2-Minute Neuroscience: Periaqeuductal Gray (PAG) Video Lecture | A-Z Guide to Neuroscience - Personal Learning

Welcome to 2 minute neuroscience, where I
explain neuroscience topics in 2 minutes or
less.
In this installment I will discuss the periaqueductal
gray, or PAG.
The PAG is an area of gray matter found in
a part of the brainstem called the midbrain.
The PAG surrounds a structure called the cerebral
aqueduct, hence the name “periaqueductal.”
There are a number of functions that have
been connected with the PAG, including the
regulation of heart rate and blood pressure,
management of autonomic processes like bladder
control and contraction, production of vocalizations,
and production of fearful and defensive reactions.
The PAG is best known, however, for its role
in analgesia, or pain reduction.
Since the 1960s, the PAG has been known to
play a role in analgesia, and stimulation
of the PAG has been observed to inhibit pain
in both rodents and humans.
The mechanisms underlying this PAG-induced
analgesia are not completely understood, but
the main pathway is thought to involve neurons
that project from the PAG to serotonin-producing
neurons of the medulla oblongata known as
the raphe nuclei.
These activated raphe nuclei neurons project
down to the dorsal horn of the spinal cord
where they inhibit neurons that are responsible
for transmitting pain signals.
In this way, they inhibit the ability of pain
signals to reach the brain.
Through this pathway, the PAG is thought to
be able to inhibit pain naturally---a phenomenon
that may occur, for example, in situations
of extreme stress like that experienced by
soldiers in battle.
The pathway may also be involved in analgesia
that occurs as part of the placebo effect,
or in other scenarios where we experience
a capacity to control pain through top-down
mechanisms.
Additionally, the PAG is rich in opioid receptors
and believed to play an important role in
the analgesia elicited by opioid drugs.