Exitatory Amino Acid Receptors in the In Vitro Mammalian Spinal Cord
The excitatory synapse between group la afferents and α-motoneurons is one of the most frequently used models for central synaptic transmission in mammals. Most of the knowledge regarding this synapse originates from studies of the in vivo cat spinal cord preparation (for reviews see Burke,3 Mendell,21 Redman25). Since spinal neurons in vivo are not amenable to manipulations of the external ionic environment, direct studies of neurotransmitters and the nature of their postsynaptic receptors have been carried out on cultured neurons and on mammalian CNS preparations isolated in vitro (for reviews see Ascher and Novak,1 Collingridge and Lester4, Mayer and Westbrook,20 Monaghan et al.,22). The central dogma regarding the involvement of excitatory amino acid (EAA) receptors in mediation of synaptic excitation in the spinal cord, is that transmission in monosynaptic pathways is mediated primarily by non-N-methyl D-aspartate (non-NMDA) receptors,6,7,13,27 that the NMDA receptors in these pathways may be activated only as the neurons are substantially depolarised14, and that interneuronal transmission in polysynaptic pathways is mediated by NMDA receptors.7,13,14,28 Recent studies from other systems2,5,9,11,26 and our studies of the neonatal rat spinal cord (see below; see also,28 for monosynaptic transmission in the embryonic rat spinal cord), have indicated that this concept may not be completely accurate.
KeywordsNMDA Receptor Excitatory Amino Acid Excitatory Amino Acid Receptor EPSP Amplitude Polysynaptic Pathway
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