Systemic physostigmine shows antiallodynic effects in neuropathic rats

The aim of this study was to examine the antiallodynic and antinociceptive effects of subcutaneously administered physostigmine (50, 100, 200 mu g/kg) , compared with morphine (2.5, 5, 10 mg/kg) and NaCl after spinal nerve lig ation in rats. The following stimuli were used: acetone (cold allodynia), v an Frey hairs (mechanical allodynia), and paw flick test (thermal nocicepti on). Motility bares were used to investigate the effects of the drugs on mo tor performance. Physostigmine attenuated both mechanical and cold allodyni a dose-dependently but had no effect on the paw flick test. The effect was antagonized by atropine (muscarinic receptor antagonist) but not by mecamyl amine (nicotinic receptor antagonist) or naloxone (opioid receptor antagoni st). Morphine produced dose-dependent antiallodynic and antinociceptive eff ects. In the antiallodynic doses, morphine caused severe rigidity. Physosti gmine 200 mu g/kg impaired locomotor activity,but no rigidity was observed. Implications: Physostigmine has different effects on allodynia and nocicep tion, which suggests that different cholinergic (muscarinic) mechanisms may be involved in neuropathic and nociceptive pain.