Melatonin is linked to fentanyl used on 900 theatre hostages during the Dubrovka crisis (see www.), as well as rhythms in fish, these rhythms signaling time to migrate which is another form of travel.
'The classification of cell surface adenosine receptors into two types is generally based on the ability of adenosine to stimulate or inhibit adenylyl cyclase.'
(Falcon J, Regulation of the Rhythmic Melatonin Secretion by Fish Pineal Photoreceptor Cells, in Rhythms in Fishes, Plenum Press)
These things are now being studied and manipulated in dark-grown salmon in aquaculture facilities in South Dakota.
Joggers know well the effects of enkephalin, post-running.
Enkephalin / Fentanyl / Opioid Receptors
Enkephalin / Pertussis-Cholera Toxin / Adenylyl Cyclase
Suggested viewing: The Matrix