Physiology Exam 2 Chapter 7 Monoamines A variety of chemicals in the CNS function as neurotransmitters Among these are the monoamines a chemical family that includes dopamine norepinephrine and serotonin Monoamines are regulatory molecules derived from amino acids Monoamines Dopamine norepinephrine and epinephrine are derived from the amino acid tyrosine and placed in a subfamily of monoamines called catecholamines Dopamine is a neurotransmitter norepinephrine is a neurotransmitter and a hormone from the adrenal medulla and epinephrine is the primary hormone secreted by the adrenal medulla Serotonin is derived from the amino acid tryptophan and functions as an important neurotransmitter Monoamines Monoamines are produced and stored in synaptic vesicles Action potentials open gated Ca2 channels monoamine neurotransmitters are released by exocytosis from presynaptic vesicles diffuse across the synaptic cleft and interact with specific receptor proteins in the membrane of the post synaptic cell Monoamines The stimulatory effects of those monoamines must be quickly inhibited to maintain proper neural control The action of monoamine neurotransmitters at the synapse is stopped by the reuptake of the neurotransmitter molecules from the synaptic cleft into the presynaptic axon terminal and degradation of the monoamine by an enzyme within the axon terminal called monoamine oxidase MAO MAO Inhibitors Monoamine oxidase MAO inhibitors are drugs that block MAO the enzyme primarily responsible for degrading the monoamine neurotransmitters By preventing the breakdown of monoamines these drugs increase the amount of neurotransmitters in the synaptic cleft MAO inhibitors have proven useful in treatment of depression suggesting that a deficiency in monoamine neurotransmission contributes to this disorder An MAO inhibitor drug called catecholomethyltransferase COMT is used to treat Parkinson s disorder because it increases the amount of dopamine at the synapse COMT inactivates catecholamines by putting methyl group on catecholamines Monoamines Monoamines cross plasma membrane through the signal transduction pathway Monoamine neurotransmitters act with the help of a second messenger to open ion channels in post synaptic membrane Monoamines STP In some synapses that use catecholamines for synaptic transmission this second messenger is cyclic adenosine monophosphate cAMP For example binding of norepinephrine with its receptor in the post synaptic membrane stimulates the dissociation of the G protein alpha subunit from the others in its complex This subunit diffuses in the membrane until it binds to an enzyme known as adenylate cyclase This enzyme converts ATP to cyclic AMP cAMP and pyrophosphate 2 inorganic phosphates within the post synaptic cell cytoplasm Cyclic AMP in turn activates enzyme protein kinase which phosphorylates add phosphate group other proteins Through this action ion channels are opened in the post synaptic membrane Pathway turns off by enzyme Phosphodiesterase PDE by it breaking down cAMP Protein Phosphate takes off phosphate reverse activity of protein kinase Anatomy of Vertebrate Brain Forebrain divides into Telencephalon and Diencephalon Midbrain is Mesencephalon Hindbrain divides into the Metencephalon and Myelencephalon Telencephalon Telencephalon is the cerebral hemispheres which form the cerebrum Cerebrum has four lobes and is involved in the limbic system and basal nuceli The four lobes are responsible for conscious thought process and intellectual functions Limbic system involves the amygdala emotion processing and hippocampus memory storage and processing Basal nuclei is involved in movement regulation and skill learning Diencephalon The Diencephalon is much smaller and shaped like a box The roof of the box is the epithalamus pineal gland the side walls of the box is the thalamus relay and processing center for sensory information and the floor of the box is the hypothalamus controls emotions autonomic functions interacts with ANS and hormone production The ganglion from floor of hypothalamus is the pituitary gland Mesencephalon Mesencephalon is the midbrain processes visual and auditory data and control of reflexive responses and maintenance of consciousness Mesencephalon is enlarged and most important in fish Two important regions are the tectrum roof and the tegmentum floor Neurons producing dopamine have cell bodies in tegmentum of mesencephalon Metencephalon Metencephalon has two major components the pons part of the brainstem and cerebellum Cerebellum is important in the unconscious control of skeletal muscles like learning how to ride a bike If you stimulate the cerebellum it can t make the muscles contract Animals that have the most complex movements like birds and fish have large cerebellums Myelencephalon Myelencephalon is the brainstem The medulla oblongata in the brain stem relays information between the spinal cord and the brain and is involved in controlling the ANS heart rate and respiratory rate The pons is between midbrain and medulla oblongata and a fiber tract that relays information back and forth from the cerebellum Pons also contains Raphe nucleus where Serotonin is synthesized Serotonin as a Neurotransmitter Serotonin is used as a neurotransmitter by neurons with cell bodies in the raphe nuclei that are located in the midline of the brainstem LSD exert their effects primarily by binding to and activating serotonin receptors in the cerebral cortex Serotonin and LSD both have a ring and both effect mood and emotion Serotonin Serotonin is also involved in depression migraine headaches bipolar disorder and anxiety Antidepressant drugs are SSRIs Serotonin specific reuptake inhibitors SSRIs such as Prozac Zoloft etc reduce the production of serotonin transporter proteins SERT thereby reducing the ability of SERT proteins in the presynaptic neuron plasma membrane to clear serotonin from the synaptic cleft This increases the ability of serotonin to stimulate its receptors in the post synaptic membrane an ability that aids in the treatment of depression Serotonin There are many different subtypes of serotonin receptors that are involved in many different functions Neurons that produce serotonin are serotonergic axons that project and extend in cerebral hemispheres Dopamine as a Neurotransmitter Neurons that use dopamine as a neurotransmitter are dopaminergic neurons The cell bodies of dopaminergic neurons are highly concentrated in the midbrain Their axons