Glutamate receptor functions in sensory relay in the thalamus

Abstract

It is known that glutamate is a major excitatory transmitter of sensory and cortical afferents to the thalamus. These actions are mediated via several distinct receptors with postsynaptic excitatory effects predominantly mediated by ionotropic receptors of the a-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-d-aspartate varieties (NMDA). However, there are also other kinds of glutamate receptor present in the thalamus, notably the metabotropic and kainate types, and these may have more complex or subtle roles in sensory transmission. This paper describes recent electrophysiological experiments done in vitro and in vivo which aim to determine how the metabotropic and kainate receptor types can in uence transmission through the sensory thalamic relay. A particular focus will be how such mechanisms might operate under physiological conditions.

Pharmacological dissection of the paradoxical pain induced by a thermal grill

“…Dougherty et al 1992;Salt and Eaton, 1996). The reduction of paradoxical pain induced by ketamine may be a consequence of its action in the spinal dorsal horn and/or in the brain, particularly in the thalamus where there are numerous glutamate receptors, including the NMDA subtype (Salt, 2002). The neuropharmacology of COLD and HPC spinal neurons is not well established, so it is difficult to interpret our results directly within the framework of the thermosensory disinhibition theory.…”

“…The corticofugal inputs to the thalamic sensory relay nuclei also involve glutamate and NMDA receptors (Salt and and Eaton, 1996;Salt, 2002). Thus, the reduction of paradoxical pain by ketamine may be the results of its action on the transmission of somatosensory signals and/or on the cortico-thalamic (top-down) modulation of sensory processes.…”

A Review of Glutamate Receptors I: Current Understanding of Their Biology

“…Most NMDA functional receptors are formed by combination of NR1 and NR2 subunits, which express the Gly and Glu recognition sites respectively 327,328 . NR1 is more concentrated in rostral structures such as cortex, caudate, and hippocampus, while the latter are principally found in more caudal regions such as thalamus 329 , colliculi, locus coeruleus and cerebellum 330 . The NR2 subfamily consists of four individual subunits: NR2A to NR2D 263 .…”

Forward and backward connections in the brain: A DCM study of functional asymmetries

“…This is relevant because voltage sensitive (i.e., nonlinear) receptors like NMDA receptors populate, largely, the supra-granular layers (Fox et al 1989;Rosier et al 1993), suggesting that backward connections may have preferential access to modulatory, voltage-dependent post-synaptic effects with long time-constants (c.f., Eaton and Salt 1996;Gentet and Ulrich 2004). Similarly, backward connections have also been found to target metabotropic glutamate receptors which, like NMDA receptors, have long time-constants and are thus able to mediate context-sensitive effects (Rivadulla et al 2002;Salt 2002).…”

“…However, there is some empirical evidence that forward connections may also exhibit nonlinear properties. For example, transmission of sensory information along forward connections can involve NMDA receptors (Fox et al 1990;Kelly and Zhang 2002;Salt 2002). According to predictive coding theories, forward connections mediate the influence of error units in lower levels on representational units in higher levels, and these bottom-up influences are linear in prediction error (Friston 2003).…”