Histidine release from brain slices and synaptosomes

The release of radioactive histidine was studied in a superfusion system by using preloaded rat cerebral cortical slices and guinea pig synaptosomes. ATP/ADP ratios in both preparations were used to assess the energy levels and thus the oxygenation of brain slices and synaptosomes. ATP/ADP ratios similar to the intact brain and nerve terminals were found in slices and synaptosomes even after hours of superfusion with oxygenated buffer. Depolarization by 30 or 50 mM K+ induced release of histidine from slices and synaptosomes. The results confirm that under physiological energetic conditions, histidine is released both from slices and synaptosomes after depolarization with potassium.     

CNS tumours in south-western Finland: high location, high incidence

The Department of Paediatrics at the University Central Hospital of Turku, Finland has 130 000 children under 17 y of age within its catchment area. We collected all 103 cases of newly diagnosed CNS tumours from the 15-y period of 1981–95. The incidence was 5. 3: 100 000, a figure twofold those usually presented. During the period 1981 -85 the incidence was lower (4) than during the subsequent 5-y periods (5. 7 and 6. 2). There were no statistical differences between the incidences of the supra- vs infratentorial brain tumours. Optic glioma was unusually common (17%, CI 13. 9–20%).     

Release and inhibition of uptake of 5-hydroxytryptamine in blood platelets in vitro by copper and methyl mercury

Divalent copper (Cu) and methyl mercury (Met-Hg) are potent inhibitors of the uptake of 5-hydroxytryptamine (5-HT) in rat hypothalamic synaptosomes in vitro. To assess the usefulness of blood platelets as a peripheral model of central serotonergic nerve endings for neurotoxicological studies, for comparison human and rabbit platelets were utilized. Cu inhibited 5-HT uptake into human platelets when platelets were separated from plasma (the IC50 0.7-0.8 microM). Plasma added with platelets abolished the toxic influence of Cu towards platelets. Met-Hg inhibited 5-HT uptake both in washed platelets (the IC50 0.2 microM) and in platelets added in plasma (the IC50s 10-15 microM). The inhibition of uptake by Met-Hg did not depend on buffer Ca and Mg. At low concentrations of Cu, the uptake tended to be more inhibited in the presence of Ca and Mg. Zn and Hg did not affect 5-HT uptake up to 100 microM. Pb inhibited it transiently (28% at 1 microM) in the presence of Ca and Mg. Met-Hg induced the release of endogenous 5-HT from rabbit platelets when they were in a suspension in Ca-free buffer, but Cu did not, even at 100 microM concentration. The results suggest firstly, that blood platelets give results comparable with brain synaptosomes regarding inhibitory effects of metals on 5-HT uptake provided plasma is decanted. Secondly, the inhibition of 5-HT uptake by Cu appears to be purely plasma membrane related but Met-Hg may, in addition, induce release of 5-HT from storage granules.     

Effects of TCDD on vitamin A status and liver microsomal enzyme activities in a TCDD-susceptible and a TCDD-resistant rat strain

To investigate the relationship between vitamin A status and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) lethality, the influence of TCDD on tissue and serum vitamin A levels was determined in the most TCDD-susceptible (Long-Evans) and the most TCDD-resistant (Han/Wistar) rat strains. The TCDD LD50 values of these two strains differ by a factor of more than 300. Groups of three rats per strain were used in a dose-response study (given single ip doses of 0, 4, 40, 400, 800 or 1600 micrograms TCDD/kg body weight and killed on day 11) and in a time-course experiment (given single ip doses of 0, 4 and, in the case of Han/Wistar rats only, 1600 micrograms TCDD/kg body weight, and killed on days 4, 11, 23, 50 and 76). The strains showed similar response over the 76-day study with respect to vitamin A levels in the liver, kidneys, testicles and serum after exposure to a sublethal dose of TCDD (4 micrograms/kg body weight). In contrast, TCDD doses lethal to the Long-Evans strain only (40-1600 micrograms/kg, day 11) markedly increased kidney and serum vitamin A levels in Han/Wistar rats, while they were practically without effect in Long-Evans rats. Hepatic cytochrome P-450 concentration, and the activities of 7-ethoxyresorufin O-deethylase, ethylmorphine N-demethylase, and uridine diphosphate glucuronosyltransferase (towards p-nitrophenol) were affected by the TCDD doses in much the same manner in both strains. These findings show that the correlations between TCDD lethality and changes in vitamin A status found among species of laboratory animals do not hold for Long-Evans and Han/Wistar strains of rat.     

