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  • Title: Interactions in the behavioral effects of methylxanthines and adenosine derivatives.
    Author: Katims JJ, Annau Z, Snyder SH.
    Journal: J Pharmacol Exp Ther; 1983 Oct; 227(1):167-73. PubMed ID: 6194284.
    Abstract:
    The role of adenosine receptors in behavioral effects of alkylxanthines was evaluated in mice. The relative potencies of alkylxanthines in reversing locomotor activity depression elicited by L-phenylisopropyladenosine (L-PIA) were similar to relative potencies in competing for adenosine receptors labeled by [3H]cyclohexyladenosine. Whereas L-PIA at i.p. doses of 0.10 mumol/kg and higher depressed locomotor activity, lower doses (0.01 and 0.05 mumol/kg) augmented locomotor activity. At the doses evaluated, caffeine did not further augment the L-PIA (0.05 mumol/kg)-enhanced locomotor activity. Low doses of diazepam, like L-PIA, augmented locomotor activity. Combining locomotor depressant doses of diazepam and caffeine produced a paradoxical stimulation of activity, as observed also for L-PIA and caffeine. Low doses of diazepam but not L-PIA increased crossings between the light and dark sites in a shuttle box, indicating a difference in the behavioral profile of these two agents. At behaviorally effective doses, L-PIA did not alter blood pressure or heart rate, but elicited some premature ventricular contractions which, however, occurred to a similar extent at locomotor depressant and stimulant doses of L-PIA. Brain levels of L-PIA at the lowest behaviorally active doses were adequate to occupy more than 50% of adenosine receptors. Thus, the behavioral effects of L-PIA appeared to be mediated in the brain and were not secondary to the cardiovascular effects.
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