How peptidergic neurons cope with variation in physiological stimulation.

A general scheme for neuropeptide metabolism is outlined and the potential sites of regulation are discussed. Two major sites of regulation are distinguished: transcription which ultimately limits the rate of translation to form the prepropeptide, and post-translational processing steps. The consequences of up-regulation of these steps in response to increased metabolic demand are discussed. An alternative strategy for peptidergic neurons, reliance on a large pool of neuropeptide, is proposed. Data on the response of enkephalin-containing cells to increased levels of stimulation are reviewed. It is concluded that there is good evidence for genomic up-regulation, perhaps in association with regulation of processing. Evidence based on studies on enkephalin-containing amacrine cells in the chicken retina is also reviewed. It is suggested that these cells rely on a large pool of neuropeptide to cope with changes in demand.