Structure and function of barrel 'precursor' cells in trigeminal nucleus principalis

Intracellular recording, electrical stimulation, receptive field mapping, HRP injection, and computer reconstruction techniques were used to study principalis cells in rat. They (n = 80) responded within 1.2 ± 0.2 ms of trigeminal ganglion shocks and 69% were antidromically activated by thalamic shocks; 69% were vibrissa-sensitive, of which 80% responded to only a single vibrissa. The remainder responded only to guard hairs, skin, teeth, or nociceptors. Stained thalamic-projecting cells with one vibrissa receptive fields had stereotyped morphologies. Small somata gave rise to dendrites which extended only a short distance from the soma, where they branched extensively. Each tree was polarized, spanning no more than a hemisphere around the soma; however, there was no consistent direction of polarity. Dendritic trees extended 68 ± 14, 95 ± 48, and 91 ± 29 μm in the transverse, sagittal and horizontal planes, respectively. Dendritic spines were rare, yet swellings were common. Axons never branched locally.