Synaptic properties of thalamic input to layers 2/3 and 4 of primary somatosensory and auditory cortices.
We studied the synaptic profile of thalamic inputs to cells in layers 2/3 and 4 of primary somatosensory (S1) and auditory (A1) cortices using thalamocortical slices from mice age postnatal days 10-18. Stimulation of the ventral posterior medial nucleus (VPM) or ventral division of the medial geniculate body (MGBv) resulted in two distinct classes of responses. The response of all layer 4 cells and a minority of layers 2/3 cells to thalamic stimulation was Class 1, including paired-pulse depression, all-or-none responses, and the absence of a metabotropic component. On the other hand, the majority of neurons in layers 2/3 showed a markedly different, Class 2 response to thalamic stimulation: paired-pulse facilitation, graded responses, and a metabotropic component. The Class 1 and Class 2 response characteristics have been previously seen in inputs to thalamus and have been described as drivers and modulators, respectively. Driver input constitutes a main information bearing pathway and determines the receptive field properties of the postsynaptic neuron, whereas modulator input influences the response properties of the postsynaptic neuron but is not a primary information bearing input. Because these thalamocortical projections have comparable properties to the drivers and modulators in thalamus, we suggest that a driver/modulator distinction may also apply to thalamocortical projections. In addition, our data suggest that thalamus is likely to be more than just a simple relay of information and may be directly modulating cortex.
Department of Neurobiology, University of Chicago, Abbott J-117, 947 E. 58th St., Chicago, IL 60637, USA.
Angela N
AN
Viaene
Iraklis
I
Petrof
S Murray
SM
Sherman
D000818:Animals; D001303:Auditory Cortex / Q000502:physiology*; D004558:Electric Stimulation; D005971:Glutamates / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008856:Microscopy, Fluorescence; D023421:Models, Animal; D009474:Neurons / Q000502:physiology; D018408:Patch-Clamp Techniques; D013003:Somatosensory Cortex / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D055366:Synaptic Potentials / Q000502:physiology; D013788:Thalamus / Q000502:physiology*
D005971:Glutamates