Abstract

We characterized the effect of a novel selective histamine H1 receptor antagonist, (R)-1-(3-(10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5-ylidene)-1-propyl)-3-piperidine carboxylic acid (ReN-1869), on the responses of dorsal horn neurons in anesthetized rats after carrageenan induced-inflammation and peripheral neuropathy (L5/6 spinal nerve ligation; SNL). ReN-1869 was administered systemically (0.1-4 mg/kg), and drug effects were assessed using a wide range of peripheral electrical and natural stimuli (brush, von Frey filaments, and heat). Comparisons were made between unoperated naive groups and either carrageenan inflamed or SNL rats. ReN-1869 produced little effect on the electrically evoked responses (wind-up, Aβ-, Aδ-, and C-fiber-evoked responses); however, it significantly attenuated neuronal responses to noxious heat in carrageenan and SNL rats. A robust effect was seen with the low-threshold mechanical punctate (von Frey 9 g) stimuli, which were selectively inhibited by ReN-1869 after tissue and nerve injury. These inhibitory actions were in marked contrast to the naive animal group, where only nonsignificant effects were observed. To investigate whether the actions of ReN-1869 are mediated via the antagonism of histamine H1 receptors, the effects of this novel compound were compared with that of another H1 receptor antagonist, mepyramine (1-20 mg/kg). Systemic mepyramine produced strong inhibitions of the 9-g von Frey-evoked responses in carrageenan and SNL rats. The similar pharmacological profile of these two compounds suggests for a similar mechanism of action. We propose that ReN-1869 may represent a novel agent for the treatment of certain modalities of persistent pain states, in particular for the treatment of mechanical allodynia.