Of the environmental factors which have an impact on body weight, nutrients are most influential. Within normal limits, hypothalamic and related neuronal populations correct perturbations in energy metabolism, to return the body to its nutritional set-point, either through direct response to nutrients or indirectly via peripheral appetite signals. Excessive intake of certain macronutrients, such as simple carbohydrates and SFA, can lead to obesity and attendant metabolic dysfunction, also reflected in alterations in structural plasticity, and, intriguingly, neurogenesis, in some of these brain regions. Neurogenesis, previously thought to occur only in the embryo, is now known to take place in the adult brain, dependent on numerous stimulating and inhibiting factors, including dietary components. Because of classic associations between neurogenesis and the hippocampus, in learning and cognition, this brain region has also been the focus of attention in the study of links between diet and neurogenesis. Recently, however, a more complete picture of this relationship has been building: not only has the hypothalamus been shown to satisfy the criteria for a neurogenic niche, but appetite-related mediators, including circulating hormones, such as leptin and ghrelin, pro-inflammatory cytokines and the endocannabinoid intracellular messengers, are also being examined for their potential role in mediating neurogenic responses to macronutrients. The present review draws together these observations and investigates whether PUFA may exert their attenuating effects on body weight through the stimulation of adult neurogenesis. Exploration of the effects of nutraceuticals on neurogenic brain regions may encourage the development of new rational therapies in the fight against obesity.

The increasing appreciation of structural plasticity, namely the capacity of the nervous system to alter not only its function but also its constitution in response to changing conditions, indicates a profound transformation in the scientific comprehension of the human brain. The research on adult neurogenesis, i.e. on the de novo formation of neurons in the mature brain, has been chosen as a circumscribed field to study the controversies that accompany the transition from the concept of a stable to that of a structurally plastic mammalian brain. Building on the concepts of thought style and thought collective developed by Ludwik Fleck, this article investigates the ways in which neurogenesis in the adult brain has changed from being negated to being accepted and highly valued, and consequently has become the focus of a novel research field. This analysis covers a period from the second half of the twentieth century up to the present. The development of research on adult neurogenesis has been shaped by two opposing views: the understanding of a particularly immutable and thus specifically human brain on the one hand, and a plastic brain which remains malleable during the entire adult life, on the other hand. This plastic human brain has created new space for the articulation of the ‘therapeutic promise’, since it lends itself much more readily to therapeutic intervention than a stable brain: the article argues this to be decisive in promoting the transformation of thought style within the neurosciences.

The zebrafish has recently assumed a central position in the study of vertebrate development. Numerous studies of other fish have shown that their central nervous systems, and especially their visual systems, continue to add new neurons throughout life, which is probably related to their abilities to regenerate axons and whole nervous tissue. Retinal neurogenesis had not been examined in adult zebrafish, and two reports concluded that the optic tectum ceased neurogenesis early in life, so the question arose whether the zebrafish was anomalous in this regard. We labeled embryonic (24- and 48-h postfertilization) and adult zebrafish with the thymidine analog, bromo-deoxyuridine, and, after short and long survivals, examined the retina and brain for labeled cells. They were abundant in both the optic tectum and the retina. Although the rate of retinal growth slows considerably between embryonic and adult stages, the patterns of neurogenesis in both the embryo and the adult are similar to those described in other fish, so these “fish-specific” features of general interest can justifiably be studied in zebrafish.