Abstract
The mammalian target of rapamycin (mTOR) signaling pathway in neurons integrates a variety of extracellular signals to produce appropriate translational responses. mTOR signaling is hyperactive in neurological syndromes in both humans and mouse models that are characterized by epilepsy, autism, and cognitive disturbances. In addition, rapamycin, a clinically important immunosuppressant, is a specific and potent inhibitor of mTOR signaling. While mTOR is known to regulate growth and synaptic plasticity of glutamatergic neurons, its effects on basic parameters of synaptic transmission are less well studied, and its role in regulating GABAergic transmission is unexplored. We therefore performed an electrophysiological and morphological comparison of glutamatergic and GABAergic neurons in which mTOR signaling was either increased by loss of the repressor Pten or decreased by treatment with rapamycin. We found that hyperactive mTOR signaling increased evoked synaptic responses in both glutamatergic and GABAergic neurons by ∼50%, due to an increase in the number of synaptic vesicles available for release, the number of synapses formed, and the miniature event size. Prolonged (72 h) rapamycin treatment prevented these abnormalities and also decreased synaptic transmission in wild-type glutamatergic, but not GABAergic, neurons. Further analyses suggested that hyperactivation of the mTOR pathway also impairs presynaptic function, possibly by interfering with vesicle fusion. Despite this presynaptic impairment, the net effect of Pten loss is enhanced synaptic transmission in both GABAergic and glutamatergic neurons, which has numerous implications, depending on where in the brain mutations of an mTOR suppressor gene occur.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Action Potentials / drug effects
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Analysis of Variance
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Animals
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Animals, Newborn
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Biophysics
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Corpus Striatum / cytology
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism
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Dendrites / drug effects
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Dendrites / metabolism
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Electric Stimulation
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Female
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Gene Expression Regulation / drug effects
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Gene Expression Regulation / genetics
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Glial Fibrillary Acidic Protein / genetics
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Glial Fibrillary Acidic Protein / metabolism
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Glutamates / metabolism*
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Glutamates / pharmacology
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Green Fluorescent Proteins / genetics
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Hippocampus / cytology
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Humans
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Male
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Mice
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Mice, Transgenic
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Nerve Tissue Proteins / metabolism
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Neurons / drug effects
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Neurons / physiology*
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism
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PTEN Phosphohydrolase / deficiency
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Patch-Clamp Techniques
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Signal Transduction / drug effects
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Signal Transduction / genetics
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Signal Transduction / physiology*
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Sirolimus / pharmacology
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Sodium Channel Blockers / pharmacology
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Synapses / drug effects
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Synapses / genetics
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Synapses / physiology*
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Synaptic Transmission / drug effects
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Synaptic Transmission / genetics
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Synaptic Transmission / physiology*
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TOR Serine-Threonine Kinases / drug effects
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TOR Serine-Threonine Kinases / physiology*
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Tetrodotoxin / pharmacology
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Time Factors
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Transfection
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Ubiquitin-Protein Ligases
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Vesicular Glutamate Transport Protein 1 / metabolism
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Vesicular Inhibitory Amino Acid Transport Proteins / metabolism
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gamma-Aminobutyric Acid / metabolism*
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gamma-Aminobutyric Acid / pharmacology
Substances
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DNA-Binding Proteins
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Glial Fibrillary Acidic Protein
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Glutamates
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Nerve Tissue Proteins
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Nuclear Proteins
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Slc17a7 protein, mouse
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Sodium Channel Blockers
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Vesicular Glutamate Transport Protein 1
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Vesicular Inhibitory Amino Acid Transport Proteins
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Viaat protein, mouse
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Green Fluorescent Proteins
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Tetrodotoxin
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gamma-Aminobutyric Acid
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Trim27 protein, mouse
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Ubiquitin-Protein Ligases
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mTOR protein, mouse
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TOR Serine-Threonine Kinases
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PTEN Phosphohydrolase
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Pten protein, mouse
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Sirolimus