Agonist selective modulation of tyrosine hydroxylase expression by cannabinoid ligands in a murine neuroblastoma cell line.

Functional interactions between catecholamines and cannabinoid transmission systems could explain the influence of Δ⁹-tetrahydrocannabinol on several central activities. Hence, the presence of cannabinoid CB₁ receptors in tyrosine hydroxylase (TH) containing cells has been suggested, providing clue for a direct control of catecholamines synthesis. In the present study, we evidenced the constitutive expression of functional cannabinoid CB₁ receptors in N1E-115 neuroblastoma and reported on the use of this model to examine the influence of diverse cannabinoid ligands on TH expression. Exposure of the cells to the high-affinity agonist HU 210 (5 h) resulted in a significant decrease in TH content (pEC₅₀: 6.40). In contrast, no change was observed after a similar treatment with the structurally unrelated agonist CP 55,940. Besides, the use of a luciferase reporter assay revealed that these two agonists showed opposite influences on TH gene promoter activity. Thus, in cells expressing pTH-luc constructs, inhibition and induction of luciferase activity were respectively observed with HU 210 (pEC₅₀: 8.95) and CP 55,940 (pEC₅₀: 9.09). Pharmacological characterisation revealed that these reciprocal responses were both related to the specific activation of cannabinoid CB₁ receptor, suggesting an agonist-dependent modulation of distinct signalling pathways. While these data points out the possible pharmacological manipulation of TH expression by cannabinoid ligands, such approach should take into account the existence of agonist selective trafficking of cannabinoid CB₁ receptor signalling. [ABSTRACT FROM AUTHOR]