ORIGINAL RESEARCH Synthesis and evaluation o i

ki ra Glutamate is a dominant neurotransmitter in the mam- largely focused on group I (mGlu1 and mGlu5) and II Yamasaki et al. EJNMMI Research 2013, 3:54 http://www.ejnmmires.com/content/3/1/54mice have directly demonstrated that mGlu7 plays theRadiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan Full list of author information is available at the end of the articlemalian central nervous system (CNS), inducing excita-tory neurotransmission by binding to its receptors. Glutamate receptors are classified as metabotropic or iontropic types based on their biological functions and molecular structures [1,2]. Eight subtypes of metabotro-pic glutamate receptors (mGlu1 to 8) have been identi-fied and divided into three groups based on sequence homology, pharmacology, and coupling pathway to G (mGlu2 and mGlu3), which have been implicated in various neuropathological and psychiatric disorders [4-6]. On the other hand, the group III receptors includ-ing four subtypes, such as mGlu4 and mGlu6 to 8, are less understood, mainly due to the paucity of specific li-gands for these receptors. Of the group III receptors, mGlu7 is mainly localized on the presynaptic terminals of glutamatergic neurons, and its signaling pathways are activated only under con-ditions of emergency synaptic activity because of its low affinity to glutamate [7]. Studies on mGlu7-deficien