The models include an intravascular photochemical reaction that occludes blood vessels, producing spinal cord ischemia with subsequent trunk mechanical allodynia [18, 19]; anterolateral lesions of the spinal cord in monkeys and rats that produce overgrooming and mechanical allodynia [20, 21]; a clip compression model in which the thoracic spinal cord is compressed by 35 g or 50 g clip demonstrates mechanical hyperalgesia in the hindlimbs ; quisqualic acid (an AMPA/kainate and a group I glutamate metabotropic receptor
agonist) injection into the dorsal horn produces overgrooming ; and a spinal hemisection [24, 25] and spinal contusion models [26-28] demonstrate mechanical allodynia in both the hindlimbs and forelimbs.
The 22 structures were derived from 7 crystals, which 5 of them belong to ionotropic receptors and 2 belong to metabotropic receptors
Necessary additional research should make use of parallel recording of behavior and bioelectric brain activity as well as of the discoveries of molecular biology in order to further better understanding of the participation of ionotropic and metabotropic receptors
of inhibitory GABA mediators in learning.
[+ or -] i.q.r, median [+ or -] inter-quartile range; mGluR, metabotropic receptor
; NMDA, N-methyl-D-aspartate; NMDAR, NMDA receptor; P/CB, average number of pulses per contraction burst; PLP, pre-locomotor pulse; pT, pre-treatment period; RP, rhythmic potential; SUBP, small, uncorrelated body pulse; SUTP, small, uncorrelated tentacle pulse; T1, treatment period 1; T2, treatment period 2; TP, tentacle pulse.
Each neuron carries receptors for both excitatory and inhibitory neurotransmitters on its surface; moreover, some of the signals will be mediated through ionotropic receptors and induce fast responses whereas others will be mediated through metabotropic receptors
and trigger slow responses.
So-called metabotropic receptors
, responding to the same neurotransmitters, set off chemical cascades in the receiving nerve cells, so-called "second messenger" systems, chains of chemical processes activating synthesis of neurotransmitters, of receptors and of modulators, changing the reactivity of the nerve cell and of the system it subserves.
AMPA, NMDA, and metabotropic receptors
have been found in the vestibular nuclei.
This signaling involves six major functional classes of receptors: three classes of ligand-gated ion channels (ionotropic receptors) and three classes of G-protein-coupled receptors (metabotropic receptors
Binding of glutamate to metabotropic receptors
involves guanosine nucleotide-binding protein (G-protein).
In fact, in a number of in vitro and in vivo experimental models of ischemia, glutamate receptor antagonists, acting either on NMDA receptor or on group I metabotropic receptors
, are effective neuroprotective agents; none of the glutamate receptor antagonists tested in clinical trials showed positive results or had an acceptable benefit/side effects ratio .
The modulation of glutamatergic ionotropic or metabotropic receptors
is shown in Table 4.
: Receptors for neurotransmitters that indirectly lead to the opening of ion channels via second messengers.