Neurotransmitters and other Chemicals of Communication

I.   Overview of Primary chemicals of communication:

   A.   Neurotransmitters

        1.    act locally,

        2.    neuron-to-neuron communication over a short distance

    B.    Neuromodulators

        1.    somewhat more widespread distribution

        2.    affect neuronal systems

   C.    Hormones

        1.    broadcast bodywide

        2.    affect target sites (receptor complexes)

   D.    Pheromones

        1.    broadcast from one individual to another of the same species

        2.    affect basic behaviors such as reproduction

We will be talking primarily about neurotransmitters in this course, however you should remember that a given substance can fit any of the above categories (i.e. the categories are not mutually exclusive).

II.        General Types of NTs and Examples

 A. Small Molecule Neurotransmitters

    1.    amino acids

           a.    glutamate

b.    GABA

c.     glycine

                            2.    biogenic amines

                                    a.    acetylcholine (ACh)

                                    b.    catecholamines

                                            i.    dopamine (DA)

                                            ii.    norepinephrine (NE)

                                            iii.    epinephrine (EPI)

                                    c.    indolamines

                                            i.    serotonin (SE)

            B.    Large molecule transmitters

                    1.    peptides

a.    substance P

b.    CCK & Bombesin (gut peptides)

c.    morphine-like substances (endorphins and enkephalins)

III.    Synthesis of Select Neurotransmitters

   A.    Acetylcholine

        Acetyl CoA + Choline ----->1 molecule of ACh and 1 molecule of CoA

                        with ChAT

Acetylcholine is broken down by acetylcholinesterase

   B.    Catecholamines

Catecholamines begin with a catechol ring from phenylalanine.

Phenylalanine undergoes conversion to and from tyrosing

Phe ----------> Tyr---------->L dopa ----------> DA -------------------> NE --------------->Epi

                            tyrosine                    dopa               dopamine-beta-        PNMT (transferase)

                            hydroxylase          decarboxylase      hydroxylase

   C.    Indolamines

Tryp ---------------> 5-HTP ----------> 5-HT (Serotonin)

           tryptophan         5-HTP decarboxylase

         hydroxylase

The biogenic amines are broken down by MAO (monoamine oxidase)