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Dissociated GABAergic retinal interneurons exhibit spontaneous increases in intracellular calcium

Published online by Cambridge University Press:  04 October 2006

SALLY I. FIRTH
Affiliation:
Neurobiology Section, Division of Biological Sciences, University of California at San Diego, San Diego, CaliforniaCurrent address of Dr. Sally I. Firth: School of Pharmacy, Steele Building (3), University of Queensland, St Lucia, QLD, 4072, Australia
MARLA B. FELLER
Affiliation:
Neurobiology Section, Division of Biological Sciences, University of California at San Diego, San Diego, California

Abstract

Early in development, before the retina is responsive to light, neurons exhibit spontaneous activity. Recently it was demonstrated that starburst amacrine cells, a unique class of neurons that secretes both GABA and acetylcholine, spontaneously depolarize. Networks comprised of spontaneously active starburst cells initiate correlated bursts of action potentials that propagate across the developing retina with a periodicity on the order minutes. To determine whether other retinal interneurons have similar “pacemaking” properties, we have utilized cultures of dissociated neurons from the rat retina. In the presence of antagonists for fast neurotransmitter receptors, distinct populations of neurons exhibited spontaneous, uncorrelated increases in intracellular calcium concentration. These increases in intracellular calcium concentration were sensitive to tetrodotoxin, indicating they are mediated by spontaneous membrane depolarizations. By combining immunofluorescence and calcium imaging, we found that 44% of spontaneously active neurons were GABAergic and included starburst amacrine cells. Whole cell voltage clamp recordings in the absence of antagonists for fast neurotransmitters revealed that after 7 days in culture, individual retinal neurons receive bursts of GABA-A receptor mediated synaptic input with a periodicity similar to that measured in spontaneously active GABAergic neurons. Low concentrations of GABA-A receptor antagonists did not alter the inter-burst interval despite significant reduction of post-synaptic current amplitude, indicating that pacemaker activity of GABAergic neurons was not influenced by network interactions. Together, these findings indicate that spiking GABAergic interneurons can function as pacemakers in the developing retina.

Information

Type
Research Article
Copyright
2006 Cambridge University Press

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