title: Iontophoretic application of an A-type potassium channel blocker to the trigeminal ganglion neurons enhances the excitability of Aδ- and C-neurons innervating the temporomandibular joint in rats.
abstract: The present study tested the hypothesis that under in vivo conditions the iontophoretic application of a I(A) channel blocker, 4-aminopyridine (4-AP), to the TRG neurons changes the properties of Aδ-/C-TRG neurons that innervate the temporomandibular joint (TMJ) region, using extracellular electrophysiological recording with multi-barrel electrodes in pentobarbital-anesthetized rats. A total of twenty-one neurons (Aδ-: 76%; C-: 24%) responded to electrical stimulation of the TMJ region in pentobarbital-anesthetized rats. TMJ electrical stimulation-induced discharges of Aδ/C-neurons were significantly potentiated in current dependent manner (30-70 nA) by iontophoretic application of 4-AP into the TRGs. The spontaneous firing rates of Aδ- and C-neurons were also increased by 4-AP in a current-dependent manner (30-70 nA). The mean threshold current that evoked spontaneous discharges of C-neurons was significantly lower than that of Aδ-neurons. Moreover, the mean relative threshold current for electrical stimulation of TMJ-induced response of C-TRG neurons was significantly lower than that of Aδ-neuron. The relative firing rate of C-neurons induced by 4-AP-treatment (70 nA) was significantly higher than for Aδ-neurons. These results suggest that the application of 4-AP enhanced Aδ/C-TRG neuronal activities innervating the TMJ in vivo and C-neurons had significantly higher sensitivity for 4-AP than Aδ-neurons.
authors.affiliation: Department of Physiology, School of Life Dentistry at Tokyo, Nippon Dental University, 1-9-20, Fujimi-cho, Chiyoda-ku, Tokyo, 102-8159, Japan.
authors.forename: Norifumi
authors.initials: N
authors.lastname: Hara
authors.forename: Mamoru
authors.initials: M
authors.lastname: Takeda
authors.forename: Masayuki
authors.initials: M
authors.lastname: Takahashi
authors.forename: Shigeji
authors.initials: S
authors.lastname: Matsumoto
mesh_terms: D015761:4-Aminopyridine / Q000008:administration & dosage*; D000818:Animals; D007478:Iontophoresis; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D026902:Potassium Channel Blockers / Q000008:administration & dosage*; D024642:Potassium Channels, Voltage-Gated / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013704:Temporomandibular Joint / Q000294:innervation*; D012668:Trigeminal Ganglion / Q000166:cytology / Q000187:drug effects
chemical_list: D026902:Potassium Channel Blockers; D024642:Potassium Channels, Voltage-Gated; D015761:4-Aminopyridine