Mammalian target of rapamycin (mTOR) is a key regulator of translational capacity. The mTOR inhibitor rapamycin can prevent forms of protein synthesis-dependent synaptic plasticity such as long-term facilitation in Aplysia and late-phase long-term potentiation (L-LTP) in the hippocampal CA1 region of rodents. In the latter model, two issues remain to be addressed: defining the L-LTP phase sensitive to rapamycin and identifying the site of rapamycinsensitive protein synthesis. Here, we show that L-LTP is sensitive to application of rapamycin only during the induction paradigm, whereas rapamycin application after the establishment of L-LTP was ineffective. Second, we observed that Thr-389-phosphorylated p70 S6 kinase (p70 S6K ), the main active phosphoform of the mTOR effector p70 S6K , was induced in an N-methyl-D-aspartateand phosphatidylinositol 3-kinase-dependent manner throughout the dendrites but not in the cell bodies of CA1 neurons in hippocampal slices after L-LTP induction. A similar dendrite-wide activation of p70 S6K was induced in primary hippocampal neurons by depolarization with KCL or glutamate. In primary hippocampal neurons, the sites of dendritic activation of p70 S6K appeared as discrete compartments along dendritic shafts like the hotspots for fast dendritic translation. Conversely, only a subset of dendritic spines also displayed activated p70 S6K . Taken together, the present data suggest that the N-methyl-D-aspartate-, phosphatidylinositol 3-kinase-dependent dendritic activation of the mTOR-p70 S6K pathway is necessary for the induction phase of protein synthesisdependent synaptic plasticity. Newly synthesized proteins in dendritic shafts could be targeted selectively to activity-tagged synapses. Thus, coordinated activation of dendrite-wide translation and synaptic-specific activation is likely to be necessary for long-term synaptic plasticity. F orms of long-term synaptic plasticity that require protein synthesis are believed to be cellular counterparts of longterm memory storage, whereas forms of synaptic plasticity that do not require protein synthesis are believed to be counterparts of short-term memory (1). In particular, dendritic protein synthesis is believed to play a crucial role in long-term synaptic plasticity and memory (1-4). Mammalian target of rapamycin (mTOR) regulates the translation initiation complex in a rapamycin-sensitive manner. It does so primarily through its downstream targets, the kinase p70 S6 kinase (p70 S6K ) and the elongation factor binding protein 4E-BP1. p70 S6K is a major regulator of translation under the control of multiple signal transduction pathways including phosphatidylinositol 3-kinase (PI3K) (5). It increases translational capacity by promoting the expression of several members of the translational machinery whose mRNAs display oligopyrimidine tracts at their 5Ј ends (6). 4E-BP1 is an inhibitor of the cap binding protein eukaryotic initiation factor 4E. 4E-BP1 phosphorylation by mTOR leads to increased translation of capped mRNAs (7). The major d...

Several signal transduction pathways have been implicated in the induction of long-term potentiation (LTP), yet the signal transduction mechanisms behind the maintenance-expression phase of LTP are still poorly understood. We investigated the role of phosphatidylinositol 3-kinase (PI3-kinase) in LTP at Schaffer collateral/commissural fiber-CA1 synapses in rat hippocampal slices using biochemical approaches and extracellular electrophysiological recordings. We observed that PI3-kinase activity was induced in the CA1 region during LTP of field EPSPs (fEPSPs) and that two structurally unrelated PI3-kinase inhibitors, LY294002 and wortmannin, abated established LTP, suggesting that PI3-kinase is involved in the maintenance-expression phase of LTP. However, LTP recovered after washout of the reversible PI3-kinase inhibitor LY294002, confirming that LTP maintenance and expression are distinct events and indicating that PI3-kinase activity is required for LTP expression rather than for its maintenance. Interestingly, preincubation with LY294002 did not prevent LTP induction. In fact, if LY294002 was withdrawn 5 min after high-frequency stimulation, an LTP of fEPSP was seen. Last, a voltage-dependent calcium channel-dependent form of LTP in the CA1 could also be reversibly abated by LY294002, raising the possibility that PI3-kinase could be required for the expression of multiple forms of synaptic potentiation.

Dynamic assembly and disassembly of microtubules is essential for cell division, cell movements, and intracellular transport. In the developing nervous system, microtubule dynamics play a fundamental role during neurite outgrowth, elongation, and branching, but the molecular mechanisms involved are unknown. SCG10 is a neuron-specific protein that is membrane-associated and highly enriched in growth cones. Here we show that SCG10 binds to microtubules, inhibits their assembly, and can induce microtubule disassembly. We also show that SCG10 overexpression enhances neurite outgrowth in a stably transfected neuronal cell line. These data identify SCG10 as a key regulator of neurite extension through regulation of microtubule instability.

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Metabotropic glutamate receptor 7 (mGlu 7 ) has been suggested to be a promising novel target for treatment of a range of disorders, including anxiety, post-traumatic stress disorder, depression, drug abuse, and schizophrenia. Here we characterized a potent and selective mGlu 7 negative allosteric modulatorIn vitro, Schild plot analysis and reversibility tests at the target confirmed the NAM properties of the compound and attenuation of L-(1)-2-amino-4-phosphonobutyric acid-induced synaptic depression confirmed activity at the native receptor. The pharmacokinetic analysis of ADX71743 in mice and rats revealed that it is bioavailable after s.c. administration and is brain penetrant (cerebrospinal fluid concentration/ total plasma concentration ratio at C max 5 5.3%). In vivo, ADX71743 (50, 100, 150 mg/kg, s.c.) caused no impairment of locomotor activity in rats and mice or activity on rotarod in mice.ADX71743 had an anxiolytic-like profile in the marble burying and elevated plus maze tests, dose-dependently reducing the number of buried marbles and increasing open arm exploration, respectively. Whereas ADX71743 caused a small reduction in amphetamine-induced hyperactivity in mice, it was inactive in the mouse 2,5-dimethoxy-4-iodoamphetamineinduced head twitch and the rat conditioned avoidance response tests. In addition, the compound was inactive in the mouse forced swim test. These data suggest that ADX71743 is a suitable compound to help unravel the physiologic role of mGlu 7 and to better understand its implication in central nervous system diseases. Our in vivo tests using ADX71743, reported here, suggest that pharmacological inhibition of mGlu 7 is a valid approach for developing novel pharmacotherapies to treat anxiety disorders, but may not be suitable for treatment of depression or psychosis.