Excitatory Amino Acid Receptors Participate in Synaptic Transmission of Visual Responses in the Superficial Layers of the Cat Superior Colliculus

AbstractIn visual neurones of the superficial layers of the superior colliculus (SSC), repetitive stimulation causes a progressive decline in the size of the response to the stimulus, usually known as response habituation or response adaptation. A mechanism has been proposed in which habituation results from coactivation of excitatory and inhibitory neurones, and the responses of the inhibitory neurones block the response to subsequent stimulus presentations. Excitatory amino acid (EAA) neurotransmitters mediate visual responses via NMDA and non-NMDA receptors in cat SSC. We have investigated the role of these receptors in the generation of response habituation. Following the iontophoretic application of the EAA antagonists CNQX, APS or CPP, repetitive visual stimulation paradigms which normally produce response habituation no longer do so. Indeed the response to each presentation of the stimulus is similar. Intravenous administration of the dissociative anesthetic ketamine (2–10 mg/kg) had similar actions to iontophoretically applied NMDA antagonists. The data imply that intracollicular mechanisms activated by NMDA and non-NMDA receptors contribute to the generation of the inhibitory responses in SCC which lead to response habituation. Furthermore, the effects seen with ketamine anesthesia suggest that the use of ketamine in studies of sensory systems may result in the lack of habituation.

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Involvement of excitatory amino acid receptors in long-term potentiation in the Schaffer collateral–commissural pathway of rat hippocampal slices

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y91-160 ◽

1991 ◽

Vol 69 (7) ◽

pp. 1084-1090 ◽

Cited By ~ 15

Author(s):

G. L. Collingridge ◽

J. F. Blake ◽

M. W. Brown ◽

Z. I. Bashir ◽

E. Ryan

Keyword(s):

Amino Acid ◽

Synaptic Transmission ◽

Excitatory Amino Acid ◽

Hippocampal Slices ◽

Long Term Potentiation ◽

Excitatory Amino Acid Receptors ◽

Amino Acid Receptors ◽

Term Potentiation ◽

Commissural Pathway

The present article reviews studies from our laboratory, which have shown that excitatory amino acid receptors of the N-methyl-D-aspartate type are involved in the induction of long-term potentiation in the Schaffer collateral–commissural pathway of rat hippocampal slices. The nature of the excitatory amino acid receptors that mediate the response that is modified by the induction of long-term potentiation is also considered. The mechanism of induction of long-term potentiation is discussed, as are some possible stages that are required for the maintenance of this process. Some new data are presented concerning the ability of N-methyl-D-aspartate to potentiate synaptic transmission and to depress the amplitude of the presynaptic fibre volley. Concerning the potentiation, it is shown that brief (1–2 min) perfusion of slices with N-methyl-D-aspartate is sufficient to potentiate synaptic transmission for at least 3 h. The N-methyl-D-aspartate induced depression of the presynaptic fibre volley is shown to be transient and independent of synaptic transmission.Key words: long-term potentiation, N-methyl-D-aspartate, a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, synaptic plasticity, hippocampus.

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