How many neurotransmitters are there? Is there one receptor site on on a neuron for each neurotransmitter?
Scientists have managed to identify over 100 neurotransmitters in the human brain alone, but evidence suggests we have significantly more than this number.
Three types of neurotransmitters?
Acetycholine is the most commonly studied. It can be either an excitatory or inhibitory neurotransmitter depending on its location in the body. At the junction between somatic motor neurons and the muscles they supply, acetycholine is an excitatory neurotransmitter that stimulates muscle fibers to contract. However, at the site where nerves synapse with the heart, acetycholine has an inhibitory effect that slows the heart rate. Norepinephrine, dopamine, and epinephrine are all neurotransmitters that belong to a group called catecholamines. Norepinephrine is associated with arousal and fight-or-flight reactions of the sympathetic nervous system. Epinephrine is release primarily from the adrenal medulla and therefore plays more of a role as a hormone in the fight-or-lflight reactions of the sympathetic nervous system. Dopamine is found in the brain, where it is involved with autonomic functions and muscle control. There are four, good luck.
In addition to autoreceptors, as Ayon Nandi described, there are also modulatory receptors found on presynaptic membranes that can “fine tune” neurotransmission.A good example of that is the alpha 7 homomeric nicotonic acetylcholine receptor. These are found on dopaminergic neurons (and elsewhere) - and therefore couldn’t be autoreceptors as the neurotransmitter being released has no direct modulatory activity on them. Here’s a schematic of how they’re thought to be located:(image credit: National Institutes of Health science education)In this case the nicotinic receptor is receiving input from a modulatory neuron that’s not directly involved in release at the dopamine synapse we’re looking at.Nicotinic acetylcholine receptors are nonselective cation channels, so they’re conductive for sodium ions (and potassium ions, depending on the reveresal potential.) The alpha 7 homomeric channels are also calcium conductive. This is important because vesicular fusion at the presynaptic terminal is a calcium dependent process.So by “priming” a dopaminergic synapse with presynaptic acetylcholine to activate presynaptic nicotinic channels, the localized calcium concentration can be increased. This can result in calcium-dependent activation of second messenger cascades that can increase the strength of the presynaptic release (as demonstrated here at a glutamatergic synapse):(Image credit: https://www.ncbi.nlm.nih.gov/pmc...)Note that what’s being measured here is actually postsynaptic response, but the authors go to some trouble to demonstrate that these are presynaptic receptors elsewhere in the paper.This has been demonstrated in dopaminergic neurons as well, within the striatum - incidentally this is reward circuitry that is thought to be the mechanism underlying the addictive nature of nicotine in cigarette smoking - it potentiates rewarding dopaminergic signaling in circuits that essentially give pleasurable responses.
This question isn't exclusive to neurotransmitters. Ligands in general can cause variable effects depending on where and when they bind. Without having specific examples in mind, I can give some plausible mechanisms for this.Firstly, receptors rarely act alone. Typically, a receptor that has been activated by its ligand will in turn activate enzymes inside the cell, which will interact with still other components in a cascade that eventually leads to the cell's response. Consider the scenerio depicted crudely below:A red ligand binds to a yellow-green receptor. That receptor activates a blue enzyme inside the cell. That enzyme induces a cascade of events that leads to excitation. Now consider an alternate scenario.In a different cell, or even in the same cell at a different time, the blue enzyme is altogether absent. In its place is a purple enzyme which can also be activated by the receptor but might produce different effects. Here we see that the peptides present inside the cell are as important to how the cell responds to a message as the message itself.Secondly, the receptors themselves can differ. It was no accident that I drew the receptors with two colors. Most receptors have an extracellular portion that receives the message and an intracellular portion that transmits the message across the membrane. So what might happen if two receptors have a similar extracellular component but differ inside the cell?You might have a case where the same ligand (or neurotransmitter) can stimulate different receptors, and those different receptors can recruit different internal components and induce different outcomes. In this example, both the yellow-green and the yellow-orange receptors bind the red ligand, but once they do so, they have different behaviors inside the cell.
Opiates and neurotransmitters?
Now this is a question about the using of codeine cough syrup. I know that when people use some form of MDMA (ecstasy or molly) people are depressed the next day and do not return to their full level of happiness for quite some time. Now i was wondering how that translates to the world of opiates and dopamine release. Do opiates drain you dopamine supply to the point of a hangover and long term effect? If so what are they and if not what are the effects opiates have on your brain and neurotransmitters. (the physical effects such as liver damage isn't a huge concern of mine i'd only like information on the brain and the chemicals it produces)
Do neurotransmitters bind to more than one type of postsynaptic receptor?
