Long-Evans Strain Research Articles

Cannabinoid self‐administration in rats: sex differences and the influence of ovarian function

We recently demonstrated the existence of strain differences in self-administration of the cannabinoid CB1 receptor agonist WIN55,212-2 (WIN) by Long Evans (LE) and Lister Hooded (LH) but not Sprague-Dawley (SD) male rats. This follow-up study is aimed at verifying whether sex and ovarian hormones might also be critical factors in the initiation, retention and extinction of WIN self-administration. LE, LH and SD male and female rats, the latter either intact or bilaterally ovariectomized (OVX), were trained to self-administer WIN (12.5 microg kg(-1) per infusion) under a FR1 reinforcement schedule, using lever-pressing. Data showed that contrary to the findings in SD rats, LE and LH rats developed robust cannabinoid intake, with rates of responding for WIN being constantly higher in intact females than in males (+45 and +42% for LE and LH strains, respectively). In comparison with intact females, OVX females of both strains acquired self-administration at lower rates, displaying slower acquisition, lower drug intake (-42 and -52% for LE and LH, respectively) and longer extinction. These findings provide the first evidence of significant sex differences in cannabinoid self-administration, females acquiring stable WIN intake at higher rates and more rapidly than males. Moreover, when compared to intact females, a lower percentage of LE and LH OVX rats acquired and maintained stable drug intake, suggesting that ovarian hormones might represent a critical factor in modulating the reinforcing effect of cannabinoids.

Rat strain differences in startle gating-disruptive effects of apomorphine occur with both acoustic and visual prepulses

Prepulse inhibition of startle (PPI) is an operational measure of sensorimotor gating that is impaired in schizophrenia and is disrupted in rats by dopamine (DA) agonists like apomorphine (APO). Using acoustic prepulses and acoustic startle pulses, previous studies have demonstrated heritable strain differences between Sprague Dawley (SD) and Long Evans (LE) rats in the sensitivity to the PPI-disruptive effects of APO. As PPI deficits in schizophrenia are evident with both uni- and cross-modal stimuli, we tested whether strain differences in the gating-disruptive effects of APO occur with a cross-modal visual and acoustic stimulus combination. APO caused a dose-dependent disruption of both acoustic and visual PPI in SD rats. Compared to LE rats, SD rats were more sensitive to the PPI-disruptive effects of APO with both acoustic and visual PPI. These findings suggest that SD vs. LE strain differences in PPI APO sensitivity are mediated outside of the auditory system, within higher circuitry that regulates or processes multi-modal information. The present findings provide further validation for this heritable model of impaired sensorimotor gating in schizophrenia, which can be detected across multiple sensory modalities.

Individual differences in novelty- and cocaine-induced locomotor activity as predictors of food-reinforced operant behavior in two outbred rat strains

A goal of the current study was to determine if individual differences in cocaine-induced locomotion, which has been shown in outbred Sprague–Dawley (SD) rats to be correlated with differential function of dopamine transporters, were also evident in Long–Evans (LE) rats. Another objective was to determine if differences in locomotion following exposure to novelty or cocaine predicted food-reinforced behavior. Between-strain comparisons of open-field activity revealed similar effects of 10 mg/kg cocaine, although increases in rearing were prominent in LE rats. Both strains exhibited robust individual differences in cocaine-induced locomotion, with nearly identical ambulatory behavior observed in low and high cocaine responders (LCRs and HCRs, respectively) from the two strains. In a cued-discrimination operant task, LE rats learned the contingency in fewer sessions, whereas SD rats obtained more food pellets at fixed ratio 10 and maintained higher progressive ratio (PR) breakpoints. HCRs from both strains also tended to maintain higher PR breakpoints; low and high responders to novelty (LR and HR, respectively) had no consistent differences in food-reinforced behavior. Overall, these studies suggest that wide individual differences in cocaine-induced behavior are common to SD and LE strains and certain differences in food-reinforced behavior are associated with HCRs compared to LCRs.

