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Neural development describes the growth and development of the nervous system starting from embryogenesis and continuing throughout life.
After two weeks of embryogenesis, three basic cell layers, the endoderm, mesoderm and the ectoderm (collectively called the gastrula) have been formed. The notochord, an area which will later become the nervous system, is located in the ectoderm layer. Induction signals from the notochord inform the neural plate to develop by switching on specific genes. These genes upregulate a process called neurulation in the ectoderm which leads to the formation of the neural plate. The cells of the plate will later differentiate into motor neurons and the rest of the notochord cells become sensory neurons. Folding of the neural plate occurs until it forms a neural tube by approximately day 22 of embryogenesis.
The neural tube initially expands from the anterior telencephalon due to cell proliferation. Over time proliferation of the cells of the neural tube ceases and they begin to differentiate into neurons and glial cells. Newly differentiated neurons begin to migrate to various areas of the brain where they will later settle and start to organize into different structures. From here, the neurons extend long axons and dendrites so that they can interact with other neurons via neurotransmission at synapses. This communication finally establishes functional neural circuits that will mediate sensory and motor processes in the postnatal brain.
Many neurotransmitters and neuromodulators such as serotonin, dopamine and GABA are present in early embryogenesis, long before the onset of synaptogenesis, and have pleiotropic effects during the development of the brain. Alterations in these substances, pharmacological agents, toxic insult or genetic modification can all have a profound impact and negative consequences on the development of the brain and nervous system.
Development of the brain during embryogenesis can be significantly altered by drugs being taken by the mother either medicinally or recreationally, as well as by environmental toxicants and natural contaminants. Prenatal cocaine exposure can lead to long-lasting behavioral, molecular and cellular changes including attention deficit, altered cell production and changes in genetic regulation. Amphetamines and MDMA can lead to cardiac and learning defects and fetal distress. These drugs primarily alter the mechanisms of dopaminergic and 5-HT systems, which can be targeted therapeutically in neurological disorders.