The demeanour of pigs and dogs used by truffle hunters when they are close to making a find might best be described as animated. Or possibly even frantic. So what is it about the subterranean delicacies that triggers such vigorous enthusiasm in the animals trained to sniff them out?

Italian scientists may have hit on the answer. It turns out the black truffle (Tuber melanosporum) contains a “bliss molecule” similar to the substance that gives cannabis its psychoactive properties.

Mauro Maccarrone, of the Campus Bio-Medico University of Rome, Italy, and colleagues have revealed the highly-prized fungi produce anandamide, a compound that triggers the release of mood-enhancing chemicals in the human brain, and does so using the same biological mechanism as tetrahydrocannabinol (THC), the chemical responsible for producing the mind-bending effects of marijuana.

Maccarrone believes truffles use it to attract animals to eat their fruiting bodies, so that their spores are spread more widely and they have a better chance of reproducing.

Its name comes from “ananda”, the Sanskrit word for extreme delight or bliss

Black truffles get their colour from dark melanin pigments. Research published by Maccarrone and his colleagues in 2012 showed that in humans melanin production is triggered by the release of anandamide.

Some scientists call the compound the bliss molecule because of its role in mood, appetite, memory, pain, depression and fertility. Its name comes from “ananda”, the Sanskrit word for extreme delight or bliss.

Maccarrone’s team wanted to find out whether the melanin in black truffles is produced in the same way that it is made in humans.

They used polymerase chain reaction tests, which work by creating multiple copies of DNA sections, to identify the presence of the genes that make the chemical building blocks from which anandamide can be made.

They also used a mass spectrometry technique to reveal the presence of anandamide itself. Further tests found that more mature truffles had higher levels than younger ones.

Our interpretation is that they make it to attract animals

In humans, just like other brain signalling chemicals, the compound triggers changes by locking onto receptors on the surfaces of target cells - like a key fitting into a lock.

The researchers were intrigued when their tests revealed the truffles had the means to make anandamide and contained the chemical but did not have the receptors to which it binds and that would allow it to trigger effects.

“This suggests they do not make anandamide for themselves,” said Maccarrone. “Our interpretation is that they make it to attract animals that do have these receptors, and to stay on the truffle and keep on eating, so that the truffle’s spores are spread over a wider area.”

Truffles rely on being unearthed and eaten by animals so that their spores are spread in their dung.

Animals known to eat truffles include pigs, meerkats, grizzly bears, chacma baboons and a shy, elusive marsupial called the long-footed potoroo.

A short history of highs

Anandamide is part of a brain-body communication network called the endocannabinoid system, which plays vital roles in mental states and a wide variety of bodily functions.

The high generated when someone takes cannabis is the result of THC activating cannabinoid receptors. By acting on the same receptors, anandamide can trigger mood changes but does not generate a comparable high because it breaks down quickly in the body.

During the 1960s scientists puzzled over how opiate drugs such as morphine, opium and heroin could have such powerful effects on humans when they are derived from plants. They suggested they must act by binding to specific receptors, and that if these existed there must be similar chemicals produced within the body that act on the same receptors.

Molecules called enkephalins which have similar pain-killing properties to morphine and which function via the same receptors were discovered in 1975.

This led other researchers to look for the receptors affected by other drugs, and in 1988 those on which THC act were identified.

Again researchers reasoned there must be a compound produced within the body that could act on these receptors, and in 1992 Raphael Mechoulam, an Israeli chemist, identified this as anandamide.

Other research has shown the substance can induce forgetfulness in animals. US scientists found pigs given it walked less and lay down more.

The black truffle, also known as the Périgord truffle, is the second-most commercially valuable species after Italy’s white truffle.

Maccarrone added that his group is considering testing other species for the presence of anandamide.