Remarkable residual alterations in responses to feeding regulatory challenges in Han/Wistar rats after recovery from the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Adult male Han/Wistar rats were treated with 1000 micrograms 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg body weight and allowed to restabilize their body weight at a lower level. Therefore, their feeding or drinking responses were determined to the following ip challenges: NaCl (1 M, 10 ml/kg body weight); 2-deoxy-D-glucose (2DG; 400 mg/kg); sodium mercaptoacetate (MA; 800 mumol/kg); 2DG + MA (200 mg/kg + 400 mumol/kg); insulin (10 U/kg). In addition, the suppressive effects of naloxone (10 mg/kg), glucose (1.36 mg/kg) and fructose (1.36 mg/kg) on feed intake stimulated by 24-hr food deprivation were examined. After the restabilization, the body weights of TCDD-treated rats followed the course of body changes in control rats. The responses to NaCl were also similar in TCDD-treated and control rats. However, marked differences were observed in all other responses studied. Pretreatment with TCDD abolished 2DG-induced feeding, attenuated the effects of insulin and naloxone, caused an aberrant decrease in feed intake following MA, and resulted in hypersensitivity to the satiating effects of glucose and fructose. These data show that exposure to a high dose of TCDD leads to notable distortions in responses to metabolic challenges in Han/Wistar rats, which are present even when they have seemingly recovered from the acute toxicity. The results also indicate that the central nervous system plays a crucial role in TCDD toxicity, and suggest hypersensitivity to peripheral satiety signals coupled with hyporesponsiveness to metabolic cues of energy deficit to be important mechanisms in the pathogenesis of the wasting syndrome.     

Calcium-dependent histidine and histamine release from superfused synaptosomes.

The release of radioactive histidine and histamine was studied in a superfusion system by using guinea pig synaptosomes which were preloaded with 3H-histidine. Depolarization by 50 mM K+ induced a simultaneous release of histidine and histamine. The stimulated release of both of these substances was diminished when calcium was removed. The calcium-dependency of histamine release, previously demonstrated in brain slices, was confirmed using synaptosomes. It was also demonstrated that potassium-induced histidine release from guinea pig synaptosomes under superfusion conditions is at least partially calcium-dependent.     

Assessment by c-Fos immunostaining of changes in brain neural activity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and leptin in rats

The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes multiple effects in laboratory animals. One of these is a wasting syndrome (a dramatic loss of body weight over 2-5 weeks) whose mechanism is still largely unknown. We exploited the over 1000 times difference in TCDD sensitivity between Long-Evans (Turku/AB); (L-E) and Han/Wistar (Kuopio); (H/W) rats to reveal brain areas that might be activated by a single dose of TCDD (50 microg/kg) given 24 hr previously. Leptin (1.3 mg/kg intraperitoneally 2 hr before tissue harvest) was used as a reference compound, as its neural pathway for decreasing food intake in the control of energy homeostasis is fairly well known. Serial sections of the brains were immunostained with an antibody for the activity marker c-Fos, and selected areas -- primarily in the hypothalamus -- were analysed with a computer-assisted microscope. Given alone, TCDD did not elicit any major alterations in c-Fos protein levels in the hypothalamic nuclei at the early time-point studied (24 hr after administration), neither in pooled data nor in individual strains. The control substance leptin proved that the method is valid as it increased the number of c-Fos-immunopositive cells in the hypothalamic ventromedial and arcuate nuclei. Although the present findings are not suggestive of a primary role for the hypothalamus in the wasting syndrome, a time-course study covering also the feeding-active dark hours is warranted for their verification.