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First published online October 10, 2003

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The Journal of Experimental Biology 206, 4011-4020 (2003)
doi: 10.1242/jeb.00631

Electrical activity of caudal neurosecretory neurons in seawater- and freshwater-adapted flounder: responses to cholinergic agonists

M. J. Brierley, A. J. Ashworth, T. P. Craven, M. Woodburn, J. R. Banks, W. Lu, D. Riccardi, R. J. Balment and C. R. McCrohan^*

School of Biological Sciences, University of Manchester, Manchester M13 9PT, UK

^* Author for correspondence (e-mail: Cathy.McCrohan{at}man.ac.uk)

Accepted 30 July 2003

The caudal neurosecretory system (CNSS) of the euryhaline flounder is involved in osmoregulatory responses underlying adaptation to seawater and freshwater. This study compared electrophysiological activity and responses to cholinergic agonists in the neuroendocrine Dahlgren cells in an in vitro preparation taken from fully seawater- (SWA) or freshwater-adapted (FWA) fish. Resting membrane and action potential parameters showed few differences between SWA and FWA cells. The hyperpolarisation-activated sag potential and depolarising afterpotential were present under both conditions; however, amplitude of the latter was significantly greater in SWA cells. The proportions of cells within the population exhibiting different firing patterns were similar in both adaptation states. However, bursting parameters were more variable in FWA cells, suggesting that bursting activity was less robust. The muscarinic agonist, oxotremorine, was largely inhibitory in Dahlgren cells, but increased activity in a non-Dahlgren cell population, neurons. Nicotine promoted bursting activity in SWA Dahlgren cells, whereas it inhibited over half of FWA cells.

Key words: flounder, Platichthys flesus, neurosecretory system, Dahlgren cell, acetylcholine, nicotine, oxotremorine, electrophysiology, osmoregulation

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