Comparison of hippocampal metabotropic glutamate receptor 7 (mGlu₇) mRNA levels in two animal models of depression

There is increasing evidence to suggest that metabotropic glutamate (mGlu) receptors including mGlu₇ receptor are important in the pathophysiology of stress-related psychiatric disorders such as anxiety and major depression. mGlu₇ receptor is highly expressed in the hippocampus, a key region involved in the modulation of depression-related behaviour. Moreover, mice deficient in mGlu₇ receptor have an antidepressant-like behaviour and altered stress response. To our knowledge there is little information as to whether stressful phenotypes can influence hippocampal mGlu₇ receptor levels. To this end, we examined hippocampal mGlu₇ receptor mRNA expression in two models of depression, the stress-sensitive Wistar Kyoto (WKY) and the maternally separated model of early-life stress. In situ hybridization analysis revealed that the WKY, but not the maternally separated (MS) rats displayed selective increases in mGlu₇ receptor mRNA expression in subregions of the hippocampus compared to relevant controls. These data suggest that higher levels of this receptor could affect the behaviour in response to stressful conditions and may play a role in WKY animal's susceptibility to stress-related disorders. However, the data in maternally separated animals confirm that whilst hippocampal mGlu₇ receptors maybe involved in certain aspects of stress biology, an increased expression is not necessary for the manifestation of depression-related phenotype per se.