Anatomical relations between neuropeptide Y, galanin, and gonadotropin-releasing hormone in the brain of chondrostean, the Siberian sturgeon Acipenser baeri.

We investigated the immunohistochemical localization of immunoreactive (ir) cell bodies and fibers of neuropeptide Y (NPY) and galanin (GAL), and the anatomical relations between these neurons in the brain of the Siberian sturgeon Acipenser baeri to clarify the interactions between these neuropeptides. Furthermore, the anatomic relations between NPY and gonadotropin-releasing hormone (GnRH) in the brain were also examined. NPY-ir cell bodies were observed in the ventral part of the ventral telencephalon (Vv). NPY-ir fibers were observed throughout the brain, primarily in the ventral telencephalon, hypothalamus, optic tectum, and midbrain. GAL-ir cell bodies were observed in the Vv, nucleus anterioris tuberis (NAT), nucleus lateralis tuberis (NLT), and nucleus recessus posterioris (NRP). GAL-ir fibers were also observed throughout the brain. Neither NPY-ir fibers nor GAL-ir fibers were detected in the pituitary. Dual-label immunohistochemistry revealed that some GAL-ir fibers were in close contact with NPY-ir cell bodies in the Vv, and some NPY-ir fibers were in close contact with GAL-ir cell bodies in the NAT. Furthermore, some NPY-ir fibers were in close contact with GnRH-ir cell bodies in the preoptic area, and some GnRH-ir fibers were in close contact with NPY-ir cell bodies in the Vv. These findings suggest that reciprocal connections exist between the NPY and GAL neurons and between the NPY and GnRH neurons in the brain of the Siberian sturgeon.