Neuronal dye coupling in the developing rat fascia dentata

The present study describes dye coupling among neurons of the developing rat fascia dentata following impalement and intracellular filling with Neurobiotin. The number of neuronal impalements resulting in dye-coupled cells decreases from P14 to P120. The most rapid decline in dye coupling was observed between P14 and P21, the beginning of the most active period of synaptogenesis in the dentate molecular layer. Dye coupling between granule cells and axo-axonic interneurons (chandelier cells) accounts for about 10% of the dye-coupled neuronal population acquired in slices from P14 and P21 rats and declines to less than 5% by P60 and P120. Our data suggest that dye coupling is related reciprocally to the number of synapses formed on granule cells. Thus the relationship of dye coupling to synaptic density in the developing fascia dentata is similar to that reported in studies of the aging fascia dentata. Also the observation of axo-axonic interneurons coupled to granule cells at all ages suggests an interesting neuronal arrangement with the potential of limiting granule cell discharge to discrete neuronal assemblies in response to perforant path input.