Records from top to bottom: raw activity of B-fibre CVPNs, rate histogram (1 s bin), PNA and HR. A, there was no effect of 8-OH-DPAT on the CVPN at low currents (20–80 nA), while at the high current (120 nA) excitation was observed. B shows the biphasic effect of 8-OH-DPAT (on a different CVPN to that in A), at the lower current (40–80 nA) evoking inhibition, while at the higher current (120 nA) evoking excitation. Note that the dotted lines on the HR traces represent the baseline mean HR. DLH, dl-homocysteic acid.