Increases in temperature increase the intrinsic excitability and change spike shape in pyramidal neurons as predicted by the HH model.

<p>A. Increasing temperature from 21°C to 36°C and 41°C results in shorter duration action potentials that are also decreased in amplitude in layer 5 pyramidal cells in vitro. Spikes were initiated with the intrasomatic injection of a depolarizing current pulse (100 pA, 500 msec duration). B. The spike duration, measure at half peak amplitude, decreases gradually as a function of temperature for pyramidal neurons (n = 6; black). The action potentials of the simulated neuron results show a similar property (red). C. Action potential amplitude decreases with increases in temperature for both pyramidal neurons in vitro (black) and for the model neuron (red). D. For a fixed current pulse amplitude, the average firing rate of pyramidal cells in vitro (n = 6) increases gradually as a function of temperature. Notice that for temperatures >36°C, the firing rate increases more rapidly. The model neuron (red) also exhibits a non-linear increase in firing rate to a current pulse with increases in temperature. Differences between the real neuron and model results presumably arise from the complex morphology and properties of ionic channels not included in the simple HH model. E. Same data set as B, the average value of dv/dt ratio (minimum dV/dt divided by maximum dV/dt during the spike) increases gradually as a function of temperature for the recorded pyramidal cells in vitro (n = 6) (black). The model neuron exhibits a similar relationship (red).