A POPULATION OF CHOLINERGIC NEURONS IS PRESENT IN THE MACAQUE MONKEY THALAMUS

Three new cholinergic markers were employed to study the cholinergic i nnervation in the thalamus of adult macaque monkeys. They were: two an tibodies against choline acetyltransferase (ChAT), one polyclonal and one monoclonal; and a polyclonal antibody against the vesicular transp orter of acetylcholine (VAChT), a powerful new marker that colocalizes with ChAT. This approach led to an unexpected finding: the three anti bodies positively immunostained a population of neurons in the paracen tral nucleus. The immunostained cells are confined to the dorsal regio n of this nucleus along its rostrocaudal extent. Measurement of the so matic areas of the immunostained neurons indicated that they correspon d to a population of large neurons thought to be projection neurons. B ecause dorsal paracentral neurons are known to project to the dorsal s triatum and specific cortical areas involved in visual and visuomotor mechanisms, these structures might be modulated by cholinergic thalami c neurons.