A neuronal circuit driven by GLP-1 in the olfactory bulb regulates insulin secretion

Area of Science:

• Neuroendocrinology
• Metabolic Regulation
• Physiology

Background:

• Glucagon-like peptide 1 (GLP-1) is crucial for insulin secretion and metabolic control.
• The role of centrally produced GLP-1 in regulating energy homeostasis is not fully understood.
• Preproglucagon cells, the source of GLP-1, are present in the olfactory bulb (OB).

Purpose of the Study:

• To investigate the role of GLP-1 signaling in the olfactory bulb (OB) on insulin secretion and energy homeostasis.
• To elucidate the neural pathways involved in OB GLP-1-mediated regulation of insulin secretion.

Main Methods:

• Activation of GLP-1 receptors (GLP-1R) in the OB of lean and diet-induced obese male mice.
• Measurement of insulin secretion in response to oral glucose.
• Assessment of pancreatic noradrenaline content.
• Pharmacological manipulation using an α2-adrenergic receptor agonist and GABA_A receptor inhibition in the paraventricular nucleus (PVN).

Main Results:

• Activation of OB GLP-1R significantly stimulated insulin secretion following oral glucose administration in both lean and obese mice.
• This effect was associated with decreased pancreatic noradrenaline levels.
• The insulinotropic effect was blocked by an α2-adrenergic receptor agonist, suggesting sympathetic nervous system (SNS) involvement.
• Inhibition of GABA_A receptors in the PVN abolished the insulin secretion enhancement induced by OB GLP-1R activation.

Conclusions:

• Olfactory bulb GLP-1 signaling plays a key role in regulating insulin secretion.
• This regulation is mediated through a top-down neural pathway involving the sympathetic nervous system (SNS).
• The pathway involves a relay mechanism within the paraventricular nucleus (PVN) of the hypothalamus.