The effects of single and multiple episodes of theta patterned or high frequency stimulation on synaptic transmission from hippocampal area CA1 to the subiculum in rats

Long-term potentiation (LIP) is a popular model for the synaptic changes th at may occur during learning and memory; it involves a strengthening of syn aptic response and is readily induced in the hippocampus, an area of the br ain implicated in learning and memory. Previous research on LTP has focused on 'early' components of the hippocampal circuitry, that is, the dentate g yrus and areas CA1 and CA3. This paper examines the plasticity of the CA1-s ubiculum pathway; we extend our previous work in this area demonstrating th at the projection from area CA1 to subiculum sustains theta-patterned stimu lus-induced LTP in vivo. We show that this pathway remains potentiated over a long period (3 h). Furthermore, once this projection is potentiated, it seems resistant to further episodes of high-frequency stimulation. We discu ss the implications of these findings for theories of hippocampal-cortical interaction during the biological consolidation of memory. (C) 1999 Elsevie r Science Ireland Ltd. All rights reserved.