Levels of Norepinephrine and Dopamine in Mouse Brain Regions Following Microwave Inactivation‐rapid Post‐mortem Degradation of Striatal Dopamine in Decapitated Animals

Abstract

—The effects of 2 methods of killing on norepinephrine and dopamine in mouse brain regions were examined. One method utilized decapitation, while the other method utilized heating with microwave irradiation concentrated on the head. The norepinephrine and dopamine contents of the cerebellum, medulla‐pons, midbrain, diencephalon, hippocampus, corpus striatum, and cerebral cortex were determined by methods using liquid chromatography with electrochemical detection. Dopamine content in striatum was also quantitated by the method of gas chromatography with mass fragmentography. A significantly lower value for decapitated animals, as compared to the microwave heated group, was found only for dopamine exclusively in the striatum. Activities of the enzymes tyrosine hydroxylase, DO PA decarboxylase, monoamine oxidase, and catechol‐o‐methyltransferase in the striatum were also examined. These enzymes were totally inactivated by the microwave heating, except catechol‐o‐methyltransferase which was decreased approx 80%. These results support either (1) the existence of a substantial pool of dopamine in the striatum with a very rapid turnover rate or (2) a decapitation‐related release and destruction of striatal dopamine. Measurements of 3‐methoxytyramine in the striatum exhibit post‐mortem increases corresponding to the decreases of dopamine. Use of the rapid tissue enzyme inactivation technique suggests that in vivo levels of this O‐methylated dopamine metabolite are an order of magnitude lower than the results normally obtained after killing by decapitation.

Evidence for Noncanonical Neurotransmitter Activation: Norepinephrine as a Dopamine D2-Like Receptor Agonist

“…With our findings on relative potencies, the previously reported so-called cross reactivity phenomenon between dopamine and norepinephrine (Guiard et al, 2008;Gonzalez et al, 2012a;Lei, 2014) can now be better explained at the receptor-effector levels and considered as likely biologically occurring events. Furthermore, dopamine and norepinephrine concentrations in prefrontal cortex are comparable (Koob et al, 1975;Blank et al, 1979;Li et al, 1998), suggesting that actions of norepinephrine at cortical D 2 -like receptors are likely functionally significant.…”

Deamination of norepinephrine, dopamine, and serotonin by type A monoamine oxidase in discrete regions of the rat brain and inhibition by RS-8359.

“…Hence the inconsistency between the results of the previous studies and those of the present study cannot be explained simply by the difference in the methods used to sacrifice animals. However, because decapitation has been reported to change the levels of monoamines and metabolites (21,22), the levels of monoamines and metabolites could be affected by the time required for preparing the samples following decapitation. This artifact is eliminated in the present study because we used microwave irradiation to sacrifice the animals.…”

Effects of chronic neuroleptic treatment on dopamine release: Insights from studies using 3-methoxytyramine

“…In contrast, more recent studies using higher power microwave instruments and more sensitive assays have found significant increases of basal 3-MT in the striatum and accumbens following haloperidol (Wood et al, 1983(Wood et al, , 1987bKaroum and Egan, 1992). Differences may be due to the use of increased microwave power, which reduces the time required for enzyme inactivation and thus decreases the potential for 3-MT formation from agonal-related releases of dopamine (Blank et al, 1979). In contrast to basal 3-MT, 3-MT accumulation has consistently been found to be increased by doses of haloperidol above 0.1mg/kg as well as by a variety of other neuroleptics (Westerink, 1979;Waldmeier et al, 1981;Saller and Salama, 1986; see Wood and Altar, 1988 for discussion).…”

“…Westerink and Spaan, 1982) or had methodological problems, such as improper microwave fixation of brain tissue (Vulto et al, 1986; see discussion in Wood and Altar, 1988). More recent studies using improved microwave irradiators (Blank et al, 1979) have consistently found increased 3-MT accumulation in the striatum, nucleus accumbens, and prefrontal cortex under conditions shown to increase dopamine release using other methods (e.g. Wood et al, 1987b;Chrapusta et al, 1992Chrapusta et al, , 1993Egan et al, 1996;Karoum et al, 1994a,b).…”