New York, March 7 (IANS): The anxiety-relief effects of marijuana are well known but scientists have found for the first time, how the controlled use of the drug may help people in distress.

Sachin Patel, a professor of psychiatry and molecular physiology at Tennessee-based Vanderbilt University identified cannabinoid receptors in the brain through which marijuana exerts its effects.

The cannabinoid receptors are located in a key emotional hub in the brain involved in regulating anxiety and the flight-or-fight response.

"The discovery may help explain why marijuana users say they take the drug mainly to reduce anxiety," Patel said.

Led by first author Teniel Ramikie, a graduate student in Patel's lab, the researchers also showed for the first time how nerve cells in this part of the brain make and release their own natural 'endocannabinoids'.

The endocannabinoid system consists of an array of endogenously produced bioactive lipids that activate cannabinoid receptors.

The study "could be highly important for understanding how cannabis exerts its behavioural effects," Patel said.

While cannabinoids can reduce anxiety, chronic use of the drug down, regulates the receptors, paradoxically increasing anxiety.

This can trigger "a vicious cycle" of increasing marijuana use that in some cases leads to addiction.

In the study, the researchers used high-affinity antibodies to 'label' the cannabinoid receptors so they could be seen using various microscopy techniques which allowed very detailed visualisation at individual synapses or gaps between nerve cells.

"We know where the receptors are, we know their function and we know how these neurons make their own cannabinoids," Patel said in the paper published in the journal Neuron.