These findings indicate that IB cells receive less GABAA-mediated inhibitory input and …

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Biology Articles » Anatomy & Physiology » Anatomy, Physiology, and Synaptic Responses of Rat Layer V Auditory Cortical Cells and Effects of Intracellular GABAA Blockade

Abstract

- Anatomy, Physiology, and Synaptic Responses of Rat Layer V Auditory Cortical Cells and Effects of Intracellular GABAA Blockade

Anatomy, Physiology, and Synaptic Responses of Rat Layer V Auditory Cortical Cells and Effects of Intracellular GABA_A Blockade

Department of Anatomy and Neuroscience Training Program, University of Wisconsin Medical School, Madison, Wisconsin 53706

The Journal of Neurophysiology Vol. 83 No. 5 May 2000, pp. 2626-2638.

Abstract

Hefti, Brenda J. and Philip H. Smith. Anatomy, Physiology, and Synaptic Responses of Rat Layer V Auditory Cortical Cells and Effects of Intracellular GABA_AJ. Neurophysiol. 83: 2626-2638, 2000. The varied extracortical targets of layer V make it an important site for cortical processing and output, which may be regulatedby differences in the pyramidal neurons found there. Two populationsof projection neurons, regular spiking (RS) and intrinsic bursting(IB), have been identified in layer V of some sensory cortices,and differences in their inhibitory inputs have been indirectlydemonstrated. In this report, IB and RS cells were identifiedin rat auditory cortical slices, and differences in thalamocorticalinhibition reaching RS and IB cells were demonstrated directlyusing intracellular GABA_A blockers. Thalamocortical synaptic inputto RS cells was always a combination of excitation and both GABA_Aand GABA_B inhibition. Stimulation seldom triggered a suprathresholdresponse. IB cell synaptic responses were mostly excitatory, andstimulation usually triggered action potentials. This apparentdifference was confirmed directly using intracellular chloridechannel blockers. Before intracellular diffusion, synaptic responseswere stable and similar to control conditions. Subsequently, GABA_Awas blocked, revealing a cell's total excitatory input. On GABA_Ablockade, RS cells responded to synaptic stimulation with large,suprathreshold excitatory events, indicating that excitation,while always present in these cells, is masked by GABA_A. In IBcells that had visible GABA_A input, it often masked an excitatorypostsynaptic potential (EPSP) that could lead to additional suprathresholdevents. These findings indicate that IB cells receive less GABA_A-mediatedinhibitory input and are able to spike or burst in response tothalamocortical synaptic stimulation far more readily than RScells. Such differences may have implications for the influenceeach cell type exerts on its postsynaptictargets.