How LSD affects the brain and creates its trippy effect

Once you drop, you can’t stop – sometimes for up to 15 hours. Images revealing how LSD interacts with receptors in the brain could explain why a trip lasts so long, while another study involving a similar receptor unpicks how the drug makes these experiences feel meaningful.

LSD acts on with a number of different receptors in the brain, including ones for the chemicals serotonin and dopamine, but it’s not known exactly which receptors are responsible for its various effects. Daniel Wacker and his colleagues at the University of North Carolina, Chapel Hill, used crystallography to look at the structure of LSD when it binds to a receptor in the brain that normally detects serotonin. They discovered that part of this serotonin 2B receptor acts as a lid, closing around the LSD molecule and trapping it.

This could explain the extended trips the drug produces. “It takes LSD very long to get into the receptor, and once it’s stuck it doesn’t go away,” says Wacker.

However, there is conflicting evidence. Other studies have shown that LSD hangs around in the blood for a long time. “No prolonged action at the receptor is needed to explain the duration of action,” says Matthias Liechti at the University of Basel, Switzerland.

But if Wacker is right, the fact that LSD seems to get stuck inside the receptor might mean it can have effects at very low doses. In recent years, there have been reports of some people taking LSD in amounts too small to cause hallucinations, in an attempt to boost creativity or general well-being.

There’s little hard evidence about whether this microdosing works, but Wacker says psychoactive effects at low doses are plausible. “Our study suggests even very low amounts of LSD may be enough to cause psychoactive effects.” Scientific interest in LSD’s clinical use has revived in recent years – notably to relieve severe psychiatric conditions such as PTSD and anxiety. There are also signs that LSD has helpful non-psychoactive effects on other ailments, such as cluster headaches.

Suppressing bliss

A second study finds evidence that LSD affect the brain by binding to serotonin receptors, and hints at possible ways to harness some of its effects therapeutically. Katrin Preller and her colleagues at the University of Zurich, Switzerland, gave 22 volunteers 100 micrograms of LSD each to determine the role of the serotonin 2A receptor, which is similar to the one studied by Wacker’s team.

In some of the tests, subjects were also given ketanserin, a drug that blocks the serotonin 2A receptor. In those tests, the trippy effects of LSD – including hallucinations, feeling separate from the body, and feelings of bliss – were completely blocked, showing that this receptor must be responsible for them.

The researchers also played songs to the participants. Some of the songs were ones the volunteers had chosen as meaningful beforehand, while others were not. While on LSD, they rated what had been non-meaningful songs as highly meaningful – an effect that, once again, ketanserin blocked.

Preller thinks these findings suggest that the serotonin 2A receptor is important for how we decide which things are relevant to us. “This is something that’s incredibly important for our everyday life,” she says. “We do it constantly, for example if you see a familiar face.”

Some psychiatric conditions, such as schizophrenia and phobias, are associated with paying too much attention to unimportant stimuli. Preller speculates that LSD might help people refocus their attention in a different direction.

“If you have a depressed patient ruminating about negative thoughts, LSD might facilitate a process where you attribute meaning to other things,” says Preller.

Alternatively, people with these conditions might benefit from drugs that reduce the action of the serotonin 2A receptor, like ketanserin.

Source: Journal reference: Current Biology, DOI: 10.1016/j.cub.2016.12.030 Journal reference: Cell, DOI: 10.1016/j.cell.2016.12.033

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