Electrophysiological characterization of synaptic connections between layer VI cortical cells and neurons of the nucleus reticularis thalami in juvenile rats.
Corticothalamic (CT) feedback projections to the thalamus outnumber sensory inputs from the periphery by orders of magnitude. However, their functional role remains elusive. CT projections may directly excite thalamic relay cells or indirectly inhibit them via excitation of the nucleus reticularis thalami (nRT), a nuclear formation composed entirely of gamma-aminobutyric acidergic neurons. The relative strengths of these two pathways will ultimately control the effects of CT projections on the output of thalamic relay cells. However, corticoreticular synapses have not yet been fully physiologically characterized. Here, local stimulation of layer VI cells by focal application of K+ or AMPA elicited excitatory postsynaptic potentials in nRT neurons with a mean peak amplitude of 2.4 +/- 0.1 mV (n = 75, mean +/- SEM), a mean rise time (10-90%) of 0.74 +/- 0.03 ms and a weighted decay time constant of 11 +/- 0.3 ms. A pharmacological profile of responses was drawn in both current-clamp and voltage-clamp modes, showing the presence of a small N-methyl-d-aspartate receptor-dependent component at depolarized potentials. In two pairs of synaptically coupled layer VI cell-nRT neuron, moderate rates of transmission failures were observed while the latencies were above 5 ms in both cases. Our results indicate that the corticoreticular pathway fulfills the criteria for 'modulatory' inputs and is temporally restricted. We suggest that it may be involved in coincidence detection of convergent corticoreticular signals.
Institute of Physiology, University of Bern, Bühlplatz 5, 3012 Bern, Switzerland. gentet@pyl.unibe.ch
Luc J
LJ
Gentet
Daniel
D
Ulrich
D000818:Animals; D000831:Animals, Newborn; D002540:Cerebral Cortex / Q000166:cytology* / Q000502:physiology; D004347:Drug Interactions; D004558:Electric Stimulation; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009431:Neural Conduction / Q000187:drug effects; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010852:Picrotoxin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013787:Thalamic Nuclei / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D014633:Valine / Q000031:analogs & derivatives* / Q000494:pharmacology; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D010852:Picrotoxin; D011188:Potassium; D011810:Quinoxalines; D014633:Valine; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; C056723:FG 9041; C056639:2-amino-5-phosphopentanoic acid