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. 2010 Jan 20;5(1):e8780. doi: 10.1371/journal.pone.0008780

Figure 5. Only a sub-population of human C-fibres respond to GABA.

Figure 5

The magnitude of GABA (10–30 µM) evoked increases in excitability index correlate with parameters of electrical excitability. The compound C-fibre response in Type A fascicles (A) is typically sub-excitable (i.e. positive excitability index) at low rates of stimulation and shows a pronounced change in excitability index upon increasing the frequency of repetitive stimulation (open circles, C). In addition, C-fibre responses in Type A fascicles exhibit a large change in excitability index during bath application of GABA (30 µM, open circles, D). In contrast, C-fibre responses electrophysiologically classified as Type B (B) are typically super-excitable at low stimulus frequencies, show a modest change in excitability upon repetitive stimulation at 2 Hz (encircled crosses, C) and typically respond poorly or not at all to GABA (30 µM, encircled crosses, D). The filled markers in panels C and D represent fascicles for which a classification based upon the C-fibre response profile to repetitive electrical stimulation at 2 Hz was not determined.