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The differential expression of low-threshold K+ currents generates distinct firing patterns in different subtypes of adult mouse trigeminal ganglion neurones
Ist Teil von
The Journal of physiology, 2008-11, Vol.586 (21), p.5101-5118
In adult mouse trigeminal ganglion (TG) neurones we identified three neuronal subpopulations, defined in terms of their firing
response to protracted depolarizations, namely MF neurones, characterized by a multiple tonic firing; DMF neurones, characterized
by a delay before the beginning of repetitive firing; and SS neurones, characterized by a strongly adapting response. The
three subpopulations also differed in several other properties important for defining their functional role in vivo , namely soma size, action potential (AP) shape and capsaicin sensitivity. MF neurones had small soma, markedly long AP and
mostly responded to capsaicin, properties typical of a subgroup of C-type nociceptors. SS neurones had large soma, short AP
duration and were mostly capsaicin insensitive, suggesting that most of them have functions other than nociception. DMF neurones
were all capsaicin insensitive, had a small soma size and intermediate AP duration, making them functionally distinct from
both MF and SS neurones. We investigated the ionic basis underlying the delay to the generation of the first AP of DMF neurones,
and the strong adaptation of SS neurones. We found that the expression of a fast-inactivating, 4-AP- and CP-339,818-sensitive
K + current ( I A ) in DMF neurones plays a critical role in the generation of the delay, whereas a DTX-sensitive K + current ( I DTX ) selectively expressed in SS neurones appeared to be determinant for their strong firing adaptation. A minimal theoretical
model of TG neuronal excitability confirmed that I A and I DTX have properties congruent with their suggested role.