INCREASED INWARD CURRENT IN SEPTAL NEURONS FROM THE TRISOMY-16, MOUSE, A MODEL FOR DOWNS-SYNDROME

We examined the electrophysiological properties of neurons cultured fr om the septum of the trisomy 16 mouse fetus, an animal model for Down' s syndrome. The passive membrane properties were not different between trisomic and diploid septal neurons. We distinguished low-firing and high-firing populations of neurons based on differences in the firing rate evoked during current injection. Low-firing neurons fired three o r fewer action potentials, high-firing neurons fired four or more. The membrane currents of low-firing trisomic neurons were not different f rom those of low-firing diploid neurons. However, high-firing trisomic neurons had an increased inward current and conductance, and a greate r inward-to-outward conductance ratio. The increased current and condu ctance were independent of the passive electrical properties. The incr eased inward current in high-firing trisomic neurons was correlated wi th action potentials having faster depolarization rates. This greater excitability among this population of trisomic septal neurons, coupled with. a reduced excitation in hippocampal neurons, may compromise sep tohippocampal and memory function.