수유기동안 납 투여가 성숙 쥐의 불안감 관련 행동양상에 미치는 영향

Lead (Pb) exposure during development can produce neurological deficits. In this study, the effect of Pb exposure during neonatal development via lactation on anxiety of brain function was investigated. Long-Evans strain rats were raised through two generations. At the birth of the second generation, the dams were subdivided into two groups and supplied drinking water containing either 0.2% Pb (Pb-treated group) or sodium (Na, Control group) acetate until weaning. Rats were sacrificed at 3 (weaning) and 11 weeks (maturity) for brain Pb and fatty acid analysis. Motor activity and elevated plus maze tests were initiated at 9 weeks. The brains in the Pb-treated group at weaning and maturity contained 1486±98 and 270±46 ng Pb/g, respectively. The control group showed the background level of Pb (3.7±1.0 ng Pb/g) in both ages. The alterations in brain fatty acid composition induced by Pb exposure were more evident in 3 wks old than 11 wks old. For example, in 3 wks old, the percentages of 18:2n-6, 20:2n-6 and 20:3n-6 were decreased in the Pb-treated group with an increase in 20:4n-6. In motor activity test, there was a tendency of hyperactivity in the Pb-treated group compared with the control group but the difference was not significant. In elevated plus maze test, the Pb-treated group showed fewer numbers of visits to the open arms (P<0.05), indicating that Pb exposure may lead to anxiogenic effect.

A possible mechanism of resistance to cadmium toxicity in male Long–Evans rats

The susceptibility to cadmium (Cd)-induced toxicity in male Long–Evans (LE) rats was compared with that in male Fischer 344 (Fischer) and Wistar–Imamichi (WI) rats, which are sensitive and resistant, respectively, to Cd toxicity. All rats of the LE and WI strains survived for 7 days after the treatment with a toxic dose of Cd (6.5 mg/kg b.w.). However, all rats of the Fischer strain died by the following day. The strong resistance to Cd toxicity in the LE strain was confirmed to be independent of metallothionein synthesis induced by Cd. The hepatic and renal Cd contents after its administration were significantly lower in the LE strain than in the Fischer strain. Furthermore, the hepatic and renal zinc (Zn) contents after its administration were significantly lower in the LE strain than in the Fischer strain. These limited data suggest that the strong resistance to Cd toxicity in male LE rats results from, at least in part, the lower accumulation of the metal in the liver and kidney, in a similar mechanism as the lower Zn accumulation.

Lead Exposure and (n-3) Fatty Acid Deficiency during Rat Neonatal Development Affect Subsequent Spatial Task Performance and Olfactory Discrimination

Docosahexaenoic acid [22:6(n-3), DHA] is important for optimal infant central nervous system development, and lead (Pb) exposure during development can produce neurological deficits. Long-Evans strain rats were fed either an (n-3) deficient [(n-3) Def] diet to produce brain DHA deficiency, or an adequate [(n-3) Adq] diet through 2 generations. At the birth of the 2nd generation, the dams were subdivided into 4 groups and supplied drinking water containing either 5.27 mmol/L (Pb) or sodium (Na) acetate until weaning. Rats were killed at 3 wk (weaning) and 11 wk (maturity) for brain Pb and fatty acid analysis. Spatial task and olfactory-cued behavioral assessments were initiated at 9 wk. Rats in the (n-3) Def group had a 79% lower concentration of brain DHA compared with the (n-3) Adq group with no effect of Pb exposure. At weaning, Pb concentrations were 7.17 +/- 0.47 nmol Pb/g of brain (wet weight) in the (n-3) Adq-Pb group and 6.49 +/- 0.63 nmol Pb/g of brain (wet weight) in the (n-3) Def-Pb group. At maturity, the brains contained 1.30 +/- 0.22 and 1.07 +/- 0.12 nmol Pb/g (wet weight), respectively. In behavioral testing, significant effects of both Pb and DHA deficiency were observed in the Morris water maze probe trial and in 2-odor olfactory discrimination acquisition and olfactory-based reversal learning tasks. Both lactational Pb exposure and (n-3) fatty acid deficiency led to behavioral deficits with additive effects observed only in the acquisition of 2-odor discriminations.

