A Comparison of Neurotransmitter-Specific and Neuropeptide-Specific Neuronal Cell Types Present in the Dorsal Cortex in Turtles with Those Present in the Isocortex in Mammals: Implications for the Evolution of Isocortex

The posterior pretectal nucleus, which in Osteoglossum receives second order visual input and projects to the inferior lobe of the hypothalamus, was identified and characterized in species from all major groups of non-neoteleost teleosts. The hypothesis that the posterior pretectal nucleus in these species is homologous to both the pars intermedius of the superficial pretectal nucleus and nucleus glomerulosus in acanthopterygians is supported by multiple similarities in relative position and cytoarchitecture. Nucleus corticalis, which receives retinal input and projects to the posterior pretectal nucleus (or to nucleus glomerulosus), was identified in species belonging to three of the four major teleost radiations. Both the posterior pretectal nucleus and nucleus corticalis are plesiomorphic for teleosts. The presence of glomeruli in the posterior pretectal nucleus and nucleus glomerulosus in esocids and acanthopterygians, respectively, and the presence of two nuclei, the pars intermedius and nucleus glomerulosus, in acanthopterygians, as opposed to one nucleus, the posterior pretectal nucleus, are apomorphies.