Direct projections from hypothalamic orexin neurons to brainstem cardiac vagal neurons

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Autonomic Nervous System Research

Background:

• Orexin neurons are recognized for enhancing sympathetic cardiovascular control.
• The specific role of orexin neurons in parasympathetic cardiac regulation is not well understood.

Purpose of the Study:

• To investigate the contribution of orexin neurons to parasympathetic cardiac control.
• To determine if orexin neurons directly influence cardiac vagal neurons (CVNs).

Main Methods:

• Used orexin-Cre transgenic rats for selective optogenetic targeting of orexin neurons with channelrhodopsin-2 (ChR2).
• Performed electrophysiological recordings of postsynaptic currents in CVNs within the dorsal motor nucleus of the vagus (DMV).
• Utilized photostimulation to activate ChR2-expressing orexin neurons and their projections.

Main Results:

• Optogenetic activation of orexin neurons induced reliable firing and large currents, confirming effective ChR2 expression and excitation.
• Photostimulation of orexin fibers in the DMV evoked short-latency postsynaptic currents in 36% of tested CVNs.
• These responses were heterogeneous, comprising 63% excitatory glutamatergic and 37% inhibitory GABAergic currents.

Conclusions:

• Orexin neurons can exert both excitatory and inhibitory influences on cardiac vagal neurons.
• Different subpopulations of orexin neurons may differentially regulate CVNs.
• These findings suggest a complex role for orexin neurons in the parasympathetic control of heart rate.