Littermate Rats Research Articles

Effects of 5, 7-dihydroxytryptamine lesions of the nucleus accumbens on rat inravenous morphine self-administration

The role of serotonergic innervations of the nucleus accumbens in the processes maintaining intravenous morphine self-administration were assessed. Pairs of male rat littermates were implanted with intravenous jugular catheters and bilateral injection guide cannulae into the central medial nucleus accumbens, made physically dependent on morphine and then allowed to intravenously self-administer with continuous access. When stable baselines of drug intake were obtained (2–3 weeks), one of each pair received bilateral microinjections of vehicle and the other 5,7-dihydroxytryptamine (5,7-DHT) into the nucleus accumbens. Response independent infusions of morphine were delivered for 24 hours at the previous rate of self-injection and the animals were again allowed to self-administer while drug intake was monitored for thirteen days. The littermate pairs were then sacrificed by immersion in liquid nitrogen, the brains removed at −20°C and frozen sections of the cannulae tract taken for histological assessment. The nucleus accumbens, anterior caudate nucleus and pyriform cortex were removed at -20°C and biogenic monoamine content determined. The 5,7-DHT lesions resulted in a significant increase in drug intake and significantly decreased the content of serotonin (5-HT) and 5-hydroxyindoleacetic acid in the nucleus accumbens (−49% and −30%, respectively) and 5-HT in the anterior caudate nucleus (−14%) and pyriform cortex (−17%). Dose-effect relationships were assessed in four additional animals before and after similar bilateral 5,7-DHT lesions. The lesion resulted in similar rates of responding maintained by all drug doses including vehicle, thus eliminating the typical pattern of dose related decreases in responding as a function of increasing dose. 5-HT innervations of the nucleus accumbens appear to participate in neuronal activity mediating intravenous morphine self-administration.

Serum lipids and lipoprotein composition in spontaneously diabetic BB Wistar rats.

Serum lipid and lipoprotein composition in spontaneously diabetic BB Wistar rats, nondiabetic littermates, and control Wistar rats was studied to elucidate diabetes-related abnormalities of lipoprotein composition. Serum total triglycerides and pre-beta-lipoprotein concentrations of insulin-treated spontaneously diabetic BB and nondiabetic littermate rats were significantly higher than those of control Wistar rats. Serum cholesterol and HDL cholesterol concentrations of spontaneously diabetic BB and nondiabetic littermate rats did not differ from controls. Concentrations of very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL) of spontaneously diabetic BB and nondiabetic littermate rats were higher than those of normal rats. With sodium dodecylsulfate-polyacrylamide gel electrophoresis it was observed that the spontaneously diabetic BB and nondiabetic littermate rat VLDL contained higher percentages of apoE relative to total apoC when compared with control Wistar rats. With isoelectric focusing, apoC-II relative percentages in VLDL and HDL of both spontaneously diabetic BB and nondiabetic littermate rats were higher than apoC-II proportions in VLDL and HDL of controls. Apolipoprotein A-I of the control rat HDL showed four isoforms that focused at pI 5.8 (17.3%), 5.75 (30.6%), 5.65 (31.8%), and 5.55 (20.5%); however, the spontaneously diabetic BB and nondiabetic littermate rat HDL apoA-I was mainly represented by two isoforms that focused at pI 5.8 and 5.75. VLDL of both diabetic and nondiabetic BB rats contained higher levels of acidic apoE isoforms compared to their counterparts in control Wistar rats. Although HDL cholesterol concentrations of spontaneously diabetic BB rats remained normal, protein concentrations were higher resulting in a low cholesterol/protein ratio in HDL suggesting that the cholesterol-carrying capacity of spontaneously diabetic BB rat HDL could be less than normal and may be due to an abnormal apoA-I composition. Quantitative alterations of lipid and lipoprotein composition appear in the BB Wistar rat when compared to the Wistar rat, but some of the changes are more pronounced in the spontaneously diabetic BB Wistar rat.

Sex-related differences in cellular composition and surfactant synthesis of developing fetal rat lungs.

