Capsaicin-sensitive sensory-motor neurotransmission in the peripheral control of cardiovascular function

For many years studies on the neuronal control of cardiovascular function have focussed on the antagonistic actions of sympathetic and parasympathetic branches of the autonomic nervous system.Over the past two decades, improved techniques of immunohistochemistry, electron microscopy and electrophysiology have profoundly reshaped our knowledge of the autonomic control of cardiovascular function [1,2].As revealed by immunocytochemistry, a system of capsaicin-sensitive peptidergic neurons is associated with the cardiovascular system [3-51.Sensory function of capsaicin-sensitive primary afferent neurons is mostly related to the transmission of nociceptive impulses.However, once activated by peripheral stimuli, capsaicinsensitive afferent neurons can also release the transmitter content from their peripheral terminals in innervated tissue to elicit functional responses.The term of "sensory-motor nerves" has been therefore coined, in order to point out the dual afferent (sensory) and efferent (motor) activity of this neuronal population [6-91.Cardiac responses to stimulation of sensory-motor nerves consist of positive chronotropic and inotropic effects comparable in many respects to the excitatory effects of noradrenaline (NA) via /3-adrenoceptor activation.In several blood vessels, including coronary, mesenteric and pulmonary arteries, activation of perivascular sensory-motor nerves results in endothelium-independent vasodilator responses.In the skin microvasculature both vasodilatation and extravasation are mediated by release of neurotransmitters from sensory-motor nerves.In this article we will review evidence in favour of a role for the efferent component of sensory-motor nerves in the neuronal control of cardiac performance and vascular tone.Reciprocal interactions (cross-talk) with both sympathetic and parasympathetic branches of the autonomic nervous system will also be discussed.