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We evaluated the effects of treatment with the inner ester derivative of the monosialoganglioside GM1 on cortical electroencephalographic activity and hippocampal CA1 morphology after transitory, near-complete cerebral ischemia in rats. Ischemia was induced by the four-vessel occlusion method, and we studied only the 58 rats that showed amino acid neurotransmission plays an important role. Neurons selectively vulnerable to an ischemic episode receive prominent excitatory amino acid transmitter inputs, and ablation of these pathways reduces ischemia-induced neuronal loss. In addition, the extracellular concentrations of glutamate and aspartate -potential neurotoxins both in vitro and in vivo -increase during ischemia. A current hypothesis is that excessive accumulation of glutamate or related compounds, via specific postsynaptic receptors, cause neuronal overactivation, triggering a cascade of cellular events that ultimately lead to cell death. 1 A corollary to the above hypothesis is that agents capable of antagonizing specific excitatory amino acid receptor-related recognition sites or postreceptor effects may be of potential therapeutic value. In particular, great attention has recently been focused on Af-methyl-D-aspartate (NMDA) receptor antago-

In experimental animal studies, exogenous hyaluronan (HA) has been shown to exert beneficial effects on the healing of tympanic membrane perforation. As any other exogenous substance, HA may prove potentially toxic, by filling the middle ear cavity, to the sensory cells of the organ of Corti. Electrophysiological (ABR) and morphological studies were carried out in the rat to examine the auditory function and the structure of the sensory epithelium. Rats received either HA or hydroxy-propyl-methyl-cellulose by trans-tympanic injection (middle ear cavity was completely filled up) and were compared to untreated, age- and weight-matched rats. In both treated groups ABR revealed transitory, mild conduction hearing loss, in particular for high frequencies, until day 7 postinjection. This loss recovered completely within the 15th day. Morphologically, no significant degenerative/necrotic lesions were observed in the organ of Corti, from both treated groups.

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