Influence of freezer storage time on cerebral biogenic amine and metabolite concentrations and receptor ligand binding characteristics

Brains from breed and age-matched canines stored at -80 degrees C for between 3 and 44 months showed a time-dependent decline in the concentration of norepinephrine in the amygdala and dopamine and norepinephrine in the caudate. No changes were seen in the density or ligand affinities of prazosin or spiperone binding sites in the same areas nor were there changes in quinuclidinyl benzylate binding sites in the frontal cortex. The changes in dopamine concentrations in the caudate were not accompanied by changes in the concentrations of dopamine metabolites. The chromatograms from which the dopamine and norepinephrine concentrations were estimated contained several unidentified, amperometrically detectable, extraneous peaks which increased in size in the older tissue samples. These results suggest that the decline in dopamine and norepinephrine concentrations was not the result of enzymatic breakdown, but probably the result of chemical decomposition. These findings have significance for the measurement of dopamine and norepinephrine concentrations in autopsied brains kept frozen in storage.