F. E. Dudek

Synaptic Responses of Neurons in Heterotopic Gray Matter in an Animal Model of Cortical Dysgenesis

Neuronal heterotopia is a malformation of cortical development that is closely associated with epilepsy in humans. Despite emerging interest in the structure and function of the heterotopic cortex, little is known about the membrane properties and synaptic connections of these displaced neurons. We used whole-cell patch-clamp and extracellular field potential recordings from heterotopic neurons in slices from young adult rats with experimentally induced cortical dysgenesis to determine if local synaptic connections were present in nodular heterotopia. Complex synaptic responses were observed after electrical stimulation of adjacent white matter. The results suggest that neurons in nodular heterotopic gray matter can form local excitatory and inhibitory synaptic connections and may participate in epileptiform events.

Electrophysiological Responses in vivo of Hippocampal CA1 Pyramidal Neurons in an Animal Model of Neuronal Migration Disorders

Cortical dysgenesis arising from neuronal migration disorders is closely associated with intractable epilepsy in humans. We used extracellular field potential and conventional intracellular recordings from the dorsal hippocampus of intact adult rats to determine if the excitability of CA1 pyramidal cells was enhanced in rats with experimentally induced hippocampal dysplasia. Electrical stimulation of afferent fibers resulted in more robust population responses in the CA1 region of irradiated rats versus controls. Synaptic inhibition of pyramidal cells was also reduced in these animals. These results suggest that the excitability of the CA1 region in rats with hippocampal dysplasia is greater than in control animals.