Different Ca2+ dynamics between isolated hippocampal pyramidal cells and dentate granule cells

The hippocampal formation contains a variety of neuronal types. The principal neurons are granule cells in the dentate gyrus and pyramidal cells in Ammon's horn. These two neuron types show distinct cell morphology and display a different vulnerability to ischemic injury or various neurotoxins. In order to illustrate the difference in the pathophysiological properties of these neurons, we established a method for separately culturing granule cells and pyramidal cells. They were prepared from the dentate gyrus and Ammon's horn of 3-day-old Wistar rat pups and maintained for 7–9 days in culture. After transient exposure to N-methyl-D-aspartate or glutamate, both the cultured neuron populations displayed somatic Ca²⁺ transients with similar amplitudes, but the subsequent recovery to baseline was about twice as fast in granule cells than in pyramidal cells. Similar results were obtained for K⁺ depolarization-induced Ca²⁺ elevation, suggesting that the relatively rapid Ca²⁺ clearance in granule cells is independent of Ca²⁺ influx pathways. The present study provides the first evidence for a difference in Ca²⁺ dynamics and homeostasis between granule and pyramidal cells and may represent a cellular basis for the differential vulnerability of hippocampal neurons.