Morphological analogy of the rostral midline area in the chicken midbrain to the anteromedian nucleus in the mammalian midbrain

Substance P-immunoreactive neurons projecting from the midbrain to the spin al cord of the chicken were examined by the use of the retrograde tract-tra cing method combined with immunohistochemical techniques. Many small neuron s were densely clustered in the rostral midline area of the midbrain (RMA), and showed substance P-immunoreactivity. These substance P-immunoreactive neurons sent axons to the intermediomedial cell column (avian autonomic pre ganglion) and its vicinity in the lumbar spinal segments. On the basis of t he strong neuroanatomical analogy in the cytoarchitectural features, immuno reactivity, and fiber connections, the RMA was assumed to be the avian homo logue of the anteromedian nucleus in the mammalian midbrain.