PEDUNCULOPONTINE NUCLEUS IN THE SQUIRREL-MONKEY - DISTRIBUTION OF CHOLINERGIC AND MONOAMINERGIC NEURONS IN THE MESOPONTINE TEGMENTUM WITH EVIDENCE FOR THE PRESENCE OF GLUTAMATE IN CHOLINERGIC NEURONS

The topographical relationships between cholinergic neurons, identifie d by their immunoreactivity for choline acetyltransferase (ChAT) or th eir staining for beta-nicotinamide adenine dinucleotide phosphate (NAD PH)-diaphorase, and dopaminergic, serotoninergic, noradrenergic, and g lutamatergic neurons that occur in the mesopontine tegmentum, were stu died in the squirrel monkey (Saimiri sciureus). The ChAT-positive neur ons in the pedunculopontine nucleus (PPN) form two distinct subpopulat ions, one that corresponds to PPN pars compacta (PPNc) and the other t o PPN pars dissipata (PPNd). The ChAT-positive neurons in PPNc are clu stered along the dorsolateral border of the superior cerebellar pedunc le (SP) at trochlear nucleus levels, whereas those in PPNd are scatter ed along the SP from midmesencephalic to midpontine levels. At levels caudal to the trochlear nucleus, ChAT-positive neurons corresponding t o the laterodorsal tegmental nucleus (LDT) lie within the periaqueduct al gray and extend caudally as far as locus coeruleus levels. All ChAT -positive neurons in PPN and LDT stain for NADPH-diaphorase; the major ity of large neurons in PPN and LDT are cholinergic, but some large ne urons devoid of NADPH-diaphorase also occur in these nuclei. Cholinerg ic neurons in the mesopontine tegmentum form clusters that are largely segregated from raphe serotonin-immunoreactive neurons, as well as fr om nigral dopaminergic and coeruleal noradrenergic neurons, as reveale d by tyrosine hydroxylase immunohistochemistry. Nevertheless, dendrite s of cholinergic and noradrenergic neurons are closely intermingled, s uggesting the possibility of dendrodendritic contacts. In addition, nu merous large and medium-sized glutamate-immunoreactive neurons are int ermingled among cholinergic neurons in PPN. Furthermore, at trochlear nucleus levels, about 40% of cholinergic neurons display glutamate imm unoreactivity, whereas other neurons express glutamate or ChAT immunor eactivity only. This study demonstrates that 1) cholinergic neurons re main largely segregated from monoaminergic neurons throughout the meso pontine tegmentum and 2) PPN contains cholinergic and glutamatergic ne urons as well as neurons coexpressing ChAT and glutamate in primates. (C) 1994 Wiley-Liss, Inc.