藤平 篤志

It is known that pica, the consumption of non-nutritive substances such as kaolin, can be induced by administration of toxins or emetic agents in rats. In the present study, we examined the effects of intraperitoneal (i.p.) administration of cyclophosphamide on pica behavior and on the concentration of 5-hydroxyindoleacetic acids (5HIAA) in cerebrospinal fluid (CSF) in the following five strains of adult male rats: Sprague Dawley (SD), Wistar, Fischer 344 (F344), Wistar-Imamichi (WI) and Long Evans (LE). Cyclophosphamide (25 mg or 50 mg/kg) was injected (i.p.) into the rats and kaolin and food intake were measured at 24 hr after injection. The animals were anesthetized with urethane (1 g/kg) at 3 hr after injection of cyclophosphamide, and CSF was collected from the cisterna magna. WI and LE rats clearly showed pica behavior as compared with the other strains. In LE rats, the concentration of 5HIAA in CSF also increased in a dose-dependent manner of cyclophosphamide. The pretreatment with ondansetron (5-HT(3) antagonist) restored both changes (kaolin consumption and 5HIAA levels) induced by cyclophosphamide. These results suggest that the LE rat is sensitive to cyclophosphamide, that pica induced by cyclophosphamide mimics many aspects of emesis including the serotonergic response in the central nervous system and that use of the pica model would be a practical method for evaluating the effects of antiemetic drugs in addition to the mechanism of emesis.

BACKGROUND AND PURPOSE Melatonin is involved in the regulation of colonic motility, and sensation, but little is known about the influence of melatonin on 5-hydroxytryptamine (5-HT) release from colonic mucosa. A tachykinin NK2 receptor-selective agonist, [beta-Ala8]-neurokinin A(4-10) [beta Ala-NKA-(4-10)] can induce 5-HT release from guinea pig colonic mucosa via NK2 receptors on the mucosal layer. The present study was designed to determine the influence of melatonin on 5-HT release from guinea pig colonic mucosa, evoked by the NK2 receptor agonist, beta Ala-NKA-(4-10). EXPERIMENTAL APPROACH The effect of melatonin was investigated on the outflow of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) from muscle layer-free mucosal preparations of guinea pig colon, using high-performance liquid chromatography with electrochemical detection. KEY RESULTS Melatonin caused a sustained decline in the beta Ala-NKA-(4-10)-evoked 5-HT outflow from the muscle layer-free mucosal preparations, but failed to affect its metabolite 5-HIAA outflow. The specific MT3 receptor agonist, 5-methoxycarbonylamino-N-acetyltryptamine mimicked the inhibitory effect of melatonin on beta Ala-NKA-(4-10)-evoked 5-HT outflow. A MT3 receptor antagonist prazosin shifted the concentration-response curve of melatonin to the right in a concentration-dependent manner and depressed the maximum effect, but neither a combined MT1/MT2 receptor antagonist luzindole, nor a MT2 receptor antagonist N-pentanoyl-2-benzyltryptamine modified the concentration-response curve to melatonin. CONCLUSIONS AND IMPLICATIONS Melatonin inhibits NK2 receptor-triggered 5-HT release from guinea pig colonic mucosa by acting at a MT3 melatonin receptor located directly on the mucosal layer, without affecting 5-HT degradation processes. Possible contributions of MT1/MT2 melatonin receptors to the inhibitory effect of melatonin appear to be negligible. Melatonin may act as a modulator of excess 5-HT release from colonic mucosa.

The rdw rat is a hereditary hypothyroid strain isolated from Wistar-Imamichi rats. In the present study, adrenocorticotropic hormone (ACTH) and corticosterone responses to restraint stress (120 min) were examined in rdw adult male rats. ACTH response to restraint stress was higher in rdw rats than in hetero control rats. The plasma concentrations of corticosterone were lower in rdw rats than in control rats during the first 30 min after the onset of stress. Both ACTH and corticosterone responses to restraint stress in rdw rats recovered to control levels after thyroxine (T4) replacement therapy. These results suggest that hereditary hypothyroidism causes adrenal dysfunction directly and that hypersecretion of ACTH is a result of reduced corticosterone in rdw rats.

The effects of intracerebroventricular (i.c.v.) administration of pituitary adenylate cyclase activating polypeptide38 (PACAP38) on prolactin (PRL) secretion and the activity of tyrosine hydroxylase (TH) were examined in adult male and lactating rats with or without suckling stimulus. In adult male rats and lactating rats with suckling stimulus, administration of PACAP38 (0.25 or 1 nmol) decreased PRL secretion and increased the activity of TH in the stalk-median eminence. On the other hand, the injection of PACAP38 did not affect PRL secretion and TH activity in lactating rats without sucking stimulus. Administration of PACAP6-38 (4 nmol), a specific receptor antagonist, also had no effect on PRL secretion and TH activity in adult male rats. These results suggest that i.c.v. administration of PACAP inhibits PRL secretion mediated by doparmine neuron within the hypothalamus, but the effects of PACAP differ depending on the physiological condition of animals. These observed effects of PACAP on PRL release may be pharmacological responses rather than physiological responses.

