, 2010), although a pronociceptive role of endogenous spinal 5-HT was demonstrated by the reduction in nociceptive responses following selective depletion of spinal 5-HT ( Dogrul et al., 2009, Oatway et al., 2004 and Rahman et al., 2006). Nonetheless, descending serotonergic

facilitation may not be exclusive to 5-HT activating the 5-HT3 receptor, as there are several lines of evidence pointing to a pronociceptive role for the 5-HT2 receptor, although controversy exists. The complexity of effects produced by 5-HT acting on 5-HT2 receptors is due to the further existence of subtypes, namely 5-HT2A, 2B and 2C receptors (Alexander et al., 2008). Of these, the evidence to date largely points to a pronociceptive role for the 5-HT2A subtype (Eide and Hole, 1991, Kjorsvik et al., 2001, Nishiyama, 2005,

Silveira et al., 2010 and Thibault et al., 2008) but see (Honda selleckchem et al., 2006, Kommalage and Hoglund, 2005, Sasaki et al., 2001 and Sasaki et al., 2003), and an antinociceptive role for the 5-HT2C receptor subtypes in modulating spinal nociceptive transmission (Aira et al., 2010, Liu et al., 2007, Obata et al., 2004 and Obata et al., 2007). The amino acid sequence of the 5-HT2 receptors share a high degree of homology within the seven transmembrane domains; thus, it is not surprising that conflicting reports exist within the literature since many compounds bind to each subtype with high affinity (Knight etal., 2004). Behavioural studies could be confounded by the multiple functions of 5-HT in the CNS. Here, we evaluate the effect of topical spinal application DZNeP order of the selective 5-HT2A receptor antagonist, ketanserin, on the evoked responses of wide dynamic range dorsal horn neurones in response to electrical and natural stimulation of the peripheral receptive field, in order to evaluate the spinal specific role of this receptor subtype in suprathreshold responses. Ketanserin potently blocks 5-HT2A receptors, less potently blocks 5-HT2C receptors, and has no significant

effect on 5-HT3 or 5-HT4 receptors or any members of the 5-HT1 receptor family (Knight et al., 2004). We also assessed the effects of systemic delivery of the 5-HT2A/2C antagonist, ritanserin, on the same neuronal measures. Inositol oxygenase Ritanserin has equal affinity for the 5-HT2A and 2C subtypes (Knight et al., 2004), and finally, we assessed the effects of spinal application of (±)-2,5-Dimethoxy-4-iodoamphetamine hydrochloride (DOI), a mixed 5-HT2A/2C agonist, but with greater relative selectivity for 5-HT2A receptors, on these evoked spinal neuronal responses. Spinally applied ketanserin (1, 10 and 100 μg/50 μl) did not produce any significant effects on any of the electrically evoked neuronal measures, although a trend towards a dose-related inhibition was observed for the Aδ-, C-fibre and input evoked responses (Fig. 1a). In contrast a significant dose-related inhibition was observed on the natural evoked neuronal responses.