Activity-Dependent Ectopic Spiking in Parvalbumin-Expressing Interneurons of the Neocortex

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Cortical Circuitry

Background:

• Action potentials typically initiate at the axon initial segment (AIS) and propagate bidirectionally.
• Ectopic action potentials (EAPs), initiated distal to the AIS, are observed in pathological conditions and rarely in normal neurons.
• Parvalbumin-expressing (PV+) interneurons are crucial for cortical network function, mediating inhibition.

Purpose of the Study:

• To investigate the occurrence and characteristics of ectopic action potential firing in mouse neocortical interneurons.
• To determine if PV+ interneurons commonly exhibit ectopic firing patterns.

Main Methods:

• Electrophysiological recordings in mouse neocortical slices.
• Stimulation of somata in orbitofrontal and somatosensory areas.
• Identification of parvalbumin-expressing (PV+) and somatostatin-expressing interneurons.

Main Results:

• A majority of PV+ interneurons in upper cortical layers fired EAPs upon sufficient somatic activation.
• Ectopic firing in PV+ cells exhibited diverse temporal patterns and could be sustained.
• Somatostatin-expressing interneurons also showed less frequent EAP firing.

Conclusions:

• Ectopic action potential firing is a common property of PV+ interneurons in the mouse neocortex.
• The prevalence of EAPs in PV+ cells suggests a potential role in both physiological and pathophysiological cortical network dynamics.
• Understanding EAP generation may offer insights into network dysfunction in conditions like seizures and chronic pain.