Abstract
Associative LTP by two independent inputs is known to be an important feature of synaptic plasticity observed in the CA1 of rat hippocampus. However, it is still unclear what kind of physiological role, especially in relation with memory and learning mechanisms, it plays and how it is inducted by two pathways. In order to investigate these questions, the specio-temporal pattern of neuronal activities during LTP induction followed by long lasting later period were studied by using both voltage-sensitive dye optical and extracellular electrical recording. Moreover, the possible contribution of back-propagating action potentials invaded into dendritic trees to the induction mechanisms of the present LTP was investigated under the assumption of STDP (spike timing dependent plasticity) mechanisms. In order to induce associative LTP rat acute slice preparations stained with Di-4-anepps were stimulated by two independent Schaffer collateral pathways with the stimulation protocol reported previously; one pathway is stimulated weakly under threshold (single pulse) while another pathways is strong over the threshold (multiple pulses). Optical signals were recorded and analyzed by using the photo-diode array system (Neuro-plexVI; Redshirt Imaging, USA). The obtained results from the present study are discussed from the view point of non-linear summation of two independent inputs and its distribution along the dendrite, together with the possible induction mechanisms obtained from low TTX experiment. [J Physiol Sci. 2006;56 Suppl:S84]
