Neurotransmitter

Question 1

What are the four criteria for a neurotransmitters

Answer 1

• (synthesis) The NT must be made in the pre-synaptic neuron
  -(storage) The NTs must be stored presynaptically with the exception of nitric oxide
  -(release) NTs must be released on demand
• (inactivation) The NT must be inactivated

Question 2

How are Neurotransmitters inactivated?

Answer 2

Through re-uptake into the neuron or by enzymal inactivation or diffusion.

Question 3

Name the three neurotransmitter classes

Answer 3

-Amino acids
-Biogenic amines (monoamines) which are divided into catecholamines and indolamines
-Peptides

Question 4

Name the three most common amino acid transmitters

Answer 4

Glutamate - Primary excitatory NT in the CNS.
GABA - Primary inhibitory NT in the CNS (acts via chloride channels)
Glycine - Seconday inhibitory NT in the CNS but primary NT in the spinal cord and brain stem.

Question 5

Name the three types of glutamate receptors and what class are these receptors

Answer 5

-NMDA receptor - permeable to calcium ions
-Kainate receptor - permeable to Na and K
-AMPA receptor - Permeable to cations (+ve)
These are ionotropic receptors.

Question 6

How is glutamate deactivated?

Answer 6

Via re-uptake and recycling into either glutamate or GABA

Question 7

Describe some of the functions and dysfunctions of Glutamate.

Answer 7

Synaptic Plasticity - Glutamate strengthens connections between synapses which is the basics for storing short and long term memories
Excitotoxicity - The excessive stimulation of NMDA receptors causes a large influx of calcium ions causing cell death.
Migraines - Visual auras seen as a symptom of migraines is closely linked to the glutamates implication in cortical spreading depression.
Epilepsy - Associated with the mass release of glutamate. This results in uncontrolled excitation spreading over areas of the brain. Can produce partial or Grand Mal seizures.

Question 8

What can seizures be treated with?

Answer 8

Phenytoin - This increases the refractory period in sodium gated channels
Benzodiazepines - increases the action of GABA (used because it is an inhibitory NT)

Question 9

Describe how benzodiazepines work?

Answer 9

The act on the modulatory site of the GABA molecule. It controls the ability of GABA channels to open (when bound, the GABA channel can open more). Therefore only enhances the action of existing GABA channels

Question 10

Describe some of the features of GABA NTs

Answer 10

• Primary inhibitor NT in the CNS. It also acts on areas that are involved in controlling the motor function in the periphery.
• Acts on ligand gated chloride channels
  -Inactivated by re-uptake

Question 11

Describe the associated of GABA in alcoholism and how withdrawal can be treated

Answer 11

Alcoholics have a large increase in GABA, when they go through withdrawal, the sudden decrease in GABA causes convulsions and seizures. So phenytoin and benzodiazepine can be used to treat these.

Question 12

Describe some of the features of Glycine

Answer 12

Secondary most common in NT in the CNS but the primary inhibitory NT in the brain stem and spinal cord.
- In Tetanus, the toxins released inhibits the release of glycine causing restriction to muscles from cranial nerves (in the case of mild) and epileticform seizures (in severe case). Treated with anti-toxin and benzodiazepine

Question 13

Name three catecholamines

Answer 13

Dopamine - Involved in plesure, addiction and movement
Noradrenaline - A sympathetic NT. Decrease in noradrenaline is associated with parkinson’s and ADHD
Adrenaline - Involved in the sympathetic NS but it is a peripheral hormone from the adrenal medulla.

Question 14

What are the regions noradrenaline is involved in?

Answer 14

Involved in sleep, wakefulness, alertness and attention
- Involved in feeding behaviour and blood pressure regulation

Question 15

What are the regions dopamine is involved in

Answer 15

-Motor control
-Behavioural effects -Endocrine control via the anterior pituitary

Question 16

Describe the effects dopamine

Answer 16

• The tremors, muscle rigidity and bradykinesia or akinesia seen in parkinson’s is due to depleted dopamine in motor circuits
• Over production of dopamine in the mesolimbic system causes schizophrenia, treated with antipsychotics
• Addiction works through the pleasure centres of the CNS located in the mesolimbic dopamine system

Question 17

Name an example of an indolamines

Answer 17

Serotonin - which has a large family of inhibitory and excitatory receptors

Question 18

What is serotonin involved in?

Answer 18

-Sensory signals
-Sleep, wakefulness and mood

Question 19

What is associated with serotonin dysfunction?

Answer 19

Depression and obsessive compulsive disorders. This is treated using fluoxetine which is a serotonin re-uptake inhibitor

Question 20

Describe the effects of drugs of abuse on serotonin

Answer 20

LSD- acts as a receptor agonist
MDMA - causes the release and preventing subsequent re-uptake of serotonin

Question 21

Name some peptide neurotransmitters

Answer 21

Dynorpin and Enkephalin

Question 22

Describe some of the effects of endorphins and enkephalins

Answer 22

• Act on opioid receptors as endogenous ligands to mute pain

Question 23

Describe what happens with the use of opioids and what can be used to reduce withdrawal symptoms

Answer 23

Use of opioids such as morphine, codeine and heroin cause the downregulation of opioid receptors in the CNS, which leads to opioid tolerance and increased intake.
Opioid receptors can be localised in specific parts of the brain (limbic system) which can result in a psychological dependence.
- Naloxone (opioid receptor antagonist) can reduce symptoms.

Question 24

Name an ester neurotransmitter

Answer 24

Acetlycholine

Question 25

Describe some of the features of acetylcholine

Answer 25

• Found in both the PNS and CNS.
• Dysfunction of acetylcholine is associated with Alzheimer’s disease
• Nicotine acts on nicotonic acetylcholine receptors

Question 26

What is anticholinesterases?

Answer 26

It prevents the break down of ACh, prolonging it’s activity. This can have therapeutic effects (donepezil in Alzheimer’s) but can be toxic (insecticides and nerve gas)