Neurotransmitters Flashcards
Classify neurotransmitters according to structure & function
S, amino acids, biogenic amines, neuropeptides & others
F, excitatory, inhibitory or both
Mention methods of inactivation of neurotransmitters and therapeutic application
Reuptake, SSRI
Hydrolysis, MAO inhibitors
Mention the principal excitatory and principal inhibitory NT and their method of removal
E, glutamate, reuptake
I, GABA, converted to succinate semialdehyde by GABA-T, then oxidized to succinate which is used in Krebs cycle.
Describe formation of GABA
Derived from glutamic acid by glutamic acid decarboxylase enzyme and pyridoxal phosphate is required as a coenzyme.
Describe function, origin and fate of glycine
Major inhibitory NT
Can be synthesized from serine by serine hydroxymethyltransferase, removed by reuptake through high-affinity transporters.
Write equations of synthesis & degradation of Ach
S, Acetyl CoA + choline —ChAT—-> Ach + CoA
D, Ach—-AChE—>acetate + choline
…..is the precursor of catecholamines, while the enzyme directly producing dopamine is …….
Tyrosine
Dopa-decarboxylase
…..is the rate-limiting step of CA synthesis
Tyrosine hydroxylase
The enzyme catalyzing formation of NE ……, While that catalyzing formation of E
Dopamine beta-hydroxylase
Phenyl-ethanolamine N-methyl-transferase
Fates of catecholamines
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
GR: Occurrence of Parkinson’s & mention a lab result
Due to insufficient production of dopamine as a result of idiopathic loss of dopamine-producing cells in the brain.
Decreased HVA in urine
…..is used to treat Parkinson’s
L-DOPA
Justify the addition of carbidopa to L-dopa
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.
Alpha-methyl dopa mechanism
Competitive inhibition of DOPA decarboxylase
Mention drug treatment of pheochromocytoma and mechanism
Alpha-methyl tyrosine
Competes with tyrosine for enzyme tyrosine hydroxylase
Mechanism and use of MAOI
In the neuron MAOIs inactivate the enzyme and thus increase levels of NE & serotonin
Antidepressant action
Functions of serotonin
In CNS: NT, mood, appetite, temp reg, source of melatonin in the pineal body
Stimulate smooth muscle contraction (VC)
Imp for GIT motility
Describe synthesis and degradation of serotonin
- Tryptophan is hydroxylated in a tetrahydrobiopterin-requiring reaction catalyzed by tryptophan hydroxylase producing 5-hydroxytryptophan
- 5-hydroxytryptophan is decarboxylated to serotonin
Deg is by MAO producing 5-hydroxyindolacetic acid
Write a short note on carcinoid tumour
Arise from argentaffin cells, characterizied by increase production of serotonin dec in niacin causing pellagra and inc 5-HIAA in urine.
SSRI used as ….
Antidepressants
Functions of melatonin
Stimulates immune system, antioxidant, involved in sleep regulation
It follows a circadian rhythm
Mention conditions which can cause melatonin deficiency
-Cigarettes, caffeine, stress
-Antidepressents & BBs
Level dec as we age
Histamine synthesis is catalyzed by ….
Histidine decarboxylase enzyme
Functions of histamine
- Allergic & inflammatory reactions & gastric acid secretion
- Arousal, wakefulness & electrographic arousal
- VD
Synthesis of NO
From L-arginine by the action of nitric oxide synthase enzyme
Physiological functions of NO
- VD of cerebral, coronary and muscular arteries
- Dec GIT & urogenital motility
- Release of hormones from hypothalamus
- It is produced by macrophges, monocytes and neutrophils to kill mircoorganisms
Pharmacological functions of NO
Nitroglycerin for angina
NO inhalation for pulmonary VD, to treat pulmonary HTN & high-altitude pulmonary edema
The two steps of serotonin formation from tryptophan
Hydroxylation
Decarboxylation
The two steps of melatpnin formation from serotonin
Acetylation
Methylation
