Adenosine is a waste product of neurons and it is a potent nervous system depressant which is why if we don’t sleep for a long time we hallucinate, start to feel cold, and feel tired. We feel like we’re drugged because we kind of are. It also increases sleep pressure. Unlike other areas of the body the brain has no way of flushing out the adenosine unless we sleep which activates the glymphatic system. if we don’t sleep the adenosine keeps accumulating and it can kill us in a similar way an od of sleeping pills can.
It’s referring to plain adenosine. When adenosine builds up in the brain, the only way for the brain to get rid of the accumulation of it is by sleeping because it activates the glymphatic system, where CSF is used to flush out the waste/byproducts. If you don’t sleep, the adenosine continues to accumulate in the brain with nowhere to go.
Incorrect, the body reuptakes adenosine readily as part of the respiratory cycle. In the absence of external administration, it is physically impossible to build up so much adenosine that it can kill you precisely because it is so readily downregulated to inosine by ADK, or upregulated to AMP and ATP through phosphorylation.
You might be thinking of other toxic substances that build up as part of respiration; some of those like amyloid beta plaques (once thought to play a role in Alzheimer’s and other neurodegenerative diseases, but maybe not) are only cleared by the glymphatic system.
I recommend reading the last paragraph of your article again, as it doesn’t actually say adenosine is responsible. It just says that adenosine makes you sleepy, and sleeping helps clear toxic buildup from the brain via the glymphatic system (which is true). The wording is just bad and implies adenosine is one of those toxic substances.