Neurotransmitters (Ch 10)

4 criteria for a neurotransmitter

1. synthesized in presynaptic neuron

2. present in the presynaptic terminal and has a defined effect on connected site

3. when given to cells has same effect as endogenous

4. specific mechanism for removal from synaptic cleft

small molecule transmitters

• packaged in small vesicles (40nm diameter)

• released at active zones with Ca++ channel

• can also be contained in dense core vesicles

neuroactive peptides

• short polymers of amino acids

• packaged in large dense cord vesicles (70-250nm)

• not necessarily released at active zones

small synaptic vesicles

• small 40nm diameter

• Ach, glutamate, GABA, glycine

• released at active zones through exocytosis

dense core vesicles

• catecholamines (DA, EPI, NE), 5HT

• large 70-250nm diameter

• not necessarily released at active zones through exocytosis

small molecule neurotransmitters

• charged

• short biosynthetic pathways

• synthesized from essential amino acids or other precursors

• most catalyzed by cytosolic enzymes

• regulated through 1 rate-limiting enzymatic reaction

• characteristic of one type of neuron

acetylcholine exceptions to small molecule transmitter rules

• not derived from an AA

• released at all vertebrate NMJs

catecholamines are synthesized from _____ starting with the enzyme _______

tyrosine, tyrosine hydroxylase

Indolamines are synthesized from ______ starting with the _____ enzyme

tryptophan, tryptophan hydroxylase

autacoid

very locally acting substance

histamine is an autacoid in the _______

hypothalamus

glutamate is produced from

alpha-ketoglutarate

glycine is synthesized from

serine

GABA is produced from

glutamate

ATP and adenosine as neurotransmitters

activation of purinergic receptors (purines; adenine & guanine)

neuroactive peptides

• packaged into dense core vesicles by golgi

• moved to axon terminals by fast axonal transport

• no method for reuptake

• rate-limiting based on transport from cell body

neuroactive peptides and small molecules can be ….

coreleased

removal methods for small molecules

• diffusion

• enzymatic degradation (only cholinergic)

• reuptake (each as its own)

degradation methods for neuropeptides

• diffusion

• proteolysis (breakdown by enzymes)