Interaction between neuropeptide Y immunoreactive neurons and galanin immunoreactive neurons in the brain of the masu salmon, Oncorhynchus masou.

We investigated the immunohistochemical localization of neuropeptide Y (NPY) and galanin (GAL) in the brain of the masu salmon Oncorhynchus masou in order to clarify the interaction between these neuropeptide hormones in the brain. NPY-immunoreactive (ir) cell bodies were observed in the ventral and lateral regions of the ventral telencephalon (Vv and Vl, respectively), and in the dorsolateral midbrain tegmentum. NPY-ir fibers were observed throughout the brain, mainly in the ventral telencephalon, hypothalamus, optic tectum, and midbrain. GAL-ir cell bodies were observed in the nucleus preopticus parvicellularis anterioris (PPa) and the ventral zone of the periventricular hypothalamus (Hv). Both GAL-ir and NPY-ir fibers were observed throughout the brain. Furthermore, we examined the interaction between the NPY neurons and GAL neurons by performing double-staining immunohistochemistry. Some GAL-ir fibers were in close contact with the NPY-ir cell bodies in the Vv and Vl. In addition, some NPY-ir fibers were in close contact with the GAL-ir cell bodies in the PPa and Hv. These findings suggest that reciprocal connections exist between the NPY neurons and GAL neurons in the brain of the masu salmon.