1,2,3,4-Tetrahydroisoquinoline (TIQ) and its derivatives, 1-methyl-TIQ (1-MeTIQ) and 1-benzyl-TIQ (1-BnTIQ), are endogenously present in the human brain. In this study, we compared the effects of TIQ derivatives on spontaneous nigral dopaminergic discharge in rats treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In the low-to-middle dose range (0.01-1 mg/kg), intravenous administration of MPTP induced a transient and potent increase in the firing rate. TIQ (0.01-30 mg/kg) had no effects, and 1-MeTIQ and 1-BnTIQ (0.01-10 mg/kg) produced a weaker increase in the firing frequency immediately after intravenous administration. Pretreatment with 1-MeTIQ (80 mg/kg, i.p.) significantly inhibited the decrease in dopaminergic spontaneous firing induced by a high dose of MPTP. The nigral induction of thiobarbituric acid-reactive substances (TBARS) by MPTP was also significantly suppressed by pretreatment with 1-MeTIQ. These results suggest that the neurotoxicity induced by TIQ derivatives is relatively weak compared to that induced by MPTP. The neuroprotective effect of 1-MeTIQ from MPTP-induced toxicity may be partially due to a decrease in free radicals, as suggested by a decrease in TBARS. This action presumably prevents cell membrane degeneration.
Purpose: Artificial teeth that do not compromise masticatory function even after the teeth become worn are necessary to conserve the function of dentures for a long time. The purpose of this study was to observe the morphological changes of artificial teeth by wear, and to discuss the chronological changes of horizontal overlap and fissures. Methods: Three types of acrylic resin teeth and three types of hard resin teeth were selected as specimens. Artificial teeth were arranged from the first premolar to the second molar, and a sliding test was performed using a mechanical wear testing device up to 80,000 cycles in water with sand at 37°C. Every 10,000 cycles, the projected area of the horizontal overlap, fissure area, and weight were measured. The results (n=5) were analyzed by two-way ANOVA/Tukey's test (p<0.05). Results: No significant difference was found in the changes in horizontal overlap area between acrylic and hard resin teeth. Fissure area rapidly decreased up to 20,000 cycles, and there were significant differences among all the artificial teeth after 50,000 cycles. Also, with A-Bi, H-Tr and HEn , the horizontal overlap and the fissures were conserved after wear. The rate of decrease in tooth weight varied among the artificial teeth. Conclusion: The results did not depend on the hardness of the artificial teeth. It is suggested that in artificial teeth that have sufficient horizontal overlap, bucco-lingual diameter and fissures, the horizontal overlap and fissures are conserved after wearing for a long time.
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