Metabotropic glutamate 2,3 receptor stimulation desensitizes agonist activation of G‐protein signaling and alters transcription regulators in mesocorticolimbic brain regions

• Published in: Synapse (New York, N.Y.) N.Y.), 2021-04, Vol.75 (4), p.e22190-n/a
• Main Authors: Burgos‐Aguilar, Carolina, Ferris, Mark J., Sexton, Lacey L., Sun, Haiguo, Xiao, Ruoyu, Chen, Rong, Childers, Steven R., Howlett, Allyn C.
• Format: Article
• Language: English
• Subjects: [35S]GTPγS binding; Agonists; Animals; Brain; Brain - metabolism; Cyclic AMP response element-binding protein; cyclic AMP response element‐binding protein (CREB); desensitization; Drug therapy; Extracellular signal-regulated kinase; extracellular signal‐regulated kinase (ERK); Glutamatergic transmission; Glutamic Acid; Glutamic acid receptors (metabotropic); GTP-Binding Proteins - metabolism; LY379268; Nucleus accumbens; Pallidum (ventral); Prefrontal cortex; Proteins; Rats; Receptors, Metabotropic Glutamate - agonists; Signal Transduction; Transcription
• ISSN: 0887-4476; 1098-2396
• DOI: 10.1002/syn.22190

Metabotropic glutamate (mGlu) receptors are regulators of glutamate release and targets for development of therapies for hyperactive glutamatergic signaling. However, the effects of long‐term stimulation of mGlu receptors on cellular signaling in the brain have not been described. This study investigated the effects of 2‐day and 14‐day osmotic mini‐pump administration of the mGlu2,3 agonist LY379268 (3.0 mg kg−1 day−1) to rats on receptor‐mediated G‐protein activation and signaling in mesocorticolimbic regions in rat brain sections. A significant reduction in LY379268‐stimulated [35S]GTPγS binding was observed in the 14‐day group in some cortical regions, prefrontal cortex, nucleus accumbens, and ventral pallidum. The 14‐day LY379268 treatment group exhibited mGlu2 mRNA levels significantly lower in hippocampus, nucleus accumbens, caudate, and ventral pallidum. In both 2‐day and 14‐day treatment groups immunodetectable phosphorylated cAMP Response Element‐Binding protein (CREB) was significantly reduced across all brain regions. In the 2‐day group, we observed significantly lower immunodetectable CREB protein across all brain regions, which was subsequently increased in the 14‐day group but failed to achieve control values. Neither immunodetectable extracellular signal‐regulated kinase (ERK) protein nor phosphorylated ERK from 2‐day or 14‐day treatment groups differed significantly from control across all brain regions. However, the ratio of phosphorylated ERK to total ERK protein was significantly greater in the 14‐day treatment group compared with the control. These results identify compensatory changes to mGlu2,3 signal transduction in rat brains after chronic systemic administration of agonist, which could be predictive of the mechanism of action in human pharmacotherapies. Rat brain coronal sections show (top) basal (left) and LY379268‐stimulated (right) [35S]GTPγS binding and (bottom) immunohistochemistry analysis for total (left) and phosphorylated (right) cyclic AMP Response Element Binding Protein (CREB). Regulation of G‐protein activation and cellular signaling kinases occurs upon continued 14‐day exposure to mGlu2,3 receptor stimulation.