Neuropeptides, neuropeptidases and brain asymmetry

Brain asymmetry is understood as an anatomical, functional or neurochemical difference between the two hemispheres. It is not a static but rather a dynamic phenomenon in which both environmental and endogenous factors act as modulators. Aging modifies brain asymmetry, and an imbalance in specific asymmetries characterizes some brain disorders such as schizophrenia, depression, infantile autism or Alzheimer's disease. However, it is not clear whether these changes are a cause or a consequence of these disorders. Although this phenomenon has been extensively studied, its functional significance is not yet clear, and the neurochemical basis underlying anatomical or functional asymmetries in the brain is still poorly understood. In recent decades intensive research on the behaviour of neuropeptides has revealed asymmetries in their distribution in the brain, and there is evidence that the lateralized patterns of distribution are involved in the regulatory control of some neuropeptidase activities. Therefore, if these enzymatic activities are distributed asymmetrically, their endogenous substrates would presumably be affected in an asymmetrical way, as would the functions they are involved in. Here we review the most significant literature regarding human and animal brain asymmetry involving neuropeptides such as corticotropin-releasing hormone, cholecystokinin, luteinizing hormone-releasing hormone, thyrotropin-releasing hormone and angiotensin II, as well as their neuropeptidases.