Neurotrophins

In a developing fetal brain, chemicals called neurotrophins promote neuron growth. Nerve growth factor (NGF) was the first neurotrophin to be identified; others include brain-derived neurotrophic factor (BDNF); glial-derived neurotrophic factor (GDNF); neurotrophin-3; and neurotrophin-4/5 (the number depends on the species). NGF and neurotrophin-3 are known to be particularly important in the embryonic development of sensory neurons and sympathetic ganglia.

Neurotrophins also have important functions in the adult nervous system. NGF is required for the maintenance of sympathetic ganglia, and there is evidence that neurotrophins are required for mature sensory neurons to regenerate after injury. In addition, GDNF may be needed in the adult to maintain spinal motor neurons and to sustain neurons in the brain that use the chemical dopamine as a neurotransmitter.

Experiments suggest that neurons of the CNS can regenerate if they are provided with the appropriate environment. While neurotrophins promote neuron growth, some chemicals, including myelin-associated inhibitory proteins, have been shown to inhibit axon regeneration. Research in this area, with its important implications for the repair of spinal cord and brain injury, is ongoing.

The Nervous System: Neurons and Synapses 159

The Nervous System: Neurons and Synapses 159

Astrocyte Foot Process

Figure 7.10 Astrocytes have processes that end on capillaries and neurons. Astrocyte end-feet take up glucose from blood capillaries and use this to help supply energy substrates for neurons. Astrocytes also take up the neurotransmitter glutamate from synapses and convert it to glutamine (Gln), which is then recycled to the neurons.

Figure 7.10 Astrocytes have processes that end on capillaries and neurons. Astrocyte end-feet take up glucose from blood capillaries and use this to help supply energy substrates for neurons. Astrocytes also take up the neurotransmitter glutamate from synapses and convert it to glutamine (Gln), which is then recycled to the neurons.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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