Which gaseous neurotransmitter is discovered to also function in signaling processes within the brain?

The gaseous neurotransmitter that also functions in signaling processes within the brain is carbon monoxide. This molecule is unique because it can diffuse across membranes easily due to its gaseous nature, allowing it to act as a signaling molecule in various physiological processes. In the central nervous system, carbon monoxide is involved in modulating neurotransmission and has been shown to have neuroprotective effects, impacting conditions such as neurodegenerative diseases.

Cortisol, norepinephrine, and GABA are not gaseous neurotransmitters. Cortisol is a steroid hormone primarily associated with stress response, norepinephrine is a catecholamine involved in the fight-or-flight response and is not a gas, and GABA is an amino acid that serves as the primary inhibitory neurotransmitter in the brain. While these substances play crucial roles in brain function and signaling, they do not have the properties of a gaseous neurotransmitter like carbon monoxide does.