Providing straightforward information pertaining to drugs, drug use & drug policy. The Grey Pages promotes drug-related literacy and advocates a system of viable and tolerant drug policies. This is my personal collection of commentaries, essays, tid-bits, and other such writings on everything ranging from drug use, drug policy and drug-myths, to drug-science, addiction, human behavior, and the workings of the human brain. I started this blog with a particular focus on opioids, and over the past year have found my interest gravitate toward the intriguing, ever-changing world of designer intoxicants (i.e. "research chemicals" or "designer drugs").

Tuesday, February 8, 2011

Opioid Receptors Part I

Basic (Revised)

For more detailed information, see pharmacology page.

Opioid receptor density in human brain

Opioid receptors are found throughout the peripheral and central nervous systems. Receptors are located at the end of neurons both pre and post synaptically. They are distributed throughout the peripheral nervous system in smooth muscle tissue, and centrally within the spinal cord, brainstem, midbrain, and cortex. In addition to causing positive changes in mood, heavily mediated by dopamine activity within the lymbic system, opioids are effective in relieving pain, produced by their binding with receptors throughout the CNS.

Types & Function

Mu Receptors

Mu 1 - Analgesia, Euphoria, Limbic Reward, Anxiolysis, Physical Dependence, Sedation

Mu 2 - Respiratory Depression, Constipation, Pruritis, Bradycardia, Miosis, Spinal antinociception

Mu 3 - Unknown. Responds exclusively to alkaloids.

Mu receptors are located throughout the spinal cord, brainstem, midbrain, cortex, peripheral neurons throughout smooth muscle organ tissue (gastrointestinal tract). Mu1 receptors are extensively distributed throughout areas of the brain & midbrain where they inhibit perception of pain & response to pain, while mu2 receptors are distributed more throughout the spinal cord and brainstem where they affect transmission of pain.

Delta Receptors

Still Largely unknown; Analgesia, Anxiolysis, Modulation of mu-opioid analgesia & physical dependence, Antidepressive-Regulation of Mood, Tolerance Development, Respiratory Stimulation, Increase in BDNF. Located primarily in the brain. Located primarily throughout the brain, and peripheral nervous system.

Kappa Receptors

Negative feedback of mu activity, sedation, dysphoria, psychotomimesis, spinal analgesia, Diuresis, Miosis. Located in the brain, spinal cord, and peripheral nervous system. May play a compensatory role in modulating opioid addiction. Kappa activity has an inhibitory effect on mu activity, making high kappa affinity an undesireable trait in an opioid (for most purposes) The exception being antagonist properties at kappa receptors.

Receptor-Selectivity profiles of some common opioid peptides and alkaloids.
A lower nM value indicates a higher affinity.

Mu receptor distribution
Throughout the brain

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