Glutamate iontophoresis induces long-term potentiation in the absence of evoked presynaptic activity.
Protocols that induce long-term potentiation (LTP) typically involve afferent stimulation. We tested the hypothesis that LTP induction does not require presynaptic activity. The significance of this hypothesis is underscored by results suggesting that LTP expression may involve activity-dependent presynaptic changes. An induction protocol using glutamate iontophoresis was developed that reliably induced LTP in hippocampal slices without afferent stimulation. Iontophoresis LTP was Ca2+ dependent, was blocked by MK-801, and occluded tetanus-induced LTP. Iontophoresis LTP was induced when excitatory postsynaptic potentials were completely blocked by adenosine plus tetrodotoxin. Our results suggest constraints on the involvement of presynaptic mechanisms and putative retrograde messengers in LTP induction and expression; namely, these processes must function without many forms of activity-dependent presynaptic processes.
Cormier
R J
RJ
Department of Neurobiology and Anatomy, University of Texas Medical School, Houston 77225.
Mauk
M D
MD
Kelly
P T
PT
D000200:Action Potentials / Q000187:drug effects; D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005971:Glutamates / Q000008:administration & dosage / Q000494:pharmacology*; D018698:Glutamic Acid; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007478:Iontophoresis; D008297:Male; D018377:Neurotransmitter Agents / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012965:Sodium Chloride / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology
D005971:Glutamates; D018377:Neurotransmitter Agents; D018698:Glutamic Acid; D013779:Tetrodotoxin; D012965:Sodium Chloride; D004533:Egtazic Acid; D016291:Dizocilpine Maleate; D000241:Adenosine; D002118:Calcium