Efficacy of thalamocortical and intracortical synaptic connections: quanta, innervation, and reliability.
Thalamocortical (TC) synapses carry information into the neocortex, but they are far outnumbered by excitatory intracortical (IC) synapses. We measured the synaptic properties that determine the efficacy of TC and IC axons converging onto spiny neurons of layer 4 in the mouse somatosensory cortex. Quantal events from TC and IC synapses were indistinguishable. However, TC axons had, on average, about 3 times more release sites than IC axons, and the mean release probability at TC synapses was about 1.5 times higher than that at IC synapses. Differences of innervation ratio and release probability make the average TC connection several times more effective than the average IC connection, and may allow small numbers of TC axons to dominate the activity of cortical layer 4 cells during sensory inflow.
Department of Physiology, Zlotowski Center for Neuroscience, Faculty of Health Sciences, Ben-Gurion University, Beer-Sheva, Israel.
Z
Z
Gil
B W
BW
Connors
Y
Y
Amitai
D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D066298:In Vitro Techniques; D051379:Mice; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D018408:Patch-Clamp Techniques; D013569:Synapses / Q000378:metabolism / Q000502:physiology*; D013788:Thalamus / Q000166:cytology / Q000378:metabolism / Q000502:physiology*