Substance P Fiber Tracts from the Olfactory Bulb into the Telencephalon. (A–G) Using diaminobenzidine (DAB) as a substrate for the detection of a horseradish peroxidase coupled antibody yielded enhanced detection of substance P in the telencephalon (A–G). We found substance P positive neurons in the olfactory bulb (OB in A and inlet). substance P fibers emanate from the olfactory bulb toward the lateral ventralmost part of the subpallium [Vv+Vd in (B,C)]. Most importantly, some SP cells and many SP fibers label the medial amygdala (MeAa) in the dorsal tier of the subpallium (B–F). At the transition between supracommissural and postcommissural telencephalon (D–F), substance P positive fibers passing through the dorsal medial amygdala [MeAd in (D–F)] enter and label the posteromedial pallial amygdala [PMPa in (E,F)]. Substance P fibers also pass through the PMCo into the IOP, the zebrafish putative piriform cortex homology (black arrows in IOP of H), supporting the proposed homology between the zebrafish PMPa and mammalian PMCo. Note, the anterior and dorsoposterior divisions of the CeA (CeAa + CeAd) lack substance P and therefore can easily distinguished from all medial amygdaloid nuclei (MeAa, MeAd, MeAv, MeAp). (G) Schematic cross sections and sagittal view of the zebrafish telencephalon to illustrate the two solid zebrafish accessory olfactory substance P fiber systems innervating the medial amygdaloid territories. Substance P fibers seemingly form also laterally displaced diffuse projections (E).
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