MODULATION OF FACIAL AND DENTAL PAIN TRANSMISSION BY ENKEPHALIN IN TRIGEMINAL GANGLION

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Our previous report showed that leucine-enkephalin immunoreactive nerve fibers and cell bodies occurred in trigeminal ganglion of the guinea pig, suggesting the possibility that leucine-enkephalin can modulate pain transmission in trigeminal ganglion. In this research, we characterized opioid receptors and voltage-dependent calcium channels in trigeminal ganglion of giunea pig.1) The values of Kd and Bmax of ^3H-DPDPE (selective ligand for delta - type opiate receptors) and ^3H-DAMGO (selective ligand for mu - type opiate receptors) were 4.4nM, 29.1 fmol/mg protein and 0.7 nM, 7.2 fmol/mg protein, respectively.2) The values of Kd and Bmax of ^3H-PN200-110 (L-type calcium channel antagonist) and ^<125>I-omega- conotoxin (N-type calcium channel antagonist) were 48.2 pM, 18.5 fmol/mg protein and 50.1 pM, 29.5 fmol/mg protein, respectively.3) Acute administration of morphine did not affect both ^3H-PN200-110 and ^<125>I-omega-conotoxin binding. The chronic administration increased the binding of ^<125>I-omega-conotoxin.4) Using laser scanning fluorescence microscope, we found that leucine-enkephalin-immunorective fibers surrounded some nonimmunoreactive ganglionic cells.These results suggest that leucine-enkephalin may modulate the function of the primary afferent neuron through calcium dynamics in guinea pig trigeminal ganglion.