Sensitivity to cocaine conditioned reward depends on sex and age

Human and animal laboratory studies show that females and males respond differently to drugs and that drug administration during adolescence leads to different behavioral effects than during adulthood. Adult female rats are more sensitive to the behavioral effects of cocaine than adult males, but it is not known if the same effect of sex exists during adolescence. In the present study, sensitivity to the conditioned reward of cocaine was evaluated using a conditioned place preference (CPP) paradigm where adolescent (PND 34) and adult (PND 66) male and female rats were trained and tested for the development of CPP to multiple doses of cocaine. Female rats developed CPP at lower doses than males, regardless of age. In addition, adolescent male and female rats established a CPP at lower doses of cocaine than adult male and female rats, respectively. Thus, both age and sex altered cocaine conditioned reward with the order of sensitivity being adolescent females > adult females > adolescent males > adult males. These data show that adolescents are more sensitive to the conditioned rewarding properties of cocaine than adults and that females respond to lower doses of cocaine compared to males regardless of age.     

Age-and sex-related differences in rat liver microsomal enzymes and their inducibility by toluene

In the liver microsomes of toluene-treated and control Sprague-Dawley rats (n = 148, males and females aged 13-93 days), the contents of cytochrome P-450 and b5 and the activities of NADPH-cytochrome c reductase and four monooxygenases were studied. In male control rats, cytochrome contents and NADPH-cytochrome c reductase, aminopyrine N-demethylase and aniline hydroxylase activities increased to the age of one month, and after a slight decrease in cytochrome concentrations, the average adult level was reached by the age of two months. Aniline hydroxylase and 7-ethoxycoumarine O-deethylase activities decreased to about half at the same age period. In control female rats, the activities of aminopyrine N-demethylase and aniline hydroxylase decreased after the age of one month, and they remained at a considerably lower level in adult females than in males. The sex-dependence of other enzymes was negligible. Toluene induction was already well developed in the youngest age group of both sexes; in most cases the induced enzyme levels in young rats were as high or higher than in adults. In adult female rats, toluene induction of all enzymes was weaker than in males. In male rats, the toluene-induced level of aniline hydroxylase and 7-ethoxycoumarine O-deethylase showed deep minima at the age of 43-53 days, at the puberty of rats.     

Age- and Sex-related Differences in Rat Liver Microsomal Enzymes and their Inducibility by Toluene

Abstract: In the liver microsomes of toluene-treated and control Sprague-Dawley rats (n=148, males and females aged 13–93 days), the contents of cytochrome P-450 and b₅ and the activities of NADPH – cytochrome c reductase and four monooxygenases were studied. In male control rats, cytochrome contents and NADPH – cytochrome c reductase, aminopyrine N-demethylase and aniline hydroxylase activities increased to the age of one month, and after a slight decrease in cytochrome concentrations, the average adult level was reached by the age of two months. Aniline hydroxylase and 7-ethoxycoumarine O-deethylase activities decreased to about half at the same age period. In control female rats, the activities of aminopyrine N-demethylase and aniline hydroxylase decreased after the age of one month, and they remained at a considerably lower level in adult females than in males. The sex-dependence of other enzymes was negligible. Toluene induction was already well developed in the youngest age group of both sexes; in most cases the induced enzyme levels in young rats were as high or higher than in adults. In adult female rats, toluene induction of all enzymes was weaker than in males. In male rats, the toluene-induced level of aniline hydroxylase and 7-ethoxycoumarine O-deethylase showed deep minima at the age of 43–53 days, at the puberty of rats.     

