Psychological stress enhances noradrenaline turnover in specific brain regions in rats

Concentrations of noradrenaline (NA) and 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) in the hypothalamus, amygdala, cerebral cortex and pons + medulla oblongata were examined in male Wistar rats exposed to foot-shock or to psychological stress for 1 hour. Animals in the psychological stress group were prevented from receiving foot shock, but were exposed to responses of shocked rats. Foot shocked rats exhibited a significant reduction in NA content and a significant elevation in MHPG-SO4 level in all brain regions when compared to control rats which were neither shocked nor exposed to shocked rats. Rats exposed to the psychological stress displayed a significant reduction of NA level in the amygdala, significant elevation of MHPG-SO4 content in the hypothalamus and amygdala, and a moderate elevation of plasma corticosterone level. These results suggest that psychological stress produces mild enhancement of NA release preferentially in the hypothalamus and amygdala; while foot shock stress elicits a more intense response of noradrenergic neurons in more extended brain regions.

Influence of feeding situation on stomach ulcers and organ weights in rats in the activity-stress ulcer paradigm

Rats housed in running wheel activity cages except for 1 hr each day, during which time they were fed in their home cages, revealed more stomach ulceration, a higher level of brain MHPG-SO4, and larger weight changes in the thymus, spleen and adrenal gland, compared to rats housed in running-wheel activity cages and fed 1 hr daily in those same cages. Rats in the latter group showed more stress pathology than did control rats which were housed in standard home cages but which received the same restricted (1 hr per day) feeding schedule. These results did not support the idea that excessive running might occur in response to certain motivational states (e.g., frustration due to restricted feeding). The data suggested that feeding activity-stress rats in their home cages might aggravate the development of stomach ulcers coincident with the organ weight changes and the enhancement of noradrenaline turnover in the brain.

Time-related differences in noradrenaline turnover in rat brain regions by stress

Male Wistar rats were stressed by immobilization from 15 to 180 min and the effect on noradrenaline (NA) and 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) contents in eight discrete brain regions were determined. NA levels significantly decreased and MHPG-SO4 levels increased in the hypothalamus, amygdala, thalamus, hippocampus, pons+ med.obl. and cerebral cortex. By contrast, the basal ganglia exhibited increases in NA levels and transient decreases in MHPG-SO4 levels. The midbrain failed to show significant alterations. The most rapid and marked increase in MHPG-SO4 level was found in the hypothalamus. When rats were exposed to stress after treatment with probenecid 400 mg/kg, the hypothalamus and amygdala showed greater accumulations of MHPG-SO4 in the early phase of stress, while the pons+ med.obl. and basal ganglia in the later phase. The other regions showed virtually the same accumulations. These results suggest that NA release is enhanced by immobilization in the six regions mentioned above and that response of NA neurons occurs rapidly in the hypothalamus and amygdala but is delayed in other regions.

Mutagenicity of nitro derivatives induced by exposure of aromatic compounds to nitrogen dioxide

Mutagenic nitro derivatives were readily induced when 6 kinds of chemicals were exposed to 10 ppm of nitrogen dioxide (NO2). Single nitro derivatives were formed from pyrene, phenanthrene, fluorene or chrysene. Carbazole and fluoranthene each produced 2 derivatives substituted with nitro groups at different positions. The formation of nitro derivatives was enhanced by exposure of pyrene to NO2 containing nitric acid (HNO3, less than 100-fold enhancement) or sulphur dioxide (SO2, less than 15-fold enhancement). After 24 h of exposure the yields of the nitro derivative were 0.02% with 1 ppm of NO2 in air and 2.85% with NO2 (1 ppm) containing traces of HNO3. The nitro derivatives from all but phenanthrene and carbazole were chemically identified by means of gas chromatography (GC) and mass spectrometry (MS), and the mutagenicity of the 4 kinds of authentic nitro derivatives was tested by using Salmonella strains TA98 and TA1538 with or without the S9 fraction from rat liver treated with Aroclor 1254. The nitro derivative induced from pyrene was determined to be 1-nitropyrene; that of chrysene was 6-nitrochrysene; that of fluorene was 2-nitrofluorene; and those of fluoranthene were 3-nitrofluoranthene, and 8-nitrofluoranthene. Tested with strain TA98 in the absence of the S9 fraction, the first 4 of these derivatives yielded, respectively, 3050, 269, 433 and 13 400 revertants per nmole. Thus, each nitro derivative formed was potentially a direct-acting frameshift-type mutagen. Each compound exposed to NO2 showed a decreased mutagenic activity when tested in the presence of S9 mix. A possible explanation comes from experiments in which 1-nitropyrene was incubated with the S9 mix at 37 degree C for 10 min, and 1-aminopyrene was formed. The mutagenic activity of 1-aminopyrene was appreciable, but only about one-tenth of that of 1-nitropyrene in the Ames test.

Regional responses of rat brain noradrenergic neurones to acute intense stress

Contents of noradrenaline (NA) and its principal metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), in six brain regions of the rat were monitored simultaneously during 180 min of acute intense stress, i.e., electric tail shock under immobilization. In the hypothalamus and amygdala, NA contents decreased rapidly, and subsequently remained at the decreased levels while MHPG-SO4 contents increased progressively. The hippocampus and cerebral cortex showed more delayed changes in NA and MHPG-SO4 contents than the above regions. In the pons+med. obl., no decreases of NA contents were observed at any time, but MHPG-SO4 contents increased significantly. Neither NA nor MHPG-SO4 content changed significantly in the basal ganglia except for a transient increase of NA. These results suggest that, during acute intense stress, each brain region responds differently and the NA content is maintained at a decreased level despite continuously enhanced release of the amine.

Regional distribution and production rate of 3-methoxy-4-hydroxyphenylethyleneglycol sulphate (MHPG-SO4) in rat brain

The levels of noradrenaline (NA) and 3-methoxy-4-hydroxyphenylethyleneglycol sulphate (MHPG-SO4) in 15 brain regions showed a parallel distribution in male Wistar rats. The differences in regional distribution of MHPG-SO4 were similar to those in the rate of NA turnover reported by other investigators. The accumulation rates of MHPG-SO4 during 45 and 90 min after probenecid injection significantly correlated to the steady state levels of MHPG-SO4 in nine regions studied. With the results, the regional levels of MHPG-SO4 either in untreated or in probenecid-treated rats, are considered to be a useful index of NA turnover.