Toxicology Lecture 3 Toxins And The Nervous System

Front 1

What are the 5 general processes that toxins interfere with resulting in problems with the nervous system?

Back 1

1) Metabolism and protein synthesis
2) Generation and transmission of actin potentials
3) Axonal transport
4) Myelin formation
5) Synaptic transmission

Front 2

What are 5 ways that toxins affect synaptic transmission?

Back 2

1) Synaptic vesicle formation
2) Neurotransmitter formatin
-Inhibitory or excitatory
3) Neurotransmitter activation
4) Neurotransmitter access to receptor
5) Neurotransmitter irritators

Front 3

What is the function of Renshaw cells?

Back 3

Inhibitory cell in the spinal cord that squirts out glycine on lower motor neurons and hyperpolarizes it

Front 4

What results if the Renshaw cell is not working?

Back 4

Get hyperexcitability of extensors

Front 5

What is a toxin that acts on the Renshaw cell?

Back 5

Tetanus toxin

Front 6

What is the mechanism of action of Strychnine (rat poisoning)?

Back 6

Competes with glycine on at the synapse of LMNs--> hyperexcitability--> extension

Front 7

What happens when a toxin changes the cell membrane ion permeability?

Back 7

Results in change in threshold to fire on action potential

Front 8

What are 2 toxins alter cell membrane ion permeability?

Back 8

1) Lolitrem B
-Causes Ryegrass staggers
2) DDT & pyrethrins

Front 9

What is Ryegrass staggers?

Back 9

when sheep, horse, cattle eat perennial ryegrass w/ high level of endophytes which produce lolitrem B

Front 10

What's the mechanism of action of Lolitrem B?

Back 10

Alters sodium, potassium and calcium channels

Front 11

What is the mechanism of action of DDT and pyrethrins?

Back 11

Alter sodium and potassium currents

Front 12

What electrolyte movement is necessary for Ach release at LMNs?

Back 12

Calcium release

Front 13

What is an example of a toxin that blocks release of a neurotransmitter?

Back 13

Botulism toxin

Front 14

What is the mechanism of action of botulism toxin?

Back 14

Ties up calcium so don't get release of Ach --> diffuse LMN signs
-Same signs as coonhound paralysis and tick paralysis

Front 15

What is an example of a toxin that interferes with neurotransmitter degradation?

Back 15

Organophosphates

Front 16

What is the mechanism of action of organophosphates?

Back 16

Blocks acetylcholinesterase --> Ach staying around longer so get classic parasympathetic signs (SLUD)

Front 17

What is an example of a toxin that prevents neurotransmitter reuptake into presynaptic ending (therefore interfering w/ synaptic transmission)?

Back 17

Selective serotonin reuptake inhibitors (SSRIs)
-Reconcile= vet drug

Front 18

What are the 2 ways that toxins can cause neuronal necrosis?

Back 18

1) Direct effect
2) Indirect effect
- Anoxia--> neuronal death

Front 19

What is an example of a toxin that causes neuronal necrosis via the direct effect? What's the mechanism of action?

Back 19

Yellow star thistle
-Accumulates in the substantia nigra and globus pallidus causing nigropallidal encephalomalacia

Front 20

What are 2 toxins that indirectly cause neuronal necrosis (via anoxia)?

Back 20

1) Cyanide toxicosis
2) Carbon monoxide toxicosis

Front 21

Toxins can affect myelin by causing demylination or interfering with _________.

Back 21

Oligodendroglial cells making myelin

Front 22

Toxins can affect the nervous system by interfering with _____ transport.

Back 22

Axonal

Front 23

What is an example of a toxin that inhibits enzymes?

Back 23

Acetylcholinesterase inhibition by organophosphates

Front 24

What are 7 clinical signs of CNS toxicosis?

Back 24

1) Seizures
2) Depression or coma
3) Tremors
4) Autonomic nervous system
5) Muscle weakness/paralysis
6) Ataxia/cerebellar/vestibular
7) Behavior

Front 25

How does a dog appear when seizuring?

Back 25

Unconscious w/ open eyes
-Extensor rigidity w/ opisthotonus
-Chewing movements
-Running or paddling movements
-Autonomic signs---> SLUD

Front 26

How do toxins cause paresis/paralysis from a loss of peripheral nerves? Example?

Back 26

Damage to lower motor neurons or demylination
-Ex. coonhound paralysis from racoon saliva

Front 27

**What is the key to diagnosing a LMN lesion?

Back 27

Loss of reflexes

Front 28

What is tetany? What causes tetany?

Back 28

Sustained contraction of muscles---> extensors
-Secondary to metabolic or electrolyte dysfunctions

Front 29

What is a toxin that causes tetany?

Back 29

Oxalate toxicity via hypocalcemia

Front 30

What is myoclonus?

Back 30

Sudden contraction of groups of muscle cells followed by relaxation- sporadic and repetitive forms
-Shake and bake (shaking and hyperthermic)

Front 31

What are 3 examples of toxins that cause myoclonus?

Back 31

1) Lolitrem B
2) Locoweed
3) Metaldehyde

Front 32

What is narcolepsy?

Back 32

Sudden onset of "cataplexy" w/ complete loss of LMN function and decreased tone
-Sudden onset of REM sleep

Front 33

What are 2 ways toxins can cause ataxia?

Back 33

1) Loss of peripheral nerves
2) Loss of central CNS control

Front 34

What are 3 areas that can be damaged and result in loss of central CNS control--> ataxia?

Back 34

1) Cerebral cortex
2) Damage to spinocerebellar tracts or cerebellum
3) Damage to vestibular system