Psychopharmacology

Question 1

Drugs and the synapse

Answer 1

various substances such as toxins and psychoactive chemicals alter synaptic transmission

Question 2

synaptic sequence

Answer 2

1. strong stimulation leads to impulse
2. action potential is propagated further down the axon
3. when the action potential reaches the axon terminal, this initiates synaptic transmission, it interacts with neurotransmitter vesicles, pushing them towards the membrane

Question 3

synaptic transmission

Answer 3

1. once the vesicles containing the neurotransmitter reach the membrane, they open up and the neurotransmitter is released into the synaptic cleft
2. the neurotransmitter then binds to its receptors in the postsynaptic neuron, opening the channel
3. as a consequence ions enter the postsynaptic neuron, resulting in a postsynaptic potential

Question 4

neurotransmitter inactivation and recycling

Answer 4

1. diffusion - transmitter is lost in the intracellular space
2. enzymatic degradation - enzymes break down the transmitter
3. reuptake - the transmitter is recycled either in the presynaptic or postsynaptic neuron, most economical way to inactivate the transmitter as saves synthesis resources

Question 5

substances can influence different phases of the synaptic sequence

Answer 5

1. some act as early as the propagation of the action potential
2. others may influence the release of the transmitter
3. others modulate how the transmitter interacts with the postsynaptic channels
4. finally, some alter the presence of the transmitter in the synapse by modulating its inactivation and recycling

Question 6

some chemicals interfere with the signals going through the axon

Answer 6

1. by blocking the sodium channels in the axon’s membrane e.g. TTX
2. TTX can produce paralysis of the diaphram and death due to respiratory failure

Question 7

substances can interfere with the release of the transmitter

Answer 7

1. the tetanospasmin toxin interferes with the vesicles of GABA fusing with the cell membrane
2. this reduces the amount of GABA released into the synapse
3. because GABA is an inhibitory neurotransmitter this results in an imbalance between excitation and inhibition neural signals
4. this leads to a very strong uncontrollable muscle contractions which can be lethal
5. acetylcholine is a neurotransmitter that has two types of receptors - nicotinic (excitatory) and muscarinic (inhibitory)
6. botulinum toxin (formed by bacteria in improperly canned food) interferes with the release of acetylcholine at nicotinic synapses, by preventing the vesicles from fusing with the cell membrane
7. this toxin is used in botox

Question 8

substances can enhance the release of the transmitter

Answer 8

1. amphetamine is very similar in structure to the neurotransmitter dopamine
2. due to its similarity to dopamine, amphetamine can enter the dopamine-releasing neuron either directly through the membrane or by binding to the dopamine transporter
3. once inside the cell, amphetamine facilitates the release of dopamine from the vesicles when these fuse with the membrane

Question 9

amphetamine and other drugs have a profound effect on dopamine pathways in the brain

Answer 9

1. one pathway is seen as particularly crucial in explaining the potent effects of these drugs, the projections from the ventral tegmental area to nucleus accumbens
2. VTA and nucelus accumbens are thought to be involved in pleasure, reward and motivation

Question 10

substances can alter how the transmitter interacts with its receptors

Answer 10

1. certain substances simply bind to receptors without opening the channel, blocking the way of the neurotransmitter
   e.g. curare occupies acetylcholine’s receptors in excitatory synapses, blocking them and causing paralysis
2. antagonists imitate the behaviour of the neurotransmitter, thus increasing its effect
3. heroin is an agonist of endorphins

Question 11

drug influence on transmitter inactivation and recycling

Answer 11

1. the reuptake of neurotransmitters into the original cell is done by specialised proteins, transporters
2. cocaine blocks the transporter of noradrenaline and dopamine thus interfering with their reuptake and boosting their effect

Question 12

chocolate

Answer 12

1. has been found to contain several psychoactive compounds
2. including anandamide - neurotransmitter produced naturally by the brain, whose agonist is THC
3. another is phenylethylamine - a compound closely related to amphetamine
4. however such small amounts that it wouldn’t cause a noticeable effect

Question 13

coffee

Answer 13

1. caffeine competes with adenosine for its receptors, which inhibits release of catecholamines
2. caffeine also has a non-synaptic effect in neurons
3. it acts on cyclic adenosine monophosphate which controls the energy levels in the cell via the regulation of glucose metabolism
4. caffeine inhibits the enzyme that breaks down cAMP, increasing glucose metabolism in cells

Question 14

alcohol

Answer 14

1. in low doses, alcohol is an agonist of GABA so alcohol increases effectiveness of inhibitory synapses leading to a feeling of relaxation, also indirectly stimulates dopamine release, hence euphoria
2. in moderate amounts, alcohol also indirectly increases the release of endorphins
3. in high doses, the binding of alcohol to GABA channels leads to powerful inhibition and sedation
4. in very high doses, alcohol leads to the destruction of cell membranes and brain cell death

Question 15

anxiety and gaba

Answer 15

1. anxiety disorders are in part characterised by deficits in GABA-ergic transmission
2. Benzodiazepines are GABA agonists used to treat anxiety disorders
3. they bind to different sites on gaba recepors than alcohol
4. also non competitive agonist as they don’t bind to the same receptor sites as GABA

Question 16

depression

Answer 16

1. depression is associated with reduced neurotransmitter transmission
2. MAO inhibitors - interfere with MAO enzyme which breaks down serotonin, dopamine and noradrenaline
3. tricyclic antidepressants - inhibit the transporter of serotonin, dopamine, noradrenaline by preventing reuptake

Question 17

side effects

Answer 17

the drugs affect lots of systems because the neurotransmitters are involved in loads of functions, meaning they can have unwanted effects

Question 18

depression and serotonine

Answer 18

1. has been found that serotonin is the neurotransmitter closely linked to depression
2. SSRIs inhibit transport of serotonin without affecting other neurotransmitters

Question 19

schizophrenia and dopamine

Answer 19

1. schizophrenia is associated with surplus of dopamine
2. its symptoms include paranoia and hallucinations
3. neuroleptics - antipsychotic drugs that block the transmission of dopamine by binding to dopamine receptors without opening ion channels
4. they are dopamine antagonists

Question 20

cocaine

Answer 20

cocaine blocks the transporter of noradrenaline and dopamine, interfering with their reuptake and boosting their effect

Question 21

methamphetamine and amphetamine derivatives

Answer 21

1. as cocaine, these substances reduce the reuptake transport of neurotransmitters
2. they also attach to enzymes that break down these neurotransmitters
3. the overall effect is a boost in neurotransmitter transmission
4. by increasing dopaminergic transmission, they can induce schizophrenia like symptoms in high doses
5. the medication for parkinson’s and schizophrenia push dopamine in the opposite direction and can cause each other’s symptoms in high doses

Question 22

conclusions

Answer 22

1. psychoactive substances act at different stages of the synapse
2. they can affect pre-synaptic processes - axonal conduction, release
3. as well as post synaptic processes - binding to receptors, transmitter breakdown, transmitter reuptake
4. psychoactive substances that bind to receptors, imitate the molecular structure of some endogenous substances in order to fit the receptor like a key fits the lock