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SAQ sample: Agonists

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  • SAQ sample: Agonists

The following sample is for the question: Explain the role of one agonist with reference to one study.  

There are two ways to answer this question.  Neurotransmitters are endogenous agonists - that is, they bind with receptor sites on the post-synaptic neuron and cause an action potential. Drugs are exogenous agonists.  They act in the same way, but they are not natural in our nervous system.

The sample below is an exemplary response using an exogenous agonist.

What is this question asking?

  • The focus of the question is on the explanation of how agonists work.
  • A relevant study should be described in terms of the aim, procedure, and findings.
  • There should be an explicit explanation of what the study teaches us about the role of the agonist in human behaviour.

Sample response

An agonist is any chemical that binds to a receptor site on a post-synaptic neuron, causing the neuron to fire. Neurotransmitters are endogenous agonists - the brain's natural chemicals that bind to receptor sites, leading to an action potential. Drugs can play the same role and are called exogenous agonists.  One example of an exogenous agonist is alcohol.  Alcohol binds with dopamine receptor sites, causing dopamine neurons to fire. The firing of these neurons results in the activation of the brain's reward system - the nucleus accumbens. 

The study of the role of alcohol on the brain's reward system has led to theories about the origins of alcoholism. Leyton (2013) carried out a study with 26 healthy social drinkers. The researcher then categorized the drinkers based on their risk for alcoholism based on personality traits and having a lower intoxication response to alcohol - that is, they did not feel as drunk despite having drunk the same amount as other drinkers. Each participant underwent a PET scan after drinking either juice and then later, alcohol. In each condition, they were asked to drink three drinks in 15 minutes.

It was found that when drinking alcohol, those who were considered "high risk" for alcoholism showed significantly greater activity in the nucleus accumbens.  The researchers argued that alcohol is an agonist for dopamine, connecting to dopamine receptor sites and causing the neurons to fire. It is hypothesized that people with a potential for alcoholism have a greater response to the agonist than those at low-risk.  Research shows that those with a low level of dopamine neuron activity as a result of alcohol consumption often get tired after drinking a small amount of alcohol.  This is because the higher level of dopamine activity counteracts the sedative effects of alcohol.  By studying the way in which alcohol acts as an agonist on dopamine neurons, it is also possible that researchers could find ways to treat the disorder.

323 words

What are common problems when answering this question?

  • There is no clear definition of agonists - or a clearly identified example.
  • The study is not clearly described in terms of the aim, procedure and findings.
  • There is no clear explanation of what the study teaches us about the role of the agonist in understanding the brain and behaviour.

A note about Leyton et al (2013)

Just a reminder that students are not penalized for having the wrong name of a study - or the wrong year.  And thank god!

When looking for this study, it is sometimes cited as Leyton (2013), including in a biopsychology textbook that I use.  However, the publisher's citation is as follows:

Elaine Setiawan, Robert O. Pihl, Alain Dagher, Hera Schlagintweit, Kevin F. Casey, Chawki Benkelfat, Marco Leyton. Differential Striatal Dopamine Responses Following Oral Alcohol in Individuals at Varying Risk for Dependence. Alcoholism: Clinical and Experimental Research, 2013; DOI: 10.1111/acer.12218