The Rediscovery of N-Acylethanolamines

To determine whether anandamide meets the criteria of a neurotransmitter, my collaborators and I carried out a series of biochemical experiments using rat brain neurons in primary culture. We labeled the neurons in a medium containing radioactive etha-nolamine and stimulated them with a calcium ionophore or with 

Glutamate released from neuron A, excites neuron B and elicits a transient rise in intracellular calcium in astrocyte A. 

The calcium rise in astrocyte B may cause multiple effects, including release of glutamate, via reversal of the uptake system. This may in turn modify the excitability of neuron C. 

The calcium signal spreads into astrocyte B wagap junctions.This spreading cafdum wave) is blocked by anandamide. 

It turns out that our surprise at the finding of multiple NAEs was largely unwarranted. Actually, for many years it had been known that brain tissue contains such compounds they had been isolated first in 1963 by the laboratory of Sidney Udenfriend at the NIH and subsequently studied by Harald H.O. Schmid and collaborators at the Hormel Institute of the University of Minnesota (for review, see ref 31). In those studies no evidence had been found, however, for the natural occurrence of polyunsaturated NAEs (such as anandamide), probably because of technical difficulties in isolating minute amounts of these relatively unstable molecules. Technical problems may also explain why early studies did not uncover the stimulus-dependent generation of NAEs by neurons, which lead researchers in this area to conclude that NAE formation only occurred under conditions of conspicuous tissue damage, such as ischemia. 

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