The present study investigated whether pre-stimulation with intraperitoneal (i.p.) needling protects against development of diabetes in alloxan-treated transgenic (Tg) mice overexpressing the human Cu/Zn superoxide dismutase gene or non-Tg littermates of the FVB/N strain. Twenty minutes before the alloxan treatment (60 mg/kg) the mice were injected intraperitoneally with 0.05 ml saline while control mice received only the alloxan treatment. Hyperglycemic responses of the saline-injected mice to alloxan were significantly suppressed in the Tg mice (P<0.05). A similar reduction of response was also observed in non-Tg littermates, but the effect was less than that in the Tg mice. This protective effect on the diabetogenic action of alloxan was also demonstrated by an analysis of the number of days positive for urinary glucose, and by immunohistochemical analysis of pancreatic insulin-positive cells. A similar suppressive effect on the hyperglycemic response of alloxan was observed in the mice stimulated by i.p. needling alone. However, suppression of the hyperglycemic response was not observed in ICR mice receiving an i.p. injection. These results suggest that the diabetogenic action of alloxan can be suppressed by i.p. needling-mediated stimulation in mice that have a genetic background of the FVB/N strain. Since a slight protective effects of alloxan-induced diabetes was also observed in the Tg mice compared to FVB/N mice treated with only alloxan, this phenomenon could be more clearly seen in the Tg mice than in non-Tg littermates with an FVB/N background.

To investigate the androgenic effect of Kaempferia parviflora (KP), a Thai herbal plant, adult male rats were randomized into control and KP-treatment groups. Rats were treated orally with water in the control group and with 1,000mg/kg/day of KP in the treatment group for 45 days. Blood samples were collected oil days 10, 20, 30 and 45 for measurement of the serum follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone, progesterone and corticosterone levels. The reproductive and non-reproductive organs were dissected oil day 45 and weighed. Mating behavior was also observed on days 20 and 30. Body weight was measured throughout the study period. The results showed that KP induced an increase in body weight compared with the controls. There were no significant differences in the weights of either reproductive (testis, seminal vesicle plus coagulating gland, levator ani muscle plus bulbocarvernosus muscule and glans penis, except the prostate gland) or non-reproductive organs (kidney, adrenal gland and gastracnemius muscle). There were no significant differences in serum levels of either FSH or LH between the two groups. The serum testosterone and progesterone levels were insignificantly lower in the KP group during the first 30 days. The serum corticosterone levels in the KP group were lower than those in the controls throughout the study period and were significantly low oil days 20 and 30. There were no significant changes in mating behavior in the rats treated with KP. Although KP affected the body weight and serum corticosterone level, it did not affect mating behavior, reproductive and non-reproductive organ weights or hormones related to the reproductive system in the adult mal rats. Therefore, we conclude that the testosterone-like effect of KP did not disturb the hypothalamic pituitary-testicular axis or male reproduction.

Glutamate is the dominant excitatory neurotransmitter in a large number of physiological processes including neuroendocrine regulation. Some pharmacological studies have shown that different subtypes of glutamate receptor, such as the N-methyl-D-aspartic acid (NMDA) and alpha-amino-3-hydroxy-5-methy-4-isoxazolepropionic acid (AMPA) receptors, are involved in stress-induced adrenocorticotropin (ACTH) and prolactin secretion. However, the roles of the respective glutamate receptors and the mechanism of ACTH and prolactin secretion during stress via these receptors have not been investigated in detail. In the present study, we evaluated the role of AMPA-type glutamate receptor in ACTH and prolactin regulation under restraint stress in adult male rats. Male rats pretreated with a selective AMPA receptor antagonist, 2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX; 50 mu g), through a lateral ventricle cannula were stressed by immobilization. Administration of NBQX inhibited ACTH and prolactin secretion in response to restraint stress. However, NBQX had no significant effects on the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis, as measured by the accumulation of 3, 4-dihydroxyphenylalanine (DOPA). In addition, administration of NBQX suppressed stress-induced prolactin secretion in the male rats pretreated with alpha-MT, an inhibitor of dopamine synthesis, and infused with dopamine solution (2.5 mu g/200 mu l/10 min). These results indicated that the effects of NBQX on prolactin secretion might be mediated by non-dopamine mechanisms. The contents of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) in the median eminence (ME) of the male rats decreased during restraint stress; however, the fluctuations in CRH and AVP were eliminated by NBQX administration. These results suggest that stress-induced ACTH and prolactin release mediated by neurotransmission via AMPA receptors might be partly attributable to hypophysiotropic regulatory factors in the hypothalamus.

