Neurotransmitter.....HP (G) 3rd Semester

(1)  *What is neurotransmitter?

       * Name 2 amino acids act as transmitter agents .       2+(1+1),2016

(2) Write down the biosynthetic pathway of ACh .                           3, 2017

(3) Name 1 exeitatory and 1 inhibitory neurotransmitter.            1+1, 2017

(4) Name 2 inhibitory neurotransmitter and 1 chemical agent that blocks neuromuscular transmission .   1+1, 2015

(5) What is Serotonin? State its role as a neurotransmitter .                        1+2,2018

         Neurotransmitters are the chemical substances released at  the nerve endings to transmit nerve impulse to a muscle fibre / postsynaptic neurone/a gland from the presynatic neurone .

      A few neurotransmitters:

(1) Biogenic amines

         (i) Catecholamines

               * Epinephrine

               * Norepinephrine

               * Dopamine

        (ii) Histamines

        (iii) Serotonin

(2)Peptides

         (i) Opioid peptides

               *Enkephalins

               *Endorphin

               * Dynorphin

         (ii) Substance P (polypeptides)

         (iii) Neurotensin

         (iv) Somatostatin

(3) Amino acids

           *GABA                      ( Inhibitory)

           * Alanine

           * Glycine.                 ( Inhibitory)

           * Glutamic acid.     (Excitatory)

           * Aspertic acid

(4) Others

           *Acetylcholine

           *Adenosine

           *Prostaglandins

           *ATP

           * CO

           * NO

                   Acetylcholine

It is the acetyl ester of choline .

Biosynthesis : The following steps are found in its biosynthesis:

Acetyl CoA + Choline----->Acetylcholine , in presence of choline transferase enzyme

Formation of choline:

Serine----------->Ethanolamine +CO2 , in presence of  decarboxylase enzyme .

Next, ethanolamine is methylated to form choline.

Formation of Acetyl CoA:

Acetic acid +CoA.SH+ATP------> Acetyl CoA in presence of acetyl thiokinase .

 Then ACh is stored in vesicles at synaptic knob .When Ca++ enters in synaptic knob from ecf then ACh releases at nerve  endings by exocytosis.

  After the completion of function ACh is instantly hydrolysed to choline and acetic acid by enzyme cholinesterase of synaptic membrane . Choline enters in presynaptic knob to synthesise ACh again .

  ACh is found in brain synapse, autonomic ganglia, neuromuscular junction and post ganglonic autonomic fibres .

Catecholamines

               Epinephrine, Norepinephrine and Dopamine belong to Catecholamines due to the presence of a catechol nucleus (1,2-dihydrobenzene) in each of them.

Serotonin

       (i)     Chemically serotonin is an amine .      (ii)         It is the result of hydroxylation and decarboxylation of tryptophan amino acid .

      Serotonin as a neurotransmitter :

 (i)It acts as an important neurotransmitter in CNS, enteric nervous system , retina , etc.

(ii) It acts through the following receptors:

              5 HT1 (1A,1B) , 5HT2, 5HT3,  5HT4 ,