Effects of tissue storage and freezing on brain glutamate uptake

Glutamate uptake appears to be stable when measured in rat striatal synaptosomes from tissue stored for up to four hours post-mortem at 25°C. Between four and eight hours storage at room temperature there is a sharp 70% decrease in uptake. Freezing of tissue on dry ice, storage at 4°C for up to 7 days and at ?80°C for 5 days results in 20–30% residual glutamate uptake. Quantitatively similar data can be obtained in eight extrastriatal brain areas. Kinetic analysis of glutamate uptake in stored and frozen tissue reveals the loss of the majority of both sodium-dependent high affinity and temperature-sensitive low affinity sites (v_max-values) while the respective K_m-values are not significantly changed. Pharmacological properties of the high affinity uptake versus a number of specific and metabolic uptake inhibitors remain unaltered by the storage and freezing procedure. The tissue treatment chosen for the present study roughly corresponds with the preparation of human post-mortem brain tissue for enzyme-, receptor-binding- or neuro-transmitter assays. It therefore seems conceivable that meaningful uptake studies can be performed on human autopsy material, thus adding an important parameter to the battery of neurochemical markers already accessible for post-mortem $\text{in}$$\text{vitro}$ examination.