Electrophysiological properties of genetically identified subtypes of layer 5 neocortical pyramidal neurons: Ca²⁺ dependence and differential modulation by norepinephrine

Abstract

Guan D, Armstrong WE, Foehring RC. Electrophysiological properties of genetically identified subtypes of layer 5 neocortical pyramidal neurons: Ca 2ϩ dependence and differential modulation by norepinephrine. J Neurophysiol 113: 2014 -2032, 2015. First published January 7, 2015 doi:10.1152/jn.00524.2014.-We studied neocortical pyramidal neurons from two lines of bacterial artificial chromosome mice (etv1 and glt; Gene Expression Nervous System Atlas: GENSAT project), each of which expresses enhanced green fluorescent protein (EGFP) in a different subpopulation of layer 5 pyramidal neurons. In barrel cortex, etv1 and glt pyramidal cells were previously reported to differ in terms of their laminar distribution, morphology, thalamic inputs, cellular targets, and receptive field size. In this study, we measured the laminar distribution of etv1 and glt cells. On average, glt cells were located more deeply; however, the distributions of etv1 and glt cells extensively overlap in layer 5. To test whether these two cell types differed in electrophysiological properties that influence firing behavior, we prepared acute brain slices from 2-4-wk-old mice, where EGFP-positive cells in somatosensory cortex were identified under epifluorescence and then studied using whole cell current-or voltage-clamp recordings. We studied the details of action potential parameters and repetitive firing, characterized by the larger slow afterhyperpolarizations (AHPs) in etv1 neurons and larger medium AHPs (mAHPS) in glt cells, and compared currents underlying the mAHP and slow AHP (sAHP) in etv1 and glt neurons. Etv1 cells exhibited lower dV/dt for spike polarization and repolarization and reduced direct current (DC) gain (lower f-I slope) for repetitive firing than glt cells. Most importantly, we found that 1) differences in the expression of Ca 2ϩ

Roles of specific Kv channel types in repolarization of the action potential in genetically identified subclasses of pyramidal neurons in mouse neocortex

“…We studied layer 2/3 pyramidal neurons and layer 5 pyramidal neurons from two bacterial artificial chromosome lines of mice, each of which expresses EGFP in a different subpopulation of layer 5 pyramidal neurons (Gong et al 2002(Gong et al , 2003(Gong et al , 2007Guan et al 2015). In the somatosensory cortex of Tg(Etvl-EGFP)BZ192Gsat/Mmucd (etv1) mice, EGFP is primarily expressed in pyramidal neurons from superficial layer 5 (Groh et al 2010;Guan et al 2015).…”

“…In the somatosensory cortex of Tg(Etvl-EGFP)BZ192Gsat/Mmucd (etv1) mice, EGFP is primarily expressed in pyramidal neurons from superficial layer 5 (Groh et al 2010;Guan et al 2015). The etv1 gene is a transcription factor that has been shown to be involved in neurogenesis in the olfactory bulb (Stenman et al 2003) and circuit formation in the spinal cord (Arber et al 2000).…”

“…For example, consider two lines of mice that express enhanced green fluorescent protein (EGFP) in cells expressing the genes etv1 or glt (Doyle et al 2008;Gong et al 2007). In mouse somatosensory cortex, etv1 cells are a subset of IT-type neurons located primarily in superficial layer 5 and glt cells are a subset of PT-type neurons, primarily located in deep layer 5 (Bishop et al 2015;Groh et al 2010;Guan et al 2015). glt cells have narrower and more rapidly repolarizing APs than etv1 or layer 2/3 cells (Groh et al 2010;Guan et al 2015).…”

“…In mouse somatosensory cortex, etv1 cells are a subset of IT-type neurons located primarily in superficial layer 5 and glt cells are a subset of PT-type neurons, primarily located in deep layer 5 (Bishop et al 2015;Groh et al 2010;Guan et al 2015). glt cells have narrower and more rapidly repolarizing APs than etv1 or layer 2/3 cells (Groh et al 2010;Guan et al 2015). Morphology and projection targets also differ for these cell populations (Groh et al 2010).…”

“…There are transient and persistent components to outward K ϩ currents in rodent pyramidal neurons (Bekkers 2000;Foehring and Surmeier 1993;Korngreen and Sakmann 2000;Locke and Nerbonne 1997). The persistent currents are due to strong expression of K v 1, K v 2 (the largest component), and K v 7 channels (Bekkers and Delaney 2001;Bishop et al 2015;Guan et al 2006Guan et al , 2007aGuan et al , 2007bGuan et al , 2011aGuan et al , 2011bGuan et al , 2013Guan et al , 2015Murakoshi and Trimmer 1999). In addition, Nerbonne and colleagues used genetic approaches to reveal that most of the transient, A-type current in rat neocortical cells is due to K v 4.2 and K v 4.3 channels (Carrasquillo et al 2012;Norris and Nerbonne 2010;Yuan et al 2005; see also Guan et al 2011b), with a contribution from K v 1.4 channels.…”