Oral buspirone causes a shift in the dose-response curve between the elevated-plus maze and Vogel conflict tests in long-Evans rats: Relation of brain levels of buspirone and 1-PP to anxiolytic action

Most studies concerning the effects of oral buspirone in the rat elevated plus-maze (EPM) test, spontaneous motor activity (SMA) test, and Vogel conflict (VC) test have used Sprague-Dawley or Wistar rats. Although it has been documented that the behavior of Long-Evans rats is more sensitive to detection of anxiolytics when compared to the aforementioned strains, the effects of oral buspirone have not been fully characterized in the Long-Evans strain in the EPM and VC tests. Thus, we studied the effects of orally administered buspirone (0.03-10.0 mg/kg) in the EPM, SMA, and VC (0.3-60.0 mg/kg) tests in Long-Evans rats. In a separate experiment, brain and plasma concentrations of buspirone and 1-(2-pyrimidinyl)-piperazine (1-PP) were determined after oral administration of buspirone (0.3 and 10 mg/kg) to relate the behavioral effects of buspirone with brain and plasma concentrations of buspirone and 1-PP. Our results showed that buspirone exhibited an inverted-U-shaped dose-response curve in both the EPM and the VC tests. In the EPM, buspirone produced anxiolytic activity in a low, narrow dose-range (0.03, 0.1, 0.3 mg/kg, p.o.) with maximum efficacy at 0.3 mg/kg, whereas in the VC test, significant anxiolytic activity was observed in a high, narrow dose-range (10, 30 mg/kg, p.o.) with maximum efficacy occurring at 10 mg/kg. In the SMA test, buspirone (10 mg/kg, p.o.) significantly decreased horizontal activity and vertical movements suggestive of sedation. Also, one hour following oral doses of buspirone (0.3 and 10 mg/kg), both buspirone and 1-PP concentrations were higher in brain when compared with those in plasma. Additionally, the concentrations of 1-PP were always higher in brain and in plasma compared with the concentrations of buspirone. Of particular interest is our finding of the shift in the dose-response curve between the EPM and VC tests. This shift in the dose-response curve is discussed in relation to brain levels of buspirone and 1-PP levels and their anxiolytic action.

Plasma Insulin Concentration was Increased by Long-Term Ingestion of Guava Juice in Spontaneous Non-Insulin-Dependent Diabetes Mellitus (NIDDM) Rats

To investigate whether long-term ingestion of guava juice has anti-diabetes and/or anti-obese actions, we employed spontaneous non-insulin-dependent diabetes mellitus Otsuka Long-Evans Tokushima Fatty (OLETF) rats and its control strain Long-Evans Tokushima Otsuka (LETO) rats. Thirty rats of each strain were divided into three groups consisting of glucose, vitamin E, and guava juice ingestion groups. Ingestion of these test solutions was continued from 9 to 32 weeks old. Serum lipid parameters including total cholesterol, triglyceride, free fatty acid, and high-density lipoprotein (HDL)-cholesterol were measured. Oral glucose tolerance test (OGTT) was performed at 32 weeks old rats and at 42 weeks old rats (10 weeks after discontinue of ingestion of guava juice), and then blood glucose levels and plasma insulin concentrations were measured. There were no significant differences in body weight, the amount of food intake and the volume of drink among the groups in OLETF rats. Although the blood glucose level in the guava juice group was not changed as compared with the glucose group, the amount of initial insulin secretion was significantly increased in OLETF rats and was restored by discontinue of ingestion of guava juice. Therefore, the long-term ingestion of guava juice may increase plasma insulin concentration in OLETF rats.

