Speaker of Workshop 1
Will talk about: Projection-specific subnetworks in rat frontal cortex
Yasuo Kawaguchi heads the division of cerebral circuitry in National Institute for Physiological Sciences (NIPS), Okazaki, Japan. He is professor of department of physiological sciences, Graduate University for Advanced Studies (SOKENDAI). Dr. Kawaguchi holds MD from the University of Tokyo, Faculty of Medicine, and a PhD in physiology from Tokyo University (mentor: Prof. Masao Ito). He worked with Prof. Kiyoshi Hama at NIPS and with Prof. Charles J. Wilson at University of Tennessee, Memphis as a postdoctoral fellow before becoming a researcher of Frontier Research Program, RIKEN, Wako in 1989. He became head of Laboratory for Neural Circuits, Bio-Mimetic Control Research Center, RIKEN, Nagoya in 1993 and professor of NIPS in 1999.
Neurons in the neocortex are stratified into multiple layers containing both excitatory glutamatergic (primarily “pyramidal”) neurons, and inhibitory GABAergic (“non-pyramidal”) neurons. Glutamatergic neurons in the cortex, especially those in layer 5 (L5), provide cortical output by sending axons to a variety of subcortical areas. However, the functional composition of pyramidal cells within individual cortical layers has not yet been fully elucidated. Subtypes of GABAergic neurons in the cortex are also morphologically, biochemically, and physiologically diverse, and exhibit preferentially innervate specific surface domains of postsynaptic neurons, including somatic, axonal, and dendritic compartments. However, little data exist regarding the targeting selectivity of GABAergic inputs toward specific pyramidal neuron subtypes.
In addition to providing cortical output, pyramidal neurons also form diverse excitatory recurrent subnetworks locally within the cortex. To understand how these excitatory subnetworks generate discreet and parallel output, and to reveal the connection selectivity of GABAergic neuron subtypes, it will first be necessary to characterize the organization principles of projection-specific subnetworks of pyramidal cells. To accomplish this, we are investigating the characteristics of L5 pyramidal neurons in the rat frontal cortex according to their subcortical projection targets, including crossed-corticostriatal (CCS) neurons that project to the contralateral striatum as well as ipsilateral one, and corticopontine (CPn) neurons that project to the ipsilateral pons. Experiments involving pairs of CCS and/or CPn neurons revealed distinct synaptic connectivity patterns in these two classes of L5 pyramidal neuron. CPn/CPn and CCS/CCS pairs had similar connection probabilities, but CPn/CPn pairs exhibited greater reciprocal connectivity, stronger unitary synaptic transmission, and more facilitation of paired-pulse responses. Further, we observed a unidirectional connectivity from CCS neurons to CPn neurons, with few, if any, connections in the opposite direction. Finally, CCS and CPn neurons had morphological differences in their apical dendritic trees, suggesting potential differences in afferent input and synaptic integration. Here we combine these results with recent findings from other laboratories studying corticostriatal and basal ganglia internal structures to propose a functional relationship between local intracortical excitatory subnetworks and more global cortico-basal ganglia-thalamic subnetworks.