Question

3. In the first unit of this module, we discussed the neural basis for learning and memory. a. Describe the process of LTP. Be detailed in your response. b. Whereas LTP is an increase in the effectiveness of synapses, LTD is a process by which specific sets of synapses are selectively weakened. Calcium is involved in both LTP and LTD. Explain how different concentrations of calcium would lead to LTP vs. LTD. Be specific in your response, including the enzymes activated by calcium and the downstream changes to the number of receptors embedded in the postsynaptic membrane

Answer 1

a. In neuroscience, long-term potentiation (LTP) involves a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons.The opposite of LTP is long-term depression, which produces a long-lasting decrease in synaptic strength. It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength. As memories are thought to be encoded by modification of synaptic strength, LTP is widely considered one of the major cellular mechanisms that underlies learning and memory. LTP was discovered in the rabbit hippocampus by Terje Lømo in 1966. LTP is also a subject of clinical research, for example, in the areas of Alzheimer's disease and addiction medicine. In experimental psychology, researchers have induced LTP in mammals by repeatedly stimulating the synapses of nerve cells.

b. LTD has been found to occur in different types of neurons that release various neurotransmitters and the most common neurotransmitter involved in LTD is L-glutamate. L-glutamate acts on the N-methyl-D- asparate receptors (NMDARs), ?-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs), kainate receptors (KARs) and metabotropic glutamate receptors (mGluRs) during LTD. It can result from strong synaptic stimulation or from persistent weak synaptic stimulation (as in the hippocampus). Long-term potentiation (LTP) is the opposing process to LTD; it is the long-lasting increase of synaptic strength. LTD is thought to result mainly from a decrease in postsynaptic receptor density, although a decrease in presynaptic neurotransmitter release may also play a role. Hippocampal/cortical LTD can be dependent on NMDA receptors, metabotropic glutamate receptors (mGluR), or endocannabinoids. The signalling pathways used by a particular cell also contribute to the specific type of LTP present. For example, some types of hippocampal LTP depend on the NMDA receptor, others may depend upon the metabotropic glutamate receptor (mGluR), while still others depend upon another molecule altogether.