We previously implicated 5-HT7 receptors in 5-HT-induced locomotion (Cina & Hochman 1998 SFN). This observation was supported by other studies (Fyda & Jordan 1999 SFN; Fyda et al 2000 SFN). In those studies, Sprague Dawley rats were obtained from Charles River (Montreal). Another study connected 5-HT1 and 5-HT2 receptors to locomotion (Cazalets et al 1992 J Physiol). Since neurophysiological differences within and between rat strains have been noted (e.g. Xu et al 2001 Pain), we examined the pharmacology of 5-HT locomotion in Sprague Dawley and Wistar rats obtained from a different source (Charles River, NC). Experiments were employed in the isolated rat spinal cord (days 0-3). Dual L2 & L5 ventral root recordings monitored motor output. While NMDA alone (2-5 μM) never induced locomotion, the addition of 5-HT (10 - 40 μM) produced a stable long-lasting locomotor rhythm in all preparations. The following 5-HT receptor antagonists alone or in combination were incapable of blocking locomotion (≦1 μM): (i) Spr...