Discharge patterns evoked by depolarizing current injection in basal optic nucleus neurons of the pigeon

The nucleus of the basal optic root of the acces- sory optic system in birds is involved in optokinetic nystagmus, which stabilizes images on the retina by compensatory move- ments of the eyes. The present paper studies the physiological and morphological properties of basal optic neurons in the pigeon by using a brain slice preparation and intracellular recordings. Sixty-one cells examined could be categorized into six types based on their firing patterns in response to depo- larizing current injection. Type I cells (54%) fire spontaneously and more spikes as current intensity is increased. Type II cells (15%) discharge regular spikes with similar interspike inter- vals. Type III cells (5%) show an early burst followed by tonic firing. Type IV cells (5%) fire regular bursts with similar inter- burst intervals. Type V cells (16%) fire a few spikes in a cluster only at onset of current application. Type VI cells (5%) produce a hump-like depolarization or a single spike depending on current intensities. Seventeen cells stained with Lucifer yellow have multipolar or piriform perikarya (15-28 µm) with two to eight primary dendrites. In some cases, an axon is observed to originate from the cell body, traveling dorsolaterally or dorsally. The physiological significance of these findings is discussed. © 2002 Elsevier Science Inc. All rights reserved.