Influence of Gender on Thermoregulation and Cholinesterase Inhibition in the Long-Evans Rat Exposed to Diazinon

Diazinon is an organophosphate (OP)-based, anticholinesterase insecticide that irreversibly inhibits acetylcholinesterase activity and produces cholinergic stimulation in central nervous system (CNS) and peripheral tissues. Our laboratory has found that OPs administered orally in rats induce a transient period of hypothermia followed by a delayed fever that persists for several days after exposure. There is little information on the thermoregulatory effects of diazinon. Core temperature (Tc) and motor activity (MA) were monitored by radiotelemetry in male and female rats of the Long-Evans strain dosed orally with diazinon (0 [corn-oil vehicle], 100, 200, or 300 mg/kg in males and 0, 50, 100, or 200 mg/kg in females). There was a dose-dependent decrease in Tc during the first night after treatment, with females exhibiting slightly greater sensitivity than males. MA was unaffected in females exposed to diazinon at doses of 50 to 200 mg/kg; MA of males was reduced during the first night after dosing with 300 mg/kg. There was a delayed elevation in Tc of males dosed with 200 and 300 mg/kg and females dosed with 50, 100, and 200 mg/kg diazinon. The elevated Tc was only manifested during d 2 and 3 after diazinon. Administration of 200 mg/kg sodium salicylate to females 48 h after being treated with 200 mg/kg diazinon led to a rapid abatement of the fever. Diazinon doses of 50 to 300 mg/kg led to 40% to 50% inhibition in plasma cholinesterase (ChE) activity 4 h after dosing, and females displayed a significantly slower recovery of ChE activity compared to males. When compared on a molar basis, the hypothermic response to diazinon was relatively small compared to other OPs such as chlorpyrifos. The delayed fever and efficacy of sodium salicylate to block diazinon-induced fever are similar to the effects of OPs chlorpyrifos and diisopropyl fluoro-phosphate (DFP).

DNA damage triggers imbalance of proliferation and apoptosis during development of preneoplastic foci in the liver of Long-Evans Cinnamon rats

The mutant strain Long-Evans Cinnamon (LEC) rat accumulates copper, resulting in spontaneous hepatitis and subsequent development of hepatocellular carcinomas (HCCs) in the liver, providing a promising model for investigation of the relationship between hepatitis induced by oxidative stress and hepatocarcinogenesis. We examined DNA strand breaks in peripheral blood cells and p53 expression in livers during acute and chronic hepatitis in LEC rats, along with preneoplastic lesions, and cell proliferation and apoptosis in non-cancerous portions of livers from LEC rats aged 7-115 weeks. Immunohistochemistry using antibodies against glutathione S-transferase placental-form (GST-P), proliferating cell nuclear antigen (PCNA), and in situ DNA nick labeling (TUNEL) were used. Long-Evans Agouti (LEA) rats, a sibling line of the LEC strain, were used as controls. In the LEC rats, DNA strand breaks and expression of p53 were significantly higher than that of LEA rats at 24 weeks of age. The number of GST-P-positive (GST-P+) foci/cm2 increased and peaked at 48 weeks old, and the areas rapidly expanded thereafter. The level of cell proliferation increased with the development of hepatitis and was highest at about 48 weeks old. The induction of apoptosis in LEC rats was transiently higher than that in LEA rats during the period from 24 to 34 weeks of age. However, the ratio of PCNA-positive cells to the apoptotic index showed a growth imbalance in favor of cell proliferation, supporting sustained net growth in LEC rats. These findings suggest that DNA damage, reflected in DNA strand breaks, plays a critical role in the development of hepatocellular preneoplastic foci, with an imbalance between high proliferation and relatively low apoptosis.

