Prevalence and influence of cys407* Grm2 mutation in Hannover-derived Wistar rats: mGlu2 receptor loss links to alcohol intake, risk taking and emotional behaviour.

Modulation of metabotropic glutamate 2 (mGlu2) receptor function has huge potential for treating psychiatric and neurological diseases. Development of drugs acting on mGlu2 receptors depends on the development and use of translatable animal models of disease. We report here a stop codon mutation at cysteine 407 in Grm2 (cys407*) that is common in some Wistar rats. Therefore, researchers in this field need to be aware of strains with this mutation. Our genotypic survey found widespread prevalence of the mutation in commercial Wistar strains, particularly those known as Han Wistar. Such Han Wistar rats are ideal for research into the separate roles of mGlu2 and mGlu3 receptors in CNS function. Previous investigations, unknowingly using such mGlu2 receptor-lacking rats, provide insights into the role of mGlu2 receptors in behaviour. The Grm2 mutant rats, which dominate some selectively bred lines, display characteristics of altered emotionality, impulsivity and risk-related behaviours and increased voluntary alcohol intake compared with their mGlu2 receptor-competent counterparts. In addition, the data further emphasize the potential therapeutic role of mGlu2 receptors in psychiatric and neurological disease, and indicate novel methods of studying the role of mGlu2 and mGlu3 receptors. This article is part of the Special Issue entitled 'Metabotropic Glutamate Receptors, 5 years on'.

Characterization of CGRP protein expression in "satellite-like" cells and dendritic arbours of the mouse olfactory bulb.

The main olfactory bulb (OB) is made up of several concentric layers, forming circuitries often involving dendro-dendritic synapses. Important interactions between OB neurons occur in the external plexiform layer (EPL), where dendrites of tufted and Van Gehuchten cells form synapses with dendrites of deeper lying mitral, tufted, and granule cells. OB neurons display a variety of neurotransmitters. Here, the focus is on calcitonin gene-related peptide (CGRP), a 37-amino acid neuropeptide transmitter that is widely distributed in the central and peripheral nervous system. In the OB, CGRP-immunoreactive (ir) cell bodies were mostly observed in the mitral cell layer (MCL) of normal mice, and their number increased following colchicine treatment. Sparsely distributed CGRP-ir cell bodies were also found in the EPL and granular cell layer. Double-immunofluorescence experiments revealed a lack of co-localization between CGRP-like immunoreactivity (LI) and corticotropin-releasing factor- or galanin-LI, two markers for mitral cells, and no CGRP-LI was found in cholecystokinin-, parvalbumin-, or vasoactive intestinal polypeptide-ir tufted/Van Gehuchten cells. CGRP-ir cell bodies were not found to co-localize glutamic acid decarboxylase 67 (GAD67)-green fluorescence protein, gamma-aminobutyric acid (GABA)-, or calretinin-LI, although the possibility remains that CGRP-ir cells may contain low levels of GABA and/or GAD67 not detected by our methodology. Dendrites of CGRP-ir cells extensively ramified deep in the EPL and double-immunofluorescence revealed them to be adjacent with, often apparently contacting, dendrites of granule, mitral, tufted, and Van Gehuchten cells. We propose that these CGRP-ir cell bodies in the mouse OB are "satellite-like" cells within and, occasionally, close to the MCL.

Mu opioid receptor A118G polymorphism in association with striatal opioid neuropeptide gene expression in heroin abusers.

Mu opioid receptors are critical for heroin dependence, and A118G SNP of the mu opioid receptor gene (OPRM1) has been linked with heroin abuse. In our population of European Caucasians (n = 118), approximately 90% of 118G allelic carriers were heroin users. Postmortem brain analyses showed the OPRM1 genotype associated with transcription, translation, and processing of the human striatal opioid neuropeptide system. Whereas down-regulation of preproenkephalin and preprodynorphin genes was evident in all heroin users, the effects were exaggerated in 118G subjects and were most prominent for preproenkephalin in the nucleus accumbens shell. Reduced opioid neuropeptide transcription was accompanied by increased dynorphin and enkephalin peptide concentrations exclusively in 118G heroin subjects, suggesting that the peptide processing is associated with the OPRM1 genotype. Abnormal gene expression related to peptide convertase and ubiquitin/proteosome regulation was also evident in heroin users. Taken together, alterations in opioid neuropeptide systems might underlie enhanced opiate abuse vulnerability apparent in 118G individuals.

A novel soluble protein factor with non-opioid dynorphin A-binding activity.

A novel soluble non-opioid dynorphin A-binding factor (DABF) was identified and characterized in neuronal cell lines, rat spinal cord, and brain. DABF binds dynorphin A(1-17), dynorphin A(2-17), and the 32 amino acid prodynorphin fragment big dynorphin consisting of dynorphin A and B, but not other opioid and non-opioid peptides, opiates, and benzomorphans. The IC50 for dynorphin A(1-17), dynorphin A(2-17), and big dynorphin is in the 5-10 nM range. Using dynorphin A and big dynorphin fragments a binding epitope was mapped to dynorphin A(6-13). DABF has a molecular mass of about 70 kDa. SH-groups are apparently involved in the binding of dynorphin A since p-hydroxy-mercuribenzoic acid inhibited this process. Upon interaction with DABF dynorphin A was converted into Leu-enkephalin, which remained bound to the protein. These data suggest that DABF functions as an oligopeptidase that forms stable and specific complexes with dynorphin A. The presence of DABF in brain structures and other tissues with low level of prodynorphin expression suggests that DABF as an oligopeptidase may degrade other peptides. Dynorphin A at the sites of its release in the CNS may attenuate this degradation as a competitor when it specifically binds to the enzyme.