Neoplastic and nonneoplastic lesions in aging osborne-mendel rats

Neoplastic and nonneoplastic lesions in 975 male and 970 female Osborne-Mendel rats used as controls in carcinogenesis tests were tabulated and evaluated. Three types of controls were considered—untreated controls (245 males, 245 females), controls administered corn oil in feed (530 males, 525 females), and controls administered corn oil by gavage (200 males, 200 females). Few neoplasms were seen in rats less than 18 months of age; the incidence of tumors markedly increased between 18 and 24 months of age. The incidence of some of the more common neoplasms, in which the combined incidence was greater than 1%, varied among the control groups, and in most cases the differences in incidences were not statistically significant. Hemangiosarcomas at all sites and C-cell adenomas of the thyroid in female rats were marginally significantly lower in controls given corn oil by gavage than in the other two groups. The occurrence of adenocarcinomas of the mammary gland was significantly higher in male controls given corn oil by gavage than in the other two groups. In untreated controls, the incidences of adrenal cortical adenomas in males and females and of pheochromocytomas in males were significantly higher than in both groups given corn oil. In rats administered corn oil in the feed, the incidences of pituitary adenomas in males and females, follicular cell adenomas of the thyroid in males, and endometrial stromal polyps in females were significantly higher than the incidences in the other two groups. The possible reasons for these differences are discussed. However, the types of tumors seen in the three control groups were morphologically comparable. The tumors observed included two types that had not previously been well characterized in Osborne-Mendel rats—malignant fibrous histiocytomas and lipomatous tumors of the kidney. Incidences of the more common nonneoplastic lesions are reported.     

Lead acetate toxicity in rats in relation to age and sex

The toxicity of lead acetate was determined in young (3-week-old) and adult (18-week-old) rats of both sexes 8 days after a single i.p. injection. The LD₅₀ was lower in adult males than in adult females and both groups of young animals.The whole-body retention of lead-203 determined in other groups of animals of the same age and sex 8 days after i.p. application was higher in young animals than in adults.Our results indicate a lower toxicity of lead acetate in young animals than in adults and a higher toxicity of lead in adult males.     

Developmental and sex differences in cadmium distribution and metallothionein induction and localization

Age- and sex-related differences in hepatic and renal distribution of cadmium (Cd) and the effect of Cd injection (10 mumol/kg) on tissue zinc (Zn), copper (Cu) and metallothionein (MT) levels were investigated in 2- to 84-day old rats. Renal Cd accumulation increased with age of the animal. Sex differences in renal Cd accumulation were noted in young animals where the 2- and 8-day old males had significantly greater concentration than the females. There were no clear effects of Cd on renal Zn. Renal Cu levels, however, were elevated in the adults. The adult females contained about twice as much MT as the adult males. Cd treatment had no effect on renal MT levels of 8- to 84-day old animals but depressed the levels in 2-day old. Age-related increase in hepatic Cd accumulation was also found; the pattern was more clear cut in females than in males. In addition, in the females the hepatic Cd concentration was significantly higher than in the males. Cd-injection significantly increased hepatic Zn and MT concentrations only in weaned animals. While there were no sex differences in MT levels in the young animals, the weaned females had significantly more MT than the corresponding males. Immunohistochemical staining for MT showed positive staining in both cytoplasm and nuclei of the parenchymal cells. The number of MT-positive nuclei was dependent on the relative MT concentration of the liver. In spite of the intense nuclear staining in 2-day old controls and 84-day old Cd-injected rats, less than 1% of the hepatic MT was present in the nuclear fraction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lack of carcinogenicity of triethanolamine in F344 rats

The carcinogenic potential of triethanolamine was examined in F344 rats. Triethanolamine was dissolved in distilled water at levels of 0 (control), 1, and 2%, and groups of 50 males and 50 females were given these doses ad libitum as drinking water for 2 yr. The dose levels in females were reduced by half from wk 69, because of associated nephrotoxicity. A variety of tumors developed in all groups, including the control group, and all tumors observed were histologically similar to spontaneous tumors in this strain of rats. No statistically significant increase of the incidence of any tumor was observed in the treated groups of both sexes by the chi-square test. In this study, however, there was an increase in nephrotoxicity, which appeared to have an adverse effect on the life expectancy of the treated animals, especially of females. Therefore, an age-adjusted statistical analysis on incidences of main tumors or tumor groups of both sexes was also done by methods recommended by Peto et al. (1980). The result showed that a positive trend (p less than 0.05) was noted in the occurrence of hepatic tumors (neoplastic nodule/hepatocellular carcinoma) in males and of uterine endometrial sarcomas and renal-cell adenomas in females. These tumors, however, have been observed spontaneously in this strain of rats, and their incidences in the control group of the present study were lower than those of our historical controls. These results may indicate that a positive trend in the occurrence of these tumors is not attributable to triethanolamine administration. Increased incidence of renal tumors in the female high-dose group may have been connected with renal damage. Histological examination of renal damage observed in the treated groups, especially in the female high-dose group, revealed acceleration of so-called chronic nephropathy. In addition, mineralization of the renal papilla, nodular hyperplasia of the pelvic mucosa, and pyelonephritis with or without papillary necrosis were also observed. Thus, it is concluded that under these experimental conditions triethanolamine is not carcinogenic in F344 rats but is toxic to the kidneys.     

