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  • Title: Electron microscopy of in vivo recorded and intracellularly injected inferior olivary neurons and their GABAergic innervation in the cat.
    Author: Ruigrok TJ, de Zeeuw CI.
    Journal: Microsc Res Tech; 1993 Jan 01; 24(1):85-102. PubMed ID: 8382092.
    Abstract:
    This paper reports on the detailed morphology of inferior olivary neurons in the cat following electrophysiological examination, intracellular injection with horseradish peroxidase, and gamma aminobutyric acid (GABA) immunocytochemistry. The activity of olivary cells was recorded intracellularly in vivo and their response to mesodiencephalic stimulation was tested. In a number of cases their response to stimulation of the contralateral superior cerebellar peduncle was also tested. Mesodiencephalic stimulation resulted in monosynaptic, and superior peduncle stimulation in disynaptic activation of cells in the medial accessory and principal olivary subdivisions. Rebound olivary activity was usually only found after mesodiencephalic stimulation. Light microscopic investigation of osmicated and Araldite embedded Vibratome sections was facilitated considerably when performing the osmication in a glucose solution. Peroxidase labeled olivary cells, like that earlier described for Golgi-impregnated material, possess a complex globular dendritic geometry. Especially, and unlike Golgi material, the abundance of exceptionally long and complex spiny appendages could be appreciated. The axons usually stemmed from first order dendrites and did not give rise to recurrent axon collaterals. The ultrastructural analysis of this material, mainly from serial sections, was combined with postembedding GABA immunohistochemistry. In this way, GABAergic as well as non-GABAergic profiles were studied in conjunction with HRP labeled cellular elements. The GABAergic terminals usually contained pleomorphic vesicles and made symmetrical synapses whereas non-GABAergic terminals nearly always formed asymmetrical synapses and contained round or oval vesicles. Most, if not all, HRP labeled spiny appendages were incorporated in glomeruli. A particular spiny appendage may contribute more than one spine head to a glomerular core, which, on average, consisted of spiny elements of six different neurons. A glomerular core is surrounded by approximately the same amounts of GABAergic and non-GABAergic boutons. Also, all spiny appendages, and most of their individual spine heads, are contacted by GABAergic as well as non-GABAergic boutons. Spiny appendages on the axon hillock may be incorporated in dendritic glomeruli, however, most synapses with the hillock were made by GABAergic boutons. The combined physiological and morphological observations imply that 1) the cerebellar nuclei can exert an excitatory influence on inferior olivary neurons through a mesodiencephalic relay, 2) the GABAergic nucleo-olivary input seems to be capable of diminishing the oscillatory tendencies of olivary neurons, and 3) the mesodiencephalic (non-GABAergic) and cerebellar (GABAergic) input may subserve a timing function since these inputs systematically impinge upon the same olivary spines.
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