A quantitative immuno-electron microscopic study of dopamine terminals in forebrain regions of the domestic chick involved in filial imprinting.
The mediorostral neostriatum/hyperstriatum ventrale and neostriatum dorsocaudale of the domestic chick are crucially involved in filial imprinting and are major targets of mesotelencephalic dopaminergic projections. To better understand the functional role of dopamine in these forebrain regions, the ultrastructure of dopamine terminals was studied by serial section electron microscopy using immunohistochemical labeling with antibodies to tyrosine hydroxylase and dopamine. At light as well as electron microscopic level, dopamine and tyrosine hydroxylase-immunoreactive fibers were present at moderate densities in the mediorostral neostriatum/hyperstriatum ventrale and high densities in the neostriatum dorsocaudale. The frequency of tyrosine hydroxylase-immunoreactive profiles per unit area was significantly higher in the neostriatum dorsocaudale than in the mediorostral neostriatum/hyperstriatum ventrale. In both regions, tyrosine hydroxylase-immunoreactive terminals were relatively small, with mean areas of 0.55 microm(2) in the mediorostral neostriatum/hyperstriatum ventrale and 0.48 microm(2) in the neostriatum dorsocaudale. The majority of tyrosine hydroxylase-immunoreactive synapses were symmetrical (83% in the mediorostral neostriatum/hyperstriatum ventrale, 75% in the neostriatum dorsocaudale) as opposed to asymmetrical (17 and 25%, respectively), but there were also tyrosine hydroxylase-immunoreactive terminals which lacked clear synaptic specializations. The preferred targets of the synaptic tyrosine hydroxylase-immunoreactive terminals were dendritic shafts (64% in the mediorostral neostriatum/hyperstriatum ventrale, 63% in the neostriatum dorsocaudale) and less frequently dendritic spines (17 and 23%, respectively) or perikarya (19 and 14%, respectively). In both forebrain regions, immunoreactive terminals were often found in close apposition to unstained terminals making asymmetrical synapses. In conclusion, these results indicate that the ultrastructural features of dopamine terminals in the avian telencephalon are very similar to those described in mammals and that dopamine may exert its effects primarily by modulating excitatory inputs.
Metzger
M
M
Heart Institute (InCor), Pathological Anatomy, University of São Paulo Medical School, Brazil. anpmetzger@incor.usp.br
Jiang
S
S
Braun
K
K
D000818:Animals; D002452:Cell Count; D002645:Chickens; D004298:Dopamine / Q000096:biosynthesis*; D005260:Female; D007173:Imprinting, Psychological / Q000502:physiology; D008297:Male; D016253:Microscopy, Immunoelectron; D017072:Neostriatum / Q000378:metabolism / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure*; D016548:Prosencephalon / Q000378:metabolism / Q000648:ultrastructure*; D014446:Tyrosine 3-Monooxygenase / Q000096:biosynthesis*
D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine