Characterization of hippocampal synaptic plasticity in the freely behaving neonatal rat

In a previous study, we demonstrated that long-term depression (a lasting diminishment in synaptic strength) can be reliably induced in the hippocampal dentate in the anesthetized adult rat. Subsequently, we reported on findings of bidirectional plasticity in freely behaving rats at two ages of development (15 and 90 days of age). However, key questions concerning the age at which bidirectional regulation of synaptic plasticity begin to occur in the hippocampus remain unanswered. In the present study, we address these questions by examining electrophysiological data in freely behaving rats at 12 days of age. Specifically, we recorded extracellular field potentials from the hippocampal subfield known as the dentate gyrus evoked by stimulation of the lateral perforant pathway at 1 Hz. Preliminary results indicate that long-term depression, a neuronal response mechanism impacting on synaptic transmission efficacy, is already in place by the 12th day of postnatal development. These preliminary findings may provide evidence of age-related changes in dynamic gain regulation of synaptic response and, therefore, may have important implications for memory and learning in developing neural circuits.