Studies on the behavioral development of rats treated neonatally with l-thyroxine

The effect of l-thyroxine administration from 2 to 10 days of age (Neo-T4) on the behavioral development was studied. Serum T4 levels in Neo-T4 rats showed a marked and dose-related decrease at 15 days of age and a less marked decrease at 62 days of age. The locomotor activity of the Neo-T4 rats was higher at 13 approximately 19 days of age and tended to be lower at 62 days of age than in the controls. At 17 days of age, apomorphine (0.1 mg/kg, s.c.) induced a marked increase in the frequency of sniffing down in the control males, whereas a decrease was noted in the Neo-T4 males. Age-matched females in both groups responded to apomorphine with a slight decrease in sniffing down behavior. An increase in the frequency of sniffing down by apomorphine (0.5 mg/kg) in adult Neo-T4 rats was less marked. TRH administration failed to induce hyperthermia in adult Neo-T4 males. The results indicate that neonatal administration of T4 in the rat induces alterations in the functional development of the brain in varying degrees dependent upon the functional integration of the neurons. An involvement of sex hormones is suggested.     

Influence of age, sex, pregnancy and protein-calorie malnutrition on the pharmacokinetics of salicylate in rats

The influence of age, sex, pregnancy and protein-calorie malnutrition (PCM) on the plasma t1/2, plasma clearance (Clp) and apparent volume of distribution (Vd) of sodium salicylate (62 mumol kg-1) was determined in Sprague-Dawley rats. Female and male rats of five different age groups (ages in weeks: pups 1, weanling 3, young 8-9, adult including pregnant 14-15, old 56-60) including three age groups with PCM (8-9, 14-15 and 56-60 weeks old) were used. Plasma and urinary salicylates were assayed by h.p.l.c. Plasma t1/2 was longer and Clp smaller in pups than in weanling and young rats and comparable to values for old rats; Vd of salicylate in pups was larger than in any other group of rats. Plasma t1/2 was longer and Clp as well as Vd of salicylate were smaller in adult females than in males of comparable age. Relative to nonpregnant adult females, Vd of salicylate in pregnant rats was larger but plasma t1/2 and Clp were unchanged. In all groups of rats studied, PCM decreased the plasma t1/2 and increased the Clp of salicylate; Vd was unchanged. Changes in salicylate pharmacokinetics were not due to any differences in serum protein-salicylate binding or to serum testosterone levels. Ovariectomy decreased the plasma t1/2 of salicylate but castration of male rats had no significant effect. Administration of testosterone to ovariectomized female rats exerted no significant effect on salicylate pharmacokinetics. It is concluded that the physiological state and the nutritional status can modify salicylate pharmacokinetics; in so far as the rat model reflects the human situation, these variables should be taken into account for a rational salicylate therapy.     

Sexual dimorphism in rats with respect to locomotor activity and circling behavior

Male and female rats were tested for locomotor activity and spontaneous circling (rotation) at 4, 6, 8, 11, 13 and 15 weeks of age. Locomotor activity of females increased with age, and significant intersex differences which became apparent by 8 weeks of age were attributed to the greater persevering tendency of the females. Spontaneous rotation, on the other hand, did not change with age and significant intersex differences were not evident. Moreover, locomotor activity and rotation were not correlated at any age. In contrast to spontaneous rotation, amphetamine induced significantly more rotation in older (18 week) than in younger (5 week) females and males of both ages. Apomorphine, on the other hand, also elicited more rotation in older than in younger females, but not in males. In addition, intersex differences were not evident in younger animals tested with either drug. These data suggested that the greater persevering tendency and lateralization of females compared to males may be related to bilateral functional imbalances in nigrostriatal activity.     

Hepatocellular iron accumulation and increased cell proliferation in polychlorinated biphenyl-exposed Sprague-Dawley rats and the development of hepatocarcinogenesis.

