PRE AND POST SYNAPTIC MECHANISMS INVOLVED IN THE INDUCTION AND MAINTENANCE OF LONG-TERM POTENTIATION

Changes in the strength of the synaptic connections is critical to man y aspects of the nervous system physiology, included learning, memory (24, 34, 40), and some neuropathologies. A model that displays a long term modification of synaptic responses, therefore, presents us with a n opportunity to analyze the plastic and adaptive mechanism of the ner vous system to various influences, such as the effect of certain psych iatric drugs or to pathological conditions. Long-term potentiation (LT P) is a useful model for the study of neural plasticity. it is general ly agreed that LTP, defined as a long-lasting enhancement of synaptic transmission, has two phases: induction and maintenance. Several studi es have suggested that the main mechanisms involved in the induction o f LTP include the participation (mainly in CA1 and dentate area of the hippocampus) of both NMDA and non-NMDA types of glutamate receptors, of calcium, etc. The dynamics of these mechanisms may explain, at leas t in part, the main properties of LTP, viz., synapse specificity, coop erativity and associativity. With respect to the maintenance phase, so me scientists believe that it is exclusively presynaptic, while others believe that only postsynaptic mechanisms are involved, Recent experi mental evidence suggests, however, that both presynaptic and postsynap tic components are involved. Several investigations have shown that bo th induction and maintenance of LTP can be altered by various factors: by the administration of glutamatergic and GABAergic agonists or anta gonists, by the anatomical site of stimulation as well as the paramete rs of stimulation, among others. Of particular relevance to medical pr actice, it has been the demonstration that several drugs used in the p sychiatric pharmacotherapy can modify LTP. LTP is also known to be cha nged in experimental models of epilepsy, and some cellular mechanisms important in LTP are altered while others are preserved in the brains of patients whit neurodegenerative diseases, such as Alzheimer disease . Since LTP is very important in the understanding of plastic mechanis ms in the nervous system, this review provides several lines of eviden ce about the pre and postsynaptic mechanisms involved in the induction and maintenance of this interesting phenomenon.