Dynamics of a pyramidal neuron in hippocampus (CA3 neuron) is modeled in a discrete form based on physiological findings, which is known to involve dendritic calcium-activated dynamics. Responses of the CA3 neuron model to excitatory stimulus on the apical dendrites is studied under the varied somatic inhibition. Computer simulations show the following phenomena: The CA3 neuron model behaves in the spatially cooperative manner under the weak somatic inhibition. On the other hand, when the somatic inhibition is strong, dendritic activities are forced to be localized. These results suggest that proximal dendrite branches could control the dendritic interaction among more distal ones. Highly organized neuronal information processing might be possible by the cooperation of the hierarchically interacting dendrite system and the distribution pattern of synapses on it.