The essential oil of Croton nepetaefolius selectively blocks histamine-augmented neuronal excitability in guinea-pig celiac ganglion.

OBJECTIVES Croton nepetaefolius is a medicinal plant useful against intestinal disorders. In this study, we elucidate the effects of its essential oil (EOCN) on sympathetic neurons, with emphasis on the interaction of EOCN- and histamine-induced effects. METHODS The effects of EOCN and histamine were studied in guinea-pig celiac ganglion in vitro. KEY FINDINGS Histamine significantly altered the resting potential (E(m)) and the input resistance (R(i)) of phasic neurons (from -56.6 +/- 1.78 mV and 88.6 +/- 11.43 MOmega, to -52.9 +/- 1.96 mV and 108.6 +/- 11.00 MOmega, respectively). E(m), R(i) and the histamine-induced alterations of these parameters were not affected by 200 microg/ml EOCN. The number of action potentials produced by a 1-s (two-times threshold) depolarising current and the current threshold (I(th)) for eliciting action potentials (rheobase) were evaluated. Number of action potentials and I(th) were altered by histamine (from 2.6 +/- 0.43 action potentials and 105.4 +/- 11.15 pA to 6.2 +/- 1.16 action potentials and 67.3 +/- 8.21 pA, respectively). EOCN alone did not affect number of action potentials and I(th) but it fully blocked the histamine-induced modifications of number of action potentials and I(th). All the effects produced by histamine were abolished by pyrilamine. CONCLUSIONS EOCN selectively blocked histamine-induced modulation of active membrane properties.