Physiological activity depresses synaptic function through an effect on vesicle priming.
Neurons engage compensatory, homeostatic synaptic changes to maintain their overall firing rate. We examined the induction and expression of a persistent presynaptic adaptation. We explored the effect of mild extracellular potassium elevation to increase hippocampal pyramidal neuron spiking over a physiological range. With several days of mild depolarization, glutamate release adapted, as revealed by an increased mismatch between the number of active, FM1-43-positive, glutamatergic synapses and the total number of synapses defined by vesicular glutamate transporter-1 antibody staining. Surprisingly, the adaptation of glutamate terminals was all-or-none; recycling vesicle pool size at remaining active synapses was not significantly altered by the adaptation. Tetrodotoxin (TTX), but not postsynaptic receptor blockade, reversed depolarization-induced adaptation, and TTX added to normal incubation medium increased the number of active synapses, suggesting that normal spiking activity sustains a steady-state percentage of inactive terminals. Chronic mild depolarization depressed EPSCs and decreased the size of the readily releasable pool of vesicles (RRP). Several hours of 10 Hz electrical stimulation also depressed the RRP size, confirming that spiking alone induces adaptation and that strong stimulation induces more rapid presynaptic adaptation. Despite the importance of RRP alteration to the adaptation, ultrastructural experiments revealed no changes in docked or total synaptic vesicle numbers. Furthermore, alpha-latrotoxin induced vesicle release at adapted synapses, consistent with the idea that adaptation resulted from changes in vesicle priming. These results show that glutamatergic neurotransmission persistently adapts to changes in electrical activity over a wide physiological range.
Moulder
Krista L
KL
Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Jiang
Xiaoping
X
Taylor
Amanda A
AA
Olney
John W
JW
Mennerick
Steven
S
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000200:Action Potentials / Q000502:physiology / Q000528:radiation effects; D000818:Animals; D000831:Animals, Newborn; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology; D007150:Immunohistochemistry / Q000379:methods; D046529:Microscopy, Electron, Transmission / Q000379:methods; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques / Q000379:methods; D011189:Potassium Chloride / Q000494:pharmacology; D011726:Pyridinium Compounds / Q000493:pharmacokinetics; D000644:Quaternary Ammonium Compounds / Q000493:pharmacokinetics; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D013569:Synapses / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009435:Synaptic Transmission / Q000502:physiology; D013572:Synaptic Vesicles / Q000502:physiology* / Q000648:ultrastructure; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism
D018691:Excitatory Amino Acid Antagonists; C073804:FM1 43; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D011810:Quinoxalines; D050598:Vesicular Glutamate Transport Protein 1; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D011189:Potassium Chloride; D015763:2-Amino-5-phosphonovalerate