Dietary exposure to chlorpyrifos alters core temperature in the rat

Administration of the organophosphate pesticide chlorpyrifos (CHP) to the male rat at a dose of 25–80 mg/kg (p.o.) results in hypothermia followed by a delayed fever lasting for several days. These are high doses of CHP that cause marked cholinergic stimulation. It is important to understand if chronic exposure to CHP would evoke changes in thermoregulation that are comparable to the acute administration. Male rats of the Long-Evans strain were subjected to dietary treatment of 0, 1, or 5 mg/(kg day) CHP for 6 months. A limited amount of food was given per day to maintain body weight at 350 g. The constant body weight allowed for the regulation of a consistent dosage of CHP per kg body weight throughout the feeding period. Core temperature ( T a) and motor activity (MA) were monitored by radio telemetric transmitters implanted in the abdominal cavity. After 5 months of treatment, T c and MA were monitored in undisturbed animals for 96 h. CHP at 5 mg/(kg day) led to a slight elevation in T c without affecting MA. The rats were then administered a challenge dose of CHP (30 mg/kg, p.o.) while T c and MA were monitored. Rats fed the 1 and 5 mg/kg CHP diets showed a significantly greater hypothermic response and reduction in MA following CHP challenge compared to controls. The restricted feeding schedule resulted in marked changes in the pattern of the circadian rhythm. Therefore, in another study, rats were treated ad libitum for 17 days with a CHP diet that resulted in a dosage of 7 mg CHP/(mg day). There was a significant increase in T c during the daytime but not during the night throughout most of the treatment period. Overall, chronic CHP was associated with a slight but significant elevation in T c and greater hypothermic response to a CHP challenge. This latter finding was unexpected and suggests that chronic exposure to CHP sensitizes the rat's thermoregulatory response to acute CHP exposure.

Pathogenesis of obesity by food restriction in OLETF rats-increased intestinal monoacylglycerol acyltransferase activities may be a crucial factor

Obesity was considered to be one of the causes of non-insulin-dependent diabetes mellitus (NIDDM). However, the mechanism responsible for obesity has not yet been fully elucidated. In this study, we first examined the relationship between food intake amount and obesity in a NIDDM model animal, and then we focused on triacylglycerol (TG) synthetase activity, which play important roles in hypertriglyceridemia (HTG) associated with obesity. Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an animal model of NIDDM, characterized by obesity, HTG and insulin resistance. In this study, OLETF rats were allocated to a food-satiated group (satiated) or food-restricted group (to eliminate the effects of hyperphagia on obesity, amount of daily food intake was the same as that in their control strain Long-Evans Tokushima Otsuka (LETO) rats). Changes in body weight, body fat, intraabdominal fat weight, and TG content in liver were measured and biochemical blood tests and activity assay of TG synthetase (monoacylglycerol acyltransferase (MGAT) and diacylglycerol acyltransferase (DGAT)) were performed. Results: (1) The body weight in the restricted OLETF rats was significantly decreased to 71.7% of that in the satiated OLETF rats, which was almost the same value as that in the LETO rats. However, body fat and intraabdominal fat weight were significantly increased in restricted OLETF rats and satiated OLETF rats compared with LETO rats. (2) Plasma TG, insulin, glucose, leptin and hepatic TG content were significantly higher in OLETF rats than the values in LETO rats. (3) MGAT activity in the small intestine from both satiated and restricted OLETF rats was significantly higher than that in LETO rats. DGAT activity in OLETF rats was not significantly different from that in LETO rats. In conclusion, the body fat weight and plasma TG were still significantly accelerated in OLETF rats at the same food intake as LETO rats. MGAT activity in the small intestine from OLETF rats was also significantly higher than those of LETO rats. Therefore, high MGAT activity in the small intestine may play an important role in HTG and obesity, subsequently hastening the development of NIDDM in OLETF rats.

Effect of response effort on the reward value of distinctively flavored food pellets.

