OBJECTIVES: Since among others also our previous studies suggested an interaction between the endocannabinoid system and methamphetamine brain mechanisms we focused on possible changes in relative expression of cannabinoid CB1 receptor mRNA in mesencephalon from mice sensitized by repeated treatments to methamphetamine stimulatory effects and cross-sensitized by cannabinoid CB1 receptor agonist methanandamide pre-treatment.
METHODS: The Open Field Test was used to measure changes in terms of behavioural sensitization or cross-sensitization to drug effects on locomotion in male mice treated repeatedly with either methamphetamine or methamphetamine after pre-treatment with methanandamide. After each measurement one third of animals were sacrificed and the brain was stored. RNA was isolated from the midbrain and used for reverse transcription and subsequent real-time PCR.
RESULTS AND CONCLUSION: The evaluation of behavioural drug effects showed both development of sensitization to methamphetamine stimulatory effects after repeated treatment and cross-sensitization to them by pre-treatment with cannabinoid receptor CB1 agonist methanandamide. Real-time PCR analyses revealed an increase in CB1 receptor mRNA expression after the first dose of methanandamide followed by decrease after the combined treatment with methamphetamine challenge dose. Our findings suggest that particularly repeated pre-treatment with CB1 agonist methanandamide can elicit increase in the mRNA expression level at least in the mouse mesencephalon neurons associated with cross-sensitization to methamphetamine stimulatory effects.