Three GABA Receptor-Mediated Postsynaptic Potentials in Interneurons in the Rat Lateral Geniculate Nucleus

Inhibition is crucial for the thalamus to relay sensory information from the periphery to the cortex and to participate in thalamocortical oscillations. However, the properties of inhibitory synaptic events in interneurons are poorly defined because in part of the technical difficulty of obtaining stable recording from these small cells. With the whole-cell recording technique, we obtained stable recordings from local interneurons in the lateral geniculate nucleus and studied their inhibitory synaptic properties. We found that interneurons expressed three different types of GABA receptors: bicuculline-sensitive GABAA receptors, bicuculline-insensitive GABAAreceptors, and GABAB receptors. The reversal potentials of GABA responses were estimated by polarizing the membrane potential. The GABAA receptor-mediated responses had a reversal potential of approximately −82 mV, consistent with mediation via Cl− channels. The reversal potential for the GABAB response was −97 mV, consistent with it being a K+ conductance. The roles of these GABA receptors in postsynaptic responses were also examined in interneurons. Optic tract stimulation evoked a disynaptic IPSP that was mediated by all three types of GABA receptors and depended on activation of geniculate interneurons. Stimulation of the thalamic reticular nucleus evoked an IPSP, which appeared to be mediated exclusively by bicuculline-sensitive GABAA receptors and depended on the activation of reticular cells. The results indicate that geniculate interneurons form a complex neuronal circuitry with thalamocortical and reticular cells via feed-forward and feedback circuits, suggesting that they play a more important role in thalamic function than thought previously.