Abstract
The spiking patterns of neocortical pyramidal neurons are shaped by the conductances in their apical dendrites. We have previously shown that the spiking patterns of layer 5 pyramidal neurons change with temperature, probably because temperature modulates the electrical coupling between somatic and dendritic compartments. Here we determine whether temperature has similar effects on the spiking patterns of layer 2/3 and layer 6 pyramidal neurons in acute slices of mouse primary motor cortex. In both cell types, decreasing temperature led to more irregular spiking patterns. Our results indicate that a decrease in spiking regularity with decreasing temperature, probably mediated by increased electrical coupling between soma and dendrites, is common to all pyramidal neurons in motor cortex.
Highlights
Differences in inter-spike interval (ISI) variability and spike frequency adaptation have been reported among regularly spiking pyramidal neurons and it is unclear whether these differences reflect neuron-to-neuron variablity or result from the different recording conditions employed in different studies (Agmon and Connors, 1992; Nuñez et al, 1993; Dégenètais et al, 2002; Cho et al, 2004)
In an earlier study of layer 5 pyramidal neurons, we classified neurons as bursting or regularly firing based on the variation in ISI during a depolarizing current pulse at the soma, with neurons characterized as regularly spiking if none of the ISIs differed more by than 15% from the mean ISI and bursting if any ISI differed from the mean by 15% or more (Hedrick and Waters, 2011)
Layer 2/3 pyramidal neurons can adopt any of three spiking patterns at physiological temperatures: regular spiking, weak bursting, or adapting
Summary
The spiking patterns of pyramidal neurons in layers 2/3 and 6 of the neocortex are generally described as regular, meaning that spikes are evenly spaced during constant current injection (Connors et al, 1982; McCormick et al, 1985; Agmon and Connors, 1989; Chagnac-Amitai et al, 1990; Connors and Gutnick, 1990; Nuñez et al, 1993; Cho et al, 2004). In contrast with layer 2/3 and layer 6 pyramidal neurons, layer 5 pyramidal neurons have been classified as intrinsically bursting or regularly firing (Connors et al, 1982; McCormick et al, 1985; Agmon and Connors, 1989; Chagnac-Amitai et al, 1990; Mason and Larkman, 1990). Bursting is associated with the regenerative activation of sodium and calcium currents in the apical dendrite that cause prolonged depolarization of the axon initial segment (Silva et al, 1991; Schwindt and Crill, 1999; Williams and Stuart, 1999; Larkum et al, 2001; Larkum and Zhu, 2002). As a result depolarization of the axon initial segment is relatively brief and does not cause a burst (Waters et al, 2003; Larkum et al, 2007; Ledergerber and Larkum, 2010)
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