Previously, we demonstrated that plasma cortisol (Cor) levels were increased by road transportation in castrated male goats, but the extent of the increase was significantly reduced by 5 alpha-dihydrotestosterone (DHT) implantation. This study aims to clarify whether the reduction of Cor secretion by androgen during transportation results from reduced plasma adrenocorticotropic hormone (ACTH). Castrated goats were implanted separately with cholesterol (Cho), testosterone (T) or DHT, followed by transportation. Plasma Cor levels increased during transportation regardless of hormone treatment, but the levels in T and DHT treated animals were lower than those in animals treated with Cho. Plasma ACTH levels also increased during transportation, and those in T treated animals were significantly lower than in those treated with Cho. However, plasma ACTH levels in DHT treated animals varied among the animals and did not differ from those in Cho treated animals. Significant and highly positive correlations between the logarithm of plasma ACTH levels and plasma Cor levels were found in every treatment group. The areas under the regression curves between plasma ACTH levels and plasma Cor levels associated with T and DHT treatments were significantly lower than those with Cho treatment. In conclusion, T was shown to reduce ACTH secretion in response to transportation in castrated goats. However, this suppression of the increase in Cor secretion during transportation by androgen is suggested to be mainly a result of suppression of the responsiveness of the adrenal cortex to ACTH.

The estrous cycle influence on the number of ovulated eggs after injection of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) was investigated in 12, 18, and 24 weeks old adult female Wistar-Imamichi (WI) rats. PMSG (150 IU/kg) was injected at metestrus, diestrus, proestrus, or estrus, followed by hCG (75 IU/kg) 55 h later. Ovulation was induced at all ages and stages of the estrous cycle. The number of ovulated eggs was not affected by stage for similarly aged rats, however, the number of ovulated eggs obtained after treatment decreased with age. These results demonstrate that the PMSG/hCG treatment can induce ovulation at any stage of estrous cycle in WI rats and efficient superovulation at 12 weeks of age.

In order to clarify the functional relationship between thyroid, adrenal and gonadal hormones, hypothyroidism was induced by administration of thiuoracil in adult male and female rats, and the effects of hypothyroidism on the adrenal and the gonadal axes were investigated in the present study. 1. The functional relationship between thyroid and adrenal hormones: Adrenal weights and corticosterone were lowered, whereas the secretion of ACTH, corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) increased in hypothyroid rats compared to euthyroid rats. These results indicate that hypothyroidism causes adrenal dysfunction directly and results in hypersecretion of CRH and AVP from the hypothalamus. 2. The functional relationship between thyroid and gonadal hormones: The pituitary response to LHRH was lowered, whereas the testicular response to hCG was not changed in hypothyroid rats. Hypothyroidism suppressed copulatory behavior in male rats. These results suggest that hypothyroidism probably causes dysfunction in gonadal axis at the hypothalamic-pituitary level in male rats. In adult female rats, hypothyoidism inhibited the follicular development accompanied estradiol secretion, whereas plasma concentrations of progesterone and prolactin (PRL) increased in hypothyroid female rats. Hypothyroidism significantly increased the pituitary content of vasoactive intestinal peptide (VIP) though it did not affect dopamine synthesis. These results suggest that hypothyroidism increases pituitary content of VIP and this increased level of VIP likely affects PRL secretion in a paracrine or autocrine manner. In female rats, inhibition of gonadal function in hypothyroid rats mediated by hyperprolactinemia in addition to hypersecretion of endogenous CRH.

In the present study, we used closed colony-Wistar-Imamichi (WI), inbred W1 and Long Evans (LE) adult male rats to examine the secretion of ACTH and corticosterone in response to restraint stress. Blood (0.3 ml) was withdrawn through a jugular cannula at 0, 15, 30, 60 and 120 min after the onset of restraint stress. Plasma concentrations of ACTH and corticosterone increased after stress in all groups, but the responses of ACTH and corticosterone secretion were higher in LE rats than in W1 rats. Present data suggest that the LE rat might be a good model as a high-response strain and the closed colony or the inbred WI rat might be a good model as a low-response strain in restraint stress experiments.

