Chapter 3: Chemistry of Behaviour

Question 1

What does it mean to say that the brain is an electro-chemical system?

Answer 1

The brain uses both electric activity (to process information WITHIN a neuron) and chemical activity (to process information BETWEEN neurons)

Question 2

What is the difference between an endogenous substance and an exogenous substance?

Answer 2

Endogenous means the substance originated in the body. Exogenous means that it came from outside the body.

Question 3

What happens when an action potential reaches the axon terminal?

Answer 3

The action potential depolarizes the terminal and triggers the opening of voltage gated Ca2 channels. the Ca2 triggers the synaptic vesicles to migrate to the presynaptic cell membrane, fuse, and rupture, releasing neurotransmitters into the synaptic cleft.
The neurotransmitters briefly bind to the postsynaptic receptor and then are either broken down by enzymes in the cleft or brought back to the presynaptic cell to be recycled.

Question 4

What are the two categories of receptors?

Answer 4

ionotropic receptors: a receptor protein containing an ion channel that opens when the receptor is bound by an agonist.

Metabotropic Receptor: does not contain an ion channel, it uses a second messenger system to open nearby ion channels or produce other effects. Metabotropic receptors use g-proteins to communicate.

Question 5

What are the qualifications of a neurotransmitter?

Answer 5

• It can be synthethesized by the presynaptic neuron
• It is released when action potentials reach the axon terminals
• It is recognized by specific receptors in the post synaptic cell
• It causes changes in the postsynaptic cell
• blocking its release interferes with effects on the postsynaptic cell.

Question 6

What are the different families of neurotransmitters, the characteristics of the family, and examples of each?

Answer 6

Amino-acid transmitters: the transmitter is an amino acid. E.g. GABA, glutamate, histamine

Peptide Neurotransmitters: the transmitter is made from chains of amino acid. Opioid peptides are a subclass of peptide neurotransmitters. e.g. oxytocin

Amine Neurotransmitters: the transmitter is made from modified amino acids. e.g. serotonin, norepinephrine, acetylcholine, dopamine

Gas Neurotransmitters: soluble gases that diffuse between neurons e.g. nitric oxide, carbon monoxide

Question 7

Describe the characteristics of the following neurotransmitters:

• Acetylcholine
• Dopamine
• Serotonin
• Norepinephrine

Answer 7

1. Acetylcholine: affects learning and memory, loss is associated with Alzheimer’s. Found primarily in the basal forebrain
2. Dopamine: found primarily in the midbrain and basal forebrain. Has two main pathways with different functions:
   - The mesostriatal pathway: moves from the substania nigra in the midbrain to the basal ganglia. This pathway is implicated in motor control.
   - the mesolimbocortical pathway: starts in the ventral tegmental area of the midbrain and projects through the limbic system and cortex. It is implicated in our reward pathway.
3. Serotonin: originates in the midline of the midbrain and brain stem in an area called raphe nuclei. Influences behaviour such as mood, anxiety, and sleep
4. Norepinephrine: originates in the locus coeruleus and lateral tegmental area of the midbrain and brainstem and spreads through the cereburm, cerebral cortex, limbic system, and thalmic nuclei. Affects alertness, mood, sexual behaviour, and more.

Question 8

What are the characteristics of gaseous neurotransmitters; how are they different than other neurotransmitters?

Answer 8

They are not produced in the axon terminals nor are they contained in vesicles

they do not use postsynaptic receptors

they use retrograde transmission: they can move backwards across the cleft into the presynaptic neuron to affect its functioning

Question 9

What is the difference between an agonist and antagonist?

Answer 9

An Agonist is a substance that acts like a neurotransmitter. If something is having an agonist affect, it is increasing the effect of the neurotransmitter.

An Antagonist is a substance that reduce the normal action of a neurotransmitter (e.g. blocking or partially blocking the receptors). An antagonist effect is something that decreases the effect of a neurotransmitter

Question 10

What does it mean to say that a drug is bioavailable?

Answer 10

It means the drug is present in a form that is able to interact with physiological mechanisms

Question 11

What is a biotransformation?

Answer 11

Biotransformation is when the drug is processed by enzymes which transform the drug into metabolites. the metabolites are capable of acting in ways quite different than the original substance. This can cause some of the side effects associated with drugs.

Question 12

Drug affects depend on which two factors?

Answer 12

Affinity –> the degree of chemical attraction between the ligand (drug) and the receptor

Efficacy –> how good the drug is at activating the receptor

Question 13

What is Tolerance and what are different types?

Answer 13

Tolerance is the reduced effectiveness of a drug due to repeated exposure.
–> metabolic tolerance is when our body becomes too effective at eliminating the drug.
–> Functional tolerance is when the target tissue shows altered sensitivity to the drug due to changes in the number of receptors
Neurons can down regulate (make fewer receptors available) in response to agonist drugs.
Neurons can up regulate (make more receptors available) in response to antagonist drugs

–> cross tolerance is when our tolerance to a drug extends to other drugs in the same class.

Question 14

What are ways that drugs can affect presynaptic mechanisms?

Answer 14

They can:

• affect the amount of transmitter produced
• affect the amount of transmitter released by acting on autoreceptors (receptors that monitor the amount of transmitters released)
• affect the clearance of the transmitter in the cleft

Question 15

What are ways that drugs can affect postsynaptic mechanisms?

Answer 15

They can:

• be agonistic and mimic neurotransmitters
• be antagonistic and block receptors
• alter intercepllular processes such as the number of receptors or the activity of second-messenger systems

Question 16

What are the the uses of Antipsychotic drugs and how do they work

Answer 16

• Antipsychotics: used to treat schizophrenia. First generation drugs were selective antagonists of D2 receptors (receptors for dopamine). They were good at treating positive symptoms (things added to behaviour). Atypical antipsychotics block 5-HT (serotonin) receptors. Good at treating negative symptoms (things that were taken away from behaviour) which were resistant to the first generation of drugs.

Question 17

What are the different classes of drugs?

Answer 17

• Antipsychotics
• Antidepressants
• Anxiolytics
• Stimulants
• Opiates
• Cannabinoids

Question 18

What are the uses of Antidepressants and how to they work?

Answer 18

Used to treat affective disorders.
Monoamine oxidase (MAO) inhibitors work to prevent the breakdown of monoamines such as serotonin and dopamine, therefore prolonging neurotransmitter activity
Tricyclic antidepressants block the reuptake of serotonin and norepinephrine
SSRIs selectively block the reuptake of serotonin

Question 19

What are the uses of Anxiolytics and how do they work?

Answer 19

Used to treat anxiety symptoms

• Depressants reduce nervous system activity
• Barbiturates were early forms of anxiolytics. They are highly addictive and easy to overdose on
• Benzodiazepines are a newer form. They are GABAa agonists in that they bind to the receptors and increase the level of attraction to GABAa. They are also very addictive (e.g. ativan)

Question 20

What are the uses of stimulants and how do they work?

Answer 20

Stimulants increase the activity of the nervous system (such as raising heart rate and blood pressure, increasing digestive action, and alertness.
e.g. Nicotine is an agonist to the ACh receptor in the VTA (dopamine reward system) It can enhance some cognitive effects in the short term but is addictive.

Question 21

What are the uses of opiates and how do they work?

Answer 21

Opiates can be used as strong painkillers. Examples include morphine, fentanyl, and heroin. They bind to opioid receptors

Question 22

Cocaine: What type of drug is it, how does it work and what are it’s basic effects

Answer 22

Cocaine is a stimulant
It blocks dopamine transporters that remove excess dopamine from the synaptic cleft. This leaves the dopamine in the cleft longer and leads to it overstimulating the post synaptic cell.
It activates the reward pathway and can affect our voluntary movement leading to fidgety behaviour.

