Proliferation, neurogenesis and regeneration in the non-mammalian vertebrate brain

Abstract

Post-embryonic neurogenesis is a fundamental feature of the vertebrate brain. However, the level of adult neurogenesis decreases significantly with phylogeny. In the first part of this review, a comparative analysis of adult neurogenesis and its putative roles in vertebrates are discussed. Adult neurogenesis in mammals is restricted to two telencephalic constitutively active zones. On the contrary, non-mammalian vertebrates display a considerable amount of adult neurogenesis in many brain regions. The phylogenetic differences in adult neurogenesis are poorly understood. However, a common feature of vertebrates (fish, amphibians and reptiles) that display a widespread adult neurogenesis is the substantial post-embryonic brain growth in contrast to birds and mammals. It is probable that the adult neurogenesis in fish, frogs and reptiles is related to the coordinated growth of sensory systems and corresponding sensory brain regions. Likewise, neurons are substantially added to the olfactory bulb in smell-oriented mammals in contrast to more visually oriented primates and songbirds, where much fewer neurons are added to the olfactory bulb. The second part of this review focuses on the differences in brain plasticity and regeneration in vertebrates. Interestingly, several recent studies show that neurogenesis is suppressed in the adult mammalian brain. In mammals, neurogenesis can be induced in the constitutively neurogenic brain regions as well as ectopically in response to injury, disease or experimental manipulations. Furthermore, multipotent progenitor cells can be isolated and differentiated in vitro from several otherwise silent regions of the mammalian brain. This indicates that the potential to recruit or generate neurons in non-neurogenic brain areas is not completely lost in mammals. The level of adult neurogenesis in vertebrates correlates with the capacity to regenerate injury, for example fish and amphibians exhibit the most widespread adult neurogenesis and also the greatest capacity to regenerate central nervous system injuries. Studying these phenomena in non-mammalian vertebrates may greatly increase our understanding of the mechanisms underlying regeneration and adult neurogenesis. Understanding mechanisms that regulate endogenous proliferation and neurogenic permissiveness in the adult brain is of great significance in therapeutical approaches for brain injury and disease.

Interaction of Atoms with Grain Surfaces in Steel: Periodic Dependence of Binding Energy on Atomic Number and Influence on Wear Resistance

“…The cells formed in proliferative (PCNAcontained) diencephalic zones migrate to preglomerular area, where their further differentiation and growth take place. The presence of D 1 and D 2 dopamine receptors [6,8] and benzodiazepine receptors B type [9] in these nuclei in the teleost fishes brain confirms these idea. The period of the blood-brain barrier shaping, during the first year of life [10] in the salmon brain may be considered as a critical stage of the paracrine interrelations predominance in the salmon brain.…”

“…In the brain of a few nonmammalian vertebrates the volume of the sensory projective zones is assumed to increase during the entire life of the animal. This is provided at the expense of proliferation of neural stem cells, located in specific regions, neurogenic niches [6]. This is related with necessity of adaptation of the CNS of such animals to increase in the body dimensions and, respectively, increase in the volume of primary sensory signaling.…”

The Continuously Growing Central Nervous System of the Nile Crocodile (Crocodylus niloticus)

“…Continuous neurogenesis has been well established in reptiles (e.g., Kaslin et al, 2008), which lends support to the supposition that the increase in mass of CNS structures does result from the addition of neurons, as well as of other cells, to these structures as body mass grows. There is, however, the possibility that the growth of the CNS structures accompanying body growth occurs solely through the increase in average cell size, as axons and dendrites become more elongated and possibly the cell soma increases in size.…”

Wandering Neuronal Migration in the Postnatal Vertebrate Forebrain

“…In mammals, this process is completed before or soon after birth, except in the dentate gyrus of the hippocampus (Altman and Das, 1965;van Praag et al, 2002) and the olfactory bulb (Altman, 1969;Lois and Alvarez-Buylla, 1994) in which it continues throughout life. In contrast, postnatal neurogenesis is found throughout the forebrain of many other vertebrate species (Kaslin et al, 2008). Since its discovery, postnatal neurogenesis has stimulated interest as a potential therapeutic treatment (Nottebohm, 1985;Okano and Sawamoto, 2008) and as a substrate for behavioral plasticity (Alvarez-Buylla et al, 1990a).…”