Reversible changes in goldfish brain polyamine concentrations and synthetic enzymes after cold exposure.

Exposure of goldfish to the cold (5 degrees C) caused a sharp increase in brain putrescine level during the first week. Such increase continued at a minor rate for the whole period of exposure (2 months). In contrast, the content of spermidine and spermine remained unchanged. Putrescine increase was concomitant with a remarkable rise in ornithine decarboxylase activity (ODC), which reached a maximum stimulation after 1 week of cold exposure, and declined thereafter, remaining significantly higher than the control for the entire period of study. Cold exposure caused also a reduction of S-adenosylmethionine decarboxylase (AdoMetDC) activity and an increase of ornithine level, whereas methionine content was unchanged. When fish exposed to cold temperature were returned to 20 degrees C, the modifications observed on brain polyamine metabolism were completely reversed. Supported by previous observations, our results suggest that the changes in the polyamine metabolism induced in goldfish brain by cold exposure could represent an homeostatic mechanism carried out by the goldfish to minimize the possible effects of thermal changes.