Synaptic Plasticity: Hyperexcitability and Synaptic Silencing

Summary

Synaptic plasticity is defined as any sort of change in intensity of the synaptic response or in the number of synapses that occurs in nervous structures. Long-lasting increase or decrease of synaptic efficacy — termed long-term potentiation (LTP) and long-term depression (LTD), respectively — has been related to the establishment of memory traces. Experimental induction of both types of long-lasting changes has contributed effectively to the study of the mechanisms that underlie the learning processes. Although the wealth of mechanisms related to synaptic plasticity still remains partially unveiled, at the core of this phenomenon lies the glutamate receptor system together with neurotrophins and their receptors, second-messenger cascades, and changes of gene expression. An increase in the numbers of synapses is termed structural plasticity, and is governed mainly by molecules belonging to the neurotrophin and cytokine families. This form of plasticity participates in the establishment of the intricate arrays of nervous connections during normal development, and in rearrangements of the neuronal circuitries that occur after nervous lesions.