Orexin neurons project to diverse sympathetic outflow systems

Area of Science:

• Neuroscience
• Autonomic Nervous System Research

Background:

• Orexin (hypocretin) neurons in the lateral hypothalamic area (LHA) are known to regulate sleep-wake cycles and arousal.
• The precise connections of orexin neurons to the sympathetic nervous system are not fully understood.

Purpose of the Study:

• To investigate the multisynaptic connections between orexin-containing neurons in the LHA and various sympathetic outflow systems.
• To determine if individual orexin neurons can influence multiple sympathetic pathways.

Main Methods:

• Viral transneuronal tracing using Bartha pseudorabies virus (PRV) was employed.
• Single-virus injections into sympathetic targets (stellate ganglion, adrenal gland, celiac ganglion, kidney) were performed.
• Double-virus tracing with two isogenic PRV strains (one expressing beta-galactosidase, the other GFP) was used to label neurons projecting to multiple targets.

Main Results:

• Single-virus injections revealed multisynaptic connections from LHA orexin neurons to sympathetic targets.
• Double-virus tracing demonstrated that individual orexin LHA neurons can be connected to at least two different sympathetic outflow systems (e.g., stellate ganglion and adrenal gland).

Conclusions:

• Orexin neurons in the LHA possess the capacity to modulate multiple sympathetic outflow systems.
• These findings suggest a role for orexin neurons in the integrated regulation of general sympathetic functions, including arousal and the fight-or-flight response.