Single neurons in Barrington's nucleus projecting to both the paraventricular thalamic nucleus and the spinal cord by way of axon collaterals: a double labeling study in the rat.

Barrington's nucleus, a center for the micturition reflex in the pontine tegmentum, was recently reported to send projection fibers to the paraventricular thalamic nucleus (PVT). In the present study, we examined whether or not Barrington's nucleus neurons projecting to the PVT issue axon collaterals to the lowest lumbar cord segment (L6) containing the spinal micturition center. Our retrograde double-labeling study revealed that a subset of Barrington's nucleus neurons send projection fibers to both the L6 and the thalamic midline including the PVT via axon collaterals. Such neurons projecting directly to the thalamic midline and L6 by way of axon collaterals were additionally scattered in the locus coeruleus, subcoeruleus nucleus and sublaterodorsal nucleus.