Abstract
BackgroundNumerous functional studies have shown that nitrergic neurotransmission plays a central role in peristalsis and sphincter relaxation throughout the gut and impaired nitrergic neurotransmission has been implicated in clinical disorders of all parts of the gut. However, the role of nitric oxide (NO) as a neurotransmitter continues to be controversial because: 1) the cellular site of production during neurotransmission is not well established; 2) NO may interacts with other inhibitory neurotransmitter candidates, making it difficult to understand its precise role.Methodology/Principal FindingsImaging NO can help resolve many of the controversies regarding the role of NO in nitrergic neurotransmission. Imaging of NO and its cellular site of production is now possible. NO forms quantifiable fluorescent compound with diaminofluorescein (DAF) and allows imaging of NO with good specificity and sensitivity in living cells. In this report we describe visualization and regulation of NO and calcium (Ca2+) in the myenteric nerve varicosities during neurotransmission using multiphoton microscopy. Our results in mice gastric muscle strips provide visual proof that NO is produced de novo in the nitrergic nerve varicosities upon nonadrenergic noncholinergic (NANC) nerve stimulation. These studies show that NO is a neurotransmitter rather than a mediator. Changes in NO production in response to various pharmacological treatments correlated well with changes in slow inhibitory junction potential of smooth muscles.Conclusions/SignificanceDual imaging and electrophysiologic studies provide visual proof that during nitrergic neurotransmission NO is produced in the nerve terminals. Such studies may help define whether NO production or its signaling pathway is responsible for impaired nitrergic neurotransmission in pathological states.
Highlights
Nitric oxide (NO) has been proposed as a neuromuscular neurotransmitter of nonadrenergic noncholinergic (NANC) inhibitory nerves in the parasympathetic [1] and the enteric nervous systems [2]
The purpose of the present studies was to examine the effect of electrical field stimulation of mice gastric muscle strips: 1) on NO and Ca2+ signals at the cellular level by fluorescent imaging; 2) on the effect of pharmacological treatments on these signals; 3) on nitrergic slow inhibitory junction potential in electrophysiological studies; and 4) to compare the effects of the pharmacological treatments on NO in the imaging studies and slow inhibitory junction potentials (sIJP) in the electrophysiological studies. These results provide, for the first time, visual identification of nerve varicosities in situ in the gut and provides proof that on NANC nerve stimulation, NO is produced in the myenteric nitrergic nerve varicosities and not in the smooth muscle cells, thereby demonstrating that NO is a neurotransmitter rather than a mediator produced in the smooth muscles
Effect of various antagonists on the slow IJPs in mice gastric muscle strips In order to correlate pharmacology of imaging studies with functional neurophysiological studies of smooth muscle membrane potentials, we examined the effects of antagonists on the nitrergic slow inhibitory junction potentials
Summary
Nitric oxide (NO) has been proposed as a neuromuscular neurotransmitter of nonadrenergic noncholinergic (NANC) inhibitory nerves in the parasympathetic [1] and the enteric nervous systems [2]. Clinical importance of this signaling pathway is evidenced by the fact that animal models of impaired nitrergic neurotransmission reveal phenotypes resembling major human gastrointestinal motility disorders [3,4,5,6,7]. While there is strong physiological evidence that NO is involved in inhibitory neurotransmission [8,9], its role as a true neurotransmitter has been questioned. The role of nitric oxide (NO) as a neurotransmitter continues to be controversial because: 1) the cellular site of production during neurotransmission is not well established; 2) NO may interacts with other inhibitory neurotransmitter candidates, making it difficult to understand its precise role
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
