FM1-43 imaging reveals cGMP-dependent long-term depression of presynaptic transmitter release.
A persistent question concerning mechanisms underlying long-term, activity-dependent synaptic plasticity is whether the sites of alterations are presynaptic, postsynaptic, or both. Recently, we discovered a chemical method of inducing long-term depression (LTD) of synaptic strength at Schaffer collateral-CA1 synapses by simultaneously elevating [cGMP] and inhibiting cAMP-dependent protein kinase (PKA). Chemical LTD (CLTD) is activity-independent, occluded by stimulus-evoked LTD, and requires access of pharmacologic agents to presynaptic terminals. In the present study, we used fluorescence and two-photon imaging of presynaptic terminals with the fluorescent dye N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide (FM1-43) to determine directly if inducing CLTD is associated with a long-term reduction in transmitter release. In presynaptic Schaffer collateral-CA1 terminals of control hippocampal slices loaded with FM1-43, electrical stimulation (10 Hz/2 min) elicited a frequency-dependent destaining that peaked at 20% reduction in fluorescence. In contrast, when we first induced CLTD by a 30 min treatment of slices with the type V phosphodiesterase inhibitor zaprinast (20 microm) plus the PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89; 10 microm), then washed for 60 min, the destaining of FM1-43 fluorescence evoked by the same stimulation was reduced to 4%. Treatment and washout of slices with either drug singly had a significantly smaller effect on stimulus-evoked FM1-43 destaining. Only CLTD was associated with virtually complete suppression of stimulus-evoked FM1-43 release, the first direct evidence for at least one form of LTD being mediated by persistent reduction of presynaptic transmitter release.
Stanton
P K
PK
Departments of Neuroscience and Neurology, Albert Einstein College of Medicine, Bronx, New York 10461-1602, USA. stanton@aecom.yu.edu
Heinemann
U
U
Muller
W
W
D015106:3',5'-Cyclic-GMP Phosphodiesterases; D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D006152:Cyclic GMP / Q000378:metabolism*; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005456:Fluorescent Dyes; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D066298:In Vitro Techniques; D008856:Microscopy, Fluorescence / Q000379:methods; D009433:Neural Inhibition / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism*; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D051381:Rats; D017208:Rats, Wistar
D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; C073804:FM1 43; D005456:Fluorescent Dyes; D018377:Neurotransmitter Agents; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D017868:Cyclic AMP-Dependent Protein Kinases; D010727:Phosphoric Diester Hydrolases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517384:Pde5a protein, rat; D006152:Cyclic GMP