Neuroprotection
Bluelighter
- Joined
- Apr 18, 2015
- Messages
- 1,264
Caffeine is inverse agonist, so it does opposite of what adenosine does in the target neuron https://pubmed.ncbi.nlm.nih.gov/25268872/ Also preventing adenosine of binding in the first place
Theacrine binds to different site in neuron than adenosine does, but it decreases the amount of signaling adenosine causes once it binds to its site
Also; I found this claim:
"At high doses, however, it has been demonstrated that caffeine may not act as an adenosine receptor antagonist, and other underlying mechanisms seem responsible of its negative effects (for a recent review Fredholm et al., 2017)."
"The mechanism(s) underlying high dose effects of caffeine are less well known. There is an association between caffeine-induced anxiety and one genetic variant of the A2AR gene (Alsene et al., 2003), but not with several other variants (Rogers et al., 2010). The down-ward slope of the biphasic dose-response curve to caffeine remains in A2AR knockout (KO) mice even though the stimulatory effect was eliminated, and it was suggested that A1 receptors may mediate the negative effects (El Yacoubi"
Does anyone have any knowledge if caffeine has any affinity to any other system? I recall, and I am pretty sure about this, that I once found complete affinity chart and there was affinity for some serotonin receptors and stuff, but I can not recall any Ki-values or stuff (not like I would be able to relate them to each other and be definitive about relevance of such anyway).
The main stimulant effects of caffeine at any dose are due to adenosine receptor antagonism. at high concentrations, caffeine may inhibit phosphodiesterase enzymes and trigger intracellular calcium release from endoplasmic reticulum sites if I remember correctly. however, these effects are likely irrelevant to the psychoactive effects of caffeine in humans and animals, even at large doses. assuming this is correct, the question becomes which adenosine receptor is responsible for negative effects of caffeine when blocked. The holistic answer is that both A1 and A2A adenosine receptors are involved. however, A1 receptor blockade is likely the main cause of caffeine induced anxiety/stress, unpleasant arousal and perhaps temporary cognitive impairment. blocking this receptor is somewhat similar to, though nowhere near as dangerous as blocking GABAA receptors with antagonists used in scientific research to mimic seizures and panic disorder. A1 adenosine receptor activation can promote sleep, suppress anxiety and general arousal and protect against seizures. caffeine does the opposite of these effects.
A2A receptor blockade is actually associated with all the positive effects of caffeine like mood lift, antidepressant and reward enhancing affects. Unlike A1 receptors, A2A receptors mainly function to restrain dopamine D2 receptor signalling in the indirect pathway of the striatum through various mechanisms. activation of these receptors can induce depressive behaviours, decreased locomotion and apathy. due to their unique role, selective antagonists are being investigated for Parkinson’s disease and major depression as they can increase dopamine receptor signalling via a novel mechanism. though not clear, it is possible that A2A blockade by caffeine might contribute to symptoms of insomnia and heightened alertness which could indirectly contribute to anxiety. However, I don’t believe there is a direct link to this mechanism of caffeine and anxiety.
I’m going to do more reading on this and I’ll get back to you all if anything I said needs to be updated.