Comparative neurochemistry of the avian forebrain and striatum: a microdialysis study

The mammalian and avian striatum are homologous structures, while the mammalian prefrontal cortex (PFC) and the avian neostriatum caudolaterale (NCL) represent functionally equivalent, possibly homoplastic structures. We used brain microdialysis to study basal levels and release mechanisms of dopamine (DA) and serotonin (5-HT) in the pigeons' forebrain to be able to compare the biochemical characteristics between these structures and different species. Basal DA levels in the pigeons' NCL were different from those in the rats' PFC, but were similar in the striatum. This was converse for 5-HT. As in mammals, perfusion with artificial cerebrospinal fluid (aCSF) with elevated potassium significantly increased DA levels, whereas calcium-free aCSF decreased the DA efflux. In summary, the avian and mammalian forebrains show a complex pattern of neurochemical similarities and differences. These data suggest that absolute and relative concentrations of modulatory systems may change considerably over evolutionary time, while basic biochemical mechanismsm stay unaltered.