So, the mechanism of learning and a memory, so as we mentioned, some critical molecules in the LTP. This critical molecules or proteins are also suggested to have great functions in the learning and the memory. One is to see and peek, one in this calmodulin and PKA pathway, and of course the CREB, the binding protein. So inside of the nucleus, we have gene expression regulation by CRE and CREB, the binding protein. So the first related CREB bind to the CRE element, what regulate to the gene expression in the nucleaus. So, the mechanism for short-times sensitization. So the sensitization, is a process that we repeatedly stimulate and it organelle. And then this response of the organelle or the tissue would become sensitized after long time stimulation. So this is the effect, the opposite way of hypertization. Hypertization, is when we repeatedly stimulate an organelle or tissue that we swells of this tissue will becomes smaller than original one. So the synthesization is becomes stronger, the responsible becomes stronger than the original one. So the mechanism of this sensitization, the short term sensitization involves a interneuron that release 5-HT, serotonin. Normally serotonin is an inhibitory neurotransmitter. So on the sensory neuron, there are 5-HT receptors that can bind to 5-HT. So the interneuron release 5-HT and then these 5-HT will bind to its receptor at the sensory neuron. And then upon binding, the 5 HTR will activate two kinds G protein. One is called Gs protein, the other type Go protein. So, the Gs protein will activate AC pathway. The Go protein will activate PLC pathway. So for the Go protein, activating PKC password, that this password will eventually activate a PKC password and will open L type calcium channel. Before the AC pass the GS protein activated AC pathway. The AC pathway will activate PKA pathway will then the PKA pathway will eventually make a vesicle mapping zone to the actively, the activation of this, the activation of PKC pathway will then eventually make the same, in fact will make the vesicle more ready to release at the presynaptic membrane. So the transmitter get released, the more transmitter will get released to the synaptic cleft. So, the response will be more stronger than the original one. And also there's other effect made by the PKC- PKA activation. As the PKA activation will close the potassium channel. And then this will eventually lead to the opening of one type. Calcium channel and then will make calcium influx into the presynaptic membrane. And then the calcium, the increase level of calcium in the presynaptic membrane will then lead to more transmitter release. So, two ways to make the transmitter release become increased. And then the response will become stronger than before. So, this is the short term sensitization. But for the long term sensitization, the mechanism is not as the same as the short term sensitization. So, more or less, like we talk about shorthand early LTP and late LTP. So the long term sensitization is also interneuron release 5HT, the neurotransmitter. 5HT binds to 5HT receptor at the sensory neuron. The sensory neuron. The binding of 5-HT to its receptor will activate cAMP and activate PKA pathway. So, the PKA pathway measured before the activation of this PKA pathway will cause neurotransmitter release increase so here, the PKA pathway will cause the up-regulation of neurotransmitter release as well. But in the long term sensitization, the active of PKA pathway also activate MAP kinase pathway. MAP kinase will phosphorylate CREB protein to phosphorylated CREB protein. The phosphorylated CREB protein get into nucleus, binds to CRE element. The CRE element will start gene expression of two sets of protein. One set of protein were produced new synapsis. The growth of new synaptic connection and that the other sets of DNA that get extracted by CRE element will get of the ubiquitine hydrolase. And then this ubiquitin hydrolase will make the persistent activation of PKA. It's like a feet forward or positive feedback loop. So make this PKA activation last longer, so lead to neurotransmitter release become more and more. So, this desensitization process can lasts for even long time. So this is the water mist that we use to test learning and memory function in animal. It's really simple module, it is a really simple behavior module. This is a water tank. So in the water tank, we have water filled of this tank. And in one place we have a platform underneath the water so, the little mouse can not see the platform. When we put the mouse into this water tank, the mouse can swim underneath the water tank. And then we can link this for the modulation of this behavioral module. We can make some recording in the brain area in the animal. So we do tape the behavior of the animal, as well we can make the electrophysiology recording of certain brain area in the one animal move inside this tank. So, the animal is put into this water tank and then the little square shows the platform underneath the water. And then you can make some cues or some clues on the walls like this picture this symbol pictures for the animal to recognize and then for example here the dot line here the wild type animal you put the first trial the first time you put it the animal in to the tank. The animal doesn't know there's a platform so, it will just swim around randomly and then suddenly it happened, there's a platform so that the animal will stand on it. And then the second time when you put the animal into the water tank, normally if it's a wild type mouse, it will go directly to the platform. We'll now spend as much time as the first trial, first round. So the latency, the waxes is our latency that animal found the platform. So the latency will decrease dramatically from trial to trial that indicates that the animal can learn and can memorize the location of this platform. But for this yellow line here, this mutant mice here. If the cognitive function is impaired in this mutant animal, in this mice. The animal cannot find the platform can now either not learn or cannot memorize the location of the platform, the latency of finding this platform is significantly longer than the type one. So, we use this simple behavioral module to test the learning and the memory ability of the animal. So, this is the same behavior module just used a different parameters. The trail, the trace recorded the mouse searching or swimming inside of this water tank. So for wild type one, this is the spot we put in the animal. This is where we have the platform. So, the mouse will swim directly to this quarter. And then, will spend much time here but for mutant one, the cognitive function is impaired one. We'll just swim around and we'll spend equal time to each quadrant in the water tank. So, we can use the time that is spent in the target quadrant compare to the other three quadrant to measure the cognitive function for the animal as well.
