Masashi Akaike

Hyperactivity and spatial maze learning impairment of adult rats with temporary neonatal hypothyroidism

Temporary hypothyroidism was induced in neonatal rats by 0.02% propylthiouracil (PTU) administration to lactating dams during days 0-19 after delivery, and its effects on the behavior and learning of their male offspring were examined. The serum T4 (thyroxine) level was returned to normal around 1 week after the last PTU administration, but the body weight gain was still depressed. The open field and Biel water maze tests at the age of 6 weeks showed an increased number of ambulations and an increase in errors with prolonged swimming time in the PTU rats. The radial arm maze test started at 13 weeks revealed that the PTU animals required more trials until they showed the first well-performed trial. The total number of choices was also larger, with less correct choices, and treatment effects on the response distribution and pattern were significant. Thus, the rats, which had suffered from temporary hypothyroidism in the neonatal period, showed hyperactivity and irreversible impairment in maze learning. These results suggest an involvement of temporary neonatal hypothyroidism in hippocampal dysfunction.

Trimethyltin syndrome as a hippocampal degeneration model: temporal changes and neurochemical features of seizure susceptibility and learning impairment

The effects of trimethyltin on the hippocampus were investigated in terms of changes in histology, depth electroencephalography, learning acquisition and memory retention, choline acetyltransferase and neuropeptides, and seizure-induced c-fos messenger RNA expression. The results were as follows. (1) Morphologically, trimethyltin produced a progressive loss of hippocampal CA3 and CA4 pyramidal cells, starting from four days after peroral treatment with trimethyltin hydroxide (9 mg/kg), as described previously. (2) Neurophysiologically, the increased seizure susceptibility to pentylenetetrazol treatment reached a maximum at four days post-trimethyltin and then declined after five days post-trimethyltin. The maximal seizure susceptibility at four days post-trimethyltin was confirmed by the immediate and long-lasting appearance of spike discharge in the hippocampus. However, this was not verified by the expression of c-fos messenger RNA in the hippocampus, which was comparable between trimethyltin-treated and control rats. (3) Behaviorally, the time-courses of aggression and learning impairment were similar to that of the seizure susceptibility. (4) Neurochemically, trimethyltin treatment caused changes of neurochemical markers, which were manifested by the elevation of neuropeptide Y content in the entorhinal cortex, and of choline acetyltransferase in the hippocampal CA3 subfield. Trimethyltin may offer potential as a tool for investigations on the relationship between neuronal death in the hippocampus and the development of seizure susceptibility and learning impairment. Alterations in glucocorticoids, glutamate and neuropeptides may all contribute to the manifestation of the trimethyltin syndrome.

Perinatal bisphenol A affects the behavior and SRC-1 expression of male pups but does not influence on the thyroid hormone receptors and its responsive gene.

Bisphenol A (BPA) has been shown to interfere with thyroid hormone receptors (THRs) and to influence the expression of THR-responsive elements in vivo and in vitro, while some studies reported hyperactivity induced by BPA treatment. In the present study, our purpose was to investigate the effect of BPA exposure on behavioral alteration and its mechanism of action, especially focusing on the thyroid hormone pathway. Significant sexual difference on behaviors was observed in perinatal BPA exposure, as manifested by hyperactivity and impaired spatial learning/memory in male pups after matured. Dams treated with 0.1mg/l BPA showed transient hypothyroidism, while male pups were found to exhibit a transient hyperthyroidism followed by hypothyroidism. Furthermore, significant up-regulated expression levels of mRNA and protein of SRC-1 in the hippocampus were observed in male pups by 0.1mg/l BPA treatment. However the expression of THRalpha/beta and RC3/neurogranin were not affected by BPA treatment. These results indicate that perinatal BPA exposure at a very low level may influence thyroid function and then consequently affects brain development, but at the same time, suggest that thyroid hormone receptor may not be a direct target of BPA action, but instead, another factor may be involved in this action.

A Collaborative Study in Japan on Optimal Treatment Period and Parameters for Detection of Male Fertility Disorders Induced by Drugs in Rats

The tripartite-harmonized International Conference on Harmonization reproductive guideline (1993) recommends administration of test substances for 4 weeks to male rats before mating. However, scientific or experimental rationale for this recommendation is not firmly based, and the most appropriate parameters have not been established in experimental models. Therefore, a team consisting of 16 Japanese pharmaceutical companies and the National Institute of Health Sciences performed a collaborative study to determine the optimal period and parameters for detection of male fertility disorders in rats. Sixteen compounds, including four anticancer drugs, two psychotropic drugs, two nootropic drugs, two vitamins, two hormones, one antihypertensive agent, one diuretic drug, and two general chemicals were administered to male rats for 4 or 9 weeks before mating. Parameters used to examine effects on the male reproductive system were organ weights, sper-matogenic endpoints, mating behavior, cesarean section findings, and histopathology. From the results, treatment for 4 weeks before mating was concluded to be sufficient to detect adverse effects on male fertility, with the histopathology of the testis being the most sensitive index for the drugs used. Sperm parameters, especially number, and genital organ weight determination provided information confirming toxicity. Tests of reproductive activity were generally found to be insensitive, except where the drugs affected sperm maturation. Based on this study, it is concluded that a 4-week treatment period is appropriate for detection of drug effects on male fertility, and that histopath-ological examination of the testis is the most sensitive approach.

Changed preference for sweet taste in adulthood induced by perinatal exposure to bisphenol A-A probable link to overweight and obesity.

BACKGROUND The preference of obesity has risen dramatically worldwide over the past decades. Some latest reports showed significant increase of obesity in men compared to women. Implication of environmental endocrine disruptors has been focused more and more. Numerous studies in vitro and vivo implied metabolic actions of bisphenol A (BPA), however much less consideration is given to the possibility of BPA exposure-induced change in gender-specific behaviors which result in obesity and overweight. OBJECTIVES To examine whether perinatal exposure to BPA at relative dose to environmental levels can influence sweet preference of male and female rats and consequently lead to alteration in bodyweight. METHODS Rats perinatally exposed to BPA at doses of 0.01, 0.1 and 1.0 mg/L were tested sweet preference for 0.25%, 0.5% saccharin and 15% sucrose by two-bottle choice (water vs. saccharin/sucrose). The food intake, liquid consumption and bodyweight of each rat were monitored daily. At the end of the test, the fat percentage and tail blood pressure were measured. RESULTS Significant sex difference of preference for 0.25% and 0.5% saccharin was shown in control and all BPA-treated groups (p < 0.001, female vs. male). 0.1 and 1.0 mg/L BPA treatment induced the increase of preference for 0.25% saccharin solution in males, but not in females. 0.1 mg/L BPA treatment increased sucrose preference in males at postnatal day (PND) 70 and 140 (p < 0.05 and p < 0.001, compared to control respectively) but decreased sucrose preference in females at PND 140 (p < 0.05, compared to control). The males treated by BPA showed overweight (p < 0.001), high fat percentage (p < 0.001) and tail blood pressure (p < 0.05) than control at PND 140. CONCLUSION Perinatal exposure to a low dose of BPA could increase sweet preference of male rats. Calorie intake may be programmed during early life, leading to changes of body weight depending on the gender. Although further researches concerning the mechanism are required, the results of the present study are particularly important with regards to the more significant increasing prevalence of obesity in men and the environmental endocrine disruptors.

Nitric oxide synthase-containing neurons in the hippocampus are preserved in trimethyltin intoxication

We studied the effects of trimethyltin (TMT) (9 mg/kg, p.o.) on the nitric oxide synthase (NOS)-containing neurons in the rat hippocampus by NADPH-diaphorase histochemistry and a biochemical assay of NOS activity. TMT exposure caused the typical behavioral changes and a loss of the CA3/4 pyramidal cells, which were NADPH diaphorase-negative. The scattered interneurons and the CA1 pyramidal cells, which were NADPH diaphorase-positive, were spared. Hippocampal NOS activity showed no reduction in the TMT-treated rats compared with the controls. These results provide evidence of the preservation of the NOS-containing neurons in TMT intoxication.

Learning/Memory Impairments in Rat Offspring Prenatally Exposed to Phenytoin

Phenytoin (PHT) was orally administered in dosages of 50 and 100 mg/kg/day to pregnant rats on days 7-18 of gestation. Offspring were tested on the negative geotaxis test, a figure-eight maze (F8), the Biel water maze (BM), the Morris maze (MM), and the radial maze (RM). In addition, a delayed nonmatching-to-sample (DNMTS) test was employed. The levels of neuropeptides in brain and brain weights were determined. The maturation of negative geotaxis was delayed in both PHT groups. PHT groups showed no differences in F8, BM, and MM. In the RM, the total number of choices was high, whereas the number of correct choices was low. In the DNMTS, PHT groups showed low for correct choices with a long interval. The concentrations of neuropeptides were changed in the mesolimbic cortex, hippocampus, and amygdala. Brain weights were lower at 6 weeks of age in the 100 mg/kg/day PHT group, but were comparable at 16 weeks of age. This study suggests that the RM is a detectable task for the learning/memory impairments induced by PHT. In addition, it is surmised that the learning deficit is due to a working memory impairment arising from abnormal changes in neuropeptides and an injury in the fetal hippocampus.

Impaired Spatial Learning in Rats with a Trimethyltin-Induced Hippocampal Lesion and the Effect of Fetal Septal Grafting on the Impairment

Trimethyltin (TMT), an organotin compound, is a by-product in the manufacture of dimethyltin chloride, a stabilizing agent for certain plastics. Exposure to TMT causes neuopathological changes in the limbic system of the brain (Brown et al.,1979; Bouldin et al., 1981). An accidental exposure to TMT in humans has been reported to induce a status of mental confusion with generalized epileptic seizures (Fortemps et al., 1987). Among the regions of the central nervous system in rats, the hippocampus subsequently became the focus of research in TMT neuotoxicity. The pyramidal cells of the CA3 and CA4 hippocampal subfields appear to be particularly sensitive to acute toxicity with a single dose of TMT (Dyer et al., 1982). The long-term behavioral sequelae of TMT intoxication have revealed marked hyperactivity and learning impairments (Hagan et al., 1990).

Trimethyltin (TMT)‐Treated Rats with Specific Hippocampal Lesion as a Possible Model of Endocrine Abnormality in Depression

The hippocampus is not only involved in learning and memory processes, but also exercises a regulatory role on hypothalamo-pituitaryadrenal axis (HPA-axis) in response to physiological and psychological stressors. This inhibitory regulation of the HPA-axis has been reported to be exerted by negative feedback via type 1 and type 2 glucocorticoid receptors largely present in the hippocampus. A long-term exposure to a large amount of glucocorticoids insults the hippocampal neurons and the hippocampal ablation results in the elevation of mRNA coding for corticotropin-releasing factor (CRF) in the hypothalamus and circulating corticosterone levels. We found that TMT, an organotin compound, induced a marked hyperactivity and learning impairments with a specific hippocampal lesion in rats. Neuropathologically, the pyramidal cells of CA3 and CA4 subfields are particularly sensitive to acute toxicity with a single peroral dose of TMT. In the present study, we studied changes in hypothalamic peptides, somatostatin (SRIF), neuropeptide Y (NPY) and CRF, following TMT treatment in rats. The effect of fetal septal grafts on the hypothalamic peptide contents was further investigated in TMT treated rats.