Non-cholinergic basal forebrain neurons project to the contralateral basal forebrain in the rat

Following injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) or the fluorescent tracer fluoro-gold into the magnocellular preoptic area and the horizontal limb of the diagonal band, retrogradely labelled neurons were found in the homotopic region of the contralateral basal forebrain. Labelled fibers apparently arising from these neurons travelled in the stria medullaris and the habenular commissure to terminate in the contralateral basal forebrain. Although the neurons retrogradely labelled with fluoro-gold in the contralateral basal forebrain were similar in size to choline acetyltransferase (ChAT)-immunoreactive neurons, and were intermingled with them, none was ChAT-positive. WGA-HRP injections into the nucleus basalis magnocellularis did not result in retrograde labelling in the contralateral basal forebrain. These findings suggest that non-cholinergic neurons may serve as a direct link between the two sides of selective magnocellular basal forebrain regions.