Abstract: In this paper the brain levels of NE, DA and 5-HT in rats killed bydecapitation or by being frozen in liquid nitrogen were compared. Furthermore,the changes of these transmitters contents in the brain were determined afterthe brain was placed in a-6℃ refrigerator for 2 and 5 days after being frozenin liquid nitrogen. It was found that rio significant difference between decapita-tion and being frozen in liquid nitrogen was detected in neurotransmittercontents. But the longer the samples were placed in the refrigerator, themore loss in monoamine neurotransmitters was observed.

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