Firing mode-dependent synaptic plasticity in rat neocortical pyramidal neurons.
Pyramidal cells in the mammalian neocortex can emit action potentials either as series of individual spikes or as distinct clusters of high-frequency bursts. However, why two different firing modes exist is largely unknown. In this study, we report that in layer V pyramidal cells of the rat somatosensory cortex, in vitro associations of EPSPs with spike bursts delayed by +10 msec led to long-term synaptic depression (LTD), whereas pairings with individual action potentials at the same delay induced long-term potentiation. EPSPs were evoked extracellularly in layer II-III and recorded intracellularly in layer V neurons with the whole-cell or nystatin-based perforated patch-clamp technique. Bursts were evoked with brief somatic current injections, resulting in three to four action potentials with interspike frequencies of approximately 200 Hz, characteristic of intrinsic burst firing. Burst-firing-associated LTD (Burst-LTD) was robust over a wide range of intervals between -100 and +200 msec, and depression was maximal (approximately 50%) for closely spaced presynaptic and postsynaptic events. Burst-LTD was associative and required concomitant activation of low voltage-activated calcium currents and metabotropic glutamate receptors. Conversely, burst-LTD was resistant to blockade of NMDA receptors or inhibitory synaptic potentials. Burst-LTD was also inducible at already potentiated synapses. We conclude that intrinsic burst firing represents a signal for resetting excitatory synaptic weights.
Birtoli
Barbara
B
Institute of Physiology, University of Bern, Bern 3012, Switzerland.
Ulrich
Daniel
D
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D017774:Long-Term Potentiation / Q000502:physiology*; D019579:Neocortex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism; D013569:Synapses / Q000502:physiology*
D016194:Receptors, N-Methyl-D-Aspartate; D015763:2-Amino-5-phosphonovalerate