Astrocytes (Astro from Greek astron = star and cyte from Greek “kytos” = cavity but also means cell), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. The proportion of astrocytes in the brain is not well defined. Depending on the counting technique used, studies have found that the astrocyte proportion varies by region and ranges from 20% to 40% of all glia. Overall, astrocytes outnumber neurons by over fivefold. They perform many functions, including biochemical support of endothelial cells that form the blood–brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, and a role in the repair and scarring process of the brain and spinal cord following traumatic injuries.
Research since the mid-1990s has shown that astrocytes propagate intercellular Ca2+ waves over long distances in response to stimulation, and, similar to neurons, release transmitters (called gliotransmitters) in a Ca2+-dependent manner. Data suggest that astrocytes also signal to neurons through Ca2+-dependent release of glutamate.
- Exercise and nutrition can influence brain development.
- Exercise and nutrition can slow down and reverse cognitive decline in the elderly.
- Exercise and nutrition influence brain health through several mechanisms to stimulate nerve cell generation or neurogenesis.
- Polyphenols have the potential to stimulate neurogenesis.
- Polyphenols improve memory, learning and general cognitive ability.
- Fruits, berries and vegetables are rich in antioxidants and bioactive compounds that may reduce disease risk stemming from reactive oxygen species and are also associated with cognitive benefits.
Note: The accumulation of bioactive compounds is highly dependent on the plant species.
Nutrition has a specific role in providing energy and building material for the body. The ability of nutrients to prevent and protect against diseases is starting to be recognized. Physical activity has also been associated with the reduction of a number of physical and mental disorders. Therefore, both nutrition and exercise are used as interventions to stimulate health. Recent data indicates that not only general health, but also brain functioning is influenced through exercise and nutritional interventions (Gomez-Pinilla, 2011). This Sports Science Exchange will describe how exercise and nutrition can influence neurogenesis or the generation of new nerve cells, and therefore have a neuroprotective effect.
NEUROGENESIS AND NEUROPLASTICITY
Neurogenesis is the process of generating new nerve cells, including neurons, astrocytes, glia and others. Neuroplasticity refers to the ability of the brain and the central nervous system (CNS) to adapt to environmental change, respond to injury and to acquire novel information by modifying neural connectivity and function. Neurotrophins are molecules that support neuroplasticity and in particular, are capable of signaling neurons to survive, differentiate or grow (Knaepen et al., 2010). Therefore, neurotrophins have gained increasing attention in research for the treatment and prevention of neurodegenerative and, more recently, metabolic diseases. Neurotrophic factors not only play a role in neurobiology, but also in central and peripheral energy metabolism. Their effect on synaptic plasticity in the CNS involves elements of cellular energy metabolism, and in the periphery, they take part in metabolic processes such as enhancing skeletal muscle lipid oxidation via activation of adenosine monophosphate-activated protein kinase (AMPK). Neuroplasticity is an “activity-dependent” process and therefore nutrition and physical activity (exercise and training) appear to be key interventions that trigger the processes through which neurotrophins mediate energy metabolism and in turn neuroplasticity (Knaepen et al., 2010). Of all the neurotrophins, brain-derived neurotrophic factor (BDNF) seems to be the most sensitive to regulation by exercise and physical activity.
THE IMPORTANCE OF BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF)
BDNF is most abundant in brain areas that are associated with cognitive and metabolic regulation: the hippocampus and the hypothalamus. Hypothalamic BDNF appears to inhibit food intake and increase energy expenditure, leading to a negative energy balance. In the hippocampus, the involvement of BDNF in neural plasticity and neurogenesis is important to learning and memory. BDNF stimulates the development and differentiation of new neurons and promotes long-term potentiation (LTP), which is widely considered to be one of the major mechanisms underlying memory acquisition, consolidation and storage in the brain. It is also known to be controlled at the molecular level by the activation of a number of neuronal signaling pathways.