Differential expression of AMPA receptor subunits in dopamine neurons of the rat brain: A double immunocytochemical study

We have examined the distribution of dopamine neurons expressing alpha -ami no-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunits (glut amate receptors 1, 2/3 and 4) in the A8-A15 regions of the rat brain using double immunofluorescence. The distribution of glutamate receptor 1- or 2/3 -like immunoreactive, neurons completely overlapped that of tyrosine hydrox ylase-like immunoreactive neurons in dopamine cell groups in the retrorubra l field (A8), the substantia nigra (A9), the ventral tegmental area and the nucleus raphe linealis (A10), and the rostral hypothalamic periventricular nucleus (A14, A15). In the caudal hypothalamic periventricular nucleus (Al l), arcuate nucleus (A12) and zona incerta (A13), the distribution was part ially overlapping. Neurons double-labeled for tyrosine hydroxylase and glut amate receptor I or 2/3 immunoreactivities were, however, exclusively found in certain dopamine cell regions: in areas A14-A15, 85-88% of tyrosine hyd roxylase-containing neurons expressed glutamate receptor I and 22-25% expre ssed glutamate receptor 2/3, while in areas A8-A10, 20-43% expressed glutam ate receptor 1 and 63-84% expressed glutamate receptor 2/3. In contrast, th e double-labeled neurons were hardly detected in the A11-A13 regions. No ty rosine hydroxylase-positive neurons displayed glutamate receptor 4 immunore activity, though a partially overlapping distribution of tyrosine hydroxyla se- and glutamate receptor 4-immunopositive neurons was also seen in region s A8-10, A11 and A13. The present study has demonstrated the morphological evidence for direct mo dulation of dopamine neurons via AMPA receptors in rat mesencephalon and hy pothalamus. This distribution may provide the basis for a selective dopamin e neuron loss in neurodegenerative disorders, such as Parkinson's disease. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.