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 μm² in the mediorostral neostriatum/hyperstriatum ventrale and 0.48 μm² 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.