Effects of 1,8-cineole on electrophysiological parameters of neurons of the rat superior cervical ganglion.
1. 1,8-Cineole is a non-toxic small terpenoid oxide believed to have medicinal properties in folk medicine. It has been shown to have various pharmacological effects, including blockade of the compound action potential (AP). In the present study, using intracellular recording techniques, we investigated the effects of 1,8-cineole on the electrophysiological parameters of neurons of the superior cervical ganglion (SCG) in rats. 2. 1,8-Cineole (0.1-6 mmol/L) showed reversible and concentration-dependent effects on various electrophysiological parameters. At 3 and 6 mmol/L, but not at 0.1 and 1 mmol/L, 1,8-cineole significantly diminished the input resistance (R(i)) and altered the resting potential (E(m)) to more positive values. At 6 mmol/L, 1,8-cineole completely blocked all APs within 2.7 +/- 0.6 min (n = 12). In neurons exposed to 3 and 1 mmol/L 1,8-cineole, the effects regarding excitability varied from complete AP blockade to minor inhibition of AP parameters. The depolarization of E(m) and the decrease in R(i) induced by 6 mmol/L 1,8-cineole were unaltered by 200 micromol/L niflumic acid, a well known blocker of Ca(2+)-activated Cl(-) currents. 3. Significant correlations (Pearson correlation test) were found between changes in E(m) and decreases in AP amplitude (r = -0.893; P < 0.00282) and maximum ascendant inclination (r = -0.799; P < 0.0173), but not for maximum descendant inclination (r = 0.598; P < 0.117). Application of current to restore the transmembrane potential equal to control E(m) values in the presence of 6 mmol/L 1,8-cineole resulted in the partial recovery of AP. 4. The present study shows that 1,8-cineole effectively blocks the excitability of SCG neurons, probably through various mechanisms, one of which acts indirectly via depolarization of the neuronal cytoplasmatic membrane.
Laboratory of Electrophysiology, Superior Institute of Biomedical Sciences, Campus of Itaperi, State University of Ceará, Fortaleza, Ceará, Brazil.
Francisco W
FW
Ferreira-da-Silva
Roseli
R
Barbosa
Luiz
L
Moreira-Júnior
Tiago
T
dos Santos-Nascimento
Maria D
MD
de Oliveira-Martins
Andrelina N
AN
Coelho-de-Souza
Francisco S A
FS
Cavalcante
Vânia M
VM
Ceccatto
Telma L G
TL
de Lemos
Pedro J C
PJ
Magalhães
Saad
S
Lahlou
José Henrique
JH
Leal-Cardoso
D000818:Animals; D003511:Cyclohexanols / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D000077591:Eucalyptol; D005260:Female; D008297:Male; D008519:Medicine, Traditional; D008564:Membrane Potentials / Q000187:drug effects*; D039821:Monoterpenes / Q000494:pharmacology*; D009474:Neurons / Q000502:physiology*; D009544:Niflumic Acid / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017783:Superior Cervical Ganglion / Q000187:drug effects*
D003511:Cyclohexanols; D039821:Monoterpenes; D009544:Niflumic Acid; D000077591:Eucalyptol