Fish Neurogenesis in Context: Assessing Environmental Influences on Brain Plasticity within a Highly Labile Physiology and Morphology

Abstract

Fish have unusually high rates of brain cell proliferation and neurogenesis during adulthood, and the rates of these processes are greatly influenced by the environment. This high level of cell proliferation and its responsiveness to environmental change indicate that such plasticity might be a particularly important mechanism underlying behavioral plasticity in fish. However, as part of their highly labile physiology and morphology, fish also respond to the environment through processes that affect cell proliferation but that are not specific to behavioral change. For example, the environment has nonspecific influences on cell proliferation all over the body via its effect on body temperature and growth rate. In addition, some fish species also have an unusual capacity for sex change and somatic regeneration, and both of these processes likely involve widespread changes in cell proliferation. Thus, in evaluating the possible behavioral role of adult brain cell proliferation, it is important to distinguish regionally specific responses in behaviorally relevant brain nuclei from global proliferative changes across the whole brain or body. In this review, I first highlight how fish differ from other vertebrates, particularly birds and mammals, in ways that have a bearing on the interpretation of brain plasticity. I then summarize the known effects of the physical and social environment, sex change, and predators on brain cell proliferation and neurogenesis, with a particular emphasis on whether the effects are regionally specific. Finally, I review evidence that environmentally induced changes in brain cell proliferation and neurogenesis in fish are mediated by hormones and play a role in behavioral responses to the environment.

Plasticity and Adult Neurogenesis in Amphibians and Reptiles: More Questions than Answers

“…Enriched environments have been shown to increase the number of new cells in the brains of mammals, of course, both in the hippocampus [Kempermann et al, 1997; for a review, see Kempermann et al, 2010] and, if the olfactory environment was enhanced, in the olfactory bulb [Rochefort et al, 2002;Rochefort and Liedo, 2005]. They have also been shown to increase neurons in the brains of crustaceans [Ayub et al, 2010], insects [Scotto-Lomassese et al, 2000], and fish [Dunlap, 2016]. A recent study also showed enhancement in pigeons given an enriched environment [Melleu et al, 2016], but only in the hippocampus; other areas of the telencephalon showed no effect or even a decrease in cells.…”

“…In addition, studies on fish by Dunlap and his colleagues [reviewed in Dunlap, 2016] show important effects of social novelty on new cell production. In contrast, group housing without physical enrichment of the environment does not enhance neurogenesis in the dentate gyrus of rats [Brenes et al, 2015].…”

“…In the single study of day length, longer photoperiods increased the production of new cells. The long day length and warm conditions may cause the lizards to be more active, thus stimulating neurogenesis due to increased mitosis throughout the body (hence a generalized response) [see Dunlap, 2016]. Clearly the effects could be directly on the physiology of these ectothermic species as well.…”

Brain evoked potential Analysis of Effects of Popular Music Training on Adolescents' Cognitive Neurobehavioral Plasticity

“…Meanwhile, pop music training also promoted the changes in other cognitive functions of the individual. The plasticity of the brain referred to the ability of neurons to respond to stimuli and make changes (Dunlap, 2016). In addition, the requirements for each type of training were different, so the areas and levels of activation were also different in the training (François et al, 2016).…”

Can juvenile Baltic sturgeon ( Acipenser oxyrinchus ) smell the enemy?

“…In a recent study (Camara-Ruiz, Santo, Gessner, & Wuertz, 2019), an increase of neuroplasticity markers in fish that were trained to feed prey buried in the sand compared to fish that were not trained was observed. Among these markers pcna, neuroD and bdnf are established markers for neuronal activity and neurogenesis and have been used as tools to understand how external stimuli influence the brain (Dunlap, 2014(Dunlap, , 2016Mes, Krogh, Gorissen, Mayer, & Vindas, 2018). Neuropeptides such as brain-derived neurotrophic factor (bdnf) promote neurogenesis, neuron survival and differentiation as well as synaptic plasticity, thereby modulating the brain in response to the rearing environment (Ebbesson & Braithwaite, 2012;Mattson, Maudsley, & Martin, 2004;Shors, Anderson, Curlik, & Nokia, 2012).…”