The organisation of catecholamine-containing neurons in the brain of the rhesus monkey (Macaca mulatta).

The distribution of catecholamine neurons in the brains of several rhesus monkeys (Macaca mulatta) was studied by means of the Falck-Hillarp formaldehyde histofluorescence technique. Catecholamine-containing cell bodies in the medulla and pons were found to correspond essentially to the noradrenaline cell groups A1-A7, originally defined in the rat. The pontine catecholamine neurons of the locus coeruleus (A6) and subcoeruleal tegmental areas (A6, A5 and A7) are, however, far more numerous in M. mulatta; observations which agree with reports in other primate species and carnivores. Rostrally projecting fibres, analogous to the ascending 'ventral' and 'dorsal' noradrenaline bundles described in other species, have also been observed in addition to those equivalent to the dorsal periventricular system. The large number of cells present throughout the mesencephalon represent dopamine cell groups A8-A10, while small populations of catecholamine neurons within the periventricular regions of the hypothalamus correspond to groups A11-A14. A prominent terminal innervation of the diencephalon (hypothalamus) is also evident in M. mulatta. Although similar in general terms to that in other species, several important variations are apparent. These and other differences noted above may underlie species specific variations in behaviour.