Effect of naloxone on tooth pulp-evoked jaw-opening reflex in the barbiturate-anaesthetized cat

The threshold of the tooth pulp-evoked jaw-opening reflex was uninfluenced by administration of 0.5 or 5.0 mg kg-1, i.v. naloxone, a specific opioid antagonist, in the barbiturate-anaesthetized cat. Furthermore, facilitatory or inhibitory interactions between two successive tooth pulp-evoked jaw reflex responses were not influenced by naloxone. It is concluded that naloxone-sensitive opioid receptor-mediated mechanisms do not contribute to the modulation of tooth pulp-evoked reflexes by conditioning dental stimuli. Also they do not exert a tonic inhibition on the sensory or motor part of the tooth pulp-driven reflexes. Experiments performed for comparison showed that the non-nociceptive polysynaptic reflex discharge in the flexo-motor neurons of the limb was not influenced by naloxone either.