Polychlorinated biphenyls (PCBs) are liver-tumor promoters in rodents, but the underlying mechanisms have not been fully elucidated. Tissue sections from the PCB bioassay reported by Mayes et al. 1998, Toxicol Sci., 41-66, were evaluated by histopathological techniques that included immunohistochemistry. In females, and to a much lesser extent in males, iron accumulation in hepatocytes was found at the 26th-week sacrifice, which was pronounced in the mid- and high-dose Aroclor-1254 and -1260 groups. At 52 weeks, large accumulations of iron were also present in Kupffer cells of females, and dose-related increases in proliferating cell nuclear antigen (PCNA) hepatocyte labeling indices were found in both males and females. These changes preceded the formation of liver tumors, which were not generally found until 78 weeks. Glutathione S-transferase placental (GSTP) positive foci were present at 52 weeks in high-dose Aroclor-1254 and -1260 female groups, and small foci were found in some Aroclor 1254-exposed female rats at 26 weeks, along with centrilobular hepatocytes expressing GSTP. The results of this study suggest that PCB-induced iron accumulation in hepatocytes is an early event that may be related to tumor formation, especially in female rats. In both males and females, increases in cell proliferation at 52 weeks were statistically significantly correlated with tumor incidences at termination among the various PCB dosage groups. Consequently, iron accumulations producing oxidative damage, and enhanced cell proliferation resulting in tumor promotion may be components in the mode of action for PCB-induced hepatocarcinogenesis in rodents.     

Influence of sex, estrous cycle, and drug-onset age on cocaine self-administration in rats (Rattus norvegicus)

The influence of sex, phase of the estrous cycle, and age of drug onset on cocaine self-administration was examined. Adult male, adult female, and adolescent male rats (Rattus norvegicus) were evaluated using low fixed-ratio (FR) schedules of drug delivery with a single fixed cocaine unit dose or a range of cocaine unit doses with a single FR schedule. Sex differences in adults were observed for mg/kg consumption of the 3.0-mg/kg unit dose, with consumption being significantly less in estrus females than in males. Over the estrous cycle, mg/kg consumption of this unit dose was significantly less during estrus than during metestrus-diestrus. Differences due to age of drug onset were also observed, with mg/kg consumption of the 3.0-mg/kg unit dose being significantly less in adolescent males than adult males or adult females during metestrus-diestrus. In contrast, these various groups did not have significantly different mg/kg intakes of cocaine unit doses <3.0 mg/kg, nor did they significantly differ in the rates and patterns of responding and number of infusions earned as a function of FR schedule or unit dose of cocaine available. The role of sex, estrus cycle, and drug-onset age on cocaine self-administration appears to be minimal under these experimental conditions. Experimental conditions that favor no sex or age differences in cocaine intake (1.0-mg/kg unit dose and low FR) may be useful for evaluating potential sex or age differences in the consequences of cocaine self-administration more reliably, as cocaine intake would not be an uncontrolled factor.     

Gonadal steroids mediate the opposite changes in cocaine-induced locomotion across adolescence in male and female rats

Evidence from both human studies and animal models indicates that cocaine elicits more behavioral stimulation in females than males. The present study sought to determine whether sex-specific responses to cocaine emerge during adolescence and to determine if gonadal steroid action during puberty affects adult responsiveness to cocaine. We administered cocaine using an escalating dose model in male and female rats at ages postnatal (PN) 28, 42, and 65 days. To assess the effects of pubertal gonadal steroid action, we compared the effects of binge cocaine administration on intact and prepubertally gonadectomized male and female rats in adulthood. Cocaine responses changed in opposite directions in males and females as they progressed through adolescence. At most doses, adolescent males were more responsive than adult males whereas adult females were more responsive than adolescent females. Ambulatory activity was age-dependent in males whereas non-ambulatory activity was age-dependent in females. Prepubertal gonadectomy increased behavioral responsiveness to the highest dose of cocaine in males whereas it decreased behavioral responsiveness to lower doses of cocaine in females. We conclude that sex differences in behavioral responses to cocaine arise during adolescence from a concurrent decrease in male responsiveness and increase in female responsiveness. Our results suggest that gonadal steroids exert lasting and opposing effects on the sensitivity of males and females to psychostimulants during development.     

