a b s t r a c tBrain-derived neurotrophic factor (BDNF) is an important regulator of synaptic transmission and longterm potentiation (LTP) in the hippocampus and in other brain regions, playing a role in the formation of certain forms of memory. The effects of BDNF in LTP are mediated by TrkB (tropomyosin-related kinase B) receptors, which are known to be coupled to the activation of the Ras/ERK, phosphatidylinositol 3-kinase/Akt and phospholipase C-g (PLC-g) pathways. The role of BDNF in LTP is best studied in the hippocampus, where the neurotrophin acts at pre-and post-synaptic levels. Recent studies have shown that BDNF regulates the transport of mRNAs along dendrites and their translation at the synapse, by modulating the initiation and elongation phases of protein synthesis, and by acting on specific miRNAs. Furthermore, the effect of BDNF on transcription regulation may further contribute to long-term changes in the synaptic proteome. In this review we discuss the recent progress in understanding the mechanisms contributing to the short-and long-term regulation of the synaptic proteome by BDNF, and the role in synaptic plasticity, which is likely to influence learning and memory formation.This article is part of the Special Issue entitled 'BDNF Regulation of Synaptic Structure, Function, and Plasticity'.

No abstract

No abstract

Neuronal excitability depends on the balance between inhibitory and excitatory neurotransmission, which in the CNS are mainly mediated by GABA and glutamate respectively. The plasticity of glutamatergic synapses and the underlying molecular mechanisms have been characterized to a large extent. In comparison, much less is known regarding the plasticity of GABAergic synapses, which is also important in the maintenance of the excitatory/inhibitory balance. GABAergic synapses, similarly to the glutamatergic synapses, adjust their strength depending on the pattern of neuronal activity. These alterations take place in the pre-and postsynaptic compartments, and short-and long-term alterations have been described. At the postsynaptic level the plasticity of inhibitory synapses is largely mediated by modulation of the expression, localization and function of GABA A receptors, by mechanisms involving the participation of scaffold proteins and structural molecules. This review is focused on the key mechanisms that regulate GABA A receptor trafficking in response to alterations in neuronal activity or to stimulation of plasma membrane receptors. These alterations in GABAergic neurotransmission are important in the refinement of the pattern of activity of neuronal networks.

Overactivation of glutamate receptors contributes to neuronal damage (excitotoxicity) in ischemic stroke but the detailed mechanisms are not fully elucidated. Brain ischemia is also characterized by an impairment of the activity of the proteasome, one of the major proteolytic systems in neurons. We found that excitotoxic stimulation with glutamate rapidly decreases ATP levels and the proteasome activity, and induces the disassembly of the 26S proteasome in cultured rat hippocampal neurons. Downregulation of the proteasome activity, leading to an accumulation of ubiquitinated proteins, was mediated by calcium entry through NMDA receptors and was only observed in the nuclear fraction. Furthermore, excitotoxicity-induced proteasome inhibition was partially sensitive to cathepsin-L inhibition and was specifically induced by activation of extrasynaptic NMDA receptors. Oxygen and glucose deprivation induced neuronal death and downregulated the activity of the proteasome by a mechanism dependent on the activation of NMDA receptors. Since deubiquitinating enzymes may regulate proteins half-life by counteracting ubiquitination, we also analyzed how their activity is regulated under excitotoxic conditions. Glutamate stimulation decreased the total deubiquitinase activity in hippocampal neurons, but was without effect on the activity of Uch-L1, showing that not all deubiquitinases are affected. These results indicate that excitotoxic stimulation with glutamate has multiple effects on the ubiquitin-proteasome system which may contribute to the demise process in brain ischemia and in other neurological disorders.