Hatano high- and low-avoidance (in a two-way active avoidance task) animals (HAA and LAA, respectively) were successfully selected from a Sprague-Dawley rat population. Pup growth of both strains was dependent on the maternal strain in a cross-fostering study. To determine whether there are strain-specific differences between HAA and LAA in maternal care, both strains of dams were subjected to a test battery as measured by nest building, home cage behavior, pup retrieval, and milk ejection tests. In addition, changes in plasma concentrations of lactotropic and corticotropic hormones such as prolactin, ACTH, and corticosterone were examined during lactation. The test battery indicated that the dams of both strains built good nests and spent an identical amount of time with their offspring. However, LAA dams showed a prolonged latency time for pup retrieval and often left pups outside the nest until the end of the test period. LAA dams also showed a decreased amount of milk ejection, whereas no strain differences were observed in milk ejection after oxytocin treatment. During lactation, a lesser increase in plasma concentrations of prolactin and a greater increase in ACTH were found in LAA dams. There were no differences between the two strains in plasma concentrations of corticosterone. These results clearly demonstrated decreases in maternal behavior and milk ejection in LAA as compared to HAA dams. The present results also suggest that maternal motivation and mechanisms responsible for maternal hormones related to suckling are involved in the degree of pup growth. (C) 2002 Elsevier Science (USA).

The influence of the phytoestrogen, isoflavones, on vasodilating responses of the thoracic aorta precontracted with norepinephrine, together with the stimulatory effect on uterine weight (uterotrophic effect), was investigated in ovariectomized rats. In comparison with intact rats, acetylcholine (ACh)-induced vasodilation showed a tendency to be decreased by ovariectomy. On the other hand, isoprenaline (ISO)induced vasodilation was significantly increased by ovariectomy. Estrogen replacement (17 beta -estradiol dipropionate, 300 mug/kg per week, for 1 month) completely restored the impaired ACh- and ISO-induced vasodilation caused by ovariectomy. Dietary isoflavone aglycones (containing 52% genistein, 42% daidzein and 6% glycitein) of 157 mg/kg per day (not 67 mg/kg per day) for 1 month, in addition to the effects of estrogen replacement, completely restored the impaired vasodilation caused by ovariectomy. However, the uterotrophic effect of dietary isoflavones of 157 mg/kg per day was incomplete as compared with that by estrogen replacement. These results indicate that phytoestrogen, isoflavones, certainly possess estrogenic actions on the vasodilating responses caused by ACh and ISO, as well as a weaker uterotrophic effect.

Tsukuba High Emotional (THE) and Tsukuba Low Emotional (TLE) strains of rats have been congenitally bred for use in studies of emotionality The current study investigated THE and TLE strain differences in the footshock-induced ultrasonic vocalization responses of adult male rats. Ultrasonic vocalization response inducibility (ratio of rats emitting ultrasounds) and vocalization activity in THE rats were statistically higher than in TLE rats. We next examined the causal relation between the ultrasonic vocalizations and the activation of the pituitary-adrenocortical axis in response to footshocks in these two strains of rats. Rats were sorted into two groups, vocalizing and non-vocalizing, after being exposed to the shock regimen daily for 5 successive days. Basal plasma concentrations of ACTH and corticosterone were not different between THE and TLE rats. After receiving footshocks, significant increases in plasma concentrations of ACTH and corticosterone were induced in both strains of rats. These increases in plasma concentrations of ACTH and corticosterone were significantly higher in THE than in TLE rats. However, in vocalizing and non-vocalizing rats of both strains, no statistical differences in plasma concentrations of ACTH and corticosterone were observed after footshocks. These findings suggest that the high emotionality of the adult male rats was reflected in the emission of ultrasounds, and that the emission of ultrasonic vocalizations might not be related to the activation of the pituitary-adrenocortical axis.

In the present study, we have examined whether the effects: of dexamethasone on follicle stimulating hormone (FSH) secretion were mediated by hypophysiotropic factors, and whether the increased levels of FSH induced by dexamethasone can stimulate ovarian functions in equine chorionic gonadotropin (eCG)-primed immature female rats. Dexamethasone (500 mug) significantly increased serum concentrations of FSH in hypophysectomized rats implanted with pituitary under the kidney capsule, as well as in intact rats. Serum concentrations of inhibin and estradiol in eCG (2.5, 5 i.u.)-primed rats were significantly increased by simultaneous treatment with dexamethasone (500 mug) and eCG, These simultaneous effects were not confirmed in hypophysectomized rats. The results had shown that hypophysiotropic factors do not mediate the selective increase of FSH secretion caused by dexamethasone. Dexamethasone induces the excess amount of FSH secretion from anterior pituitary and this FSH can stimulate inhibin and estradiol secretion in eCG-primed immature female rat. (C) 2001 Elsevier Science Inc. All rights reserved.