Fig. 4. LTP can be transferred between animals.

Area of C-fiber–evoked field potentials was normalized to baseline values before transfer of the superfusate and plotted against time (min). Data are expressed as mean ± 1 SEM. Horizontal bars indicate application of superfusate or drugs. (A) Spinal application of superfusates collected from donor animals shown in Fig. 3A 1 hour after HFS induced potentiation of C-fiber–evoked field potentials in all recipient animals tested (n = 10, P = 0.009). (B) Superfusates collected from naïve donor animals (no HFS) had no effect on synaptic strength in recipient animals (n = 7, P = 0.477). (C) Superfusion of the recipient spinal cord dorsum with fluoroacetate (10 μM) or (D) interleukin-1 receptor antagonist (IL1Ra) (80 pg·ml⁻¹) did not block LTP induction [n = 9, P < 0.001 in (C) and n = 10, P = 0.001 in (D)]. (E to G) LTP was, however, blocked by topical application of soluble tumor necrosis factor receptor type I (1 μg·ml⁻¹; n = 10, P = 0.38), DAAO (1 U·ml⁻¹; n =6 out of 7, P = 0.519) or D-AP5 (100 μM; n = 6, P = 0.652). Insets show original traces of field potentials recorded at indicated time points. Calibration bars indicate 0.2 mV and 50 ms. In (A), data were analyzed using RM ANOVA on ranks followed by Dunnett’s test. In all other experiments, statistical significance was determined by using RM ANOVA.