This study was designed to test whether distinctively flavored food pellets, used as rewards for lever-pressing by rats, would acquire different reward values as a function of the differential effort involved in making the lever pressing response which would be predictable from the concept of cognitive dissonance. Subjects were seven Long-Evans strain hooded rats, 301-308 days old at the start of the study and had had their body weights reduced to 80%, of their free-feeding weights. Testing was done in a Y-maze, with food pellets associated with the difficult lever-press response serving as the reward for one choice and pellets associated with the easy lever-press response for the other. Analysis showed there was no preference in the choice of either the "easy" or the "difficult" pellets, the choice not being significantly different from chance. This indicated that the effort involved in making a response did not affect the reward strength of food pellets when used to reward a response with a different topography.

High incidence of allelic loss on chromosome 5 and inactivation of p15INK4B and p16INK4A tumor suppressor genes in oxystress-induced renal cell carcinoma of rats.

Ferric nitrilotriacetate induces oxidative damage in renal proximal tubules, a consequence of Fenton-like reaction, that ultimately leads to a high incidence of renal cell carcinoma (RCC) in rats. In order to find common genetic alterations in this oxystress-induced carcinogenesis model, RCCs were produced in F1 hybrid rats between Wistar and Long-Evans strains and genomes were screened for loss of heterozygosity (LOH) with microsatellite polymorphic markers by PCR. Five consecutive markers on chromosome 5 (D5Mgh5, D5Mit9, D5Mgh6, D5Mit11 and D5Mit6) showed LOH in >40% of the RCCs. As possible candidate tumor suppressor genes on chromosome 5, p15INK4B and p16INK4A were investigated for genetic alteration and aberrant methylation by Southern blot, PCR/SSCP/ sequencing and methylation-specific PCR. Genetic alteration (homozygous or hemizygous deletion with or without point mutation) or aberrant methylation were found in 30.7 and 53.8% of the RCC cases, respectively, which was proportionally associated with the histological nuclear grade and metastatic activity. Our data suggest that inactivation of p15 and p16 genes could be one of the major pathways responsible for oxystress-induced carcinogenesis.

Loss of function of the tuberous sclerosis 2 tumor suppressor gene results in embryonic lethality characterized by disrupted neuroepithelial growth and development.

Germline defects in the tuberous sclerosis 2 (TSC2) tumor suppressor gene predispose humans and rats to benign and malignant lesions in a variety of tissues. The brain is among the most profoundly affected organs in tuberous sclerosis (TSC) patients and is the site of development of the cortical tubers for which the hereditary syndrome is named. A spontaneous germline inactivation of the Tsc2 locus has been described in an animal model, the Eker rat. We report that the homozygous state of this mutation (Tsc2(Ek/Ek)) was lethal in mid-gestation (the equivalent of mouse E9.5-E13.5), when Tsc2 mRNA was highly expressed in embryonic neuroepithelium. During this period homozygous mutant Eker embryos lacking functional Tsc2 gene product, tuberin, displayed dysraphia and papillary overgrowth of the neuroepithelium, indicating that loss of tuberin disrupted the normal development of this tissue. Interestingly, there was significant intraspecies variability in the penetrance of cranial abnormalities in mutant embryos: the Long-Evans strain Tsc2(Ek/Ek) embryos displayed these defects whereas the Fisher 344 homozygous mutant embryos had normal-appearing neuroepithelium. Taken together, our data indicate that the Tsc2 gene participates in normal brain development and suggest the inactivation of this gene may have similar functional consequences in both mature and embryonic brain.

Impaired Male Sexual Development in Perinatal Sprague–Dawley and Long–Evans Hooded Rats Exposedin Uteroand Lactationally top,p′-DDE

Although the pesticide DDT has been banned in the United States for decades, it remains at low levels in the environment.p,p′-DDE, a metabolite of DDT, was recently shown to inhibit the binding of androgens to the androgen receptor and to exert antiandrogenic effects in perinatal Long–Evans (LE) rats at a dose of 100 mg/kg/day administered to pregnant dams. In this study, we compared the effects ofp,p′-DDE on male sexual development in offspring of Sprague–Dawley (SD) and LE rats. The chemical was dosed by gavage to pregnant dams at 10 or 100 mg/kg body wt from gestation day 14 to 18. The developing male rats were examined for sexual developmental landmarks, while the effects ofp,p′-DDE on androgen receptor expression were evaluated in the testis and other reproductive organs. The tissue dosimetry ofp,p′-DDE was also determined at different stages of development followingin uteroand lactational exposures. The higherp,p′-DDE dose induced a reduction in the male anogenital distance, an increase in retention of male thoracic nipples and alterations in expression of the androgen receptor in either one or both strains. A much weaker response was seen in the lower dose groups. Tissue and body fluid concentrations ofp,p′-DDE were similar in the two strains in some tissues but dissimilar in others, particularly in the serum levels. Higher serump,p′-DDE levels in the LE strain during pregnancy corresponded with an overall greater sensitivity of the LE strain to the antiandrogenic effects ofp,p′-DDE. These results support the previous findings ofp,p′-DDE antiandrogenicity in LE rats, extend the findings to SD rats, and suggest that the developmental effects ofp,p′-DDE on male rat sexual differentiation are minimal at maternal doses below 10 mg/kg/day.

NaCl Appetite in Two Strains of Rat Reported to Be Resistant to Mineralocorticoid- induced Hypertension

ROWLAND, N. E. NaCl appetite in two strains of rat reported to be resistant to mineralocorticoid-induced hypertension. Physiol Behav 64(1) 49–56, 1998. Both Long–Evans (LE) and Wistar–Furth (WF) strains of rat are known to be resistant to development of hypertension by mineralocorticoid (MC) treatment. MC-induced hypertension is, in part, mediated by the brain. We have examined another aspect of central MC action, the induction of NaCl appetite in these strains, by using the more common Sprague–Dawley (SD) and Wistar (WS) strains for comparison. In the first experiment, LE and SD rats were administered three treatments known to induce an appetite for NaCl solution in rats. Administration of deoxycorticosterone acetate (DOCA) increased the intake of 0.45 M NaCl in both strains, but the amounts consumed were about 2-fold greater in LE rats than in SD rats. Administration of captopril also increased NaCl intake, but there were no differences between LE and SD rats. NaCl depletion with furosemide induced NaCl appetite in both strains, but the amounts consumed were about 2-fold greater in LE rats than in SD rats. In the second experiment, adult male WF and WS rats were administered DOCA, enalapril, or furosemide and NaCl appetite was determined. Both strains showed comparable NaCl appetite during each of these treatments. However, during a 5-week regimen of DOCA with only NaCl–KCl solution to drink, uninephrectomized WF rats consumed less than WS rats. Thus, despite reported resistance to MC-induced hypertension, neither LE nor WF strains of rats showed correspondingly marked deficits in induced NaCl appetite.

Measurement of Abdominal Fat by Magnetic Resonance Imaging of OLETF Rats, an Animal Model of NIDDM

We measured abdominal fat masses (intra-abdominal visceral fat summing retroperitoneal, mesenteric, and epididymal fat and subcutaneous fat) and analyzed abdominal fat distribution of Otsuka Long-Evans Tokushima Fatty (OLETF) rats with non-insulin-dependent diabetes mellitus and control strain Long-Evans Tokushima Otsuka (LETO) rats using magnetic resonance imaging. Intra-abdominal visceral and subcutaneous fat were highly correlated with body weight both in OLETF and in LETO rats. Both intra-abdominal visceral and subcutaneous fat of OLETF rats significantly accumulated compared with those of LETO rats. Intra-abdominal visceral fat mass correlated positively with subcutaneous fat mass, and the accumulation of intra-abdominal visceral fat mass was about 3.5 times that of subcutaneous fat. Thus, obesity of OLETF rats was characterized by marked accumulation of intra-abdominal visceral fat compared with that of subcutaneous fat. Body weight and abdominal fat of OLETF rats were closely correlated with the level of total plasma glucose measured by oral glucose tolerance test. However the ratio of intra-abdominal visceral to subcutaneous fat of OLETF rats was not correlated with the level of total plasma glucose.

Tolerance to the hypothermic and hyperthermic effects of chlorpyrifos

Hypothermia is a commonly reported thermoregulatory response in rodents acutely exposed to ogranophosphates (OP); however, our laboratory has recently found a delayed hyperthermic response following the initial hypothermia when exposed to the OP, chlorpyrifos. It is well known that rodents display tolerance to OP-induced hypothermia but little is known about tolerance to OP-induced hyperthermia. Twenty female rats of the Long-Evans strain were made tolerant to chlorpyrifos by administering 0 or 10 mg/g chlorpyrifos by gavage daily for four days. Core temperature (T c) and motor activity (MA) were monitored continuously by telemetry. Twenty-four hours after the fourth 10 mg/kg injection, the animals were administered a challenge dose of 25 mg/kg chlorpyrifos or corn oil while the telemetry data were monitored for the next 72 h. Non-tolerant rats displayed an initial hypothermic response with reduced MA followed by a delayed increase in T c 24 h after exposure. The tolerant animals displayed a blunted hypothermic response with virtually no change in MA, but a delayed increase in T c similar to that of non-tolerant animals. The hyperthermic response of the non-tolerant animals persisted for two days, whereas the tolerant animals recovered by the second day. The data indicate that tolerance to the hypothermic and hyperthermic effects of chlorpyrifos involve separate neurochemical pathways.

Outputs of hepatic copper and cadmium stimulated by tetrathiomolybdate (TTM) injection in Long-Evans Cinnamon (LEC) rats pretreated with cadmium, and in Fischer rats pretreated with copper and cadmium

The Long-Evans Cinnamon (LEC) rat, an inbred mutant rat derived from the Long-Evans strain, is characterized by spontaneous hepatitis due to gross accumulation of hepatic Cu. The accumulation, accompanied by marked induction of metallothionein (MT), is believed to be due to the inherent lack of output of Cu into the bile duct and blood vessels. In this study, the acute effect of tetrathiomolybdate (TTM), a chelator for output of hepatic Cu and Cd in LEC rats treated with Cd, was investigated. Female LEC rats were injected subcutaneously with Cd (Cd; 1.0 mg/kg) to induce Cd, Cu-MT. Fischer rats were treated with Cd (Cd; 1.0 mg/kg) and Cu (Cu; 3.0 mg/kg). Forty-eight hours after the injections of metals, TTM (5 mg/kg bw) was injected intravenously under anesthesia. The TTM injection rapidly stimulated biliary excretions of Cu (at a μg/ml level) and Cd (at a ng/ml level). Furthermore, Cu and Cd concentrations were increased in serum sampled 60 min after the TTM injection. The increase of biliary Cu excretion was not accompanied by increased biliary excretion of MT. The TTM injection caused the hepatic Cu concentrations to decrease from 306 ± 2 to 262 ± 12 and from 43 ± 6 to 20 ± 5 μg/g in LEC and Fischer rats, respectively. The hepatic Cd concentration was not decreased by TTM treatment. Hepatic MT and Cu, but not Cd, concentrations in the MT fraction were also reduced by TTM injection. Our results showed that TTM can rapidly remove Cu from MT to increase bile and blood Cu levels. The output of Cd stimulated by TTM injection may be related to MT reduction resulting from removal of MT-bound Cu. Our results indicate that to avoid the toxic effect of Cu, TTM injection is an effective initial treatment, although it remains to be established how metals, including Cu, are finally metabolized.