Here we studied whether descending control of mechanical nociception by glutamate in the central nucleus of the amygdala (CeA) of healthy control animals is induced by amygdaloid NMDA receptors and relayed through the midbrain periaqueductal gray (PAG). Mechanical nociception in the hind paws was assessed in rats with chronic guide cannulae for glutamate administration in the right CeA and for inducing local anesthesia in the PAG. In a separate electrophysiological study, ON-like PAG neurons giving an excitatory response to noxious pinch of the tail were recorded in anesthetized rats following glutamate administration into the CeA. A high dose of glutamate (100 μg) in the CeA induced mechanical antinociception in the contra- but not ipsilateral hind limb. Antinociception was prevented by an NMDA receptor antagonist in the CeA or local anesthesia of the PAG. Discharge rate of ON-like PAG neurons was increased by a high dose of glutamate (100 μg) in the CeA and this increase was prevented by an NMDA receptor antagonist in the CeA. The results indicate that amygdaloid NMDA receptors in the CeA may induce contralaterally mechanical antinociception through a circuitry relaying in the PAG. Activation of ON-like PAG neurons is associated with the descending antinociceptive effect. Mechanisms and causality of this association still remain to be studied., N. Bourbia, A. Pertovaara., and Obsahuje bibliografii
Ionotropic glutamate receptors function can be affected by neurosteroids, both positively and negatively. N-methyl-D-aspartate (NMDA) receptor responses to exogenously applied glutamate are potentiated or inhibited (depending on the receptor subunit composition) by pregnenolone sulphate (PS) and inhibited by pregnenolone sulphate (3α5βS). While PS effect is most pronounced when its application precedes that of glutamate, 3α5βS only binds to receptors already activated. Synaptically activated NMDA receptors are inhibited by 3α5βS, though to a lesser extent than those tonically activated by exogenous glutamate. PS, on the other hand, shows virtually no effect on any of the models of synaptically activated NMDA receptors. The site of neurosteroid action at the receptor molecule has not yet been identified, however, the experiments indicate that there are at least two distinct extracellularly located binding sites for PS mediating its potentiating and inhibitory effects respectively. Experiments with chimeric receptors revealed the importance of the extracellular loop connecting the third and the fourth transmembrane domain of the receptor NR2 subunit for the neurosteroid action, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors are inhibited by both PS and 3α5βS. These neurosteroids also affect AMPA receptors-mediated synaptic transmission, however, in a rather indirect way, through presynaptically located targets of action., M. Sedláček, M. Kořínek, M. Petrovič, O. Cais, E. Adamusová, H. Chodounská, L. Vyklický Jr., and Obsahuje bibliografii a bibliografické odkazy
Pregnenolone sulfate (PS), an endogenously occurring neurosteroid, has been shown to modulate the activity of several neurotransmitter-gated channels, including the NMDA receptor (NMDAR). NMDARs are glutamate-gated ion channels involved in excitatory synaptic transmission, synaptic plasticity, and excitotoxicity. In this study, we analyzed the effects of PS on calcium signaling in cultured hippocampal neurons and HEK293 cells expressing NMDAR. The ce lls were loaded with the Ca 2+ sensor Fura-2. In agreement with previous electrophysiological experiments, PS potentiated the increases in intracellular Ca 2+ induced by an exogenous application of glutamate; however, PS also increased intracellular Ca 2+ in the absence of exogenous NMDA agonist. The agonist-independent effect of PS was induced in all neurons studied and in HEK293 cells expressing GluN1/GluN2A-B receptors in a neurosteroid-specific manner. We conclude that PS is an endogenous NMDA agonist that activates the GluN1/GluN2A-B receptors., E. Adamusová ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy