Steroid biosynthesis within the frog brain : a model of neuroendocrine regulation

• There is now clear evidence that the brain, similar to the adrenal gland, gonads, and placenta, is a steroidogenic organ. Notably in the frog brain, the presence of various steroidogenic enzymes has been detected by immunohistochemistry in specific populations of neurons and/or glial cells. These steroidogenic enzymes are biologically active, as shown by the ability of brain tissue explants to convert [(3)H]pregnenolone into various radiolabeled steroids. The frog brain has also been extensively used as a model to study the mechanism of regulation of neurosteroidogenesis by neurotransmitters and neuropeptides. It has been demonstrated that the biosynthesis of neurosteroids is inhibited by gamma-aminobutyric acid (GABA), acting through GABA(A) receptors, and neuropeptide Y, acting through Y1 receptors, and is stimulated by the octadecaneuropeptide (ODN), acting through central-type benzodiazepine receptors, triakontatetraneuropeptide (TTN), acting through peripheral-type benzodiazepine receptors, and vasotocin, acting through V1a-like receptors. These data indicate that some of the neurophysiological effects of neurotransmitters and neuropeptides may be mediated through modulation of neurosteroid biosynthesis.

Nyckelord

eurosteroids

brain

neuropeptides

neurotransmitters

amphibians

MEDICINE

MEDICIN

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