The Rolando substance of the rat spinal cord was investigated by means of standard electron microscopy and by light-and electron microscopic histochemical demonstration of acid phosphatase. In accordance with previous studies, electron dense, large sinusoid terminals in the Rolando substance, constituting the central element of Rolando glomeruli, are shown to establish numerous axo-axonal and axo-dendritic synapses. Acid phosphatase reaction of the Rolando substance, resistant to 0.2 mM sodium fluoride inhibition, is located in and around the large sinusoid terminals. By using various incubation parameters and cryo-protection, the most plausible physiological localization of this enzyme, probably related to transmission processes appears to be in the greater membrane (glycocalyx) of large sinusoid terminals.
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