Dopamine : active during emotional responses, addictive behaviors, and pleasurable experiences. In addition, dopamine-releasing neurons help regulate skeletal muscle tone and some aspects of movement. NE, epinephrine and dopamine are classified as Catecholamines and are synthesized from the amino acid Tyrosine. Catecholamines are inactivated by reuptake into the synaptic end bulbs or destroyed by enzymes. Serotonin AKA 5-hydroxytrypamine (5-HT): involved in sensory perception, temperature regulation, control of mood, appetite, and induction of sleep.
Purines
The ring structure of ATP is called a Purine ring. Over the last couple of decades, science has discovered that ATP is not just an energy storage molecule but a potent NT. Its effects are excitatory in both the PNS and CNS (ex: in the PNS ATP and norepinephrine are released together in some sympathetic neurons while some parasympathetic neurons release ATP and ACh together. ATP’s NT effects are seen in the GI tract as well as other places.
Nitric Oxide (NO)
This NT has widespread effects in the body and is most commonly known for its use as an anesthetic in dental work. Approx. 2% of the neurons in the brain produce NO. Unlike other NTs which are packaged in synaptic vesicles, NO is not synthesized in advance. NO is produced on demand and acts briefly but immediately. Its action is brief due to a high reactivity and therefore, it exists as NO only for ~ 10 seconds before reacting with O2 and H2O to form inactive nitrates and nitrites.
NO is lipid-soluble and therefore it can diffuse directly into neighbouring cells
where
it
activates enzyme reactions within that cell. Endothelial
cells in blood vessel walls release NO
which diffuses into neighbouring smooth muscle cells and causes relaxation. The result is vasodilation (increase blood vessel diameter). The effects range from lowering blood pressure to erectile dysfunction in males. In large amounts NO is toxic and some phagocytic cells produce NO to kill microbes and tumor cells.
B. Neuropeptides
Neurotransmitters consisting of 3-40 amino acids linked by peptide bonds called Neuropeptides are located within the CNS and the PNS.
Both excitatory and inhibitory effects depending upon the receptor.
They are formed in the cell body, packaged into vesicles, and transported to axon terminals. They also serve as hormones that regulate other physiological responses.
164
Made with FlippingBook Publishing Software