What is the Difference Between Long-Term Potentiation and Long-Term Depression

The main difference between long-term potentiation and long-term depression is that long-term potentiation (LTP) is the selective weakening of specific synapses due to persistent enhancement of synaptic transmission, whereas long-term depression (LTD) is the activity-dependent reduction of the efficacy of the neuronal synapses lasting hours.

LTP and LTD are two types of processes of enduring changes in synaptic strength. They are induced by specific patterns of synaptic activity.

Key Areas Covered

1. What is Long-Term Potentiation
     – Definition, Structure, Function
2. What is Long-Term Depression
     – Definition, Structure, Function
3. Similarities Between Long-Term Potentiation and Long-Term Depression
    – Outline of Common Features
4. Difference Between Long-Term Potentiation and Long-Term Depression
    – Comparison of Key Differences

Key Terms

Long-Term Depression, Long-Term Potentiation

What is Long-Term Potentiation

Long-term potentiation is the persistent strengthening of synapses according to recent patterns of activity. It results in long-lasting, increased signal transduction between two neurons. It is a phenomenon of synaptic plasticity that depends on the ability of chemical synapses to change their strength. Long-term potentiation is a major cellular mechanism of learning and memory. Apart from that, long-term potentiation can occur in a variety of neural structures, including the cerebral cortex, amygdala, cerebellum, etc.

Figure 1: LTP First Stage: Repeatedly stimulating the Synapse

Furthermore, there are many types of long-term potentiation. They include repeatedly stimulating synapses, more dendritic receptors, more neurotransmitters, and a stronger network between neurons. For example, some long-term potentiation depends on NMDA receptors, and another type of long-term potentiation depends on metabotropic glutamate receptors (mGluR). In addition, a variety of signaling pathways and a variety of parts in the brain contribute to long-term potentiation. 

What is Long-Term Depression

Long-term depression is the activity-dependent reduction in the efficacy of the synaptic function lasting for a long period of time. It occurs in many areas of the central nervous system with varying mechanisms depending upon the regions of the brain. In long-term depression, the activity of the postsynaptic neuron decreases. Therefore, long-term potentiation is the complementary process of long-term depression, increasing the activity of the postsynaptic neuron. The best characterized long-term depression occurs in the hippocampus and the cerebellum. Although many neurons and neurotransmitters involve in long-term depression, the most common type of neurotransmitter that involves in long-term depression is the L-glutamate.

Figure 2: LTP second Stage: More Receptors on Dendrite

Moreover, the receptors of the L-glutamine are N-methyl-D- aspartate receptors (NMDARs), kainate receptors (KARs), α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs), and metabotropic glutamate receptors (mGluRs). Long-term depression may result in strong synaptic stimulation or persistent weak synaptic stimulation. It also results in a decrease in the activity of post-synaptic neurons.

Similarities Between Long-Term Potentiation and Long-Term Depression

• Long-term potentiation and long-term depression are two types of long-term changes in the synaptic strength that occur due to the induced specific patterns of synaptic activity.

Difference Between Long-Term Potentiation and Long-Term Depression

Definition

Long-term potentiation refers to a persistent strengthening of synaptic connections induced by a brief period of high-frequency presynaptic activity, while long-term depression refers to an activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer following a long-patterned stimulus.

Occurrence

Long-term potentiation involves post-synaptic strengthening through the increased recruitment receptors, while long-term depression occurs when post-synaptic neurons are increasingly activated, causing calcium ion influx. 

Significance

Moreover, long-term potentiation is the increased activity of the post-synaptic neuron, while long-term depression decreases the activity of the post-synaptic neuron.   

Conclusion

In brief, long-term potentiation and long-term depression are two types of processes that occur in synapses. Long-term potentiation is the persistent strengthening of synapses, causing an increase in the recruitment of receptors. Therefore, it increases the activity of the post-synaptic neuron. In comparison, long-term depression is the activity-dependent reduction of the efficacy of the synapses. It causes calcium ion influx and the removal of receptors. Long-term depression decreases the activity of the postsynaptic neuron. Hence, the main difference between long-term potentiation and long-term depression is their activity in the synapse.

References:

1. Bliss TV, Cooke SF. Long-term potentiation and long-term depression: a clinical perspective. Clinics (Sao Paulo). 2011;66 Suppl 1(Suppl 1):3-17. doi: 10.1590/s1807-59322011001300002. PMID: 21779718; PMCID: PMC3118435.

Image Courtesy:

1. “LTP First Stage” By Tomwsulcer – Own work (CC0) via Commons Wikimedia
2. “LTP Second Stage” By Tomwsulcer – Own Work (CC0) via Commons Wikimedia