing and physiological operation.
Mice ; Animals ; Neurons/physiology* ; Pyramidal Cells/physiology* ; Interneurons ; Action Potentials/physiology* ; Synaptic Transmission

The back-propagating action potential (bpAP) is crucial for neuronal signal integration and synaptic plasticity in dendritic trees. Its properties (velocity and amplitude) can be affected by dendritic morphology. Due to limited spatial resolution, it has been difficult to explore the specific propagation process of bpAPs along dendrites and examine the influence of dendritic morphology, such as the dendrite diameter and branching pattern, using patch-clamp recording. By taking advantage of Optopatch, an all-optical electrophysiological method, we made detailed recordings of the real-time propagation of bpAPs in dendritic trees. We found that the velocity of bpAPs was not uniform in a single dendrite, and the bpAP velocity differed among distinct dendrites of the same neuron. The velocity of a bpAP was positively correlated with the diameter of the dendrite on which it propagated. In addition, when bpAPs passed through a dendritic branch point, their velocity decreased significantly. Similar to velocity, the amplitude of bpAPs was also positively correlated with dendritic diameter, and the attenuation patterns of bpAPs differed among different dendrites. Simulation results from neuron models with different dendritic morphology corresponded well with the experimental results. These findings indicate that the dendritic diameter and branching pattern significantly influence the properties of bpAPs. The diversity among the bpAPs recorded in different neurons was mainly due to differences in dendritic morphology. These results may inspire the construction of neuronal models to predict the propagation of bpAPs in dendrites with enormous variation in morphology, to further illuminate the role of bpAPs in neuronal communication.
Action Potentials/physiology* ; Dendrites/physiology* ; Neurons/physiology* ; Neuronal Plasticity ; Pyramidal Cells/physiology*

OBJECTIVE: To investigate the effects of acid-sensing ion channels (ASICs) on electrophysiological epileptic activities of mouse hippocampal pyramidal neurons in the extracellular acidotic condition. METHODS: We investigated effects of extracellular acidosis on epileptic activities induced by elevated extracellular K concentration or the application of an antagonist of GABA receptors in perfusate of mouse hippocampal slices under field potential recordings. We also tested the effects of extracellular acidosis on neuronal excitability under field potential recording and evaluated the changes in epileptic activities of the neurons in response to pharmacological inhibition of ASICs using a specific inhibitor of ASICs. RESULTS: Extracellular acidosis significantly suppressed epileptic activities of the hippocampal neurons by converting ictal-like epileptic activities to non-ictal-like epileptic activities in both high [K ]o and disinhibition models, and also suppressed the intrinsic excitability of the neurons. ASICs inhibitor did not antagonize the inhibitory effect of extracellular acidosis on ictal epileptic activities and intrinsic neuronal excitability, but exacerbated non-ictal epileptic activities of the neurons in extracellular acidotic condition in both high [K]o and disinhibition models. CONCLUSIONS ASICs can differentially modulate ictal-like and non-ictallike epileptic activities via its direct actions on excitatory neurons.
Acid Sensing Ion Channels ; metabolism ; Acidosis ; Animals ; Epilepsy ; physiopathology ; Hydrogen-Ion Concentration ; Mice ; Pyramidal Cells ; pathology ; physiology

OBJECTIVE: To investigate the effects of acid-sensing ion channels (ASICs) on electrophysiological epileptic activities of mouse hippocampal pyramidal neurons in the extracellular acidotic condition. METHODS: We investigated effects of extracellular acidosis on epileptic activities induced by elevated extracellular K concentration or the application of an antagonist of GABA receptors in perfusate of mouse hippocampal slices under field potential recordings. We also tested the effects of extracellular acidosis on neuronal excitability under field potential recording and evaluated the changes in epileptic activities of the neurons in response to pharmacological inhibition of ASICs using a specific inhibitor of ASICs. RESULTS: Extracellular acidosis significantly suppressed epileptic activities of the hippocampal neurons by converting ictal-like epileptic activities to non-ictal-like epileptic activities in both high [K ]o and disinhibition models, and also suppressed the intrinsic excitability of the neurons. ASICs inhibitor did not antagonize the inhibitory effect of extracellular acidosis on ictal epileptic activities and intrinsic neuronal excitability, but exacerbated non-ictal epileptic activities of the neurons in extracellular acidotic condition in both high [K]o and disinhibition models. CONCLUSIONS ASICs can differentially modulate ictal-like and non-ictallike epileptic activities via its direct actions on excitatory neurons.
Acid Sensing Ion Channels ; Acidosis ; Animals ; Hippocampus ; Hydrogen-Ion Concentration ; Mice ; Pyramidal Cells

