Neurotransmitters

Question 1

Classify neurotransmitters according to structure & function

Answer 1

S, amino acids, biogenic amines, neuropeptides & others
F, excitatory, inhibitory or both

Question 2

Mention methods of inactivation of neurotransmitters and therapeutic application

Answer 2

Reuptake, SSRI
Hydrolysis, MAO inhibitors

Question 3

Mention the principal excitatory and principal inhibitory NT and their method of removal

Answer 3

E, glutamate, reuptake
I, GABA, converted to succinate semialdehyde by GABA-T, then oxidized to succinate which is used in Krebs cycle.

Question 4

Describe formation of GABA

Answer 4

Derived from glutamic acid by glutamic acid decarboxylase enzyme and pyridoxal phosphate is required as a coenzyme.

Question 5

Describe function, origin and fate of glycine

Answer 5

Major inhibitory NT
Can be synthesized from serine by serine hydroxymethyltransferase, removed by reuptake through high-affinity transporters.

Question 6

Write equations of synthesis & degradation of Ach

Answer 6

S, Acetyl CoA + choline —ChAT—-> Ach + CoA
D, Ach—-AChE—>acetate + choline

Question 7

…..is the precursor of catecholamines, while the enzyme directly producing dopamine is …….

Answer 7

Tyrosine
Dopa-decarboxylase

Question 8

…..is the rate-limiting step of CA synthesis

Answer 8

Tyrosine hydroxylase

Question 9

The enzyme catalyzing formation of NE ……, While that catalyzing formation of E

Answer 9

Dopamine beta-hydroxylase
Phenyl-ethanolamine N-methyl-transferase

Question 10

Fates of catecholamines

Answer 10

1- Active uptake by sympathetic nerve endings
2- Catabolism to biologically inactive products by MAO & COMT
D to homovanillic acid
NE & E to vanillylmandelic acid

Question 11

GR: Occurrence of Parkinson’s & mention a lab result

Answer 11

Due to insufficient production of dopamine as a result of idiopathic loss of dopamine-producing cells in the brain.
Decreased HVA in urine

Question 12

…..is used to treat Parkinson’s

Answer 12

L-DOPA

Question 13

Justify the addition of carbidopa to L-dopa

Answer 13

It is an inhibitor of dopa-decarboxylase and reduced the decarboxylation of L-dopa in peripheral tissues thus allowing higher concentration of the precursor to reach the brain.

Question 14

Alpha-methyl dopa mechanism

Answer 14

Competitive inhibition of DOPA decarboxylase

Question 15

Mention drug treatment of pheochromocytoma and mechanism

Answer 15

Alpha-methyl tyrosine
Competes with tyrosine for enzyme tyrosine hydroxylase

Question 16

Mechanism and use of MAOI

Answer 16

In the neuron MAOIs inactivate the enzyme and thus increase levels of NE & serotonin
Antidepressant action

Question 17

Functions of serotonin

Answer 17

In CNS: NT, mood, appetite, temp reg, source of melatonin in the pineal body
Stimulate smooth muscle contraction (VC)
Imp for GIT motility

Question 18

Describe synthesis and degradation of serotonin

Answer 18

1. Tryptophan is hydroxylated in a tetrahydrobiopterin-requiring reaction catalyzed by tryptophan hydroxylase producing 5-hydroxytryptophan
2. 5-hydroxytryptophan is decarboxylated to serotonin
   Deg is by MAO producing 5-hydroxyindolacetic acid

Question 19

Write a short note on carcinoid tumour

Answer 19

Arise from argentaffin cells, characterizied by increase production of serotonin dec in niacin causing pellagra and inc 5-HIAA in urine.

Question 20

SSRI used as ….

Answer 20

Antidepressants

Question 21

Functions of melatonin

Answer 21

Stimulates immune system, antioxidant, involved in sleep regulation
It follows a circadian rhythm

Question 22

Mention conditions which can cause melatonin deficiency

Answer 22

-Cigarettes, caffeine, stress
-Antidepressents & BBs
Level dec as we age

Question 23

Histamine synthesis is catalyzed by ….

Answer 23

Histidine decarboxylase enzyme

Question 24

Functions of histamine

Answer 24

1. Allergic & inflammatory reactions & gastric acid secretion
2. Arousal, wakefulness & electrographic arousal
3. VD

Question 25

Synthesis of NO

Answer 25

From L-arginine by the action of nitric oxide synthase enzyme

Question 26

Physiological functions of NO

Answer 26

1. VD of cerebral, coronary and muscular arteries 2. Dec GIT & urogenital motility 3. Release of hormones from hypothalamus 4. It is produced by macrophges, monocytes and neutrophils to kill mircoorganisms

Question 27

Pharmacological functions of NO

Answer 27

Nitroglycerin for angina NO inhalation for pulmonary VD, to treat pulmonary HTN & high-altitude pulmonary edema

Question 28

The two steps of serotonin formation from tryptophan

Answer 28

Hydroxylation Decarboxylation

Question 29

The two steps of melatpnin formation from serotonin

Answer 29

Acetylation Methylation