Preparing for adulthood: thousands upon thousands of new cells are born in the hippocampus during puberty, and most survive with effortful learning

Abstract

The dentate gyrus of the hippocampal formation generates new granule neurons throughout life. The number of neurons produced each day is inversely related to age, with thousands more produced during puberty than during adulthood, and many fewer produced during senescence. In adulthood, approximately half of these cells undergo apoptosis shortly after they are generated. Most of these cells can be rescued from death by effortful and successful learning experiences (Gould et al., 1999; Waddell and Shors, 2008; Curlik and Shors, 2011). Once rescued, the newly-generated cells differentiate into neurons, and remain in the hippocampus for at least several months (Leuner et al., 2004). Here, we report that many new hippocampal cells also undergo cell death during puberty. Because the juvenile brain is more plastic than during adulthood, and because many experiences are new, we hypothesized that a great number of cells would be rescued by learning during puberty. Indeed, adolescent rats that successfully acquired the trace eyeblink response retained thousands more cells than animals that were not trained, and those that failed to learn. Because the hippocampus generates thousands more cells during puberty than during adulthood, these results support the idea that the adolescent brain is especially responsive to learning. This enhanced response can have significant consequences for the functional integrity of the hippocampus. Such a massive increase in cell proliferation is likely an adaptive response as the young animal must emerge from the care of its mother to face the dangers, challenges, and opportunities of adulthood.

Born this way: Hippocampal neurogenesis across the lifespan

“…It was found that more than 7,000 proliferating cells retained BrdU expression within a week. However, most of them were no longer detected 3 weeks after the injection, indicating a similar rate of apoptosis as in the adult hippocampus (Curlik et al, ; Epp, Spritzer, & Galea, ).…”

“…The mechanisms by or purpose for which this occurs are poorly understood and only a limited number of studies to date have focused on investigating the process of hippocampal neurogenesis during adolescence. Interestingly, it has been shown that the process and time course of apoptosis of newborn granule cells in the adolescent DG closely reflect that of the adult DG, albeit to an exaggerated degree (Curlik, Difeo, & Shors, ). Specifically, juvenile rats (P21–P23) were administered an intraperitoneal (i.p.)…”

Neuroplasticity and MRI: A perfect match

“…Numerous studies revealed an up-regulation or increased survival of newly generated neurons in response to physical exercise (van Praag, Christie et al 1999, van Praag, Shubert et al 2005, complex environmental stimulation (Kempermann, Kuhn et al 1997, Olson, Eadie et al 2006, and after mastering an effortful learning task such as eye-blink conditioning (Curlik, DiFeo et al 2014), etc. Moreover, both in humans and rodents it has been shown that hormones e.g.…”

Differential effects of adolescent and adult‐initiated exercise on cognition and hippocampal neurogenesis

“…In order for these new neurons to process information, extensive neurite arborization occurs so that neurons are capable of receiving and integrating complex synaptic inputs. Thus, adolescence may be a critical period during which alterations in hippocampal function may result in organizational effects which last throughout adulthood (Blakemore & Choudhury, ; Curlik, Difeo, & Shors, ; Fuhrmann et al, ; Schneider, ; Spear, ). The prefrontal cortex also undergoes significant maturation during the adolescent period which continues into early adulthood, with increases in synaptic pruning and myelination (Blakemore & Choudhury, ; Casey, Getz, & Galvan, ; Giedd et al, ; Spear, ).…”