Morphological and electrophysiological identification of gigantocellular tegmental field neurons with descending projections in the cat: I. Pons

AbstractTwo different descending projections from the pontine gigantocellular tegmental field (PFTG) were denned by the use of intracellular recording and intracellular horseradish peroxidase (HRP) techniques in the cat. Type I neurons (reticulospinal neurons) had antidromic spike potentials produced by stimulation of the ipsilateral medial longitudinal fasciculus (MLF) and sent axons to the ipsilateral MLF. Most type I neurons had large ellipsoidpolygonal somata (mean, 59.7 μm), thick axons (average diameter, 3.33 μm), and slightly oblate large dendritic fields. The mean anteroposterior extent of the dendritic field was 1,492 μm, the mean mediolateral extent was 1,784 μm, and the mean dorsoventral extent was 1,562 μm. There were no type I neurons with axon collaterals. In contrast, type II neurons (reticuloreticular neurons) had antidromic spike potentials produced by stimulation of the bulbar reticular formation (BRF) and sent axons directly to the BRF. In comparison with type I neurons, most type II neurons had smaller ellipsoid‐polygonal somata (mean, 40.2 μm), thinner axons (average diameter, 2.32 μm), and smaller, slightly oblate dendritic fields. The mean anteroposterior extent of the dendritic field was 1,264 μm; the mean mediolateral extent was 1,511 μm; and the mean dorsoventral extent was 1,226 μm. Also in contrast to type I neurons, 36% of type II neurons had axon collaterals.