Hormonal and humoral influences on brain development.

This review discusses evidence for neurotransmitters as developmental signals in such ontogenic processes as neural tube formation (neurulation), germinal cell proliferation, and neuronal and glial differentiation during brain organogenesis, as well as evidence for other roles of these neurotransmitters in non-neuronal tissues of vertebrates and invertebrates. Evidence also is presented for hormonal regulation of brain development during postnatal neurogenesis and for interrelationships which may link neurotransmitters and hormones in a humoral milieu, providing a variety of control mechanisms for the central and peripheral nervous system during key phases of their development. Given the evidence for neurotransmitters and hormones as coordinating influence on neural ontogeny, it is possible that drugs, stress, and environmental influences may have the ability to perturb particular aspects of these developmental systems if present during those "critical periods" when such humoral influences are important for normal ontogeny.