The developing brain can be regarded as one the embryonic and fetal structures most susceptible to teratogenic insults, because of its longlasting sensitive period, a great vulnerability of the undifferentiated neural cells and no further reproductive capacity of neurons. Among the factors in manifestation of brain malformations, developmental stage-dependent susceptibility to teratogens and sensitive period for teratogenesis are the most important one which characterize developmental toxicity. The mammalian proliferating matrix cells in the developing brain are particularly sensitive to teratogenic insults at the time when the matrix cells start to differentiate into cortical neuron. As the factors determining the vulnerability of matrix cells, proliferative and metabolic state, restoration capacity and phase of chemical differentiation prior to acutual differentiation were discussed.
Behavioral teratogenicity of chlorpromazine (CPZ) was studied in rats by observing the spontaneous motor activity level and learning behavior of light-dark discrimination in the second generation. The dams were treated with CPZ from day 17 of gestation to postpartum day 21 at doses of 2 mg/kg sc. once daily in one group and 4 mg/kg sc. twice daily in the other. The activity level of F1 was measured at 6 to 7 weeks of age for 68 hrs by a magnetic field counter. The learning experiments were started at 5 weeks of age in one group and 15 weeks of age in the other on the behaviors of the continuous food reinforcement at the beginning, then the light-dark discrimination, and finally the reversal discrimination learning. As the results, no influence of the CPZ treatment was observed in the activity level and learning behaviors of the continuous food reinforcement and light-dark discrimination. But, in the reversal learning of the light-dark discrimination an impairment or delay was observed in some F1 of the CPZ groups. Thus, the significance of observing reversal learning behavior in the assessment of the behavioral teratogenicity of drugs has been shown.
Many attentions have long been paid to the question about the reason why benz [a]-anthracene (BA), a very weak carcinogen, increases its carcinogenic activity to the level of the most potent carcinogenic hydrocarbons, such as benzo [a] pyrene (BP) and 3-methylcholanthrene (3-MC), by the substitution of methyl group(s) for the "L-region" (7-and 12-positions) hydrogens, e.g. 7, 12-dimethyl-BA (DMBA) has a higher carcinogenic activity than BP, and 7-methyl-BA (7-MBA) is as carcinogenic as 3-MC (Cavalieri, 1979; Selkirk, 1980). In addition, 3-MC is also an alkyl-substituted BA. The marked increase in carcinogenicity of aromatic hydrocarbons by a methyl substituent is observed not only with BA but also with other aromatic hydrocarbons, such as chrysene and anthrabene (Cavalieri, 1979; Selkirk, 1980). 5-Methylchrysene, for instance, has as highly carcinogenic activity as 3-MC whereas carcinogenicity of chrysese is very weak. Similarly, 9, 10-dimethylanthracene is carcinogenic whereas the mother compound; anthracene, is not carcinogenic (Fig. 1). Several attempts have been made to know active metabolites of DMBA in relation to epoxide formation. DMBA 5, 6-oxide has been isolated and identified as an active metabolite from a hepatic mitrosomal reaction mixture (Keysell et al., 1973). DMBA 3, 4-diol-1, 2-epokide was also strongly assumed to be an active metabolite, but has not been detected yet from the in vitro system (Jerina et al., 1978 ; Malaveille et al., 1978 ; Wislocki bt al:, 1980). These studies, however, were carried out by using liver microsomes from rats pretreated with the P-448 inducer, 3-MC or polychlorinated biphenyls. 8, 9- and 10, 11-epoxides of DMBA might also be candidates for the active metabolites since their hydrolysis products, 8, 9- and 10, 11-dihydrodiols, have been isolated from a rat liver microsomal system (DiGiovanni and Juchau, 1980).
The recovery period of the taste responses of rat chorda tympani after application of toothpaste was examined. The response observations of four kinds of essential taste stimuli, 0.1 M sodium chloride, 0.005 M quinine hydrochloride, 1.0 M sucrose, and 0.05 M tartaric acid, were repeated every 2 or 5 minutes. After five observations of summated responses of the chorda tympani with each taste stimulus, a toothpaste solution diluted 3 to 1 was applied to rat tongues for 3 minutes and then they were washed with distilled water for 1.5 minutes. Thereafter, observations of the responses to each taste stimulus were repeated at 2 or 5 minute intervals for 30 or 60 minutes. The responses caused by four kinds of essential taste stimuli became smaller immediately after application of toothpaste, and then gradually returned to normal. The same experimental procedure was also applied using an application of distilled water instead of an application of toothpaste to rat tongues. A t-test was performed between the response ratios after application of toothpaste and those after application of distilled water. Significant differences disappeared at 18 minutes after application on the 0.1 M sodium chloride stimulus, at 23 minutes on the 0.005 M quinine hydrocbloride stimulus, at 15 minutes on the 1.0 M sucrose stimulus, and at 15 minutes on the 0, 05 M tartaric acid stimulus. The authors estimated that all kinds of taste responses recovered within at least 50 minutes.
Effects of barbital dosing on the neural hexokinase (EC 188.8.131.52) and phosphofructokinase (EC 184.108.40.206) activities in the rat, were examined. The barbital dependence in the rat was acquired by giving the barbital-admixed food. These two enzyme activities were investigated in the following three dissected portions of the brain: cerebral cortex, brain stem and cerebellum. The both enzyme activities in these three portions were depressed by the barbital dosing; while them being increased at the early stage of its withdrawal. From these results, it is considered that the measurements of hexokinase and phosphofrubtokinase activities probably give a possibility to estimate the degree of barbital dependence and its withdrawal, and that these two enzyme activities can be good indeces in these conditions.
Paraquat, intradermally injected in the dorsal skin of rats, demonstrated three phasic actions; enhancement of vascular permeability within 30 min (Phase I) and at 6-24 hr after the injection (Phase II) by dye leakage method and bleeding in skin at 2-7 days after the injection (Phase III). Phase I was induced in the presence of paraquat in the skin. However, phases II and III occurred in the absence of paraquat. Morphological study indicated inflammatory observations such as infiltration of mononuclear cells and swelling of venular endothelial cells throughout these three phases. And the most severe morphological changes occurred in phase II. Aspirin, indomethacin, tripelennamine and dexamethasone decreased dye leakage but superoxide dismutase increased it in phase I. These drugs including superoxide dismutase decreased dye leakage in phase II. Bleeding in phase III was decreased by the administration of aspirin and indomethacin. Because of higher effective dose of indomethacin used in this experiment as compared with a clinical dose, aspirin seemed among drugs examined in our experimental models to be the most potent drug that depressed the progression of paraquat-induced enhancement of permeability.
A practical technique was described for collecting blood sample periodically from a conscious rat. Blood obtained from a tail vein, warmed for 10 seconds in water bath (at 50°C), by inserting of a 22 G needle from which the adapter was cut off. Using this method, the influence of phlebotomy on hematologic parameters was determined. This technique was simple, easy, and reliable, and required no special skill and equipment.