Neurotransmitters

What are neurotransmitters

They are chemical messengers that trasnmit signals between neurons in the brain and nervous system.

They play a crucial role in regulating mood, memory, learning, arousal and mental health.

What are some characteristics of neurotransmitters?

• Produced by neurons and released into the synaptic gap.

• Bind to specific receptor sites on the postsynaptic neuron to pass on the signal.

• Once neurotransmitters are used, they are either:

  • Broken down by enzymes (e.g., acetylcholinesterase breaks down acetylcholine)

  • Reabsorbed into the neuron in a process called reuptake.

What types of neurotransmitters exist?

1. Excitatory

   • increase the likelihood that the next neuron will send a signal.

   • Acetylcholine, dopamine, glutamine.

2. Inhibitory

   • decrease the likelihood of the next neuron will send a signal.

   • Serotonin.

How do neurotransmitters affect behavior?

• they are endogenous agonists

• Their effect on behavior include:

  1. Mood regulation (serotonin and dopamine in depression)

  2. Memory and learning (acetylcholine in spatial memory)

  3. Arousal and alertness (norepinephrine in flight or fight response)

  4. Mental health (imbalances on neurotransmitters are linked to disorders like schizophrenia, depression, and anxiety)

What kind of chemicals affect neurotransmission?

Agonists and Antagonists

What are agonists?

A chemical that enhances (amplifies) the action of a neurotransmitter.

BUT, NTs themselves are agonists for receptor sites, called ENDOGENOUS AGONISTS, since they are already in the nervous system and not an external chemical substance, and because neurotransmission is a chemical enhancing action→ an example of endogenous agonists is acetylcholine.

Drugs can also act as agonists. Since they are external to our system, they are referred to as EXOGENOUS AGONISTS. For example, nicotine is an agonist for AcH receptor sites and short-term appears to have some positive effects on memory.

What are the two types of agonists?

• Endogenous agonists → naturally occurring in the body (AcH)

• Exogenous agonists → drugs or substances that imitate neurotransmitters (nicotine)

What are antagonists?

A chemical that inhibits (reduces) the action of a neurotransmitter.

Antagonists are drugs that block the receptor site and do not allow the neurotransmitter to do its job, sending an action potential down the neuron.

Scopolamine is an antagonist for AcH.

Tell me about Acetylcholine

• A neurotransmitter involved in learning, memory, and muscle contraction.

• Found in the hippocampus, which is essential for memory formation.

• Higher levels of AcH enhances memory, while lower levels impair memory.

Tell me about nicotine.

Nicotine mimics AcH by binding to nicotinic acetylcholine receptors, leading to:

1. Enhanced cognitive performance (better attention and faster processing).

2. Increased dopamine release, making nicotine addictive.

3. Stimulation of the hippocampus, improving memory function.

Tell me about scopolamine.

Scopolamine blocks AcH receptors, preventing it from exerting its effect. Resulting in:

1. Memory impairment (difficulties in learning and recall)

2. Reduced hippocampal activity, as shown in brain imaging studies.

3. Cognitive deficits, making it useful for research on Alzheimer’s disease and amnesia.

What is the process of neurotransmission?

1. Synthesis → neurotransmitters aer produced within the neuron.

2. Release → they are released into the synaptic gap.

3. Binding → the bind to the receptors of the next neuron.

4. Effect → the signal is passed on (excitation or inhibition)

5. Termination →

   • Enzymatic breakdown (e.g., AcH is broken down by acetylcholinesterase)

   • Reuptake (e.g., neurotransmitters are reabsorbed into the presynaptic region)

What are the strengths of the neurotransmitter theory?

1. Strong empirical support → numerous controlled experiments demonstrate the role of neurotransmitters in behaviour.

2. Biological basis for behaviour → the theory explains how brain chemistry influences mental processes like memory, mood and decision-making.

3. Practical applications → helps develop drug therapies for mental health disorders:

   • SSRIs → increase serotonin for depression

   • Dopamine agonists → for Parkinson’s disease

   • Cholinergic drugs → for Alzheimer’s disease

4. Explains individual differences in behaviour → variations in NT levels help explain why some people have stronger memories, better focus, or higher stress resilience.

What are the limitations of the neurotransmission theory?

1. Indirect measurement → we cannot measure neurotransmitter activity; we rely on brain imaging and behavioural observations.