Vascular endothelial growth factor (VEGF)-C and its receptor, vascular endothelial growth factor receptor (VEGFR)-3, are responsible for lymphangiogenesis in both embryos and adults. In epilepsy, the expression of VEGF-C and VEGFR-3 was significantly upregulated in the human brains affected with temporal lobe epilepsy. Moreover, pharmacologic inhibition of VEGF receptors after acute seizures could suppress the generation of spontaneous recurrent seizures, suggesting a critical role of VEGF-related signaling in epilepsy. Therefore, in the present study, the spatiotemporal expression of VEGF-C and VEGFR-3 against pilocarpine-induced status epilepticus (SE) was investigated in C57BL/6N mice using immunohistochemistry. At 1 day after SE, hippocampal astrocytes and microglia were activated. Pyramidal neuronal death was observed at 4 days after SE. In the subpyramidal zone, VEGF-C expression gradually increased and peaked at 7 days after SE, while VEGFR-3 was significantly upregulated at 4 days after SE and began to decrease at 7 days after SE. Most VEGF-C/VEGFR-3-expressing cells were pyramidal neurons, but VEGF-C was also observed in some astrocytes in sham-manipulated animals. However, at 4 days and 7 days after SE, both VEGFR-3 and VEGF-C immunoreactivities were observed mainly in astrocytes and in some microglia of the stratum radiatum and lacunosum-moleculare of the hippocampus, respectively. These data indicate that VEGF-C and VEGFR-3 can be upregulated in hippocampal astrocytes and microglia after pilocarpine-induced SE, providing basic information about VEGF-C and VEGFR-3 expression patterns following acute seizures.
Adult ; Animals ; Astrocytes ; Brain ; Embryonic Structures ; Epilepsy ; Epilepsy, Temporal Lobe ; Hippocampus ; Humans ; Immunohistochemistry ; Lymphangiogenesis ; Mice ; Microglia ; Pyramidal Cells ; Receptors, Vascular Endothelial Growth Factor ; Seizures ; Status Epilepticus ; Vascular Endothelial Growth Factor A ; Vascular Endothelial Growth Factor C ; Vascular Endothelial Growth Factor Receptor-3

It is known that top-down associative inputs terminate on distal apical dendrites in layer 1 while bottom-up sensory inputs terminate on perisomatic dendrites of layer 2/3 pyramidal neurons (L2/3 PyNs) in primary sensory cortex. Since studies on synaptic transmission in layer 1 are sparse, we investigated the basic properties and cholinergic modulation of synaptic transmission in layer 1 and compared them to those in perisomatic dendrites of L2/3 PyNs of rat primary visual cortex. Using extracellular stimulations of layer 1 and layer 4, we evoked excitatory postsynaptic current/potential in synapses in distal apical dendrites (L1-EPSC/L1-EPSP) and those in perisomatic dendrites (L4-EPSC/L4-EPSP), respectively. Kinetics of L1-EPSC was slower than that of L4-EPSC. L1-EPSC showed presynaptic depression while L4-EPSC was facilitating. In contrast, inhibitory postsynaptic currents showed similar paired-pulse ratio between layer 1 and layer 4 stimulations with depression only at 100 Hz. Cholinergic stimulation induced presynaptic depression by activating muscarinic receptors in excitatory and inhibitory synapses to similar extents in both inputs. However, nicotinic stimulation enhanced excitatory synaptic transmission by ~20% in L4-EPSC. Rectification index of AMPA receptors and AMPA/NMDA ratio were similar between synapses in distal apical and perisomatic dendrites. These results provide basic properties and cholinergic modulation of synaptic transmission between distal apical and perisomatic dendrites in L2/3 PyNs of the visual cortex, which might be important for controlling information processing balance depending on attentional state.
Animals ; Automatic Data Processing ; Dendrites ; Depression ; Inhibitory Postsynaptic Potentials ; Kinetics ; Pyramidal Cells ; Rats ; Receptors, AMPA ; Receptors, Muscarinic ; Synapses ; Synaptic Transmission ; Visual Cortex