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Volume 16, Number 23, Issue of December 1, 1996 pp. 7583-7598
Copyright ©1996 Society for Neuroscience

Ionic Currents Underlying Developmental Regulation of Repetitive Firing in Aplysia Bag Cell Neurons

Received May 24, 1996; revised Sept. 9, 1996; accepted Sept. 9, 1996.

Teresa A. Nick¹, Leonard K. Kaczmarek^{1, 3}, and Thomas J. Carew^{1, 2}

¹ Interdepartmental Neuroscience Program, ² Departments of Psychology and Biology, Yale University, New Haven, Connecticut 06510, and ³ Departments of Pharmacology and Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510

We have investigated the developmental regulation of the ability to fire repetitively in the bag cell neurons of Aplysia californica, a neuronal system in which the behavioral effects of repetitive firing are well characterized. Adult bag cell neurons exhibit an afterdischarge, consisting of prolonged depolarization and repetitive firing, which causes the release of several peptides from these neurons that induce egg-laying behaviors. Afterdischarge can be triggered in vitro by a variety of stimuli, including electrical stimulation and exposure to the potassium channel blocker tetraethyl ammonium chloride (TEA). In contrast to adults, juvenile neurons did not exhibit afterdischarge in response to pleural-abdominal connective shock or TEA. Juvenile neurons did exhibit, however, prolonged depolarizations in the presence of TEA, perhaps reflecting the anlage of the mechanism responsible for afterdischarge in the adult.

To investigate developmental mechanisms underlying the regulation of repetitive firing, we compared ionic currents in adult and juvenile bag cell neurons. We found that during the period in which these neurons acquire the capacity to fire repetitively, a number of currents are regulated: (1) three K⁺ currents decrease (Ca²⁺-dependent K⁺ and two components of voltage-dependent delayed-rectifier K⁺ current); (2) A-type K⁺ current increases; and (3) two Ca²⁺ currents increase (basal and PKC-activated). This pattern is consistent with the increase in the ability to fire repetitively that we observe during maturation: our results indicate that developmental control of repetitive firing in this system is accompanied by selective regulation of specific ionic currents which, after maturation, play important roles in generating the afterdischarge and triggering egg-laying behaviors.

Key words: ion channel; bag cell neurons; Aplysia; development; neuroendocrine; delayed rectifier; potassium current; calcium current; culture; bursting; voltage clamp

This article has been cited by other articles:

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