Orexin neurons express a functional pancreatic polypeptide Y4 receptor

Area of Science:

• Neuroscience
• Endocrinology
• Molecular Biology

Background:

• Neuropeptide Y (NPY) plays a role in regulating food intake, but the specific receptor subtypes involved are not fully understood.
• The NPY Y4 receptor is a recently identified candidate for mediating NPY's effects on appetite.
• The central actions and specific neuronal targets of the Y4 receptor remain to be elucidated.

Purpose of the Study:

• To investigate the central site of action of the NPY Y4 receptor.
• To determine the functional interaction between Y4 receptors and orexin neurons in the lateral hypothalamic area (LHA).
• To characterize the role of Y4 receptor signaling in the regulation of food and water intake.

Main Methods:

• Immunocytochemistry to visualize Y4 receptor distribution.
• In situ hybridization to confirm Y4 mRNA expression in specific neurons.
• Direct administration of Y4-selective (rPP) and non-selective (NPY) ligands into the LHA to assess effects on food/water intake and c-Fos expression.

Main Results:

• Y4-like immunoreactivity and Y4 mRNA were found in orexin neurons within the LHA.
• Both rPP and NPY administered into the LHA increased food and water intake, with NPY being more potent.
• rPP, but not NPY, specifically stimulated c-Fos expression in orexin neurons, indicating Y4 receptor activation.
• Both ligands activated other neuronal populations in the LHA, but not melanin-concentrating hormone neurons.

Conclusions:

• A functional Y4 receptor is expressed on orexin neurons in the LHA.
• Activation of Y4 receptors by rPP leads to the activation of orexin neurons.
• These findings support a role for central Y4 receptors, potentially mediated by orexin neurons, in appetite control, though the endogenous ligand requires further identification.