Reward Pathway in Brain Flashcards
Brain reward pathway
Dopamine released from VTA of midbrain, o VTA sends dopamine to the amygdala (controls emotions), nucleus accumbens (NAcc , controls motor functions), prefrontal cortex (focus attention and planning), and hippocampus (part of the temporal lobe, involved in memory formation).
o NAcc, amygdala and hippocampus are part of the mesolimbic pathway.
Dopamine and serotonin relationship
• At same time dopamine goes up (increase sense of euphoria), serotonin goes down.
o Serotonin - partially responsible for feelings of satiation. So if serotonin goes down, you are less likely to be satiated or content.
• Evidence of reward pathway/biological basis of drug dependence:
• Evidence of reward pathway/biological basis of drug dependence: Comes from animal models
o Scientists gave rats hooked up IV that gives them cocaine if they push a lever. When the rats do this, the rats learn quickly to push the lever. Rats will seek the drug and also will try to increase dosage if allowed.
• Addiction/reward pathway takes over rational choices. Negative consequences paired with drug don’t affect the brain.
o Animal model:
If you give a non-addicted rat regular food it likes with a substance that makes it sick, the rat learns to avoid the food. It stops liking it.
If you give an addicted rat its favorite drug paired with a substance that makes it sick, it still wants that drug. I don’t care! I need the reward!
• Addiction has physiological components as well
o Increased genetic risk – if someone in your family has drug addiction, you have an increased risk as well.
o Environment/your choices make a difference too.
• Tolerance
Tolerance is a rightward shift in the dose-response curve that causes decreased sensitivity to a drug due to repeated exposure.
• Cross tolerance
• Cross tolerance - is a reduction in the efficacy or responsiveness to a novel drug due to a common CNS target.
withdrawal
o Withdrawal is when you stop after using for prolonged time. We get withdrawal symptoms. Can become sick or ill, or it can be fatal (depending on the substance/drug)
Two Stages: acute and post acute
• Acute (- physical withdrawal symptoms, different for each drug/person). For alcohol, only 2 days after cessation of consumption, improvement seen 4-5 days.
• Post Acute (fewer physical symptoms, more emotional/psychologic symptoms, same symptoms for everyone)
o Common symptoms: (PAWS – Post acute withdrawal symptoms) Mood swings, Anxiety, Irritability, Tiredness, Variable energy, Low enthusiasm, Variable concentration, Disturbed sleep
intoxication
when drug enters body and exerts effect on somebody
o Intoxication refers to behavioural and psychological effects on the person. These are drug-specific.
o Post-acute withdrawal
o Post-acute withdrawal feels like a rollercoaster of symptoms. (In the beginning, your symptoms will change every hour. Later as you recover further they will disappear for a few weeks or months only to return again. As you continue to recover the good stretches will get longer and longer. But the bad periods of post-acute withdrawal can be just as intense and last just as long.)
o Each post-acute withdrawal episode usually last for a few days.
o Post-acute withdrawal usually lasts for 2 years.
o Can be trigger for relapse
substance-induced disorders
substance-induced disorders – conditions that are caused by post-acute withdrawal or use of substance. Can be substance induced mood disorders (high mood -mania/low mood - depression), or disorders related to anxiety, sleep, sexual function, psychosis (loss of contact with reality, characterized by seeing things, hearing voices, becoming paranoid).
substance-use-disorders
- post-acute withdrawal can lead to substance-use-disorders - Occurs when use the drug causes a serious/real degree of impairment in functioning in life, at work, school, or home. Not everyone experiences this
- With caffeine, only drug for which we can’t develop substance-use disorder.
o How do you know someone has a substance use disorder
- usage/dependence
- withdrawal – start feeling sick or unwell (after having stopped using drug). Suggests you’re physiologically dependent. Can be dangerous (ex. alcohol withdrawal can lead to seizures which can lead to death). Withdrawal is specific to the substance.
- tolerance – your body adapts or builds a tolerance to the substance. Effect decreases with equal dose. They increase dose to get same level of intoxication.
Alcohol withdrawal:
Withdrawal symptoms can begin as soon as blood alcohol concentrations decline sharply. This often occurs within four to twelve hours after alcohol consumption has stopped. Symptoms of alcohol withdrawal can be alleviated through the use of benzodiazepines. Typically, acute withdrawal symptoms reach their peak two days after the cession of alcohol consumption and improve within four or five days. Peak of symptoms is around 2 days ~ and then start showing improvement 4-5 days.
Drug Addiction Treatments (meds)
- Hospitalization (rapid detoxification) - give a bolus of drug antagonist and general anesthetic to experience withdrawal while sleeping
- detoxification (detox) – separating addict from the drug. Sometimes require strong medications for strong addictions (have to break the addiction cycle). Often have to address symptoms such as vomiting, nausea, pain, etc.
o Ex. Opioids such as heroine act at neural receptor site for endorphins to reduce pain and give euphoria (a highly addicting substance). Methadone (given p.o at clinic) activates opiate receptors, but acts more slowly, so it dampens the high. Reduces cravings, eases withdrawal, and if heroine is taken the user can’t experience the high because receptors are already filled with longer-acting methadone.
- nicotine- patches/gums
- alcohol - meds block receptors in reward system of alcohol. Also reduce symptoms of withdrawal and cravings. Reduce withdrawal symptoms such as anxiety, insomnia, and dysphoria (dissatisfaction with life)). Important to prevent relapse during this early stage by minimizing negative symptoms.
