The Dentate Gyrus Grows Throughout Life Despite Turnover of Developmentally-Born Neurons

Area of Science:

• Neuroscience
• Cell Biology
• Aging Research

Background:

• Adult neurogenesis in the hippocampus is highly plastic, but its population-level impact is uncertain.
• Theoretical models predict significant dentate gyrus (DG) growth, yet studies often show stable total neuron counts.
• This discrepancy may stem from reduced neurogenesis in older animals or be masked by the natural loss of existing neurons.

Purpose of the Study:

• To quantify the dynamics of neuronal birth and death in the rat dentate gyrus across adulthood.
• To reconcile the predicted growth from adult neurogenesis with observed changes in total DG neuron numbers.
• To investigate the role of neuronal turnover in shaping hippocampal cell populations.

Main Methods:

• Quantified developmentally-born neurons, Ki67+ cells (proliferating, proxy for adult-born neurons), and total DG neurons in rats aged 2-18 months.
• Estimated the number of adult-born neurons added and developmentally-born neurons lost.
• Calculated net changes in DG neuron population over the study period.

Main Results:

• Approximately 670,000 adult-born neurons were added, constituting 30% of the total DG population.
• The total number of DG neurons increased across adulthood, but net growth was only 385,000 cells.
• An estimated 20% of developmentally-born neurons were lost during the same interval, explaining the lower-than-predicted net growth.

Conclusions:

• Adult neurogenesis contributes significantly to the DG neuron population, but this growth is counterbalanced by neuronal turnover.
• Neuronal persistence and turnover are critical factors in understanding adult hippocampal neurogenesis and DG population dynamics.
• These findings have implications for theories of hippocampal long-term memory and psychiatric conditions involving hippocampal changes.