The Journal of Neurophysiology Vol. 85 No. 3 March 2001, pp. 1167-1177
Copyright ©2001 by the American Physiological Society

Encoding of Different Aspects of Afferent Activities by Two Types of Cells in the Corpus Glomerulosum of a Teleost Brain

 ¹Misaki Marine Biological Station, Graduate School of Science, The University of Tokyo, Kanagawa 238-0225; and  ²Department of Anatomy, Laboratory for Comparative Neuromorphology, Nippon Medical School, Tokyo 113-8602, Japan

Tsutsui, Hidekazu, Naoyuki Yamamoto, Hironobu Ito, and Yoshitaka Oka. Encoding of Different Aspects of Afferent Activities by Two Types of Cells in the Corpus Glomerulosum of a Teleost Brain. J. Neurophysiol. 85: 1167-1177, 2001. The corpus glomerulosum (CG) is an expansive nucleus in acanthopterigian teleosts that has been suggested to be involved in vision-related information processing and the control of the hypothalamic function. The CG has only two types of constituent cells, the large cell and the small cell, and well-defined afferent/efferent fiber connections. One of the three types of teleostean CG, type III has additional outstanding morphological characters: clearly laminated organization and giant (>50 µm in diameter) tips of postsynaptic dendrites. Although such histological architecture is potentially advantageous for the study of information processing in a brain nucleus based on the physiological properties of identified cells and synapses, previous studies on the CG have been limited to anatomy. In this study, we developed a slice preparation of the type III CG in a teleost, Stephanoplepis cirrhifer, and studied the morphology and physiology of individual cells and synaptic transmission by means of dendritic intracellular and somatic whole cell recordings. The characteristic morphology of the two types of cells was revealed by intracellular staining. While both of them received similar glutamatergic and GABAergic projections from the nucleus corticalis mediated by AMPA, N-methyl-D-aspartate, and GABA_A receptors, they showed quite distinctive firing properties and postsynaptic responses with current injection and synaptic inputs: the large cell fired a single spike, and the small cell fired a spike train whose frequency was dependent on the stimulus intensity. Furthermore, the large cell showed low-pass temporal filtering properties with paired stimuli. These results suggest that the large cell and the small cell may encode different aspects of the corticalis activities.