The effect of freezing and extraction upon striatal dopaminergic function.

Determinations of striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations were compared under conditions where tissue was either frozen followed by extraction (FE) or extracted followed by freezing (EF). In Experiment 1, these determinations were performed at 0 (control), 0.5, 1 or 2h postmortem. In Experiment 2, these two protocols were compared at 0 (control), 0.5 or 72 h after a neurotoxic regimen of methamphetamine. In Experiment 3, potassium-stimulated DA release from superfused striatal tissue was compared between frozen and fresh tissue. The results from the 0 h (control) groups of Experiments 1 and 2 revealed that FE results in significant reductions in DA concentrations as compared with the EF procedure. However, FE diminishes the time-dependent reductions in striatal DA and increases in DOPAC present in the EF group, as obtained under conditions of natural (Experiment 1) or neurotoxin-induced (Experiment 2) degradation. Potassium-stimulated DA release from superfused striatal tissue is significantly decreased when measured from frozen versus fresh tissue. While freezing seems to produce an initial detrimental effect upon measuring striatal DA concentrations and potassium-stimulated release, there appears to be a capacity for preservation of striatal DA and diminution in DOPAC production by freezing when tissue is undergoing degradation. Such results demonstrate the significance of the protocol used for determination of neurotransmitters in postmortem tissue and suggest a potential means for diminishing the adverse effects of insult to striatal tissue that may result from conditions like stroke and exposure to neurotoxins.