Spiking activity of neurons in the pigeon nucleus rotundus in slice preparations

SUMMARY The thalamic nucleus rotundus in birds relays visual information from the mesencephalic tectum to the telencephalic ectostriatum. The present study examined the firing behaviors of rotunda1 cells in response to depolarizing current injections in pigeon’s brain slices. Eighty-five cells examined could be classified into five types according to their firing patterns. Type I cells (58.8%) evoked a spike, bursts or regular spiking depending on current intensity. Type II cells (14.1 Oh) produced a hump-like depolarization that gave rise to a single spike at higher intensity. Type III cells (15.3%) fired a spike or burst only at the onset of current injections. Type IV cells (8.3%) accelerated regular spiking as current intensity increased. Type V cells (3.5%) produced spontaneous spikes that were eliminated by current at higher intensity. The spiking patterns seem to be not correlated to the recording sites. Thirteen neurobiotin-stained cells are multipolar neurons whose morphology is not related to firing patterns. The functional significance of these firing patterns is discussed.