FIRING PROPERTIES AND Na +-DEPENDENT PLATEAU POTENTIALS OF NEURONS IN NUCLEUS PRINCIPALIS TRIGEMINI OF THE GERBIL

11 W e invest igated the electrophysiological propert ies of neurons in the nucleus pr inc ipal is tr igemini (PrV), using w h o l e c e l l recordings in in vitro sl ice preparations of brainstem. We i d e n t i f i e d three groups mainly by their f iring propert ies: type 1 neurons w e r e spontaneously act ive and able to discharge action potent ials in doublets or bursts; type 2 neurons, depolar ized by current p u l s e s , fired action potentials in a nonadapting (tonic) pattern; and the l e s s commonly encountered type 3 neurons also fired in such patterns but with b iphasic a f te rhyperpo lar iza t ions . Neurobiot in staining and reconst ruct ion did not reveal s igni f icant morphological d i f f e r e n c e s between types 1 and 2 neurons which were mult ipolar, w i t h dendri t ic trees distr ibuted mainly along one axis. Type 3 neurons had more expansive and circular dendritic arbor izat ions. Hyperpolar izat ion beyond -75 mV or down to the K + r e v e r s a l potential due to current pulse inject ion, resulted in an i n w a r d rectification which was expressed as a sag in the voltage r e s p o n s e s of types 1 and type 2 neurons. A rebound sub th resho ld depolar izat ion or spike burst was evident on terminat ion of a pu lse . In type 1 neurons, the appl icat ion of C s + (2 mM), a blocker of a