Inhibition of Dendritic L-Type Calcium Current by Memantine in Frog Tectum

The aim of the study was to explore the effects of memantine on responses elicited in the frog tectum by the bursts of spikes of moderate strength of a single retina ganglion cell and to gain an insight about the effect of memantine on the L-type Ca²⁺ current.
Material and Methods. The experiments were performed in vivo on adult frogs (Rana temporaria). An individual retina ganglion cell (or its retinotectal fiber) was stimulated by current pulses delivered through a multichannel stimulating electrode positioned on the retina. Responses to the discharge of a single retinal ganglion cell were recorded in the tectum by an extracellular carbonfiber microelectrode positioned in the terminal arborization of the retinotectal fiber in the tectum layer F. The solution of memantine (1-amino-3,5-dimethyladamantane) hydrochloride (30 or 45 μM) was applied onto the surface of the tectum by perfusion at a rate of 0.4 mL/min.
Results. Memantine (30–45 μM) largely inhibited the L-type Ca²⁺ channel-mediated slow negative wave and late discharges seen in the tectum responses without any effect on fast synaptic retinotectal transmission.
Conclusions. Our results suggest that the neuroprotective effect of memantine could arise not only through the inhibition of the NMDA receptor current but also through the suppression of the L-type Ca²⁺ current.