Figure 4
Action potential firing patterns, subthreshold voltage-activated currents and primary afferent input for iCRs. (a) Examples of action potential firing patterns observed in iCRs in response to 1-s current injections. (b) Most iCRs exhibited tonic firing, with smaller proportions displaying transient or single spike firing. (c) Representative traces showing hyperpolarisation-activated (Ih) and low-threshold calcium (ICa,T) currents, in response to a voltage step protocol (bottom left). Each trace shows an average of 5 sweeps. (d) Most iCRs displayed Ih and/or ICa,T, while A-type potassium currents (IA) were rarely observed. (e) Representative traces of monosynaptic C fibre input to iCRs, revealed in response to electrical stimulation of dorsal roots. Low frequency traces are an average of 3 sweeps, high frequency trace shows 20 superimposed sweeps. (f) The majority of iCRs received primary afferent input that was classified as monosynaptic from C fibres; for the remaining cells the input was classified as polysynaptic only. In six cells we found primary afferent input from both L4 and L5 dorsal roots; an example of a cell with monosynaptic C fibre input from both roots is shown in (g). Grey traces are 20 individual sweeps, black traces are an average of the grey traces. In most iCRs (8/11) the monosynaptic C fibre input was sufficient to drive action potential firing, and an example is shown in (h). This shows three individual traces superimposed.
