L8 - NT Identification And Proof Of Function

Question 1

Establish NT:

Answer 1

1. Identify biological activity
2. Identify active principle
3. Meet NT criteria:
   - mimic response
   - synthesis pathway
   - storage mechanism
   - release from nerve
   - specific receptor activate
   - enzyme degradation
   - neuronal uptake of NT
4. Find physiological roles

Question 2

Identification of NA biological activity:

Answer 2

Found extract in adrenal medulla and not adrenal cortex.
Found that it increased rate and contractility of heart in frog.
Found that it increased blood pressure in dog.

Question 3

Identification of NA active principle:

Answer 3

Abel who found epinephrine. And then Takamine found it to be adrenaline.

Question 4

Identification of NA physiological role:

Answer 4

Langley in 1901 found that extract had similar activities to when sympathetic nerve is activated.

Elliott in 1905 found that extract was a sympathetic neurotransmitter as adrenaline mimics effects of sympathetic nerves.

Question 5

Rank order of potency analysis:

Answer 5

Found that piloerection was influenced by sympathetic simulation. NA had a greater effect than A.

Found that bladder relaxation was not influenced as well by sympathetic stimulation. A had greater effect that NA.

Question 6

How did they confirm presence of NA in nerves:

Answer 6

NA + formaldehyde = fluorescent product.
Found that removing nerve (denervation), causes loss of fluorescence.

1960s they found that sympathetic nerves release NA.

Question 7

Synthesis of NA:

Answer 7

Tyrosine is converted to dopa by tyrosine hydroxylase.
Dopa is converted to dopamine by dopa decarboxylase.
Dopamine is converted to NA by dopamine-B-hydroxylase.

No enzyme to convert NA to A like in adrenal gland.

Question 8

How is NA stored:

Answer 8

Found NA is stored in vesicles - can see in EM as small granular vesicles.

Vesicles protect NA from MAO (mono-amine oxidase). MAO breaks down NA.
Vesicles can then fuse with membrane and release contents.

Vesicles can be separated by ultracentrifugation and can analyse contents.

Question 9

How is NA released:

Answer 9

Finkleman in 1930 found that nerve is stimulated when it’s released.

Now we can monitor release by radio labelling and chromatography.

Question 10

Activation of specific receptors:

Rank order of potency

Answer 10

Of A receptors:
NA>A>Isoprenaline

Of B receptors:
Isoprenaline>A>NA

Can identify potency of each by:

• differing antagonist affinity
• differ radio ligand binding affinity
• alter transduction (ion channels and second messenger)
• alter gene transcription for receptors

Question 11

NA termination:

Answer 11

1960 study shows that their taken up in nerve tissue or effector cells and become inactivated.