Journal o f Physiology (1995), 486.2, pp.439-451 A-current modifies th e spike o f C-type neurones i n th e rabbit nodose ganglion Christian Ducreux and Jean-Jacques Puizillout Laboratoire d e Neurobiologie, Neuroregulations Cellulaires, B P . 71, 13402 Marseille Cedex 20 , France 1 . I n t h e rabbit nodose ganglion, C-type fibre neurones ( C neurones) c a n b e divided into t w o subtypes according t o their after-hyperpolarizing potential (AHP) i.e. those with a fast A H P only a n d those with a fast A H P a n d a subsequent slow A H P produced b y a slow calcium-dependent potassium current. I n addition w e have shown that some C neurones can b e divided into t wo groups according t o t h e effect of membrane hyperpolarization o n their spikes i.e. type 1 i n which duration a nd amplitude d o n o t change a n d type 2 i n which duration a n d amplitude decrease significantly. 2 . I n t h e present report w e studied t h e effect of A-current (IA) o n spike duration, amplitude an d slow AHP using intracellular recording techniques. 3 . T o detect t h e presence o f I A , w e first applied a series of increasing rectangular hyperpolarizing pulses t o remove I A inactivation a nd then a short depolarizing pulse t o trigger a spike. I n type 1 C neurones t h e l a g time o f t h e spike i n relation t o hyperpolarization remains constant whereas i n type 2 C neurones t h e spike only appears after IA inactivation a nd l a g time i n relation t o hyperpolarization i s lengthened. Thus, type 2 C neurones have a n I A while type 1 C neurones d o not. T h e fact thataddition o f cadmium did not change t h e l a g time i n type 2 C neurones shows that t h e I A is n o t calcium dependent. 4 . Nodose neurones can be orthodromically activated by stimulation o f t h e vagal peripheral process. In this way, after a hyperpolarizing pulse, I A c an be fully activated b y th e orthodromic spike itself. Under these conditions it i s possible t o analyse t h e effects o f I A o n t h e spike. This w a s done b y increasing either t h e hyperpolarizing potential, pulse duration, o r th e delay of t h e spike after t h e e n d o f t h e pulse. W e observed that maximum I A inactivation removal w a s always associated with t h e lowest duration a nd amplitude of th e spike. 5 . When I A inhibitors, 4-aminopyridine (4-AP) o r catechol, were applied t o type 2 C neurones, t h e delay o f t h e spike after t h e hyperpolarization-depolarization test w a s n o longer observed. I n addition 4-AP abolished t h e shortening o f the duration o f t h e spike induced b y steady hyperpolarization. 6 . I n type 2 C neurones with slow AHP, t h e IA-related decrease i n spike duration w a s associated with a disappearence o f t h e slow AHP. This indicates that ' A decreases t h e calcium influx during t h e spike. 7. I n conclusion, since I A regulates the amplitude a nd duration o f t h e spike i n prehyper- polarized cells, i t i s logical t o assume that I A i s able t o regulate t h e calcium influx into t h e cell. If this mechanism occurs a t axon terminals, it could interfere with transmitter release a n d thus modulate synaptic transmission. A-current, first observed by Hagiwara e t a l . (1961) in polarization (de-inactivation). I A h a s been implicated in molluscan neurones a n d later termed I A by Connor & several processes. I t slows repetitive discharges b y decreasing Stevens (1971a), i s a fast transient outward voltage- t h e rate o f decay o f th e fast after-hyperpolarizing potential dependent potassium current. At resting potential, I A i s (Connor & Stevens, 1971 b ; Hille, 1992). I t modulates t h e inactivated b u t this inactivation c an be removed b y hyper- efficacy o f synaptic transmission (Rogawski, 1985). It h as 3801 4 3 9 ) by guest on October 27, 2010 jp.physoc.org Downloaded from J Physiol (

Christian Ducreux and Jean-Jacques Puizillout- A-current modifies the spike of C-type neurones in the rabbit nodose ganglion

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