Behavioral and Brain Sciences

Open Peer Commentary

Principles of brain tissue engineering

William J. Freeda1 and Thressa D. Smitha2

a1 Neuropsychiatry Branch

a2 Clinical Brain Disorders Branch, National Institute of Mental Health Neuroscience Center at St. Elizabeths, Washington, DC 20032.


It is often presumed that effects of neural tissue transplants are due to release of neurotransmitter. In many cases, however, effects attributed to transplants may be related to phenomena such as trophic effects mediated by glial cells or even tissue reactions to injury. Any conclusion regarding causation of graft effects must be based on the control groups or other comparisons used. In human clinical studies, for example, comparing the same subject before and after transplantation allows for many interpretations of the causes of clinical changes.