HMB200 Lec4

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University of Toronto St. George
Human Biology
Ingrid L.Stefanovic

Lecture 4 - Transmitters and Secondary Messenger -Transmitters are usually amines(derived from single A.A tryptophan or tyrosine). Others can be other A.As, like Glutamate and Glycine, and some can be derived from converting the amino acids, like GABA which is made from Glutamate by Glutamic Acid Decarboxylase (GAD) - Glutamate: is an amino acid that can act as transmitter. It is the most important excitatory trasnmitter. (exclusively) - Glycine and GABA is the most important inhibitory transmitter. (exclusively) - GABA is the most common inhibitatory transmitter in the forebrain. Its made from glutamate by the enzyme GAD. (excitatory -> inhibitatory) The presence of GAD can thus be used to find inhibitatory neurons. - If you have GAD, the glutamate will always be converted to GABA, so it CANT be excitatory. Meaning there is a seperation between exc. glutamate neurons and inhi. GAD positive GABA neurons. - Other transmitters like ACh and Serotonin can be both inh. and exc. depending on the receptors. They act on different types of receptorts and thus either have exc. effect or inhibitatory effect. - These are found in small number of neurons inside the brain since the most common ones are GABA and Glutamate. - Transmitters that have mixed effects are found in identified cell groups throughout the brain: -ACh: 1% - 2% of the neurons in the brain have ACh. All of the motor neurons are ACh. - in the spinal cord, ACh is the exc. transmitter to muscles, and in the brainstem, the exc. motor neurons that go to muscles of the face and neck also use ACh. - Cholinergic Cell Groups Ch 1 - 6 - Cetecholamines are derived from the amino acid tyrosine. - Tyrosine -> (tyorisine hydroxidase) L DOPA -> Dopamine -> Norepi -> Epinephrine. - you can tell which cetacholamine is present by looking at which enzyme is present. All the neurons that use catecholamines must have tyrosine hydroxidase to start to conversion. - Catecholamines are found in cell groups A1-A17 in brain. - Norepi: A1- A7 = in the brainstem. - Dopamine: A8 - A17 = start in midbrain, and go up into the olf. bulb and retina. - these were identified by looking the certain enzyme that converts them. - These neurons are low in numbers, but they have projections all over the brain. (ex: locus coerulues) These are therefore called diffuse accending cell groups. (same with cholinergic cell groups) - Diffuse accending cell groups are importatnt for arousal - Other amines are tryptophan derivatives: - Tryptophan -> 5 HydroxyTryptamine (5HT) [a.k.a = serotonin] - Cell groups B1-B9 - serotonin important for depression. - ACh = Alzheimers, Dopamine = Parkinsons, Serotonin = Depression. *** dont have to know any cell groups*** - Many hormones are made up of polypeptides. They were found to be released as neurotransmitters in many brain neurons. - endorphin, enkaphalin (opiate like peptides) - Peripheral hormones were found to get in the brain, and they were found to be localized in many brain neurons. - Other classes of transmitters that ARENT polypeptides. - Adenosine is a purine, related to ATP. ATP and purines work together, and can be released together. - NO was shown to be a second messenger, and shown to act presynaptically, as a ret
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