THE ROLE OF OPIATE RECEPTORS IN THE MECHANISM OF NEUROMODULATION OF ENDOGENIC ANTIBIOTIC DEFENSINE IN THE FROG VESTIBULAR EPITHELIUM

Abstract

Antibacterial peptides defensins display multifunctional activity. Our previous study revealed a modulating effect of rabbit and human (HNP-1) defensins on afferent synaptic transmission in the vestibular epithelium of the frog. The current study investigated the possible involvement of the opiate receptors in defensin modulation of glutamatergic synaptic transmission. Hair cell synaptic transmission was examined using the methods of electrophysiological recording of multiunit nerve fibers activity and externally applied drugs. Specific agonist μ-opioid receptor (OR) DAGO (0,1-100 μM) and specific agonist К-OR U-50448 (1 nM -10 μM) decreased the level of background discharge in the afferent fibers. The resting activity was increased during application of specific antagonist κ-OR nor-Binaltorphimine (nor-Bin) in concentration 0,01-10 μM. Specific antagonist Ц-OR CTAP (0,01-1 μM) provided two-phase positive-negative action. Application of specific agonist 5-OR DSLET (0,1-10 ЦМ) and antagonist δ-OR naltrindole (1 nm-10 μM) did not modify the resting activity. CTAP (100 nm) and nor-Bin (10 ЦМ) antagonized the depressive effect of HNP-1 (1 nm), supporting the evidence for competitive interaction of HNP-1 and μ- and κ-opioid receptor ligands. The results obtained suggest that the immune system can modulate afferent synaptic transmission of the vestibular epithelium of the frog. Cross talk between glutamatergic and immune system by means of μ-and κ-opiate receptor subtypes is discussed.