The midline thalamus: Alterations and a potential role in limbic epilepsy

Purpose: In limbic or mesial temporal lobe epilepsy, much attention has bee n given to specific regions or cell populations (e.g., the hippocampus or d entate granule cells). Epileptic seizures may involve broader changes in ne ural circuits. and evidence suggests that subcortical regions may play a ro le. In this study we examined the midline thalamic regions for involvement in limbic seizures. changes in anatomy and physiology, and the potential ro le for this region in limbic seizures and epilepsy Methods: Using two rat models for limbic epilepsy (hippocampal kindled and chronic spontaneous limbic epilepsy) we examined the midline thalamus for e vidence of involvement in seizure activity, alterations in structure. chang es in the basic in vitro physiology of the thalamic neurons. We also explor ed how this region may influence limbic seizures. Results: The midline thalamus was consistently involved with seizure activi ty from the onset, and there was significant neuronal loss in the medial do rsal and reuniens/rhomboid nuclei. In addition, thalamic neurons had change s in synaptically mediated and voltage-gated responses. Infusion of lidocai ne into the midline thalamus significantly shortened afterdischarge duratio n. Conclusions: These observations suggest that this thalamic region is part o f the neural circuitry of limbic epilepsy and may play a significant role i n seizure modulation. Local neuronal changes can enhance the excitability o f the thalamolimbic circuits.