Group II metabotropic glutamate receptor activation attenuates peripheral sensitization in inflammatory states

Several lines of evidence indicate that Group II metabotropic glutamate receptor (mGluR) activation can depress sensory transmission. We have reported the expression of Group II mGluRs on unmyelinated axons, many of which were presumed to be nociceptors, in the rat digital nerve [Carlton SM, Hargett GL, Coggeshall RE (2001b) Localization of metabotropic glutamate receptors 2/3 on primary afferent axons in the rat. Neuroscience 105:957-969]. The goals of the present study are to further our understanding of Group II modulation of nociceptor processing in the periphery, documenting behavioral changes using inflammatory models and documenting, for the first time, cutaneous single fiber activity following exposure to a Group II agonist (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (APDC) and antagonist (2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495, LY). The data indicate that peripheral Group II mGluR activation does not depress nociceptive behaviors or nociceptor fiber responses in the non-sensitized state (i.e. following brief nociceptive mechanical or thermal stimulation) but can depress these responses when nociceptors are sensitized by exposure to formalin or inflammatory soup. Group II mGluR agonist-induced inhibition can be blocked by a selective Group II antagonist. Peripheral Group II mGluR-induced inhibition evoked in these studies occurs through activation of local receptors and not through spinal or supraspinal mechanisms. The data indicate that administration of selective Group II agonists may be potent therapeutic agents for prevention of peripheral sensitization and for treatment of inflammatory pain.     

Involvement of group I mGluRs in LTP induced by strong high frequency stimulation in the dentate gyrus in vitro

The involvement of group I metabotropic glutamate receptors (mGluRs) and ryanodine receptors was investigated in the induction of LTP induced either by application of one standard high frequency stimulation (HFS) or by strong multiple HFS in the medial perforant path to granule cell synapse of the rat dentate gyrus. Whilst a standard brief HFS induced LTP close to 50%, strong stimulation consisting of multiple HFS induced a much larger LTP. mGluR5 was found to be partially involved in the induction of the enhanced LTP induced by the strong HFS but not in the standard LTP induced by the brief HFS. Thus the mGluR5 antagonists LY341495 and MPEP partially inhibited the induction of LTP induced by strong HFS but did not inhibit LTP induced by a standard HFS. Ryanodine was found to partially inhibit LTP induced by the strong HFS but not to inhibit the standard LTP induced by the brief HFS, demonstrating the involvement of Ca-induced Ca release from ryanodine-sensitive Ca stores in the former. These studies demonstrate that the large amplitude LTP induced by strong stimulation involves additional mechanisms to the LTP induced by brief HFS, in particular involving activation of mGluR5 and RyR-sensitive Ca stores.     

Detailed radiosynthesis of [18F]mG4P027 as a positron emission tomography radiotracer for mGluR4

We report here the detailed radiosynthesis of [¹⁸F] mG4P027 , a metabotropic glutamate receptor 4 (mGluR4) PET radiotracer, which showed superior properties to the currently reported mGluR4 radiotracers. The radiosynthesis in the automated system has been challenging, therefore we disclose here the major limiting factors for the synthesis via step-by-step examination. And we hope this thorough study will help its automation for human use in the future.