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.

The juxtacapsular bed nucleus of the stria terminalis (jcBNST) is activated in response to basolateral amygdala (BLA) inputs through the stria terminalis and projects back to the anterior BLA and to the central nucleus of the amygdala. Here we show a form of long-term potentiation of the intrinsic excitability (LTP-IE) of jcBNST neurons in response to high-frequency stimulation of the stria terminalis. This LTP-IE, which was characterized by a decrease in the firing threshold and increased temporal fidelity of firing, was impaired during protracted withdrawal from self-administration of alcohol, cocaine, and heroin. Such impairment was graded and was more pronounced in rats that self-administered amounts of the drugs sufficient to maintain dependence. Dysregulation of the corticotropin-releasing factor (CRF) system has been implicated in manifestation of protracted withdrawal from dependent drug use. Administration of the selective corticotropin-releasing factor receptor 1 (CRF 1 ) antagonist R121919 [2,5-dimethyl-3-(6-dimethyl-4-methylpyridin-3-yl)-7-dipropylamino-pyrazolo[1,5-a]pyrimidine)], but not of the CRF 2 antagonist astressin 2 -B, normalized jcBNST LTP-IE in animals with a history of alcohol dependence; repeated, but not acute, administration of CRF itself produced a decreased jcBNST LTP-IE. Thus, changes in the intrinsic properties of jcBNST neurons mediated by chronic activation of the CRF system may contribute to the persistent emotional dysregulation associated with protracted withdrawal.

Despite considerable evidence that ethanol can enhance chloride flux through the y-aminobutyric acid type A (GABAA) receptor-channel complex in several central neuron types, the effect ofethanol on hippocampal GABAergic systems is still controversial. Therefore, we have reevaluated this interaction in hippocampal pyramidal neurons subjected to local monosynaptic activation combined with pharmacological isolation of the various components of excitatory and inhibitory synaptic potentials, using intracellular currentand voltage-clamp recording methods in the hippocampal slice. In accord with our previous findings, we found that ethanol had little effect on compound inhibitory postsynaptic potentials/currents (IPSP/Cs) containing both GABAA and GABAB components. However, after selective pharmacological blockade of the GABAB component of the IPSP (GABAB-IPSP/C) by low It is common knowledge that alcohol intoxication and the resulting loss of motor and cognitive control in humans have led to untold trauma and suffering. Despite the likelihood that such problems arise from the action of ethanol on the central nervous system (CNS) and several decades of alcohol research suggesting a general depressant effect of intoxicating doses of ethanol on CNS neurons, until recently little has been known about the mechanisms behind this depression. Studies over the past decade have shown that the most sensitive site for ethanol action is the synapse (1-5), and more recently it has been suggested that ethanol-evoked neuronal depression might arise from either a blunting of excitatory glutamatergic synaptic transmission (see, e.g., refs. 6-8) and/or an enhancement of inhibitory y-aminobutyric acid (GABA)ergic transmission (see refs. 4 and 9).With regard to inhibitory neurotransmission, ethanol has often been reported to enhance GABAA receptor activation, and the resulting Cl-currents or fluxes, in neurons or isolated preparations of several brain regions (4,9 (see refs. 24-26). In addition, the development of local or focal stimulation techniques (27,28), combined with these selective antagonists, now allows study of pharmacologically isolated synaptic components. Therefore, we have repeated earlier studies of ethanol effects on GABAergic monosynaptic IPSPs with two different slice preparation methods, including the one used in previous studies from our laboratory (13), but now with pharmacologically isolated IPSP components. We now report that, under these conditions, low ethanol concentrations reproducibly enhance GABAAergic IPSPs of hippocampal pyramidal neurons (HPNs), but only when GABAB receptors are blocked.MATERIALS AND METHODS Preparation. The two hippocampal slice preparations used were as described (13,29,30). In brief, male Sprague-Dawley Abbreviations: IPSP/C, inhibitory postsynaptic potential/current; IPSC, inhibitory postsynaptic current; HPN, hippocampal pyramidal neuron; GABA, y-aminobutyric acid; CNQX, 6-cyano-7-nitroquinoxaline-2,3-dione; d-APV, DL-2-amino-5-phosphonovaleric acid; ACSF, artificial cer...