preproenkephalin and 1-3-dipropyl-8-cyclopentylxanthine

There is a large body of evidence indicating important interactions between the adenosine and the opioid systems in regulating pain, opioid dependence and withdrawal. Mice lacking the proenkephalin gene and therefore lacking the endogenous enkephalin peptides have been successfully developed and exhibit decreased locomotor activity, are hyperalgesic and show enhanced anxiety and aggression. In addition, an upregulation of mu and delta receptors was also observed in the brains of knockout mice. To investigate if there are any compensatory alterations in adenosine systems in the brains of mutant mice, we have carried out quantitative autoradiographic mapping of A(1) and A(2A) adenosine receptors and nitrobenzylthioinosine (NBTI)-sensitive adenosine transporters in the brains of wild-type and homozygous enkephalin knockout mice. Adjacent coronal brain sections were cut from brains of +/+ and -/- mice for the determination of binding of [(3)H]1,3-dipropyl-8-cyclopentylxanthine ([(3)H]DPCPX), [(3)H]2-[p-(2-carbonylethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine ([(3)H]CGS21680) or [(3)H]NBTI to A(1) and A(2A) adenosine receptors and NBTI-sensitive adenosine transporters, respectively. A small but significant increase in [(3)H]DPCPX and [(3)H]NBTI binding but no significant change in [(3)H]CGS21680 binding was detected in enkephalin knockout brains. The results provide further evidence of functional interactions in the brain between opioid receptors and A(1) adenosine receptors as well as NBTI-sensitive adenosine transporters but not A(2A) receptors.

Topics: Animals; Autoradiography; Brain; Enkephalins; Male; Membrane Transport Proteins; Mice; Mice, Inbred C57BL; Mice, Knockout; Nucleoside Transport Proteins; Protein Binding; Protein Precursors; Receptors, Purinergic P1; Thioinosine; Xanthines

The effect of adrenalectomy on the expression of adenosine receptors and their mRNA in rat brain was examined using quantitative autoradiography and in situ hybridization. 1,3-[3H]Dipropyl-8-cyclopentylxanthine ([3H]DPCPX), a selective adenosine A1 receptor antagonist, and [3H]CGS 21680, a selective adenosine A(2A) receptor agonist, were used as radioligands. One week after adrenalectomy, the expression of mRNA for adenosine A1 receptors was significantly decreased, as was the number of binding sites for [H]DPCPX. These effects were significantly counteracted by replacement treatment with dexamethasone (1.5 mg/kg i.p., twice daily). Addition of GTP caused a similar increase of [3H]DPCPX binding in sham-operated rats, adrenalectomized rats and rats adrenalectomized and treated with dexamethasone. Moreover, no differences in displacement of [3H]DPCPX by the adenosine receptor agonist N6-(R-phenylisopropyl)adenosine were found among these groups. Adrenalectomy did not significantly affect the number of [3H]CGS 21680 binding sites in striatum or the mRNA encoding adenosine A(2A) receptors. No changes in the affinity of [3H]CGS 21680 for adenosine A(2A) receptors or in the potency of the adenosine receptor agonist 2-chloroadenosine to displace [3H]CGS 21680 were found. Dexamethasone treatment decreased cAMP formation induced by the nonselective adenosine agonist 5'-N-ethylcarboxamidoadenosine in Jurkat cells, which express adenosine A(2B) receptors, but did not alter it in PC-12 cells, which express mostly A(2A) receptors. The results suggest that endogenous corticosteroids positively regulate the expression of adenosine A1 receptors, at least partly at the transcriptional level. In contrast, corticosteroids do not regulate the expression of adenosine A(2A) receptors.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Adrenalectomy; Analysis of Variance; Animals; Autoradiography; Brain; Cyclic AMP; Dexamethasone; Enkephalins; Gene Expression; Glucocorticoids; Humans; In Situ Hybridization; Jurkat Cells; Male; Organ Specificity; PC12 Cells; Phenethylamines; Protein Precursors; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A2A; Receptors, Purinergic P1; RNA, Messenger; Transcription, Genetic; Tritium; Xanthines