Excitatory Effect of GABAergic Axo-Axonic Cells in Cortical Microcircuits

  title={Excitatory Effect of GABAergic Axo-Axonic Cells in Cortical Microcircuits},
  author={J{\'a}nos Szabadics and Csaba Varga and G{\'a}bor Moln{\'a}r and Szabolcs Ol{\'a}h and P{\'a}l Barz{\'o} and G{\'a}bor Tam{\'a}s},
  pages={233 - 235}
Axons in the cerebral cortex receive synaptic input at the axon initial segment almost exclusively from γ-aminobutyric acid–releasing (GABAergic) axo-axonic cells (AACs). The axon has the lowest threshold for action potential generation in neurons; thus, AACs are considered to be strategically placed inhibitory neurons controlling neuronal output. However, we found that AACs can depolarize pyramidal cells and can initiate stereotyped series of synaptic events in rat and human cortical networks… 

Strategically Positioned Inhibitory Synapses of Axo-axonic Cells Potently Control Principal Neuron Spiking in the Basolateral Amygdala

A fine organization of AAC innervation maximizing their inhibitory efficacy by strategically positioning synapses along the AISs is uncovered, and the threshold for the action potential generation along PC axons is the lowest between 20 and 40 μm from soma, which axonal segment received the highest density of GABAergic inputs.

Bi-directional Control of Synaptic Input Summation and Spike Generation by GABAergic Inputs at the Axon Initial Segment.

This work quantitatively demonstrates 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.

Neurophysiology: Cause for excitement

  • A. Rowan
  • Biology
    Nature Reviews Neuroscience
  • 2006
A dual role is reported for the first time for AACs in triggering excitatory as well as inhibitory responses in cortical microcircuitry, and a mechanism by which GABA-mediated input can have an excitatories effect on postsynaptic cells in the adult brain is pin-pointed.

Temporal Dynamics of Parvalbumin-Expressing Axo-axonic and Basket Cells in the Rat Medial Prefrontal Cortex In Vivo

The spike-timing of identified neurons in the prelimbic cortex of anesthetized rats is recorded, and it is shown that axo-axonic cells increase their firing during tail pinch-induced brain state-activation and in their coupling to gamma and spindle oscillations.

Homeostatic plasticity rules control the wiring of axo-axonic synapses at the axon initial segment

Axo-axonic synapse plasticity follows the developmental switch in polarity of GABAergic synaptic transmission, which means that increases in the activity of either pyramidal cells or individual ChCs during this temporal window results in a reversible decrease in axo-AXonic connections, at a time when they are depolarising.

Interneurons Provide Circuit-Specific Depolarization and Hyperpolarization

Evidence is provided that the postsynaptic effect of GABAergic synapses is fundamentally different in two regions of rat hippocampus, and the nature of PII output signaling is circuit-dependent and may therefore contribute differentially to information processing in the two brain areas.

Thorough GABAergic innervation of the entire axon initial segment revealed by an optogenetic ‘laserspritzer’

The laserspritzer the authors developed activates axo‐axonic synapses (AASs) with spatial resolutions of less than 40 μm, which is sufficient to inhibit action potential generation and epileptiform activities in vitro.

An excitatory GABA loop operating in vivo

The results imply that elevated chloride concentration can occur in specific intracellular compartments of mature mammalian neurons and suggest an excitatory role for GABAA receptors in the cerebellar cortex of adult mice.



Coexistence of Excitatory and Inhibitory GABA Synapses in the Cerebellar Interneuron Network

It is suggested that the coexistence of excitatory and inhibitory GABA synapses could either buffer the mean firing rate of the interneuron network or introduce different types of correlation between neighboring interneurons, or both.

Physiological properties of anatomically identified axo-axonic cells in the rat hippocampus.

The properties of a well-defined type of GABAergic local circuit neuron, the axo-axonic cell, were investigated in rat hippocampal slice preparations and it was shown that one of the physiologically characterized cells was immunoreactive for gamma-aminobutyric acid (GABA).

The role of chloride transport in postsynaptic inhibition of hippocampal neurons.

The effects of furosemide suggest that the internal chloride activity of an individual hippocampal neuron is regulated by two transport processes, one that accumulates chloride and one that extrudes chloride.

Axonal Action-Potential Initiation and Na+ Channel Densities in the Soma and Axon Initial Segment of Subicular Pyramidal Neurons

The present results suggest that orthodromic action potentials initiate in the axon beyond the AH–IS and that the minimum threshold for spike initiation of the neuron is not determined by a high density of Na+ channels in the AH-IS region.

Ionic mechanisms of neuronal excitation by inhibitory GABAA receptors

Anionic gradient shifts may represent a mechanism whereby the rate and coherence of synaptic activity determine whether dendritic GABAA receptor activation is excitatory or inhibitory.

Routing of spike series by dynamic circuits in the hippocampus

Recurrent inhibitory loops are simple neuronal circuits found in the central nervous system, yet little is known about the physiological rules governing their activity. Here we use simultaneous

GABA-mediated biphasic inhibitory responses in hippocampus

The hippocampal slice preparation is used to demonstrate that a biphasic inhibitory response results from orthodromic, but not antidromic electrical stimulation in the presence of anaesthetic concentrations of pentobarbital.