Involvement of adenosine A1 and A2A receptors in (―)-linalool-induced antinociception

In recent studies performed in our laboratory we have shown that acute administration of ()-linalool, the natural occurring enantiomer
in essential oils, possesses anti-inflammatory, antihyperalgesic and antinociceptive effects in different animal models. The antihyperalgesic
and antinociceptive effects of ()-linalool have been ascribed to its capacity in stimulating the opioidergic, cholinergic and dopaminergic
systems, as well as to its interaction with K+ channels, or to its local anaesthetic activity and/or to the negative modulation of glutamate
transmission.
Activation of A1 or A2A receptors has been shown to induce antinociceptive effects, and the possible involvement of adenosine in ()-linalool
antinociceptive effect, has not been elucidated yet. Therefore, in the present study, we have investigated the effects of 1,3-dipropyl-8-
cyclopentylxanthine (DPCPX), a selective adenosine A1 receptor antagonist and the effects of 3,7-dimethyl-1-propargilxanthine (DMPX), a
selective adenosine A2A receptor antagonist on the antinociception of ()-linalool in mice, measured in the hot-plate test. Both DPCPX (0.1 mg/
kg; i.p.) and DMPX (0.1 mg/kg; i.p.) pre-treatment significantly depressed the antinociceptive effect of ()-linalool at the highest doses tested.
These findings demonstrated that the effect of ()-linalool on pain responses is, at least partially, mediated by the activity of adenosine A1 and A2A
receptors.