The endocannabinoid system and associative learning and memory in zebrafish.

In zebrafish the medial pallium of the dorsal telencephalon represents an amygdala homolog structure, which is crucially involved in emotional associative learning and memory. Similar to the mammalian amygdala, the medial pallium contains a high density of endocannabinoid receptor CB1. To elucidate the role of the zebrafish endocannabinoid system in associative learning, we tested the influence of acute and chronic administration of receptor agonists (THC, WIN55,212-2) and antagonists (Rimonabant, AM-281) on two different learning paradigms.

Acute administration of THC impairs spatial but not associative memory function in zebrafish.

Rationale: The present study examined the effect of acute administration of endocannabinoid receptor CB1 ligand ∆-9-tetrahydrocannabinol (THC) on intracellular signalling in the brain and retrieval from two different memory systems in the zebrafish (Danio rerio).

Methods: First, fish were treated with THC and changes in the phosphorylation level of mitogen-activated protein (MAP) kinases Akt and Erk in the brain were determined 1 h after drug treatment. Next, animals of a second group learned in a two-alternative choice paradigm to discriminate between two colours, whereas a third group solved a spatial cognition task in an open-field maze by use of an ego-allocentric strategy.

Biochemical characterization of rolledSem, an activated form of Drosophila mitogen-activated protein kinase.

The rolled (rl) gene of Drosophila encodes a homologue of vertebrate mitogen-activated protein kinases. Genetic analyses have shown that the gain-of-function mutation rolledSevenmaker (rlSem) is sufficient to activate developmental pathways controlled by distinct receptor tyrosine kinases, such as Sevenless, Torso, and the Drosophila epidermal growth factor receptor homologue. Here we show that mutant RlSem protein, immunoprecipitated from transiently transfected COS cells, exhibits a moderate increase in kinase activity compared with wild-type Rl protein.

bHLH proteins encoded by the Enhancer of split complex of Drosophila negatively interfere with transcriptional activation mediated by proneural genes.

The Enhancer of split complex [E(SPL)-C] of Drosophila participates in the control of cell fate choice by uncommitted neuroectodermal cells in the embryo. It encodes seven proteins that belong to the basic helix-loop-helix (bHLH) family, six of which are expressed in very similar patterns in the neuroectoderm. Here we describe experiments aimed at unravelling the molecular basis of their function.

The ETS domain protein pointed-P2 is a target of MAP kinase in the sevenless signal transduction pathway.

The fate of the R7 photoreceptor cell in the developing eye of Drosophila is controlled by the Sevenless (Sev) receptor tyrosine kinase. Sev activates a highly conserved signal transduction cascade involving the proteins Ras1 and Raf and the Rolled/mitogen-activated protein (Rl/MAP) kinase. Here we show that the ETS domain protein encoded by the P2 transcript of the pointed (pnt) gene is a nuclear target of this signalling cascade which acts downstream of Rl/MAP kinase.