Triggering action potentials in an axodendritic inhibitory synaptic terminal

INTRACELLULAR activity of the slow adapting neurone (SAN) was recorded toge ther with extracellular action potentials (APs) of SAN, fast adapting neuro ne and inhibitory fibre in the isolated stretch receptor of the moulting cr ayfish. Following strychnine application, spontaneous APs and seizure-like AP trains were observed. A delay of the inhibitory fibre APs relative to SA N inhibitory postsynaptic potential, their waveforms and their initiation b y intracellular SAN hyperpolarization indicate that their generation was cl ose to the inhibitory nerve terminal. Such antidromic (ectopic) APs assert their postsynaptic action on both receptor neurones via the axon reflex. Th e findings provide first evidence of antidromic APs generated in the vicini ty of inhibitory terminals, their direct and axon reflex-mediated action on target neurones and support a hypothesis that increased terminal excitabil ity contributes to seizure activity. (C) 1999 Lippincott Williams & Wilkins .