Asymmetric calmodulin distribution in the hypothalamus: role of sexual differentiation in the rat

The Ca2+/calmodulin (CaM) system plays important roles both in hypothalamic sexual differentiation and in the progesterone-induced facilitation of lordosis behavior in the adult rat. We recently showed sex-dependent differences in rat hypothalamic CaM levels, both in newborn and in adult animals. Here, we evaluated the presence of left-right hypothalamic asymmetries in CaM concentration in male and female rats, as well as the changes induced on these parameters by neonatal (1 h after birth) subcutaneous administration of tamoxifen (200 microg/rat) or testosterone (30 microg/rat). CaM was measured by RIA in each half of the hypothalamus (at 2, 6, 12, and 24 h and at 90 days after birth) in both control and treated animals. In untreated young rats (2-24 h after birth), CaM concentration was significantly higher in the right half of the hypothalamus of males, whereas in females, it was higher in the hypothalamic left half. Treatment of females with testosterone or tamoxifen to males, consistently reversed these results. In the hypothalamus of treated animals, we found higher CaM levels in the left half of males, as well as in the right half of females. In control adult females, CaM concentration was also higher in the left half of the hypothalamus, as it was in the right half of adult males. However, this asymmetry was lost after neonatal hormone manipulation. These results reinforce the role of CaM in the development of sex-related hypothalamic functions.     

Anxiety- and depression-like behaviors are accompanied by an increase in oxidative stress in a rat model of fetal alcohol spectrum disorders: Protective effects of voluntary physical exercise

Prenatal ethanol exposure can damage the developing nervous system, producing long-lasting impairments in both brain structure and function. In this study we analyzed how exposure to this teratogen during the period of brain development affects the intracellular redox state in the brain as well as the development of anxiety- and depressive-like phenotypes. Furthermore, we also tested whether aerobic exercise might have therapeutic potential for fetal alcohol spectrum disorders (FASD) by increasing neuronal antioxidant capacity and/or by alleviating ethanol-induced behavioral deficits. Sprague-Dawley rats were administered ethanol across all three-trimester equivalents (i.e., throughout gestation and during the first 10 days of postnatal life). Ethanol-exposed and control animals were assigned to either sedentary or running groups at postnatal day (PND) 48. Runners had free access to a running wheel for 12 days and at PND 60 anxiety- and depressive-like behaviors were assessed. Perinatal ethanol exposure resulted in the occurrence of depressive and anxiety-like behaviors in adult rats without affecting their locomotor activity. Voluntary wheel running reversed the depressive-like behaviors in ethanol-exposed males, but not in ethanol-exposed females. Levels of lipid peroxidation and protein oxidation were significantly increased in the hippocampus and cerebellum of ethanol-exposed rats, and there was a concomitant reduction in the levels of the endogenous antioxidant glutathione. Voluntary exercise was able to reverse the deficits in glutathione both in ethanol-exposed males and females. Thus, while voluntary physical exercise increased glutathione levels in both sexes, its effects at the behavioral level were sex dependent, with only ethanol-exposed male runners showing a decrease in depressive-like behaviors.     

Gender-based profiles of developmental immunotoxicity to lead in the rat: assessment in juveniles and adults

Gender-based differences in immunotoxicity induced by the heavy metal lead (Pb) have been observed both in the juvenile chicken and the adult rat following low-level exposure during embryonic development. To better define the gender-based differences, as related to dose following in utero exposure to Pb, potential differential sensitivities were examined after exposure of F344 rats to low concentrations of Pb (0, 50, 100, or 250 ppm Pb) ad libitum throughout gestation. Immune assessment was performed in juveniles (5 wk old) and young adults (13 wk old). At the highest (250 ppm) Pb concentration examined, the delayed-type hypersensitivity (DTH) response was depressed in females relative to gender-matched controls at both ages; relative spleen weights and relative neutrophil numbers were increased while relative and absolute monocyte numbers and relative basophil numbers were decreased at 13 but not 5 wk of age. In contrast, 250 ppm Pb-treated males did not differ in these endpoints. With in utero exposure to 100 ppm Pb, 13-wk-old females again had decreased relative and absolute monocyte numbers and increased relative neutrophil numbers, although the DTH response was unchanged. Males (with 100 ppm Pb) had increased relative neutrophil numbers, decreased relative lymphocytes, and transiently increased nitrite production seen at 5, but not 13, wk of age. After gestational exposure to 50 ppm Pb, minimal immunotoxic effects were observed in either males or females at either developmental age assessed. These results suggest that differential gender-based immunotoxicity profiles exist after gestational Pb exposure depending on the concentration of Pb administered to the dam. In utero exposure of dams to 250 ppm Pb results in more profound immunotoxicity in females than males. Males arenot more sensitive to lower concentrations of Pb than females. Since the 50 ppm exposure produced minimal changes, these data may provide information to establish a no-observed-adverse-effect level (NOAEL) for in utero exposure to Pb. Additionally, while most effects were evident at both juvenile and adult ages, some changes were not fully evident until measured in the adult. Most changes were persistent with only one exception (male nitrite levels at 100 ppm).     

