A neglected 'accessory' vasomotor pathway: implications for blood pressure control

Area of Science:

• Neuroscience
• Physiology

Background:

• The sympathetic nervous system (SNS) regulates involuntary bodily functions.
• Preganglionic neurons are key components of the SNS, transmitting signals from the central nervous system to ganglia.
• Existing understanding primarily focuses on 'regular' sympathetic preganglionic neurons.

Purpose of the Study:

• To identify and characterize a distinct population of 'accessory' preganglionic neurons.
• To elucidate the functional properties and pathways modulated by these accessory neurons.
• To investigate the role of accessory preganglionic neurons in cardiovascular regulation.

Main Methods:

• Distinguishing accessory preganglionic neurons by their unmyelinated axons and unique functional properties.
• Investigating their synaptic connections with ganglion cells.
• Analyzing their activation by arterial chemoreceptors and their effects on ganglionic transmission.
• Examining their influence on cardiovascular pathways and post-ganglionic activity.
• Utilizing microinjections of GABA into the rostral ventrolateral medulla to differentiate pathway activation.

Main Results:

• Accessory preganglionic neurons possess unmyelinated axons and distinct functional characteristics.
• They mediate hexamethonium-resistant ganglionic transmission, involving muscarinic, peptidergic, or nitrergic mechanisms.
• These neurons specifically innervate cardiovascular sympathetic pathways (vasomotor, cardiac, adrenal).
• Activation of accessory neurons potentiates post-ganglionic activity for extended periods.
• GABA microinjections selectively activated the accessory pathway while inhibiting the regular pathway.

Conclusions:

• A novel 'accessory' sympathetic preganglionic neuron pathway has been identified.
• This pathway plays a significant role in cardiovascular control, distinct from regular sympathetic neurons.
• The accessory pathway is activated by arterial chemoreceptors and influences blood pressure regulation.
• Further research is needed to confirm its role in the long-term control of blood pressure in health and disease.