Amino acid receptor mediated excitatory synaptic transmission in the cat red nucleus.

Abstract

SUMMARY1. A study has been made of the effects of the selective N-methyl-D-aspartate receptor antagonist, 2-amino-5-phosphonovalerate (APV), and the broad spectrum excitatory amino acid antagonists, y-D-glutamylglycine (y-DGG), y-D-glutamylaminomethylsulphonate (GAMS), 4(p-chlorobenzoyl)-cis-piperazine-2, 3-dicarboxylate (pCB-PzDA) and kynurenate, have been examined on excitation evoked on neurones in the magnocellular red nucleus (m.r.n.) of the anaesthetized cat by stimulation of the interpositus nucleus (i.p.n.) and sensorimotor cortex, and by ionophoresed excitant amino acid agonists.2. The profile of activity of the excitatory amino acid antagonists on m.r.n. neurones was similar to that described on neurones in other areas of the central nervous system. APV selectively depressed responses to N-methyl-D-aspartate (NMDA), whereas the broader spectrum antagonists reduced responses to kainate and quisqualate as well as to NMDA. Neuronal responses to L-glutamate and L-aspartate were depressed by all the antagonists tested.3. I.p.n.-evoked monosynaptic responses ofm.r.n. neurones were reversibly reduced by the broad spectrum antagonists, but were unaffected by APV.4. Cortically evoked mono-and polysynaptic excitatory responses were reversibly depressed by APV and the broad spectrum antagonist, pCB-PzDA. The action of APV corresponded with its ability to antagonize responses to NMDA. However, the cortically evoked responses appeared to be more sensitive to the actions ofpCB-PzDA than to those of APV, although the former is a less effective antagonist of NMDA-induced excitation compared with APV.5. APV depressed excitation induced by cortical stimuli and L-glutamate and L-aspartate. However, there was no obvious correlation between the actions of the broad spectrum amino acid antagonists on synaptically evoked responses and those induced by L-glutamate or L-aspartate on the few neurones tested.6. These results are consistent with an amino acid being the transmitter in the interposito-rubral and cortico-rubral excitatory pathways which interacts with non-NMDA and both NMDA and non-NMDA receptors respectively. However, the identity of the transmitter acting at these receptors remains to be determined.

Excitatory amino acid receptor‐mediated transmission of somatosensory evoked potentials in the rat thalamus.

“…This profile of activity is similar to that reported from earlier electrophysiological and behavioural studies (Davies et al 1984;Davies, Miller & Sheardown, 1986;Klockgether et al 1986b).…”

“…Exceptions are a fast excitatory postsynaptic potential in rat cortical slices after corpus callosum stimulation (Thomson, West & Lodge, 1985), cortically evoked mono-and polysynaptic responses of rubral neurones (Davies et al 1986) and polysynaptic activation of spinal interneurones (Watkins & Evans, 1981). Poor involvement of NMDA receptors in synaptic transmission is explained by the fact that NMDA receptors generate their response via voltagedependent ion channels which are blocked by physiological concentrations of Mg2+ ions (Mayer, Westbrook & Guthrie, 1984;Nowak, Bregestovski, Ascher, Herbet & Prochiantz, 1984).…”

“…Sufficiently high doses of pCB-PzDA led to a nearly complete abolition of s.e.p.s. The available evidence indicates that pCB-PzDA blocks excitatory amino acid receptors in the absence of effects on receptors for other transmitters or local anaesthetic effects on neuronal membranes (Davies et al 1984(Davies et al , 1986). The present observations are therefore compatible with an excitatory amino acid being a transmitter at thalamic synapses mediating s.e.p.s.…”

Visual responses in adult cat visual cortex depend on N-methyl-D-aspartate receptors.

“…Incomplete blockade may also be produced by iontophoretic application if synaptic concentrations of NMDA are much larger than the concentrations achieved by NMDA iontophoresis, since blockade of the response to NMDA iontophoresis is used to calibrate the 5186 Neurobiology: Miller et al 12.00 r iontophoretic currents of APV. In some systems, it has been shown that substantially greater APV currents may be needed to block the synaptic responses mediated by NMDA receptors than to block responses to NMDA iontophoresis (26,27). Incomplete blockade may be indicated by Tsumoto and colleagues' report (12) (4)(5)(6)(7)(10)(11).…”

Projection from the cerebellar lateral nucleus to precerebellar nuclei in the mossy fiber pathway is glutamatergic: A study combining anterograde tracing with immunogold labeling in the rat

“…There is good evidence from both in vivo and in vitro electrophysiological and morphological studies that the transmission from the IN through the RNm is excitatory (Toyama et al, 1968(Toyama et al, , 1970Sakaguchi et al, 1984;Gorodnov and Fanardjian, 1987;Davies et al, 1986;Keifer and Houk, 1991;Giuffrida et al, 1993). For the RNp, however, only scant information has been available about the type of transmitter used by its cerebellar afferents.…”