Neuronal and muscle toxins

Question 1

Where does tetrodotoxin come from?

Answer 1

It is produced by marine bacteria- animals have the bacteria living inside them which produce the toxin- symbiosis

Question 2

Some animals which have TTX

Answer 2

Puffer fish- chef has to remove the part of the fish which causes the effects
Blue ringed octopus- toxin is in the bite

Question 3

What are the symptoms of TTX ingestion

Answer 3

Numbness of lips and tongue 
Facial tingling 
Headache 
Nausea 
Dizziness 
Vomiting 
Increased bodily paralysis- it spreads 
Respiratory paralysis which leads to death 
20 mins-8 hours to death depending on how much is ingested

Question 4

What are the symptoms of being bitten?

Answer 4

Same as ingested but no facial effects
Numbness in the place where you were bitten
Faster time to death because toxin goes straight to the blood

Question 5

Treatment of TTX

Answer 5

Mechanical ventilation because it is the respiratory failure which kills you
No anti-venom as TTX binds too strongly

Question 6

What is the mechanism of TTX action?

Answer 6

Blocks Nav channels which means no neuronal APs and no ACh release- no contraction of muscle- causes respiratory paralysis

Question 7

Why are sensory neurons implicated first?

Answer 7

In the neuronal bundles- the sensory neurons tend to be on the outside meaning that the toxin doesn’t have to diffuse into the fibre to have effect. This is why you get sensory effects first.
Paralysis comes second because the toxin needs time to reach the motor neurons.

Question 8

What happens to the Na conductance across the neuronal cells in the presence of TTX

Answer 8

Decreases due to much less activation of the Na channels

Question 9

Some channels are insensitive to TTX- why?

Answer 9

There are very small changes in the channel structure meaning that the TTX cannot bind

Question 10

Which channel is impacted by TTX

Answer 10

Nav1.2

Question 11

What is the effect of mutating the channels impacted by TTX

Answer 11

Mutating the channel in the pore region meant that the channel is insensitive to TTX. Only 1 AA was changed so the sensitivity is conferred by one single AA

Question 12

What did the snake study on TTX determine?

Answer 12

Small and subtle changes can lead to different channel properties.
Two geographically separated populations of the same snake had different sensitivities to the TTX
Due to differences in prey choice one population developed an insensitivity to the toxin

Question 13

Where do dendrotoxins come from

Answer 13

Sneks- mambas

Question 14

How to DDXs work

Answer 14

inhibit repolarisation- different DDX work on different channels so there are a variety of effects.

Question 15

What are the symptoms of DDX?

Answer 15

Early numbness is place of bite 
Systemic responses in 30 mins-1 hour
Ptosis- drooping eyelids 
Paralysis of eye muscles 
difficulty swallowing 
mild paralysis 
respiratory failure

Question 16

What is the effect of DDX on the K channels

Answer 16

Smaller currents- not a complete block and the effects are reversible.
Inhibition prevents repolarisation
Excess ACh release from pre-synaptic membrane
ACh depletion
Thus there is subsequent failure in neurotransmission due to lack of ACh
Problem in muscle control and respiratory paralysis

Question 17

Treatment of DDX

Answer 17

Antitoxins work- need to know the species of mamba to give right one

Question 18

Where do conotoxins come from

Answer 18

Cone snails- there are over 8000 toxins which have varying lethality
Could potentially be used in pain therapy

Question 19

What are some targets of CTX

Answer 19

nAChR
Nav 
Kv
Cav
Serotonin receptors
Depends on which type has shanked you

Question 20

General symptoms of CTX

Answer 20

Burning pain 
Swelling at site of injection 
Numbness 
Cardiac and respiratory stress 
Muscle weakness 
Loss of co-ordination 
Ptosis 
Headache 
Nausea 
Stomach cramps

Question 21

Lethal symptoms of CTX

Answer 21

Lips become stiff
Blurred vision
Paralysis
Coma

Question 22

What are some uses of conotoxins?

Answer 22

Different ion channels are being investigated for use in conotoxin pain treatment
In nociceptive neurons, the AP generates the feeling of pain
Loss of ion channels in the nerve endings an t the post-synaptic membrane in the spinal cord have been investigated to be targets for conotoxin therapies for chronic pain

Question 23

How is Cav2.2. being targeted for pain treatment?

Answer 23

Found in nociceptive neurons- release of NT and the propogation of pain
Transmits the signal from the sensory neuron to the relay neuron in the spinal cord
In the presence of EU1.6 which is a CTX- Ca currents across the membrane were decreased at the same voltage as the control experiment so it is blocking the channel- less NT release- less likely to fire an AP
The response is dosage dependent

Question 24

What were the results of the in vivo study of the CTX in rats?

Answer 24

In the DRG cells- use barium to prevent Ca feedback- currents stull decreased (not complete lack of function) in the presence of EU1.6

Question 25

How are pain models in animals set up?

Answer 25

Partial nerve ligation-

Sciatic nerve in rats exposed- tied off 1/3 of the nerve which generates a sensation of pain in the animals

Question 26

How are pain models in animals used?

Answer 26

Application of pressure to the hind paw- sciatic nerve innervation- and measure how much pressure it takes for the paw for the rat to withdraw it.
This is done with 3 sets of rats- saline, positive control (known pain medication) and EU1.6

Question 27

What were the results of the EU1.6 experiments in the rat paws?

Answer 27

In the presence of EU1.6, the rats took longer to withdraw their paws- they could withstand higher pressures- these effects wore off over time.
It blocks Cav2.2

Question 28

What is the target of the peruvian green velvet tarantula toxin (Tp1a)

Answer 28

Nav1.7-

Question 29

What is the effect of Tp1a on Nav1.7?

Answer 29

smaller inward current of Na- inhibition of the channel which affects the AP in sensory neurons- blocks the pain signal
The synthtic and native toxin have this ability

Question 30

What does the scorpion OD1 toxin do?

Answer 30

Activates Nav1.7/1.6

Increases AP- mimicks the pain response- channels stay open for longer