THE DOPAMINERGIC INNERVATION OF THE PIGEON TELENCEPHALON - DISTRIBUTION OF DARPP-32 AND COOCCURRENCE WITH GLUTAMATE-DECARBOXYLASE AND TYROSINE-HYDROXYLASE

Dopaminergic axons arising from midbrain nuclei innervate the mammalia n and avian telencephalon with heterogeneous regional and laminar dist ributions. In primate, rodent, and avian species, the neuromodulator d opamine is low or almost absent in most primary sensory areas and is m ost abundant in the striatal parts of the basal ganglia. Furthermore, dopaminergic fibres are present in most limbic and associative structu res. Herein, the distribution of DARPP-32, a phosphoprotein related to the dopamine D1-receptor, was investigated in the pigeon telencephalo n by immunocytochemical techniques. Furthermore, co-occurrence of DARP P-32-positive perikarya with tyrosine hydroxylase-positive pericellula r axonal ''baskets'' or glutamate decarboxylase-positive neurons, as w ell as co-occurrence of tyrosine hydroxylase and glutamate decarboxyla se were examined. Specificity of the anti-DARPP-32 monoclonal antibody in pigeon brain was determined by immunoblotting. The distribution of DARPP-32 shared important features with the distribution of D1-recept ors and dopaminergic fibres in the pigeon telencephalon as described p reviously. In particular, DARPP-32 was highly abundant in the avian ba sal ganglia, where a high percentage of neurons were labelled in the ' 'striatal'' parts (paleostriatum augmentatum, lobus parolfactorius), w hile only neuropil staining was observed in the ''pallidal'' portions (paleostriatum primitivum). In contrast, DARPP-32 was almost absent or present in comparatively lower concentrations in most primary sensory areas. Secondary sensory and tertiary areas of the neostriatum contai ned numbers of labelled neurons comparable to that of the basal gangli a and intermediate levels of neuropil staining. Approximately up to on e-third of DARPP-32-positive neurons received a basket-type innervatio n from tyrosine hydroxylase-positive fibres in the lateral and caudal neostriatum, but only about half as many did in the medial and frontal neostriatum, and even less so in the hyperstriatum. No case of coloca lization of glutamate decarboxylase and DARPP-32 and no co-occurrence of glutamate decarboxylase-positive neurons and tyrosine hydroxylase-b asket-like structures could be detected out of more than 2000 glutamat e decarboxylase-positive neurons examined, although the high DARPP-32 and high tyrosine hydroxylase staining density hampered this analysis in the basal ganglia. In conclusion, the pigeon dopaminergic system se ems to be organized similar to that of mammals. Apparently, in the tel encephalon, dopamine has its primary function in higher level sensory, associative and motor processes, since primary areas showed only weak or no anatomical cues of dopaminergic modulation. Dopamine might exer t its effects primarily by modulating the physiological properties of non-GABAergic and therefore presumably excitatory units. (C) 1998 IBRO . Published by Elsevier Science Ltd.