title: Strategically positioned inhibitory synapses of axo-axonic cells potently control principal neuron spiking in the basolateral amygdala.
abstract: Axo-axonic cells (AACs) in cortical regions selectively innervate the axon initial segments (AISs) of principal cells (PCs), where the action potentials are generated. These GABAergic interneurons can alter the activity of PCs, but how the efficacy of spike control correlates with the number of output synapses remains unclear. Moreover, the relationship between the spatial distribution of GABAergic synapses and the action potential initiation site along the AISs is not well defined. Using paired recordings obtained in the mouse basolateral amygdala, we found that AACs powerfully inhibited or delayed the timing of PC spiking by 30 ms, if AAC output preceded PC spiking with no more than 80 ms. By correlating the number of synapses and the probability of spiking, we revealed that larger numbers of presynaptic AAC boutons giving rise to larger postsynaptic responses provided more effective inhibition of PC spiking. At least 10-12 AAC synapses, which could originate from 2-3 AACs on average, were necessary to veto the PC firing under our recording conditions. Furthermore, we determined that 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. Single AACs preferentially innervated this narrow portion of the AIS where action potentials were generated with the highest likelihood, regardless of the number of synapses forming a given connection. Our results uncovered a fine organization of AAC innervation maximizing their inhibitory efficacy by strategically positioning synapses along the AISs.
authors.affiliation: Lendület Laboratory of Network Neurophysiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest 1083, Hungary, and János Szentágothai School of Neurosciences, Semmelweis University, Budapest 1085, Hungary.
authors.forename: Judit M
authors.initials: JM
authors.lastname: Veres
authors.affiliation: Lendület Laboratory of Network Neurophysiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest 1083, Hungary, and.
authors.forename: Gergő Attila
authors.initials: GA
authors.lastname: Nagy
authors.affiliation: Lendület Laboratory of Network Neurophysiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest 1083, Hungary, and.
authors.forename: Viktória Krisztina
authors.initials: VK
authors.lastname: Vereczki
authors.affiliation: Lendület Laboratory of Network Neurophysiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest 1083, Hungary, and János Szentágothai School of Neurosciences, Semmelweis University, Budapest 1085, Hungary.
authors.forename: Tibor
authors.initials: T
authors.lastname: Andrási
authors.affiliation: Lendület Laboratory of Network Neurophysiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest 1083, Hungary, and hajos@koki.hu.
authors.forename: Norbert
authors.initials: N
authors.lastname: Hájos
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000502:physiology*; D066272:Basolateral Nuclear Complex / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D005260:Female; D059330:GABAergic Neurons / Q000502:physiology; D007395:Interneurons / Q000502:physiology; D008297:Male; D051379:Mice; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure
keywords: GABA; action potential; axon initial segment; interneuron; mouse