The Effect of Changes in the Visual Experience during Critical Periods of Brain Development on the Synaptic Plasticity of Hippocampal CA1 Neurons in Rats

Changes in the visual experience during the critical periods of brain development lead to the dysfunction of the visual cortex.The visual cortex is a major supplier of sensory input in the mammalian hippocampus. This study aimed to investigate the effects of visual deprivation on the synaptic plasticity of CA1 neurons in this area. This experimental study was conducted on 48 male Wistar rats who had been classified into the two main groups of a 12-12 Light Reared (LR) and Dark Reared (DR) since birth.To perform the experiments, the rats were categorized under 3 subgroups of 2, 4 and 6 weeks of age. Excitatory postsynaptic potentials (EPSP) were recorded for 30 minutes from the dendrites of neurons in the CA1 area. Afterwards, long-term potentiation (LTP) was induced through Tetanic stimulation. Finally, the amplitude of the responses were measured before and after the Tetanic stimulation. The amplitude of basic responses in the 2WLR and 6WLR group were 1.28± 0.05 Mv and 1.09 ± 0.03 Mv, respectively (p<0.0001) while the range increased from 1.30 ±0.30 Mv in the 2WDR group to 1.50 ± 0.4 Mv in the 6WDR group (p<0.0001). Upon LTP induction, the highest rise in the amplitude response was observed at the age of 2 weeks in the animals. However, the increasing responses in both groups of LR and DR diminished with age (p<0.0001). Visual deprivation during the critical periods of brain development might lead to an increase in the basal synaptic activity of hippocampal CA1 neurons through an age-related process. Although it does not interrupt the induction of LTP in neurons, it might reduce its intensity and stability.