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Modulation of cyclic AMP formation by putative metabotropic receptor agonists
J Cartmell1, J A Kemp, S P Alexander
1Department of Physiology and Pharmacology, University of Nottingham Medical School, Queen's Medical Centre.
British Journal of Pharmacology
|January 1, 1994
Summary
This study investigated metabotropic glutamate receptor agonists in guinea-pig brain slices. Results confirm distinct receptor subtypes and highlight L-CCG-I as a key tool for their differentiation.
Area of Science:
- Neuropharmacology
- Receptor Pharmacology
- Signal Transduction
Background:
- Metabotropic glutamate receptors (mGluRs) are crucial G protein-coupled receptors involved in modulating neuronal excitability and synaptic transmission.
- Understanding the subtypes and their specific signaling pathways is essential for developing targeted therapeutics for neurological disorders.
Purpose of the Study:
- To investigate the effects of specific metabotropic glutamate receptor agonists on cyclic AMP (cAMP) accumulation and phosphoinositide hydrolysis in guinea-pig cerebral cortical slices.
- To characterize the pharmacological profiles of agonists like 1-Aminocyclopentane-1S,3R-dicarboxylate (1S,3R-ACPD), L-2-amino-4-phosphonobutanoate (L-AP4), and (2S,3S,4S)-alpha-(carboxycyclopropyl)glycine (L-CCG-I).
- To determine if distinct mGluR subtypes exist in the guinea-pig cortex based on their signaling responses.
Main Methods:
- Guinea-pig cerebral cortical slices were prelabelled with [3H]-adenine or [3H]-inositol to measure cAMP accumulation and phosphoinositide hydrolysis, respectively.
- The effects of various mGluR agonists (1S,3R-ACPD, L-AP4, L-CCG-I) on forskolin-stimulated cAMP levels and basal phosphoinositide turnover were assessed.
- Agonist-induced modulation of cAMP responses to other receptor systems (histamine H2, adenosine) was also examined.
Main Results:
- 1S,3R-ACPD and L-CCG-I inhibited forskolin-stimulated cAMP accumulation, while L-AP4 showed weaker inhibition.
- 1S,3R-ACPD and L-CCG-I potentiated cAMP responses to histamine H2 receptor and adenosine receptor (NECA) stimulation, with L-CCG-I's effect dependent on protein kinase C and extracellular calcium.
- L-AP4 inhibited the NECA-induced cAMP response, and only 1S,3R-ACPD and L-CCG-I stimulated phosphoinositide hydrolysis, indicating differential signaling pathways.
Conclusions:
- The results confirm the presence of at least two distinct subtypes of metabotropic glutamate receptors in the guinea-pig cerebral cortex.
- The distinct signaling profiles of the tested agonists, particularly L-CCG-I, support their utility as pharmacological tools for differentiating mGluR subtypes.