Two functional inhibitory circuits are comprised of a heterogeneous population of fast-spiking cortical interneurons

Abstract

Cortical fast spiking (FS) interneurons possess autaptic, synaptic, and electrical synapses that serve to mediate a fast, coordinated response to their postsynaptic targets. While FS interneurons are known to participate in numerous and diverse actions, functional subgroupings within this multi-functional interneuron class remain to be identified. In the present study, we examined parvalbumin positive FS interneurons in layer 4 of the primary somatosensory (barrel) cortex - a brain region well-known for specialized inhibitory function. Here we show that FS interneurons fall into two broad categories identified by the onset of the first action potential in a depolarizing train as: “Delayed Firing FS interneurons (FSD) and Early Onset Firing FS interneurons (FSE). Subtle variations in action potential firing reveal 6 subtypes within these two categories: delayed non-accommodating (FSD-NAC), delayed stuttering (FSD-STUT), early onset stuttering (FSE-STUT), early onset-late spiking (FSE-LS), early onset early-spiking (FSE-ES), and early onset accommodating (FSE-AC). Using biophysical criteria previously employed to distinguish neuronal cell types, the FSD and FSE categories exhibit several shared biophysical and synaptic properties that coincide with the notion of specificity of inhibitory function within the cortical FS interneuron class.

Loss of CLOCK Results in Dysfunction of Brain Circuits Underlying Focal Epilepsy

“…All slices were incubated at 32°C for one hour prior to recording at room temperature. We followed previously described methods for obtaining electrophysiological parameters for active and passive membrane properties including input resistance, resting membrane potential, capacitance, Rheobase, action potential threshold, amplitude and frequency (Li and Huntsman, 2014). …”

“…Biocytin-filled neurons were further processed as previously described (Li and Huntsman, 2014). Images were obtained by confocal microscopy (FluoView, Olympus).…”

Biphasic impact of prenatal inflammation and macrophage depletion on the wiring of neocortical inhibitory circuits

“…Axonal arborization of most FS-PV cells is usually confined to the home-barrel, with the exception of minor populations of basket cells (Koelbl et al, 2015;Li and Huntsman, 2014;Rudy et al, 2011;Shigematsu et al, 2018). To explore whether such spatial pattern of functional projections of developing PV cells was also affected by MIA or embryonic microglial depletion, we used PV cre/+ ;R26 Chr2/+ mice, and measured the inhibitory drive evoked by a local optogenetic activation of PV interneurons on single principal cells belonging to the same vs neighboring barrels (Figure 3A-F).…”

Persistent Gamma Spiking in Non-Sensory Fast-Spiking Cells Predicts Perceptual Success

“…Such spiking behavior strongly resembles that of the gnsFS described here in SI. Li and Huntsman (2014) reported two broad electrophysiological categories of FS within layer 4 of SI barrel cortex based on the onset of the first action potential in a depolarizing train. They found that FS that showed delayed spiking in response to current injection also had smaller thalamocortical-evoked responses compared to early spiking FS, potentially reflecting the sensory and non-sensory subtypes observed in the present study.…”