A PACEMAKER CURRENT IN DYE-COUPLED HILAR INTERNEURONS CONTRIBUTES TO THE GENERATION OF GIANT GABAERGIC POTENTIALS IN DEVELOPING HIPPOCAMPUS

The establishment of synaptic connections and their refinement during development require neural activity. Increasing evidence suggests that spontaneous bursts of neural activity within an immature network are mediated by gamma-aminobutyric acid via a paradoxical excitatory actio n. Our data show that in the developing hippocampus such synchronous b urst activity is generated in the hilar region by transiently coupled cells. These cells have been identified as neuronal elements because t hey fire action potentials and they are not positive for the glial fib rillary acidic protein staining. Oscillations in hilar cells are ''pac ed'' by a hyperpolarization-activated current, with properties of I-h. Co-activated interneurons synchronously release GABA, which via its e xcitatory action may serve a neurotrophic function during the refineme nt of hippocampal circuitry.