Toxicology and carcinogenesis study of styrene-acrylonitrile trimer in F344/N rats (perinatal and postnatal feed studies)

Styrene-acrylonitrile trimer (SAN Trimer) is a mixture of isomers formed by the condensation of two moles of acrylonitrile and one mole of styrene and has a molecular weight of 210. The mixture is composed of two structural forms: 4-cyano-1,2,3,4-tetrahydro-a-methyl-1-naphthaleneacetonitrile (THNA, CAS No. 57964-39-3) and 4-cyano-1,2,3,4-tetrahydro-1-naphthalenepropionitrile (THNP, CAS No. 57964-40-6). The THNA form consists of four stereoisomers. [Structure:see text]. The THNP form consists of two stereoisomers. [Structure:see text]. SAN Trimer is a by-product of the production of acrylonitrile styrene plastics and is created in specific manufacturing processes for polymers of acrylonitrile and styrene. In June 1998, due to community concerns about the toxicity of SAN Trimer, it was nominated to the NTP for carcinogenicity testing by a member of Congress. Male and female F344/N rats were exposed to SAN Trimer in feed in perinatal and postnatal studies for 7 weeks, 18 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and Escherichia coli, and in rat reticulocytes, leukocytes, liver cells, and brain cells. In vivo comet and micronucleus assays were performed in the juvenile rats. 7-WEEK STUDY IN RATS: Groups of 10 male and 10 female rats were fed diets containing 0, 250, 500, 1,000, 2,000, or 4,000 ppm SAN Trimer (equivalent to average daily doses of approximately 50, 90, 175, 270, or 410 mg SAN Trimer/kg body weight to males and 45, 90, 185, 295, or 430 mg/kg to females) for 2 weeks postweaning; the dams of these rats were fed the same concentrations of SAN Trimer from gestation day 7 until the pups were weaned. One 4,000 ppm male rat died 3 days after weaning; all other rats that started the postweaning phase survived to the end of the study. Mean body weights of 1,000, 2,000, and 4,000 ppm males and 2,000 and 4,000 ppm females were significantly less than those of the controls; weaning mean body weights were reduced in 4,000 ppm males and females and in 2,000 ppm females. Feed consumption by 2,000 and 4,000 ppm males and females was less than that by the control groups. Thinness in 4,000 ppm male rats was the only clinical finding related to SAN Trimer exposure. Nonneoplastic lesions were observed in the brain, thymus, spleen, liver, kidney, and reproductive organs of males and females and were considered due to overt toxicity. 18-WEEK STUDY IN RATS: Groups of 10 male and 10 female rats were fed diets of 0, 100, 200, 400, 800, or 1,600 ppm SAN Trimer (equivalent to average daily doses of 10, 20, 40, 80, or 150 mg/kg to males and females) for 3 months postweaning; the dams of these rats were fed the same concentrations from gestation day 7 until the pups were weaned. All rats survived to the end of the study. Mean body weights of 1,600 ppm males and females exposed to 200 ppm or greater were significantly less than those of the controls. At termination, brown staining of the urogenital fur was observed in females exposed to 200 ppm or greater. The liver weights of all exposed groups of males and the spleen weights of 800 and 1,600 ppm males and 1,600 ppm females were significantly greater than those of the controls. There were no significant differences in sperm parameters of male rats or the estrous cyclicity of female rats administered 400, 800, or 1,600 ppm in the diet when compared to the control groups. No exposure-related histopathologic lesions were observed. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female core study rats were fed diets of 0, 400, 800, or 1,600 ppm SAN Trimer (equivalent to average daily doses of approximately 20, 40, or 75 mg/kg to males and 20, 40, or 85 mg/kg to females) for 2 years. Special study groups of 20 males and 20 females were fed the same exposure concentrations and were evaluated at 27, 52, and 78 weeks for hematology and clinical chemistry or at 26, 51, and 77 weeks for urinalysis. The dams of core and special study rats were fed the same concentrations from gestation day 7 until the pups were weaned. Mean body weights of 1,600 ppm males were less than 90% of the controls after week 1; mean body weights of 800 and 1,600 ppm females were less than 90% of the controls after weeks 41 and 13, respectively. Feed consumption by exposed groups of males and females was generally similar to that by the control