Functional plasticity in the hippocampal

Processes of functional plasticity such as hippocampal long-term potentiation (LTP) and long-term depression (LTD) are regarded as cellular mechanisms underlying learning and memory formation. LTP and LTD are used as suitable models for the investigation of the latter processes. During the last decades LTP was intensively investigated. However, less is known about LTD and its relation to learning. Here, studies were performed to investigate whether electrically-induced LTD within rat CA1 hippocampal slices in vitro shares common cellular features with LTD in the intact animal, with particular emphasis being placed on mechanisms required for its late maintenance. My initial studies have led to the development of stimulation protocols which were able to reliably induce different forms of LTD in vitro. Depending on the induction protocol, either a transient protein synthesis-independent early-LTD (with duration of up to 3-4 h) or a de novo protein synthesis-dependent late-LTD (lasting for at least 8 h) could be induced in the hippocampal slices in vitro. Both forms required NMDAreceptor activation during their induction. Furthermore, LTD was inputspecific, i.e., the expression was shown only by those synapses specifically stimulated by a low-frequency protocol. Thus, phenotypically LTD in vitro was characterized by analog induction properties as LTP. Recently, it was described that the induction of LTP can mark a specifically activated synapse by a ́synaptic tag ́ to capture synapse nonspecific plasticity-related proteins (PRPs) and thus maintaining input-specific LTP for prolonged periods. My studies show that in rat hippocampal slices in vitro, the induction of protein synthesis-dependent late-LTD is also