what are opioid receptors

what are opioid receptors

We have heard the term for years: “the opioid crisis.” It has ripped through our Appalachian communities, taking away sons, daughters, aunts, fathers, and friends while leaving many loved ones behind with heartache. It’s hard for them to understand why opioids seem more important than the people around them. The science behind what is going on within the brain while taking opioids provides an understanding of the opioid crisis, and how we can help.

In 2022, over 3,000 drug overdose deaths were caused by opioids in Tennessee. At ReVIDA® Recovery, we understand the devastation opioid overdoses have caused and work to educate our communities on subjects surrounding opioid use disorders. Our program offers medication-assisted treatment (MAT) because we have seen firsthand the significant impact it has in helping our patients find recovery. But what leads to the development of opioid use disorders? What are opioid receptors, and do they tell the brain to keep taking opioids?

Opioid Receptors – What Are They?

Opioid receptors are classified as G protein-coupled receptors (GPCR). The responsibility of opioid receptors is to mediate responses to hormones, substances, and neurotransmitters. They are located in the brain stem, thalamus, cortex, dorsal horn of the spinal column, and in the gray matter of the brain. There are different types of opioid receptors that interact with the two different types of opioids – endogenous and exogenous. Endogenous opioids refer to neurotransmitters and hormones already within the body, such as endorphins and enkephalins. Exogenous opioids refer to outside introductions, such as ingesting morphine or fentanyl. 

What Functions Do Opioid Receptors Serve in the Brain?

As we mentioned above, there are different types of opioid receptors. The first are mu receptors (MOR), and there are 3 subtypes that have distinct functions. Second are kappa receptors (KOR) which also have 3 subtypes. Next are delta receptors (DOR) which have 2 subtypes. Lastly, nociceptin receptors (NOR) and zeta receptors (ZOR) round out the core opioid receptors and have no subtypes. Let’s explore these receptors’ functions further”

Mu receptors – the mu receptors bind with endogenous opioids including beta-endorphin and endomorphin 1 and 2. The mu 1 receptor is responsible for dependence and the inability to feel pain. The mu 2 receptor plays a key role in euphoria, dependence, decreased respiration, and reduced peristalsis in the gastrointestinal tract (the contraction of intestines to move waste). The mu 3 receptor causes the widening of the blood vessels, known as vasodilation.

Kappa receptors – the main responsibility of the 3 kappa receptors is to bind to dynorphins A and B. This causes the inability to feel pain, increased urination, and increased feelings of anxiety or dissatisfaction with life.

Delta receptors – binding to enkephalins, delta receptors contribute to the inability to feel pain and reduce peristalsis in the gastrointestinal tract.

Nociceptin receptors – causing the inability to feel pain, nociceptin receptors bind to nociceptin/orphanin FQ. However, in certain concentrations, these receptors can cause hyperalgesia, a condition causing hypersensitivity to pain or an extreme response to pain.

Zeta receptors – zeta receptors are responsible for regulating developmental events in tissues and cells.

You may be thinking that this list does not mention exogenous opioids. When outside opioids like morphine or heroin are introduced into the system, the production of endogenous opioids halts. The morphine or heroin in the body binds to the opioid receptors, essentially replacing endogenous opioids. Endorphins and other neurotransmitters are released in the process, causing the above side effects. When exogenous opioids are not introduced into the body, natural events such as stress, pleasure from activities, and pain cause the release of neurotransmitters.

How Opioid Receptors Interact With the Brain and Body

Opioid receptors are responsible for creating the effects commonly associated with opioid use. Feelings of pleasure, euphoria, and relaxation come from opioid receptors activating within the brain. Respiratory depression results from opioid receptors in the central nervous system. This is where it is most common to experience an opioid overdose.

understanding opioid receptors and their function

How Opioid Receptors Are Affected by Opioid Use Disorders

Opioid receptors are responsible for how the brain responds to the exogenous introduction of opioids. As the opioid receptors become accustomed to having substances such as fentanyl, they begin to alter the production of naturally occurring neurotransmitters. This leads to the disruption of normal functioning in scenarios such as experiencing pain, sex, eating, and mental health responses. Over time, opioid receptors only respond to exogenous opioids and forego endogenous opioids.

Opioid Tolerance

As exogenous opioids take over opioid receptors, it will take more to activate them and produce the same effects. This is referred to as building an opioid tolerance. Opioids can enter a person’s life in different ways. They may have started with a prescription for codeine after back surgery but soon were taking it every day. Some may have tried heroin and found they liked it, leading to daily use. Others may have been exposed to fentanyl accidentally but continued to use it after the fact. No matter how someone began using opioids, the longer the use continues, the higher their tolerance will become. Opioid receptors will signal a need for opioids to be in the system.

Opioid Dependence

As tolerance builds, dependence begins to form. This is where people without opioid use disorders lose understanding as they can’t relate to what the person is going through. Opioid receptors naturally produce emotions and responses to uncomfortable sensations like pain but also pleasurable experiences like having sex or a delicious meal. External opioids take away those natural responses, and as tolerance builds, the person loses the ability to feel joy or stress relief naturally. They rely on morphine, heroin, or codeine to create these feelings within their mind. Between uses, those feelings go away, causing depression, lack of motivation, and even pain until they get another dose.

This is the cycle of opioid dependence, and it should be met with compassion if the person asks for help. The opioid receptors within their brain have been conditioned to expect external opioids, and even when the person wants to stop, the receptors respond with emotional instability. However, this does not mean that the person is incapable of stopping their opioid use. With therapy, medication-assisted treatment, and support from family and friends, it is completely reasonable for the person to find recovery from opioid use and for the opioid receptors within the brain to begin functioning normally again.

Opioid Withdrawal

Besides feelings of depression and emotional instability between opioid doses, opioid withdrawal encompasses physical symptoms as well. Runny nose, muscle aches, abdominal cramping, diarrhea, and joint pain are common during opioid withdrawal. Symptoms begin around 6-12 hours after the last use and can continue for up to 5 days. The peak of these symptoms is around 24-48 hours after the last use of opioids. It is critical that once the withdrawal process has begun to not return to use. Opioid receptors are in the early stages of healing, and reintroducing opioids will restart the process. The safest and most effective way to go through opioid withdrawal is through a compassionate, medical detox.

the role of opioid receptors in pain management

Finding Help for Addiction – Heroin and Other Opioid Use Disorders

Understanding opioid receptors gives insight into just how complex opioid disorders are. The brain becomes wired differently to expect outside opioid sources to create feelings of enjoyment and pain relief. The good news is the cycle of opioid dependence can be broken with the proper tools and treatment. Opioid addiction treatment begins with a detox that is supervised 24/7 to ensure comfort and safety. From there, the person can choose inpatient treatment, outpatient treatment, and a medication-assisted treatment component. No matter which program you choose, therapy and coping skill development will be the building blocks to healing and beginning the path to recovery.

If you or someone you love is managing an opioid use disorder, help is available today. ReVIDA® Recovery is here to offer a flexible outpatient program geared to fit the many schedules of our patients. We have locations throughout Tennessee and Virginia that offer same-day appointments, so there is no need to wait to begin treatment. Our team is here to help, and living opioid-free can begin right now. Call us today at 423-631-0432 to learn more about our program offerings.

Reclaim your life.