NeuroscienceRelationship of mu opioid receptor binding to activation of G-proteins in specific rat brain regions
Section snippets
Materials
Male Sprague–Dawley rats (150–200 g) were purchased from Zivic Miller. [35S]GTPγS (1250 Ci/mmol) and [3H]naloxone (57.5 Ci/mmol) were purchased from the New England Nuclear Corp. Guanosine-5′-diphosphate and GTPγS were obtained from Boehringer Mannheim. DAMGO, naloxone, naltrindole, and adenosine deaminase were purchased from the Sigma Chemical Co. Ecolite scintillation fluid was purchased from Fisher Scientific. All other reagent grade chemicals were purchased from Sigma or Fisher Scientific.
Membrane preparations
Results
Several binding assays were used to compare the parameters of mu opioid receptor binding and mu opioid activation of G-proteins in nine rat brain regions: amygdala, brainstem, colliculus, frontal cortex, hippocampus, hypothalamus, sensomotor cortex, striatum, and thalamus. First, the potency (G-Ks) and the efficacy (G-Emax) of DAMGO in stimulating [35S]GTPγS binding to membranes were measured by constructing DAMGO concentration–effect curves. Second, DAMGO potencies in receptor binding (R-Ki)
Discussion
The present study explored three questions about the relationship between mu opioid receptor binding and activation of G-proteins in brain membranes. First, what is the relationship between agonist potencies in binding to receptors versus their potencies in activating G-proteins? Second, does agonist potency in activating G-proteins vary across brain regions? Third, does the amplification factor between mu receptor number and mu agonist-stimulated G-proteins vary across brain regions? To answer
Acknowledgements
These studies were supported by DA-02904, DA-06634 (S. R. C.), DA-07625 and DA-05957 (C. E. M.) and DA-10770 (D. E. S.) from the National Institute on Drug Abuse.
References (38)
Opioid receptor-coupled second messengers
Life Sci
(1991)- et al.
Pertussis toxin blocks the outward current evoked by opiate and α2-agonists in locus coeruleus neurons
Brain Res
(1986) - et al.
Mu-type opioid receptors in rat periaqueductal gray-enriched P2 membrane are coupled to guanine nucleotide binding proteins
Brain Res
(1989) - et al.
μ and δ opioid receptors differentially couple to G protein subtypes in membranes of human neuroblastoma SH-SY5Y cells
Neuron
(1993) - et al.
Pharmacological characterization of guanine nucleotide exchange reactions in membranes from CHO cells stably transfected with human muscarinic receptors M1–M4
Life Sci
(1993) A rapid and sensitive method for the quantification of microgram quantities of protein utilizing the principle of protein-dye binding
Anal Biochem
(1976)- et al.
Relationship between kappa1 opioid receptor binding and inhibition of adenylyl cyclase in guinea pig brain membranes
Biochem Pharmacol
(1993) - et al.
Molecular cloning and functional expression of a μ-opioid receptor from rat brain
Mol Pharmacol
(1993) - et al.
Loss of morphine-induced analgesia, reward effect and withdrawal symptoms in mice lacking the μ-opioid receptor gene
Nature
(1996) - et al.
Efficacy and tolerance of narcotic analgesics at the mu opioid receptor in differentiated human neuroblastoma cells
J Pharmacol Exp Ther
(1988)