Two Populations of Layer V Pyramidal Cells of the Mouse Neocortex: Development and Sensitivity to Anesthetics

Abstract

Christophe, Elodie, Nathalie Doerflinger, Daniel J. Lavery, Zoltán Molnár, Serge Charpak, and Etienne Audinat. Two populations of layer V pyramidal cells of the mouse neocortex: development and sensitivity to anesthetics. J Neurophysiol 94: 3357-3367, 2005. First published July 6, 2005 doi:10.1152/jn.00076.2005. Previous studies have shown that layer V pyramidal neurons projecting either to subcortical structures or the contralateral cortex undergo different morphological and electrophysiological patterns of development during the first three postnatal weeks. To isolate the determinants of this differential maturation, we analyzed the gene expression and intrinsic membrane properties of layer V pyramidal neurons projecting either to the superior colliculus (SC cells) or the contralateral cortex (CC cells) by combining whole cell recordings and single-cell RT-PCR in acute slices prepared from postnatal day (P) 5-7 or P21-30 old mice. Among the 24 genes tested, the calcium channel subunits ␣1B and ␣1C, the protease Nexin 1, and the calcium-binding protein calbindin were differentially expressed in adult SC and CC cells and the potassium channel subunit Kv4.3 was expressed preferentially in CC cells at both stages of development. Intrinsic membrane properties, including input resistance, amplitude of the hyperpolarization-activated current, and action potential threshold, differed quantitatively between the two populations as early as from the first postnatal week and persisted throughout adulthood. However, the two cell types had similar regular action potential firing behaviors at all developmental stages. Surprisingly, when we increased the duration of anesthesia with ketamine-xylazine or pentobarbital before decapitation, a proportion of mature SC cells, but not CC cells, fired bursts of action potentials. Together these results indicate that the two populations of layer V pyramidal neurons already start to differ during the first postnatal week and exhibit different firing capabilities after anesthesia.

Diversity of layer 5 projection neurons in the mouse motor cortex

“…To test for projection target specific signatures of voltage dependent conductances in the subthreshold voltage range to AP firing we assessed basic electrophysiological properties that generally differentiate between commissural and corticofugal neurons (Kasper et al, 1994; Christophe et al, 2005; Le Be et al, 2007; Dembrow et al, 2010; Sheets et al, 2011; Suter et al, 2012). Though CSp neurons were somewhat more depolarised at rest at 26°C ( Table 2 ) the resting membrane potential did not differ between the cell types when measured also at 36°C (two-way ANOVA, p = 0.19).…”

“…A limited set of up to 8 parameters including dendritic shaft width, Ri, sag, AP half width, and spike frequency adaptation allowed reliable identification of the two main groups of projection neurons; corticofugal (main axon projecting toward the spinal cord) sometimes called PT-type, and commisural (main axon projecting across the corpus callosum to the cerebral cortex and/or the striatum) sometimes called IT-type neurons as also seen in other cortical regions (Amitai and Connors, 1995; Reiner et al, 2003; Christophe et al, 2005; Hattox and Nelson, 2007; Groh et al, 2010; Suter et al, 2012). We show that in M1 the application of an extended set of electrophysiological and morphological parameters further divided neurons into two sub-groups that matched their projection targets and allowed clear segregation of CSp and CTh neurons in the corticofugal group and CC and CStr neurons in the commissural group.…”

“…Despite their different projection targets and acknowledged heterogeneity (Tseng and Prince, 1993; Cho et al, 2004a,b; Gao and Zheng, 2004) they are generally described as commissural or corticofugal projection neurons with electrophysiological, synaptic and morphological properties similar to those seen in neocortex (Chagnac-Amitai et al, 1990; Mason and Larkman, 1990; Schubert et al, 2006) and frontal, sensory and motor cortices (Kasper et al, 1994; Christophe et al, 2005; Morishima and Kawaguchi, 2006; Le Be et al, 2007; Anderson et al, 2010; Groh et al, 2010; Sheets et al, 2011; Kiritani et al, 2012; Suter et al, 2012). Given the diversity of projection targets for the motor cortex and the growing detail of cellular differences in other cortices (Hattox and Nelson, 2007; Otsuka and Kawaguchi, 2008, 2011; Brown and Hestrin, 2009; Schmidt et al, 2012), a separation based upon two broad projection neuron types in M1 seems limiting and dated.…”

Physiological consequences of selective suppression of synaptic transmission in developing cerebral cortical networks in vitro: Differential effects on intrinsically generated bioelectric discharges in a living ‘model’ system for slow-wave sleep activity

“…As immature membrane potentials only gradually attain their mature values (Bures, 1957;Christophe et al, 2005;Johnson and Buonomani, 2007;Kaspar et al, 1994;Kim et al, 1995;Mares, 1964;McCormick and Prince, 1987;Nakanishi et al, 1999;Reboreda et al, 2007;Zhang, 2004), firing thresholds could easily be low enough at first for spikes to be initiated locally on a purely stochastic basis.…”

“…It is therefore to be welcomed that a number of recent experimental studies have been devoted specifically to measuring the electrical activities of neocortical output neurons (Christophe et al, 2005;Golomb et al, 2006;Kerr et al, 2005;Kozloski et al, 2001;Kumar and Huguenard, 2001;Mao et al, 2001;Mizuno et al, 2007;Zhang, 2004). In order for ontogenetically induced changes in neural network outflow to be physiologically meaningful, however, they should also produce a significant modification of responsiveness in downstream structures which, in turn, must be reflected in the next tier of downstream targets, and so forth until a demonstrable alteration in motor output from the nervous system as a whole results.…”