groups. Brown staining of the urogenital fur was observed in all exposed groups, and the number of animals affected increased with increasing exposure concentration. Rare neoplasms were present in the central nervous system of male and female rats. In the original evaluation, the 800 and 1,600 ppm groups of male rats each had one astrocytoma and one granular cell tumor in the brain. Also in the brain, one 400 ppm female had a granular cell tumor and one control, one 400 ppm, and one 800 ppm female had a mixed cell glioma. In the spinal cord, one astrocytoma was noted in a 1,600 ppm male in the original evaluation. In the expanded review of the spinal cord, one granular cell tumor was found in a 400 ppm male and one meningioma was found in an 800 ppm female. There were statistically significant increases in the incidence of spinal nerve root degeneration in 1,600 ppm males and the incidences of sciatic nerve degeneration in 800 and 1,600 ppm females. More importantly, there were increases in the severities of both nerve lesions in males and in the severity of spinal nerve root degeneration in females. The incidences of bone marrow hyperplasia were significantly increased in 1,600 ppm males and females and 800 ppm females. Incidences of bone marrow granulomatous inflammation were increased in 1,600 ppm males and 800 and 1,600 ppm females, and the increase in the 800 ppm females was significant. Because this lesion is very rare and did not occur in control animals, it should be considered biologically significant. In the liver, the incidence of eosinophilic focus was significantly increased in 1,600 ppm males and the incidences of mixed cell focus were significantly increased in 400 and 1,600 ppm males. Incidences of mixed cell focus were increased in the liver of all exposed groups of females, and the increase was significant in the 1,600 ppm group. The incidence of transitional epithelial hyperplasia of the urinary bladder in 1,600 ppm females was significantly greater than that in the controls. There were significant decreases in the incidences of pituitary gland pars distalis adenoma in 1,600 ppm males and females, and the incidences in both sexes occurred with negative trends. The incidences of mammary gland fibroadenoma occurred in females with a negative trend, and the incidences in 800 and 1,600 ppm females were significantly less than that in the control group. The incidences of mononuclear cell leukemia in all exposed groups of males and females were significantly less than those in the controls. GENETIC TOXICOLOGY: SAN Trimer (Batch 3) was not mutagenic in Salmonella typhimurium strains TA98 or TA100 or in Escherichia coli strain WP2 uvrA/pKM101 in tests conducted with and without exogenous metabolic activation. In vivo, however, results of a comet assay indicated significantly increased levels of DNA damage in brain cells of male and female juvenile rats following administration of SAN Trimer (Batch 3) by oral gavage. Dose-related increases in DNA damage in liver cells of these rats were also observed, but the increases were smaller than those observed in brain cells and were judged to be equivocal in both males and females. Indications of DNA damage following exposure to SAN Trimer were also seen in leukocytes of male and female rats. Increases in male rats were significant, but in females, observed levels of DNA damage did not correlate with dose. Therefore, the results were judged to be positive in males and equivocal in females. In addition to the positive comet assay results, significant increases in the frequencies of micronucleated reticulocytes were observed in peripheral blood of male and female juvenile rats dosed with SAN Trimer. CONCLUSIONS: Under the conditions of this 2-year feed study preceded by perinatal exposure, there was no evidence of carcinogenic activity of SAN Trimer in male and female F344/N rats given feed containing 400, 800, or 1,600 ppm SAN Trimer. Exposure to SAN Trimer resulted in increased incidences and/or severities of peripheral nerve degeneration in male and female F344/N rats, increased incidences of nonneoplastic lesions of the bone marrow and liver in male and female F344/N rats, and of nonneoplastic urinary bladder lesions in female F344/N rats. The incidences of pituitary gland adenoma and mononuclear cell leukemia in male and female F344/N rats and mammary gland fibroadenoma in female F344/N rats were decreased.     