Question 23

Methamphetamine: What type of drug is it, how does it work and what are it’s basic effects

Answer 23

Meth is a synthetic stimulant that mimics dopamine. Dopamine transporters that remove the excess dopamine from the cleft, instead pick up the meth molecules. Once inside the cell, meth enters the dopamine vesicles, forcing the dopamine out. The dopamine loose in the cell triggers the dopamine transporters to work in reverse and pump the dopamine into the synapse where it is trapped and binds repeatedly to the receptors, overstimulating the cell

Question 24

Heroin: What type of drug is it, how does it work and what are it’s basic effects

Answer 24

Heroin is a type of opioid. In a undrugged brain, inhibitory neurotransmitters work to prevent dopamine from being released. Endogenous opiates can temporarily block these inhibitors to trigger the release of dopamine. Heroin mimics these endogenous opiates and triggers an uncontrolled release of dopamine.

Question 25

Alcohol: What type of drug is it, how does it work and what are it's basic effects

Answer 25

Is a depressant. GABA is an inhibitory transmitter that controls neuroactivity. When it is bound to a receptor, the cell is less likely to fire. Glutamate is an excitatory transmitter that makes the cell more likely to fire Alcohol interacts with GABA receptors to make them MORE inhibitory AND it binds to glutamate receptors to prevent glutamate from exciting the cell. It particularly affects areas of the brain involved in memory, decision making, and impulse control

Question 26

Marijuana: What type of drug is it, how does it work and what are it's basic effects

Answer 26

Is a cannabinoid drug. THC, the active ingredient in Marijuana, Mimics anandamide, a transmitter that blocks the release of inhibitory transmitters. When THC is in the system it blocks the release of the inhibitory neurotransmitters and allows the uncontrolled release of dopamine. THC doesn't break down as fast as anandamide and therefore produces a high feeling of being relaxed and calm and slow.

Question 27

LSD: What type of drug is it, how does it work and what are it's basic effects

Answer 27

Is a hallucinogenic Acts exclusively on serotonin receptors. It mimics serotonin, binding to the receptors. LSD interacts with particular serotonin receptors but not always in the same way, sometimes it is excititory, other times it is inhibitory. This is why LSD has complicated sensory effects and can explain why some people have a "bad trip". Hallucinogenics excite the locus coeruleus (LC) and area of the brain that interacts with our sensory systems.

Question 28

MDMA: What type of drug is it, how does it work and what are it's basic effects

Answer 28

Also called ecstasy, is a hallucinogenic. Is taken up by serotonin transporters (more readily than serotonin itself). This causes the transporters to work in reverse and propel serotonin back into the synapse where it is trapped and repeatedly binds to the receptors, overstimulating the cell. MDMA affects serotonin pathways responsible for mood, sleep, perception, and appetite. It also indirectly interacts with te reward pathway, making it slightly addictive.

Question 29

What is the difference between addiction and substance abuse?

Answer 29

Addiction is a dependence on the substance and is a severe disorder. Substance abuse is a pattern of substance use that is unhealthy but does not meet the full criteria for addiction.

Question 30

What are four basic models of substance abuse?

Answer 30

Moral model: addiction is the result of weak character. Disease Model: addiction is a medical condition Physical dependence model: we continue to consume substances to avoid withdrawal symptoms Positive Reward Model: addiction arises because the substances cause a powerful reinforcement

Question 31

What areas of the brain are associated with addiction?

Answer 31

The VTA or reward pathway is indicated in addictive behaviour As is the insula region in the frontal cortex A

Question 32

What are some ways that medication can be used to treat addiction?

Answer 32

Medications can be used: - as agonists of the addictive drug (that are nonaddictive or not as harmful as the drug itself) - As antagonists to the addictive drug (that prevent the drug from being effective - to block the reward system and prevent the rewarding reinforcement of the drug - to reduce the craving of the drug.