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Journal of Neuroscience, Vol 8, 3074-3084, Copyright © 1988 by Society for Neuroscience

ARTICLE

The neuropeptide egg-laying hormone modulates multiple ionic currents in single target neurons of the abdominal ganglion of Aplysia

RF Jansen and E Mayeri
Department of Physiology, School of Medicine, University of California, San Francisco 94143.

The bag cell neurons of the abdominal ganglion of Aplysia are a useful system for the study of peptidergic neurotransmission. A 20 min burst of impulse activity in the bag cells induces or augments repetitive firing in LB and LC neurons in the abdominal ganglion for up to several hours. Previous experiments have indicated that this effect is mediated by the putative bag cell transmitter egg-laying hormone (ELH). Using voltage-clamp analysis we found that bag cell bursts (BCBs) evoke long- lasting changes in membrane current in these neurons that are mimicked by the application of ELH. The combined ELH-evoked current is inward at all membrane potentials between -110 and -10 mV and consists of 3 separable currents persisting for 30-120 min. They include (1) a depolarizing current that is activated at membrane potentials above -40 mV. This current, termed ISI, is blocked by prolonged exposure to 10 mM Ni2+/0 mM Ca2+ and is not abolished by 0 mM Na+ or 100 mM TEA+/0 mM Na+ in the bathing medium. It is therefore a Ca2+-sensitive current and does not involve Na+ as a charge carrier. (2) There is a hyperpolarizing current that is activated at membrane potentials below approximately -70 mV. This current, termed IR, is blocked by external Rb+ (5 mM) and Cs+ (10 mM) and has a chord-conductance that shifts with the external [K+] according to the Nernst potential for potassium. It is therefore an inwardly rectifying K+ current. (3) There is a small, steady depolarizing current, termed Ix. This current is the only one that remains after prolonged exposure to 10 mM Ni2+/0 mM Ca2+- containing bathing medium. It is Na+ dependent and is associated with a small increase in membrane conductance that is largely independent of membrane voltage. All 3 currents are slow to inactivate; they appear to sum algebraically to produce the net BCB- or ELH-evoked current.

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