The hippocampus is a structure in the brain that is extremely important for learning and memory. Dr. Charles Ribak is studying the micro anatomy of the hippocampal formation. The overall objective of this research project is the understanding of neuronal circuitry within the rat hippocampal formation, including specifically the dentate gyrus and hippocampus proper. He has used a Golgi-electron microscopic method to explore the local circuit connections of basket and granule cells in the dentate gyrus, mossy cells in the hilus and non-pyramidal neurons in CA 1. The current research will utilize a similar approach to analyze other neurons in the dentate gyrus and hippocampus proper. First, non-granule cells in the outer 2/3's of the molecular layer will be analyzed to determine where their axons synapse and if their dendrites and somata are contacted by terminals which also contact granule cell dendrites. Second, the ultrastructural features and synaptic connections of other hilar neurons besides the mossy cell will be analyzed. These studies will determine if every hilar neuron receives a major synaptic input from granule cells. Third, he will begin an analysis of neurons in the CA 3 region of the hippocampus. The initial focus will be to study the local axonal connections of basket and pyramidal cells in CA 3. Finally, the last specific aim of this research project involves an analysis of the development of symmetric synapses in the granule cell layer of the dentate gyrus. These synapses are considered to be GABAergic and inhibitory and an assessment of their development will complement existing data on the development of excitatory synapses in the dentate molecular layer and of the mossy fibers in stratum lucidum of CA 3. These experiments will attempt to better define the local neuronal circuitry of both local circuit and projection neurons in the dentate gyrus and hippocampus proper.
