Hippocampal endocannabinoids inhibit spatial learning and limit spatial memory in rats.

RATIONALE: As exogenous cannabinoid agonists impair memory formation, could it be that antagonists have opposing effects and act as memory-enhancing drugs? OBJECTIVES: Here, we studied the effects of the cannabinoid antagonist SR141716A (SR; Rimonabant) on spatial learning and memory formation and assessed the possible involvement of hippocampal CB(1) receptor in these actions. MATERIALS AND METHODS: In the water maze, spatial reference memory was probed using different training protocols followed by assessment of behavioral flexibility. The CB(1) receptor antagonist SR (3 mg/kg) was intraperitoneally administered before or immediately after training in experiment 1, or via minipumps intrahippocampally (0.89 ng and 0.089 ng/day) either during or after spatial learning, or subcutaneously in experiment 2. RESULTS: In experiment 1, systemic SR impaired spatial learning when given intraperitoneally (ip) before training coincident with increasing swim speed and thigmotaxis. Pretraining before drug treatment eliminated these effects while post-training injections had no effect. In experiment 2, intrahippocampal infusion of 0.089 ng SR during training enhanced acquisition learning, but did not affect long-term consolidation of spatial memory. In contrast, subcutaneous infusion of SR via minipumps had no effect. Post-training infusion of SR did not affect reversal learning, but short-term memory (1 h post-training) was weaker, and long-term memory for the reversal platform location was enhanced. CONCLUSIONS: Systemic Rimonabant-induced deficits are due to anxiogenic properties of the drug. The difference between administration regimes is discussed in terms of CB(1) receptor blockade in multiple non-memory and memory-related brain regions and the possibility that selective inactivation of hippocampal CB(1) receptors may be memory enhancing.

Mutagenesis Screen Identifies agtpbp1 and eps15L1 as Essential for T lymphocyte Development in Zebrafish.

Genetic screens are a powerful tool to discover genes that are important in immune cell development and function. The evolutionarily conserved development of lymphoid cells paired with the genetic tractability of zebrafish make this a powerful model system for this purpose. We used a Tol2-based gene-breaking transposon to induce mutations in the zebrafish (Danio rerio, AB strain) genome, which served the dual purpose of fluorescently tagging cells and tissues that express the disrupted gene and provided a means of identifying the disrupted gene. We identified 12 lines in which hematopoietic tissues expressed green fluorescent protein (GFP) during embryonic development, as detected by microscopy. Subsequent analysis of young adult fish, using a novel approach in which single cell suspensions of whole fish were analyzed by flow cytometry, revealed that 8 of these lines also exhibited GFP expression in young adult cells. An additional 15 lines that did not have embryonic GFP+ hematopoietic tissue by microscopy, nevertheless exhibited GFP+ cells in young adults. RT-PCR analysis of purified GFP+ populations for expression of T and B cell-specific markers identified 18 lines in which T and/or B cells were fluorescently tagged at 6 weeks of age. As transposon insertion is expected to cause gene disruption, these lines can be used to assess the requirement for the disrupted genes in immune cell development. Focusing on the lines with embryonic GFP+ hematopoietic tissue, we identified three lines in which homozygous mutants exhibited impaired T cell development at 6 days of age. In two of the lines we identified the disrupted genes, agtpbp1 and eps15L1. Morpholino-mediated knockdown of these genes mimicked the T cell defects in the corresponding mutant embryos, demonstrating the previously unrecognized, essential roles of agtpbp1 and eps15L1 in T cell development.