The ascending gustatory pathway: a Golgi analysis of the medial and lateral parabrachial complex in the adult hamster.

This study examined the somal areas, dendritic features and orientations of neurons within taste responsive regions of the parabrachial complex, including the "waist" area that spans the brachium conjunctivum. The data were compared with those of a Golgi study of the gustatory zone of the nucleus of the solitary tract. Both fusiform and multipolar neurons were identified. Fusiform neurons had elongated somata that average 205 microns2 (range: 128-281 microns2) and generally possessed bipolar primary dendrites. Multipolar neurons had a stellate appearance and somal areas that averaged 230 microns2 (range: 109-443 microns2). These multipolar neurons possessed significantly more primary dendrites than fusiform neurons (4.0 versus 2.9 primary dendrites). Fusiform neurons were uncommon in the medial and lateral regions of the parabrachial complex but predominated in the solitary nucleus. Parabrachial neurons were usually larger and possessed more complex higher-order dendritic arborizations than solitary neurons. Computer-generated three-dimensional rotational analyses failed to demonstrate the strong orientation specificity in parabrachial neurons that characterizes gustatory solitary neurons. These Golgi studies described for the first time the morphological features of pontine neurons that could possibly receive ascending gustatory projections, and the morphological differences between neurons that receive direct peripheral input from taste receptors and the pontine targets of such neurons.