Presynaptic mGlu1 and mGlu5 autoreceptors facilitate glutamate exocytosis from mouse cortical nerve endings.
The effects of mGlu1 and mGlu5 receptor activation on the depolarization-evoked release of [3H]d-aspartate ([3H]D-ASP) from mouse cortical synaptosomes were investigated. The mGlu1/5 receptor agonist 3,5-DHPG (0.1-100microM) potentiated the K+(12mM)-evoked [3H]D-ASP overflow. The potentiation occurred in a concentration-dependent manner showing a biphasic pattern. The agonist potentiated [3H]D-ASP exocytosis when applied at 0.3microM; the efficacy of 3,5-DHPG then rapidly declined and reappeared at 30-100microM. The fall of efficacy of agonist at intermediate concentration may be consistent with 3,5-DHPG-induced receptor desensitization. Facilitation of [3H]D-ASP exocytosis caused by 0.3microM 3,5-DHPG was prevented by the selective mGlu5 receptor antagonist MPEP, but was insensitive to the selective mGlu1 receptor antagonist CPCCOEt. In contrast, CPCCOEt prevented the potentiation by 50microM 3,5-DHPG, while MPEP had minimal effect. Unexpectedly, LY 367385 antagonized both the 3,5-DHPG-induced effects. A total of 0.3microM 3,5-DHPG failed to facilitate the K+-evoked [3H]D-ASP overflow from mGlu5 receptor knockout (mGlu5-/-) cortical synaptosomes, but not from nerve terminals prepared from the cortex of animals lacking the mGlu1 receptors, the crv4/crv4 mice. On the contrary, 50microM 3,5-DHPG failed to affect the [3H]D-ASP exocytosis from cortical synaptosomes obtained from crv4/crv4 and mGlu5-/-mice. Western blot analyses in subsynaptic fractions support the existence of both mGlu1 and mGlu5 autoreceptors located presynaptically, while immunocytochemistry revealed their presence at glutamatergic terminals. We propose that mGlu1 and mGlu5 autoreceptors exist on mouse glutamatergic cortical terminals; mGlu5 receptors may represent the "high affinity" binding sites for 3,5-DHPG, while mGlu1 autoreceptors represent the "low affinity" binding sites.
Musante
Veronica
V
Department of Experimental Medicine, Section of Pharmacology and Toxicology, University of Genoa, Genoa, Italy.
Neri
Elisa
E
Feligioni
Marco
M
Puliti
Aldamaria
A
Pedrazzi
Marco
M
Conti
Valerio
V
Usai
Cesare
C
Diaspro
Alberto
A
Ravazzolo
Roberto
R
Henley
Jeremy M
JM
Battaglia
Giuseppe
G
Pittaluga
Anna
A
D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D002540:Cerebral Cortex / Q000166:cytology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D015870:Gene Expression / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism*; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D011189:Potassium Chloride / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000502:physiology*; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000172:deficiency / Q000502:physiology*; D012118:Resorcinols / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D050827:Syntaxin 1 / Q000378:metabolism; D014316:Tritium / Q000378:metabolism; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism
D018683:Excitatory Amino Acid Agents; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D012118:Resorcinols; C494214:Stx1a protein, mouse; D050827:Syntaxin 1; D050598:Vesicular Glutamate Transport Protein 1; C104077:metabotropic glutamate receptor type 1; D014316:Tritium; D001224:Aspartic Acid; D018698:Glutamic Acid; C079215:3,5-dihydroxyphenylglycine; D011189:Potassium Chloride; D005998:Glycine