Target-specific regulation of synaptic amplitudes in the neocortex.
In layers 2/3 in the rat visual cortex, glutamatergic synapses, between pyramidal neurons and GABAergic interneurons, show target-specific depression or facilitation. To study the mechanisms regulating these short-term synaptic modifications, we recorded from synaptically connected pyramidal neurons (presynaptic) and multipolar or bitufted interneurons (postsynaptic). Evoked AMPA receptor (AMPAR)- or NMDA receptor (NMDAR)-mediated EPSCs were pharmacologically isolated at these pyramidal-to-interneuron synapses while altering release probability (P(r)) by changing the extracellular Ca2+ concentration ([Ca2+]o). At the pyramidal-to-multipolar synapse, which shows paired-pulse depression, elevation of [Ca2+]o from physiological concentrations (2 mm) to 3 mm increased the amplitude of the initial AMPAR-mediated EPSC and enhanced paired-pulse depression. In contrast, the initial NMDAR-mediated EPSC did not change in amplitude with raised P(r) nor was paired-pulse depression altered. This lack of an increase of NMDAR-mediated currents is not a result of Ca2+-dependent effects on the NMDAR. Rather, at the pyramidal-to-multipolar synapse, raised P(r) increases the transient glutamate concentration at individual release sites, possibly reflecting multivesicular release. In contrast, at the pyramidal-to-bitufted synapse, which shows facilitation, AMPAR- and NMDAR-meditated EPSCs showed parallel increases in response to raised P(r). Thus, our results reveal differential recruitment of AMPA and NMDARs at depressing and facilitating synapses in layers 2/3 of the cortex and suggest that the mechanisms regulating dynamic aspects of synaptic transmission are target specific.
Watanabe
Junryo
J
Department of Neurobiology and Behavior, State University of New York at Stony Brook, Stony Brook, New York 11794-5230, USA.
Rozov
Andrei
A
Wollmuth
Lonnie P
LP
D000818:Animals; D002118:Calcium / Q000502:physiology; D004151:Dipeptides / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007395:Interneurons / Q000502:physiology; D019579:Neocortex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology; D017966:Pyramidal Cells / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000502:physiology; D017470:Receptors, Glutamate / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013572:Synaptic Vesicles / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology
D004151:Dipeptides; D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; C028929:gamma-glutamylglycine; D002118:Calcium