Individual differences in oral nicotine intake in rats

To study individual differences in nicotine preference and intake, male and female rats were given free access to a choice of oral nicotine (10 or 20?mg/L) or water for 24?h/day for periods of at least six weeks, starting at adolescence or adulthood. A total of 341 rats, were used in four different experiments; weight, nicotine intake and total liquid consumption were recorded weekly. Results show that rats can discriminate nicotine from water, can regulate their intake, and that there are readily detected individual differences in nicotine preference. Ward analyses indicated that the animals could be divided into minimum, median and maximum preferring subgroups in all experiments. The effect of saccharine on nicotine intake was also evaluated; although the addition of saccharine increased total intake, rats drank unsweetened nicotine solutions and those with higher preferences for nicotine, preferred nicotine over water with or without saccharine added. Nicotine reduced weight gain and the effect was more pronounced in females than males. The average nicotine consumption of adolescent rats was higher than adults and nicotine exposure during adolescence reduced nicotine intake in adult rats. About half of the rats which had access to nicotine as adolescents and also as adults had a persistent pattern of consumption; the behavior was very stable in the female minimum preferring groups and a much higher ratio of rats sustained their adolescent behavior as adults. The change in preference was more pronounced when there was an interval between adolescent and adult exposure; female rats showed a more stable behavior than males suggesting a greater role for environmental influences on males. In conclusion, marked individual differences were observed in oral nicotine intake as measured in a continuous access 2-bottle choice test. Age and sex of the subjects and previous exposure to nicotine are significant factors which affect preference in rats.     

Relationship of body-weight gain to longevity and to risk of development of nephropathy and neoplasia in Sprague-Dawley rats

The relationship of weight gain to survival, risk of development of chronic progressive nephropathy and risk of development of various neoplasms has been studied in the control groups from two routine chronic toxicity studies in Sprague-Dawley rats. The groups comprised 100 CFY strain rats of each sex observed up to the age of 109 wk and 120 CD strain rats of each sex observed up to 111 wk of age (females) or 121 wk (males). The eventual incidence of tumours was found to be related to body weight at several ages. There was also a statistically significant association between high body weight at various ages and increased mortality, particularly in the CD strain and particularly in females. The 'heavy' rats proved to have an increased risk of developing both progressive nephropathy and certain tumours. This relationship was particularly marked for pituitary tumours in both sexes and for benign and malignant mammary tumours in females, and was significant irrespective of whether tumours coexisting with marked or severe progressive nephropathy were classified as fatal or incidental. There was also some evidence that increased body weight was positively associated with risk of islet-cell tumours and lipomatous tumours in males and fibromatous tumours in females. The observations illustrate how non-specific factors, such as those that affect body weight, may profoundly influence mortality and tumour incidence in chronic toxicity studies. The findings also highlight the difficulty of classifying particular neoplasms as incidental or fatal where other potentially life-threatening pathology (e.g. progressive nephropathy) is present.     

Quantitative Evaluation of Hepatic Foci of Cellular Alteration Occurring Spontaneously in Fischer-344 Rats

Quantitative Evaluation of Hepatic Foci of Cellular AlterationOccurring Spontaneously in Fischer-344 Rats. Popp, J. A., SCORTICHINI,B. H., AND GARVEY, L. K. (1985). Fundam. Appl. Toxicol. 5, 314–319.Stereologic procedures were used to quantitate spontaneouslyoccurring liver foci of altered staining in control Fischer-344rats at 33, 59, 85, and 111 weeks of age. Foci were identifiedusing hematoxylin and eosin stained sections. In both malesand females, foci were first observed at 59 weeks. The numberof foci per cubic centimeter of liver, as well as mean focalvolume, increased significantly with age. Between 85 and 111weeks, the number of foci per liver increased 3.5 times in femalesbut was unchanged in males. When three groups of 111-week-oldanimals were evaluated, females consistently had a greater numberof foci per cubic centimeter of liver and mean focal volumethan males of the same group. For the three groups evaluatedat 111 weeks, the mean number of foci per liver ranged from431 to 1865 in males and from 727 to 1654 in females. The meanvolume fraction (% of the liver) occupied by foci ranged from0.28 to 1.0% in males and from 1.42 to 4.15% in females. Whenfocal staining characteristics were investigated, the majorityof foci were basophilic in both sexes at all time points examined.However, males consistently had a higher percentage of eosinophilicfoci than females.