Roles of the AMPA receptor subunit GluA1 but not GluA2 in synaptic potentiation and activation of ERK in the anterior cingulate cortex

Central mechanisms of pathological pain

Chronic pain is a major challenge to clinical practice and basic science. The peripheral and central neural networks that mediate nociception show extensive plasticity in pathological disease states. Disease-induced plasticity can occur at both structural and functional levels and is manifest as changes in individual molecules, synapses, cellular function and network activity. Recent work has yielded a better understanding of communication within the neural matrix of physiological pain and has also brought important advances in concepts of injury-induced hyperalgesia and tactile allodynia and how these might contribute to the complex, multidimensional state of chronic pain. This review focuses on the molecular determinants of network plasticity in the central nervous system (CNS) and discusses their relevance to the development of new therapeutic approaches.

Mu and delta opioid receptors on nociceptors attenuate mechanical hyperalgesia in rat

Sensitization to mechanical stimuli is important in most pain syndromes. We evaluated the populations of nociceptors mediating mechanical hyperalgesia and those mediating mu-opioid receptor (MOR) and delta-opioid receptor (DOR) agonist-induced inhibition of hyperalgesia, in the rat. We found that: (1) intradermal injection of both the endogenous ligand for the Ret receptor, glia-derived growth factor (GDNF), and the ligand for the tropomyosin receptor kinase A (TrkA) receptor, nerve growth factor (NGF)-which are present on distinct populations of nociceptors-both produce mechanical hyperalgesia; (2) DOR agonist 4-[(R)-[(2S,5R)-4-allyl-2,5-dimethylpiperazin-1-yl](3-methoxyphenyl)methyl]-N,N-diethylbenzamide (SNC) but not MOR agonist [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO) inhibit GDNF-induced hyperalgesia; (3) both DAMGO and SNC inhibit NGF hyperalgesia, even in rats pretreated with isolectin B4 (IB4)-saporin, a toxin that destroys IB4-binding neurons; (4) co-administration of low doses of DAMGO and SNC produce enhanced analgesia, and; (5) repeated administration of DAMGO produces cross-tolerance to the analgesic effect of SNC. These findings demonstrate that, most nociceptors have a role in mechanical hyperalgesia, only the DOR agonist inhibits GDNF hyperalgesia, and MOR and DOR are co-localized on a functionally important population of TrkA-positive nociceptors.

ERK in learning and memory: a review of recent research

The extracellular signal-regulated kinase (ERK) pathway is a member of the mitogen-activated protein kinase (MAPK) superfamily, which is an important, highly conserved family of enzymes associated with cell membrane receptors and regulative targets. In the central nervous system, there is almost no mature neuronal proliferation and differentiation, but the regulation of MAPK and its upstream and downstream molecular pathways is still widespread, with the ERK signaling pathway being one of the most actively studied signal transduction pathways. It is activated by a variety of cell growth factors and substances which promote mitotic activity, and transmits extracellular signals from the cell surface to the nucleus, which transmission plays an important role in the process of cell proliferation and differentiation. In recent years, accumulating evidence has shown that the ERK signaling pathway has an important link with the higher functions of learning and memory.

A role of periaqueductal grey NR2B-containing NMDA receptor in mediating persistent inflammatory pain

The midbrain periaqueductal grey (PAG) is a structure known for its roles in pain transmission and modulation. Noxious stimuli potentiate the glutamate synaptic transmission and enhance glutamate NMDA receptor expression in the PAG. However, little is known about roles of NMDA receptor subunits in the PAG in processing the persistent inflammatory pain. The present study was undertaken to investigate NR2A- and NR2B-containing NMDA receptors in the PAG and their modulation to the peripheral painful inflammation. Noxious stimuli induced by hind-paw injection of complete Freund's adjuvant (CFA) caused up-regulation of NR2B-containing NMDA receptors in the PAG, while NR2A-containing NMDA receptors were not altered. Whole-cell patch-clamp recordings revealed that NMDA receptor mediated mEPSCs were increased significantly in the PAG synapse during the chronic phases of inflammatory pain in mice. PAG local infusion of Ro 25-6981, an NR2B antagonist, notably prolonged the paw withdrawal latency to thermal radian heat stimuli bilaterally in rats. Hyperoside (Hyp), one of the flavonoids compound isolated from Rhododendron ponticum L., significantly reversed up-regulation of NR2B-containing NMDA receptors in the PAG and exhibited analgesic activities against persistent inflammatory stimuli in mice. Our findings provide strong evidence that up-regulation of NR2B-containing NMDA receptors in the PAG involves in the modulation to the peripheral persistent inflammatory pain.