Responsiveness of Dendrites to the Glutamate Applied Focally with Pressure Ejector and Iontophoresis into Hippocampal Slices

Glutamate is the most common excitatory amino acid in the brain. Responsiveness of dendrites to the glutamate greatly varies depending on the application sites. Especially, a point of the maximal response to the glutamate of the dendrite is called as 'hot spot'. In our experiment, the responsiveness of the hot spot to the glutamate was investigated in the CA1 pyramidal neuron of the rat hippocampal slice. CNQX, the antagonist of AMPA receptor, blocked 95% of membrane current to the glutamate focal application $(I_{gl}).$ Train ejection of glutamate on one point of the dendrite increased or decreased the amplitude of $I_{gl}$ with the pattern of train, and the changes were maintained at least for 30 min. In some cases, glutamate train ejection also induced calcium dependent action potentials. To evoke long-term change of synaptic plasticity, we adopted ${\theta}-burst$ in the glutamate train ejection. The ${\theta}-burst$ decreased the amplitude of glutamate response by 60%. However, after ${\theta}-burst$ glutamate train ejection, the calcium dependent action potential appeared. These results indicated that the focal application of glutamate on the neuronal dendrite induced response similar to the synaptic transmission and the trains of glutamate ejection modulated the change of AMPA receptor.