I was most surprised when I first discovered that neurotransmitters were actually hormones, which as we know can affect mood, perceptions, energy, appetite, sense of self and energy level, to name but a few. Many drugs, such as steroids, are neurotransmitters. Adrenaline, produced by stress, is one we are all very familiar with. The most widely known by the public are those used in treating depression, such as serotonin. Anti-depressants stop this neurotransmitter from being re-absorbed, thus keeping more of it available to the person and keeping their mood more stable. Unfortunately, there is more that we don't know about those and other chemical messengers (neurotransmitters/hormones) than we do....but it has made a lot of pharmaceutical companies very rich in the meantime. Dopamine is another "biggie", and is necessary for many of the brain's functions, one of the best known being its effect on Parkinson's disease. When the brain releases a flood of either of these two, (serotonin and dopamine) in particular, a person will feel great euphoria, and an increase in the feeling that "everything's all right with the world" .....and themselves of course. Many people love this feeling so much, they try to create it artificially with either prescription or street drugs. Then the brain uses up so much of them that the person soon doesn't feel ANYTHING is right in their world unless they take whatever they choose to take more and more frequently ~ hence the start and progression of addiction. We do know a lot about other neurotransmitters, of course, but those two, for obvious reasons, have received the most attention. If you just type "neurotransmitters" into your search engine, you will be shown more sites to go to, lists of all the known ones and what each does ~ and find more information than you know what to do with!
A neurotransmitter is a chemical molecule that is used by neurons to send signals to other neurons. The key aspect of a neurotransmitter is that it is released outside the neuron and contacts neuroreceptors on the outside of other neurons. The main neurotransmitters in the brain are glutamate (for sending "excitatory" information signals) and GABA (for sending "inhibitory" information signals). These two neurotransmitters account for possibly 99% of the neurons in the brain. Sedatives, anti-epileptic drugs, and general anesthesia act on the neuroreceptors for these neurotransmitters. The second main category of neurotransmitters are neuromodulators that are released by special neurons to control and regulate the activity in the circuits and networks of the brain. The neuromodulators include dopamine, serotonin, acetylcholine, norepinephrine, and histamine. They are released from neurons typically located in the brainstem. Most psychoactive drugs act on the neuroreceptors for these neuromodulating neurotransmitters, including drugs like antidepressants (e.g. prozac), cocaine, amphetamines and ADHD drugs, psychedelics, nicotine, and antipsychotics. The last major class are neuropeptides, like the endorphins which opiate drugs act on (morphine, codeine, hydrocodone, oxycontin, heroin). Other neuropeptides include oxytocin (the "love" neurotransmitter involved in pair-bonding) and cannibinoids that are affected by marijuana. Related:What are the main neurotransmitters?
Neuroscientists are still trying to understand what neurotransmitters do, so we don’t have a definitive answer.But if you look into the vast and complex data that have been collected, you notice that each neurotransmitter-and-receptor combination enables a distinct effect on a neuron’s function, allowing the neuron to be ‘sensitive’ to different chemical conditions and electrical patterns. Neurotransmitters can thus affect a neuron’s voltage as well as its synapses is various context- and time-sensitive ways.For example, in the basal ganglia, synapses on neurons that express dopamine D1-type receptors are strengthened by dopamine release. Synapses on neurons that express dopamine D2-type receptors respond in the opposite way, so they are weakened by dopamine release. Plasticity based on these mechanisms is crucial for various forms of learning.If we were to anthropomorphize neurons, we might say that neurotransmitters are the signals from the outside world (analogous to light and sound patterns) while the receptors are the sense organs (analogous to eyes and ears).Different types of neuron produce different combinations of neurotransmitters, so when a neuron expresses different types of receptors, it can “watch” and “hear” a diverse group of neurons.
What are the diferent types of receptors?
Receptor cells are cells that receive stimuli. Each type of receptor responds to a particular stimulus. The five main types of receptors are pain receptors, thermoreceptors, mechanoreceptors, chemoreceptors, and electromagnetic receptors. Pain receptors are probably found in all animals. However, it is difficult to understand nonhuman perception of pain. Pain often indicates danger, and the animal or individual retreats to safety. Thermoreceptors in the skin are sensitive to changes in temperature. Thermoreceptors in the brain monitor the temperature of the blood to maintain proper body temperature. Mechanoreceptors are sensitive to touch and pressure, sound waves and gravity. The sense of hearing relies on mechanoreceptors. Chemoreceptors are responsible for taste and smell. Electromagnetic receptors are sensitive to energy of various wavelengths including electricity, magnetism, and light. The most common types of electromagnetic receptors are photoreceptors that detect light and control vision...