Dopaminergic innervation of the telencephalon of the pigeon ( Columba livia ): A study with antibodies against tyrosine hydroxylase and dopamine

Abstract The dopaminergic structures in the telencephalon of the pigeon were investigated with antisera against glutaraldehyde‐conjugated dopamine (DA) and tyrosine hydroxylase (TH). Our goal was to describe the morphological patterns of the labelled axons and to provide a detailed map of the density and regional distribution of the dopaminergic innervation in relation to cytoarchitectonic areas. DA‐ and TH‐like fibers reached their highest density in the paleostriatum augmentatum and the lobus parolfactorius of the basal ganglia. The paleostriatum primitivum was characterized by a dichotomous DA‐positive innervation with a diffuse fiber network contacting en passant granular cells and a more specific input that completely wrapped up large cells, which probably represent relay neurons. Two distinct DA‐positive pathways could be followed back from the forebrain leading to the dopaminergic cell groups of the nucleus tegmenti pedunculopontinus pars lateralis and the area ventralis tegmentalis. The primary sensory areas of the visual, auditory, somatosensory, and trigeminal systems within the forebrain of the pigeon were virtually devoid of DA‐like fibers and demonstrated only TH‐positive axons, probably of a noradrenergic nature. Among the limbic structures, the neostriatum caudolaterale (a possible equivalent of the mammalian prefrontal cortex), the septum, the nucleus accumbens, and parts of the archistriatum were heavily labelled by DA‐like axons. A highly characteristic morphological feature of the catecholaminergic innervation was the presence of “baskets,” which are constituted by TH‐ and DA‐positive fibers coiled up around large perikarya, so that the surrounded somata were virtually visible by the presence of labelled axons. The density of basket and nonbasket type innervations seemed to be independently regulated, so that each forebrain structure could be characterized by a mixture consisting of the individual degrees of these two features. Our results demonstrate that the dopaminergic innervation of the forebrain of the pigeon is widespread but shows important regional variations. Similar to mammals, associative and motor structures are heavily innervated by dopaminergic fibers, whereas sensory areas are dominated by their noradrenergic input. The basket and nonbasket type innervations observed in virtually all of these subdivisions of the telencephalon may indicate the presence of two main classes of catecholaminergic afferents with different mechanisms of modulation of forebrain activity patterns. © 1995 Wiley‐Liss, Inc.