When neurotransmitters are released into the synaptic gap, do they bind with receptors only once and then disengage once, or do they bind and disengage repeatedly?
I'm a little bit confused here. Isn't endocytosed and internalized the same thing. How can the cell release something during endocytosis.Moonbear said:Others stay at the membrane where they can continue interacting until endocytosed by the cell releasing them. This would also depend on whether the action was postsynaptic or presynaptic as to how much recycling could occur.
The “all or none firing principle” has nothing to do with this. If the membrane potential of the cell body of the postsynaptic neuron changes then an action potential will be send out trough its axons only when the membrane potential at the start of an axon (the axon hillock) reaches a certain threshold. It does give an action potential or it does not, so it is “all or none”.neurocomp2003 said:its once isn't it...cuz of the all or none firing principle...that once teh NT are received by the receptors of the post synapse that they enter the knob for decomposition?
Yes, I believe both can happen.Math Is Hard said:When you say that some stay at the membrane where they can continue interacting, does that mean they release and re-bind with other receptors, or the same receptor, or maybe both?
They would not "propagate an action potential" with each binding, but modulate the membrane potential with each binding. Whether an action potential results depends on the membrane potential at the start of the axon (the so-called axon hillock).Math Is Hard said:I guess I imagine some of these little NTs bouncing from receptor to receptor, propigating a new action potential with each binding, but I am not sure if it can work that way.
Sorry, my distinction wasn't between endocytosed and internalized but between the presynaptic or postsynaptic cell. I didn't word that very well. Others have explained better anyway.quasi426 said:I'm a little bit confused here. Isn't endocytosed and internalized the same thing. How can the cell release something during endocytosis.
Just to clarify, the enzymatic destruction of a neurotransmitter at the synaptic cleft is mediated by many different enzymes, monoamine oxidase (MAO) being only one of them. MAO is typically implicated in the metabolism of catecholamines like dopamine or norepinephrine, although DA in the cleft is first hit by catechol-o-methyltransferanse (COMT) to form 3-methoxytyramine, which is then very rapidly metabolized by MAO to homovanillic acid (HVA). On the intracellular side, DA is metabolized by MAO (The b form) to dihydroxyphenylacetic acid (DOPAC). However, I think the current theory is that the main mechanism for the termination of signal produced by DA is via uptake into the presynatic terminal mediated by the dopamine transporter (I think diffusion also plays a significant role, but it probably depends on which brain regions you are discussing). The best example of a neurotransmitter which is predominantly terminated by metabolism would be acetylcholine and its degradation by acetylcholinesterase.Math Is Hard said:I thought the fate of the NT was always reuptake by the presynaptic neuron or destruction by the MAO process.
For the OP: one real-life application of this is in pesticides. Most pesticides (i.e. non-metabolic) are inhibitors of acetylchline esterase; they covalently bind the Serine protease domain and permanent destroy the esterase activity of the enzyme. Since the acetylcholine is not being degraded, this creates a surplus of acetylchloline, leading to uncontrolled neural action.DocToxyn said:The best example of a neurotransmitter which is predominantly terminated by metabolism would be acetylcholine and its degradation by acetylcholinesterase.
quetzalcoatl9, that was an interesting example. Is this also how "nerve gas" works?.. although DA in the cleft is first hit by catechol-o-methyltransferanse (COMT)
Sorry, MIH, I fell into my jargon and forgot to define the abbreviation, DA=dopamine. Nice observation about the nerve gas, sarin et al is nasty stuff!Math Is Hard said:hey Doc, this is probably a dumb question but what is the "DA" you referred to here: