Q.40 Which of the following gas(es) function(s) as signaling molecule(s) in the human nervous
system?
(A) Nitric oxide
(B) Carbon monoxide
(C) Helium
(D) Argon

Nitric oxide (NO) and carbon monoxide (CO) act as gaseous signaling molecules, or gasotransmitters, in the human nervous system, while helium and argon do not function in this capacity. Both NO and CO are endogenously produced and mediate neurotransmission through diffusion and activation of pathways like guanylate cyclase. The correct answer is (A) and (B).​

Option Analysis

Nitric oxide, produced by neuronal nitric oxide synthase (nNOS) in neurons, serves as a key neurotransmitter and retrograde messenger in processes like long-term potentiation in the hippocampus and cerebellum. It diffuses across membranes to activate soluble guanylate cyclase, raising cGMP levels for synaptic plasticity and vasodilation.​

Carbon monoxide, generated by heme oxygenase-2 (HO-2) in neurons, functions as an inhibitory neurotransmitter, often co-localized with NO in enteric and central neurons, modulating smooth muscle relaxation and neuronal signaling. It parallels NO in activating guanylate cyclase and influences vascular tone and pain modulation.​

Helium shows neuroprotective effects in preconditioning models via mechanisms like NO upregulation or anti-apoptotic signaling, but lacks evidence as an endogenous signaling molecule or neurotransmitter in the nervous system.​

Argon exhibits neuroprotective properties through Toll-like receptor inhibition and ERK1/2 pathways in injury models, yet it does not serve as a physiological signaling molecule or gasotransmitter.​

Nitric oxide and carbon monoxide emerge as pivotal signaling molecules in human nervous system functions, acting as gasotransmitters in neurotransmission and modulation. These gases, unlike inert noble gases helium and argon, are endogenously synthesized and diffuse freely to influence synaptic plasticity and neuronal communication.​

Gasotransmitter Mechanisms

Gasotransmitters like nitric oxide, produced via nNOS, regulate long-term potentiation and pain transmission by activating cGMP pathways in the central and peripheral nervous systems. Carbon monoxide, from HO-2, co-functions with NO as a coneurotransmitter in enteric neurons, promoting inhibitory signaling and vascular control.​

• Nitric oxide enables retrograde signaling in hippocampal LTP.​

• Carbon monoxide modulates hypothalamic hormone release and neuronal firing.​

Non-Signaling Gases

Helium preconditioning offers neuroprotection through NO-mediated antioxidative effects but lacks endogenous production or direct signaling roles. Argon inhibits TLR2/4 for anti-apoptotic benefits in injury, yet remains biologically inert without neurotransmitter function.​

This distinction aids CSIR NET aspirants in mastering molecular biology and neurophysiology topics.​