DISTRIBUTION OF CENTRAL CATECHOLAMINERGIC NEURONS - A COMPARISON BETWEEN UNGULATES, HUMANS AND OTHER SPECIES

In ungulates and primates, the distribution of central catecholaminerg ic neurons identified using antibodies raised against catecholamine sy nthesizing enzymes and catecholamines themselves, shows many differenc es if compared to rats. Catecholaminergic neurons are more loosely clu stered in ungulates and primates than in rat. In the medulla oblongata , the density of noradrenergic/adrenergic neurons is lower in ungulate s than in other species and, particularly in sheep, the adrenergic gro up C1 is not observed. The noradrenergic neurons of the locus coeruleu s are present in a larger area in ungulates than in rodents. In the hy pothalamus, the density of dopamine neurons is lower in ungulates and primates than in rodents. In the rostral hypothalamus of ungulates, th e dorsal part of the group A14 is missing, and these species present o nly the ventral part of the group A15. In primates the group A15 exten ds into the supraoptic and paraventricular nuclei which have large tyr osine hydroxylase-immunoreactive (TH-IR) neurons not observed in other species. In addition, in all studied species, not all cells expressin g catecholamine synthesizing enzymes also express catecholamines, as f ound in some TH-IR neurons in the arcuate nucleus, thereby demonstrati ng the necessity of using different markers to ascertain the true cate cholaminergic nature of labeled neurons. These anatomical differences between species show the difficulty in extrapolating the distribution of catecholamine neurons from one species to another and may be relate d to adaptative physiological differences between mammals.