Opposing and Complementary Topographic Connectivity Gradients Revealed by Quantitative Analysis of Canonical and Noncanonical Hippocampal CA1 Inputs
New Research Cognition and Behavior Opposing and Complementary Topographic Connectivity Gradients Revealed by Quantitative Analysis of Canonical and Noncanonical Hippocampal CA1 Inputs Yanjun Sun,1 Douglas A. Nitz,2 Todd C. Holmes,3 and Xiangmin Xu1,4,5,6 DOI:http://dx.doi.org/10.1523/ENEURO.0322-17.2018 1Department of Anatomy and Neurobiology, School of Medicine, University of California, Irvine, CA 92697-1275, 2Department of Cognitive Science, University of California, San Diego, La Jolla, CA 92093, 3Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA 92697-4560, 4Department of Biomedical Engineering, University of California, Irvine, CA 92697-2715, 5Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA 92697-4025, and 6Department of Computer Science, University of California, Irvine, CA 92697-3435 Abstract Physiological studies suggest spatial representation gradients along the CA1 proximodistal axis. To determine the underlying anatomical basis, we quantitatively mapped canonical and noncanonical inputs to excitatory neurons in dorsal hippocampal CA1 along the proximal-distal axis in mice of both sexes using monosynaptic rabies tracing. Our quantitative analyses show comparable strength of subiculum complex and entorhinal cortex (EC) inputs to CA1, significant inputs from presubiculum and parasubiculum to CA1, and a threefold stronger input to proximal versus distal CA1 from CA3. Noncanonical subicular complex inputs exhibit opposing topographic connectivity gradients whereby the subiculum-CA1 input strength systematically increases but the presubiculum- CA1 input strength decreases along the proximal-distal axis. The subiculum input strength cotracks that of the lateral EC, known to be less spatially selective than the medial EC.
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