FUNCTIONS OF IONOTROPIC AND METABOTROPIC GLUTAMATE RECEPTORS IN SENSORY TRANSMISSION IN THE MAMMALIAN THALAMUS

The thalamic relay nuclei play a pivotal role in gating and processing sensory information en route to the cerebral cortex. The major ascend ing sensory afferents and the descending cortico-fugal afferents to th e thalamus almost certainly use the excitatory amino acid L-glutamate as their transmitter. This paper reviews the nature of this transmissi on in terms of the receptor types which may be used (NMDA, AMPA, kaina te and metabotropic glutamate receptors), their electrophysiological a nd pharmacological properties, and their differential location in the thalamus on neurones, terminals and glial elements. Whilst AMPA recept ors, probably of more than one variety, are likely to mediate fast tra nsmission in the thalamus, the contributions of NMDA receptors and met abotropic glutamate receptors to sensory responses under different sti mulus conditions may be more varied. This is discussed in the context of the possible functional significance of the interplay of L-glutamat e-gated currents with intrinsic membrane currents of thalamic neurones . The interaction of L-glutamate transmission with other modulators (a cetylcholine, noradrenaline, serotonin, glycine, D-serine, nitric oxid e, arginine, redox agents) is considered.