Baclofen prevents morphine withdrawal irrespective of seasonal variation

In previous studies we have demonstrated a possible interaction between the gamma-aminobutyric acid (GABA)ergic and opioid systems involved in the antinociceptive effect of the GABAB agonist, baclofen (BAC). In addition, we have demonstrated that BAC was able to prevent the morphine (MOR) withdrawal syndrome in female, as well as male mice. On the other hand, seasonal variations have been observed in some MOR effects. In the present study, we analysed the effects of BAC on naloxone (NAL)-precipitated withdrawal, during two different seasons. The experiments were performed during two seasons: spring-summer (SS) and autumn-winter (AW) for two years, on male Swiss-Webster albino mice (27-33 g). Mice were rendered dependent by intraperitoneal (i.p.) injection of MOR (2mg/kg), twice daily for 9 days. On the tenth day the dependent animals were divided into two groups: one received NAL (6mg/kg, i.p.) 60 min after the last dose of MOR, to develop the NAL-precipitated withdrawal; the other group received BAC (2mg/kg, i.p.) followed by NAL (6mg/kg, i.p.), injected 30 and 60 min after the last dose of MOR, respectively. Behavioural signs were recorded in the open field for 30 min. Although there were seasonal variations in the MOR withdrawal syndrome, we found that BAC prevents MOR withdrawal irrespective of seasonal variation.