fg-9041 and 3-4-dihydroxyphenylglycol

Although the contribution of postsynaptic mechanisms to long-term synaptic plasticity has been studied extensively, understanding the contribution of presynaptic modifications to this process lags behind, primarily because of a lack of techniques with which to directly and quantifiably measure neurotransmitter release from synaptic terminals. Here, we developed a method to measure presynaptic activity through the biotinylation of vesicular transporters in vesicles fused with presynaptic membranes during neurotransmitter release. This method allowed us for the first time to selectively quantify the spontaneous or evoked release of glutamate or GABA at their respective synapses. Using this method to investigate presynaptic changes during the expression of group I metabotropic glutamate receptor (mGluR1/5)-mediated long-term depression (LTD) in cultured rat hippocampal neurons, we discovered that this form of LTD was associated with increased presynaptic release of glutamate, despite reduced miniature EPSCs measured with whole-cell recording. Moreover, we found that specific blockade of AMPA receptor (AMPAR) endocytosis with a membrane-permeable GluR2-derived peptide not only prevented the expression of LTD but also eliminated LTD-associated increase in presynaptic release. Thus, our work not only demonstrates that mGluR1/5-mediated LTD is associated with increased endocytosis of postsynaptic AMPARs but also reveals an unexpected homeostatic/compensatory increase in presynaptic release. In addition, this study indicates that biotinylation of vesicular transporters in live cultured neurons is a valuable tool for studying presynaptic function.

Topics: Analysis of Variance; Animals; Bicuculline; Biophysics; Biotin; Biotinylation; Electric Stimulation; Endocytosis; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; Hippocampus; Long-Term Synaptic Depression; Methoxyhydroxyphenylglycol; Microtubule-Associated Proteins; Neurons; Neurotransmitter Agents; Organ Culture Techniques; Patch-Clamp Techniques; Peptides; Potassium; Presynaptic Terminals; Protein Transport; Quinoxalines; Rats; Receptors, AMPA; Receptors, Metabotropic Glutamate; Receptors, Transferrin; Sodium Channel Blockers; Succinimides; Synaptotagmin I; Tetradecanoylphorbol Acetate; Tetrodotoxin; Vesicular Glutamate Transport Protein 1; Vesicular Inhibitory Amino Acid Transport Proteins

Alcohol addiction (alcoholism) is one of the most prevalent substance abuse disorders worldwide. Addiction is thought to arise, in part, from a maladaptive learning process in which enduring memories of drug experiences are formed. However, alcohol (ethanol) generally interferes with synaptic plasticity mechanisms in the CNS and thus impairs various types of learning and memory. Therefore, it is unclear how powerful memories associated with alcohol experience are formed during the development of alcoholism. Here, using brain slice electrophysiology in mice, we show that repeated in vivo ethanol exposure (2 g/kg, i.p., three times daily for 7 d) causes increased susceptibility to the induction of long-term potentiation (LTP) of NMDA receptor (NMDAR)-mediated transmission in mesolimbic dopamine neurons, a form of synaptic plasticity that may drive the learning of stimuli associated with rewards, including drugs of abuse. Enhancement of NMDAR plasticity results from an increase in the potency of inositol 1,4,5-trisphosphate (IP(3)) in producing facilitation of action potential-evoked Ca(2+) signals, which is critical for LTP induction. This increase in IP(3) effect, which lasts for a week but not a month after ethanol withdrawal, occurs through a protein kinase A (PKA)-dependent mechanism. Corticotropin-releasing factor, a stress-related neuropeptide implicated in alcoholism and other addictions, further amplifies the PKA-mediated increase in IP(3) effect in ethanol-treated mice. Finally, we found that ethanol-treated mice display enhanced place conditioning induced by the psychostimulant cocaine. These data suggest that repeated ethanol experience may promote the formation of drug-associated memories by enhancing synaptic plasticity of NMDARs in dopamine neurons.

Topics: Amphibian Proteins; Analysis of Variance; Animals; Biophysics; Central Nervous System Depressants; Cocaine; Colforsin; Conditioning, Operant; Corticotropin-Releasing Hormone; Dopamine Antagonists; Dopamine Uptake Inhibitors; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Interactions; Electric Stimulation; Enzyme Inhibitors; Ethanol; Excitatory Amino Acid Antagonists; In Vitro Techniques; Inositol 1,4,5-Trisphosphate; Long-Term Potentiation; Male; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred C57BL; Neuronal Plasticity; Neurons; Peptide Hormones; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Salicylamides; Ventral Tegmental Area

Marijuana is a widely used drug that impairs memory through interaction between its psychoactive constituent, Delta-9-tetrahydrocannabinol (Delta(9)-THC), and CB(1) receptors (CB1Rs) in the hippocampus. CB1Rs are located on Schaffer collateral (Sc) axon terminals in the hippocampus, where they inhibit glutamate release onto CA1 pyramidal neurons. This action is shared by adenosine A(1) receptors (A1Rs), which are also located on Sc terminals. Furthermore, A1Rs are tonically activated by endogenous adenosine (eADO), leading to suppressed glutamate release under basal conditions. Colocalization of A1Rs and CB1Rs, and their coupling to shared components of signal transduction, suggest that these receptors may interact. We examined the roles of A1Rs and eADO in regulating CB1R inhibition of glutamatergic synaptic transmission in the rodent hippocampus. We found that A1R activation by basal or experimentally increased levels of eADO reduced or eliminated CB1R inhibition of glutamate release, and that blockade of A1Rs with caffeine or other antagonists reversed this effect. The CB1R-A1R interaction was observed with the agonists WIN55,212-2 and Delta(9)-THC and during endocannabinoid-mediated depolarization-induced suppression of excitation. A1R control of CB1Rs was stronger in the C57BL/6J mouse hippocampus, in which eADO levels were higher than in Sprague Dawley rats, and the eADO modulation of CB1R effects was absent in A1R knock-out mice. Since eADO levels and A1R activation are regulated by homeostatic, metabolic, and pathological factors, these data identify a mechanism in which CB1R function can be controlled by the brain adenosine system. Additionally, our data imply that caffeine may potentiate the effects of marijuana on hippocampal function.

Topics: Adenosine; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Analysis of Variance; Animals; Benzoxazines; Biophysics; CA1 Region, Hippocampal; Caffeine; Calcium Channel Blockers; Dronabinol; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; Glutamic Acid; In Vitro Techniques; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred C57BL; Mice, Knockout; Morpholines; Naphthalenes; Neural Inhibition; Neurons; Patch-Clamp Techniques; Phosphinic Acids; Picrotoxin; Piperidines; Presynaptic Terminals; Propanolamines; Pyrazoles; Quinoxalines; Receptor, Adenosine A1; Receptor, Cannabinoid, CB1; Xanthines