The dentate gyrus-CA3 circuit in the hippocampus is highly plastic during development and morphologically responsive to various environmental outputs. The current study investigated the structural changes in CA3 pyramidal neurons during development (p18-p24) and the effect of AMPA receptor antagonism on spatial learning and memory. Exp.1 showed individual changes in the elements of CA3 pyramidal neurons. Some parts expanded with age and others retracted. Golgi analysis revealed a reduction in spine density and an increase in thorny excrescences (TE), suggesting a role for TE in spatial abilities that emerge at the same age. Exp.2 investigated the effect of AMPAr antagonism (NBQX) on spatial function and on CA3 pyramidal neuron structure. NBQX-injected rats showed impaired spatial abilities and individual remodeling in different components of CA3 pyramidal neurons including an increase in spines density and a decrease in TE. This suggest a role for TE in mediating spatial learning and memory.