Synaptic transmission in the pineal eye of young Xenopus laevis tadpoles: a role for NMDA and non-NMDA glutamate and non-glutaminergic receptors? |
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Authors: | D Jamieson |
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Institution: | (1) School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG, UK Tel.:+44-117/9280000; Fax: +44-117/9257374 e-mail: D.A.Jamieson@Bristol.ac.uk, GB |
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Abstract: | The pineal eye of Xenopus laevis tadpoles is directly photosensitive. A sudden reduction in light intensity produces a burst of activity in the pineal ganglion
cells, which is closely followed by the onset of swimming. In this paper I present the results of experiments on the effects
of agonists and antagonists of candidate pineal transmitters on ganglion cell activity. I found that NMDA and non-NMDA excitatory
amino acid (EAA) agonists increased pineal activity, indicating the presence of both types of receptor. Kynurenic acid reduced
activity, thus confirming that the photoreceptor transmitter is an EAA. Under physiological conditions, CNQX blocked activity
almost completely whilst AP5 had little effect. In Mg2+-free saline CNQX had a considerably smaller effect, but joint application of CNQX and AP5 blocked almost all activity; therefore,
the NMDA receptors are subject to blockage by Mg2+. Although GABAA and ACh receptors appear to be present, no evidence was found for GABA or ACh as pineal transmitters. In addition, 5-HT had
no effect on pineal activity. The main pineal transmitter is an EAA acting on ganglion cells through both NMDA and non-NMDA
receptors. Other receptors are present but appear to have no role in controlling pineal activity at this stage.
Accepted: 1 March 1997 |
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Keywords: | Xenopus tadpole Pineal Transmitter NMDA Photoreceptor |
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