A, continuous records of the membrane potential of a single cell in which a depolarizing current step (+0.2 nA, 600 ms) was delivered 1.0 s prior to, and 2.0 s after pathway stimulation. The stimulation was delivered at an intensity just suprathreshold for activating an EPSPM in control medium containing only the ionotropic glutamate and GABAA receptor antagonists (control), in the additional presence of 20 μm (-)-baclofen and in the additional combined presence of 20 μm (-)-baclofen and 1 μm CGP 55845A. Note that in control medium, pathway stimulation evoked an IPSPB and caused a reduction in spike frequency adaptation. (-)-Baclofen inhibited but did not abolish the stimulation-evoked reduction in spike frequency adaptation. It did, however, occlude the IPSPB. B, pooled data for the difference in the number of action potentials fired during each 600 ms depolarizing step 1.0 s before and 2.0 s after a threshold stimulus in the absence and presence of 20 μm (-)-baclofen (Bac; n = 5) and in the additional presence of 1 μm CGP 55845A (n = 5). The initial membrane potential of the neurone was -65 mV and this was maintained using DC injection. Data are means ±s.e.m.; * significant (P < 0.05); n.s., not significant (compared with control).