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Local application of morphine inhibits intra‐dental nociceptor responses to mustard oil but not to hydrodynamic stimulation of dentine
Author(s) -
NÄRHI M.
Publication year - 2002
Publication title -
journal of oral rehabilitation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.991
H-Index - 93
eISSN - 1365-2842
pISSN - 0305-182X
DOI - 10.1046/j.1365-2842.2002.01026_41.x
Subject(s) - stimulation , nociceptor , inferior alveolar nerve , nerve fiber , medicine , dentinal tubule , anatomy , dentistry , chemistry , anesthesia , nociception , dentin , molar , receptor
Mustard oil (MO) has been used to induce inflammation and nociceptor activation in various tissues. It has been proposed to selectively activate small afferent fibres but more detailed knowledge on the functional characteristics and activation mechanisms of the responding neurones seems to be limited. In the present study we recorded intra‐dental nerve responses to hydrodynamic dentinal stimulation and MO. Also, the effect of local application of morphine on the induced nerve responses was studied. The experiments were performed on six beagle dogs (three female and three male, 1–2 years old, 9·5–12·5 kg). They were anaesthetized with sodium pentobarbitone (35 mg kg −1 ). The inferior alveolar nerve of the left side was exposed for nerve dissection and recording. The intradental nerve fibres were identified by monopolar electrical stimulation of the canine tooth crown. Dentine was exposed at the tip of the test tooth and the responses of the nerve fibres to drilling, probing and air blasts were tested. The test cavity was then drilled deep close to the pulp until 1·5 m NaCl induced nerve firing. After that MO was applied in the cavity. In six other canine teeth nerve activity was recorded from cavities drilled in dentine in the midcrown and the cervical area. The same stimuli were applied in the stimulation cavity as in the single fibre recordings. Seven single intra‐dental nerve fibres responding to drilling, probing and air blasts were recorded. Mustard oil induced long lasting firing of action potentials in all seven afferents with a latency of 5–10 min. In the dentine recordings nerve responses to MO were completely abolished by pre‐treatment of the stimulation cavity with morphine (20 mg mL −1 ) for 15 min but the responses to hydrodynamic stimulation and 2·5 m NaCl were unaffected. Further, in four teeth naloxone (7·5 mg mL −1 ) was applied in the cavity for 10 min and after that the responses to MO recovered. The present results indicate that the same intra‐dental nerve fibres are activated by hydrodynamic stimulation and MO. However, the mechanism of activation induced by MO seems to be different from other stimuli and sensitive to opioids.