A long-lasting facilitation of spinal reflexes can be induced by 5-HT2 receptor activation (Machacek et al 1999; SFN). Here we further characterized the expression of long-lasting reflex facilitation (rLTP) as well as identified a long-lasting reflex depression (rLTD). Electrodes were attached to lumbar roots for stimulation of afferents and recording of ventral root reflexes in the in vitro hemisected rat spinal cord (P2-P13). Stimulation parameters were 500 μA, 50-500 μs and 0.02-0.1 Hz. Bath applied 5-HT depressed evoked reflexes, then rLTD occurred 5/12 and rLTP in 1/12 cases following wash. DOI (5-HT2 agonist) increased reflex amplitude (4/6) and rLTP was always observed following wash. MK212 (5-HT2C agonist) increased reflex amplitude in 10/14 cases, but following wash both rLTP (7/14) and rLTD (3/14) were observed. Bicuculline (BIC; GABAA antagonist) increased polysynaptic reflexes (PSR;14/14) which was further increased with MK212 (4/5). Comparison of reflex amplitudes before and after removal of M...