2. Bidirectional ambiguity → does low serotonin levels cause depression, or does depression reduce serotonin levels?

3. Reductionism → the idea that neurotransmitters alone determine behaviour ignores social, cognitive, and environmental factors.

4. Animal research limitations → may neurotransmitter studies are conducted on animals, which may not generalize to humans.

What studies help to support the neurotransmission theory?

• Antonova

• Roger & Kesner

Tell me about the study of Antonova.

Date: 2011

Aim: how neurotransmitters play a role in behaviour

Sample: twenty healthy male adults.

Conditions: randomly allocated into one of two conditions →

1. Group 1 → injected with Scopolamine 70-90 minutes before the experiment.

2. Group 2 → injected with a placebo 70-90 minutes before the experiment.

Procedure:

• put into an d fMRI where they were scanned while playing the “Arena Task”.

  • “Arena Task” →

    • Complex virtual reality game in which the researchers are observing how well the participants can ceate spatial memories.

    • The had to navigate through an arena to find a pole.

    • After they had learned where the pole was located, the screen would turn black for 30 seconds

    • During that time → had to rehearse how they found the pole.

    • After the 30 seconds → reappeared in a new location in the arena

    • They had to use their spatial memory to determine how to get to the location of the pole.

  • They first trained in the game to make sure they were familiar with the use of the joystick and that they understood the rules of the game.

• The took part in the game for six trials.

• They returned after 3-4 weeks and redid the test → they received the opposite treatment than originally (went to the other group).

Results: when injected with scopolamine, they demonstrated a significant reduction in the activation of the hippocampus compared to when they received a placebo.

Conclusion: AcH could play a key role in the encoding of spatial memories in humans.

How do you link this to the neurotransmission theory?

Link: provides insight on the role of neurotransmitters in cognitive processes. By examining the effects of acetylcholine in memory and attention, it highlights how fluctuations in neurotransmitter levels can impact brin function and behaviour.

Evaluate me the study of Antonova.

1. Without the use of fMRI there could be no way of knowing that there were significant differences in the biological level, since:

   • there was not significant differences in the rate of error between the two groups (even if the scopolamine group had a higher rate of error)

   • The difference in the hippocampus, though, was significant.

2. Repeated measure design → eliminates the effect of participant variability.

3. It was counter balanced → the ones that did the scopolamine group first then did the placebo group, and the opposite.

4. It was carried out blindly → controls for researcher bias.

5. During the debriefing, several participants expressed that they were feeling anxious (either because of the injection or because that they didn’t know what they were injected with), which could have affected the function of the hippocampus, as stress can affect memory encoding.

6. Small sample size → we can’t generalize the results, needs to be replicated to see of they are reliable.

Tell me about the study of Roger & Kesner.

Date: 2003

Aim: determine the role of acetylcholine in the formation of spatial memory.

Sample: 30 rats

Conditions: two conditions in which they were randomly allocated in.

1. Group 1 → injected with scopolamine 10 minutes before the experiment.

   • because an injection could increase adrenaline which would be a confounding variable, the injections were done directly in the hippocampus.

2. Group 2 → injected with a saline solution 10 minutes before the experiment.

Procedure:

• placed in a maze and they had to acclimate in it by finding the food in one of the corners.

  • Once they were familiar and no longer afraid in the maze the experiment could start.

Results: scopolamine group took longer and made more mistakes in the learning of the maze - that is, there was a higher average number of mistakes made on the last five trials on Day 1. However, it did not appear to affect the retrieval of memories that had already been created.

Conclusion: acetylcholine may play an important role in the consolidation of spatial memory.

How do you link this study to the neurotransmission theory?

Provides insight into the role of neurotransmitters in memory formation. By investigating the effects of AcH on spatial memory in rats, their study demonstrates how this neurotransmitter is necessary for the encoding and retrieval of memories.

Evaluate the study of Roger & Kesner.

1. Used a placebo, meaning they had a control group → avoid the effect of confounding variables.

2. Cause-and-effect relationship → though, it is reductionist in the concept of understanding memory → there are several different types of memory and the process of memory consolidation is very complex.

3. This research could lead to the development of treatments for diseases like Alzheimer’s.

4. Since it is an animal study it is difficult to generalize the results to humans.