Development of kitten hippocampal neurons.

Cells in the CA1 region of the hippocampus of kittens were studied using an in vitro slice preparation. Good quality intracellular records were obtained from over 100 cells from kittens 2 days to 4 weeks of age. Cell resistance was high in 2-day-old animals and decreased over the following 4 weeks. Both excitatory and inhibitory synaptic potentials were seen in all animals. EPSPs were only weakly effective in triggering spikes in the youngest kittens, but were greatly potentiated by repetitive stimulation at 3-10/sec; IPSPs caused a potent blockade of cell discharge in even the youngest preparations. Stimulation of the orthodromic input pathway led to a complex series of excitatory and inhibitory synaptic events which was not seen in the adult. In the 2- and 4-week-old kittens, a cell type with physiological properties different from the predominant pyramidal cell began to appear in recordings from the CA1 region. Technical difficulties inherent in in vivo recordings from neonatal animals were considerably less with the in vitro technique. Careful developmental studies may now be pursued in the slice at the single cell synaptic level.