L-type Ca2+ current in frog tectal recurrent neurons determines the NMDA receptor activation on efferent neuron.

The activity patterns of a neuronal network originate from the intrinsic properties and synaptic interactions of the constituent neurons. Our recent studies support this view, showing that the discharge of a single frog retina ganglion cell brings an elementary neuronal network of the tectum (tectum column) to a suprathreshold activity of two distinct levels that are related to the activation of the slow L-type calcium current in dendrites of the recurrent pear-shaped neurons (lower level) and the NMDA receptors in neurons (higher level) of the tectum column. We show in the present study that the dendritic slow L-type calcium current is necessary for the NMDA receptor activation in the tectum column. A small decrease of this current prevents the NMDA receptor activation and, hence, the transition of the network to the higher activity level, at which the efferent neuron of the network fires. So, the activity of the frog tectum column can be effectively controlled through the intrinsic properties of the recurrent pear-shaped neurons of the column.