In vivo investigation of the effects of light/dark cycle changes on synaptic plasticity in the dentate gyrus of the rat hippocampus

Abstract

Aim: To investigate the impact of alterations in the light-dark cycle on the activity of dentate gyrus neurons within the hippocampus.

Methods: The Light/Dark cycle was implemented in controlled environments equipped with automated lighting systems, maintaining a consistent 12-hour duration for each phase. Wistar Albino male rats were categorized into two groups. The light group was exposed to light from 08:00 to 20:00 followed by darkness, while the dark group remained in darkness from 08:00 to 20:00 and was exposed to light during the subsequent 12 hours. All periods were examined concurrently at the same time of day on the 30th experimental day.

Results: There was no statistical difference in the slopes of excitatory postsynaptic potentials (EPSP) and the amplitudes of population spikes (PS) across varying stimulation intensities (p>0.05), with the exception of the 1.5 mA intensity (p=0.04). The stimulus facilitation index for the EPSP slope was significantly greater in the light group compared to the dark group at 120, 140, and 160 ms (p<0.05). The enhancement observed in the night group relative to baseline values during the PTP, induction, and maintenance periods was significantly lower than that in the light group (p<0.001).

Conclusion: The results suggest that variations in light-dark frequency can influence the electrical characteristics of dentate gyrus neurons, indicating the presence of an endogenous timing mechanism within the hippocampus that may regulate hippocampal Long-Term Potentiation (LTP).