Differences in pulmonary surfactant production by male and female fetuses in late gestation have been suggested, but the precise relationship of these findings to the changing cellular populations in the lung as development progresses has not been investigated previously. Using sexed rat littermates from Day 18 to 22 of gestation, we correlated the epithelial, endothelial, and interstitial cell composition of the lung with disaturated phosphatidylcholine (DSPC) content and with the incidence of lamellar bodies in epithelial cells and air sacs. At Days 19 and 20, female rat lungs had a higher content of DSPC than did the lungs of male littermates. At Days 20 and 21, more cuboidal epithelial cells of female fetuses contained lamellar bodies, and more air sacs in the female lung contained lipid material, than was observed in males. Sex-related differences in lung structure were seen even earlier. From Day 18 to Day 20, there was a greater proportion of epithelial cells in female lungs than in the lungs of male littermates; just before birth the cellular composition was similar. The results show that differentiation of epithelium with lamellar body formation and DSPC production occurs sooner in females. However, it is suggested that a sex-related difference in lung development occurs much earlier in the female at the onset of a phase of epithelial growth.

The Local Effects of Topically Applied Estradiol, Cyproterone Acetate, and Ethanol on Sebaceous Secretion in Intact Male Rats

Estradiol in ethanol was applied once daily to one flank of intact male rats and sebum production on both flanks was measured over periods of 18 h alternating with 6 h by absorbing the lipid on pads of cigarette paper held in place by a harness, starting on the 15th day. Sebum production was very significantly less on the treated flanks than on the contralateral flanks that received only vehicle, indicating an unequivocal local effect of the estradiol. At the same time, the values on the contralateral flanks were significantly below those of littermate rats which received vehicle only, indicating that the estrogen had been systemically absorbed to produce a distal action. The estradiol also significantly reduced plasma testosterone and the relative weights of the seminal vesicles, ventral prostate, and preputial glands, which demonstrated that part of the general action of the estrogen could have been by suppression of endogenous androgen production. In short-term experiments, in which measurements were started concurrently with treatment, the inhibitory action of estradiol, in contrast to that of cyproterone acetate, was not detected until the 4th day. Indeed, it appeared probable that the estrogen actually stimulated sebum secretion over the first 2 days, suggesting that it had a biphasic effect.

Transverse periosteal sectioning and femur growth in the rat.

Circumferential cuts through the periosteal covering of long bones have been demonstrated to transiently increase epiphyseal growth. This effect appears to be independent of vascular changes accompanying surgery and has been hypothesized to relate to releasing tension in the periosteal envelope. This study was designed to address problems of previous investigations by controlling for the effects of the surgical procedure and by using regression analyses to analyze intra- and interanimal variations in the length and proportionality of the femur in experimental, sham, and control Sprague-Dawley male rat littermates. Experimental animals received circumferential periosteal sectioning of the right femur and no operation to the left limb. A sham operation without periosteal sectioning was performed on the right femur in the sham group. Right to left differences were analyzed using two multiple regression models; one involved three absolute length measurements as the dependent variables, while the other used the three ratios of these length measurements as the dependent variables. The ratio measures were utilized to reflect changes in bone proportionality. Circumferential periosteal section was followed by an alteration in the shape of rat femurs at 2 weeks postsurgery with a slight retardation of the length dimension from medial epicondyle to head of the femur and an overgrowth of the length dimension from the lateral epicondyle to the greater trochanter. The sham procedure produced a proportional decrease in all length measurements. The experimental procedure was also associated with surface bone apposition at the site of section. At 3 weeks postsurgery, normalization of bony contours between sham, experimental, and control groups had occurred; however, there were still some statistically significant decreases of length dimensions in the sham and experimental groups. In the experimental group the length measurement involving the weight-bearing head of the femur remained reduced at 3 weeks postsurgery. It is hypothesized that the functional demands of the long bone play an important role in the effect of periosteal regulation on growth. In situations where a normal tensive force is exerted on the bone, the periosteal envelope will act to restrain epiphyseal growth. When the bone is under a normal compressive force the release of periosteal tension is not a quantitatively significant stimulus to epiphyseal growth and the effects of surgical intervention and muscle trauma will play a more important role in the growth response of the epiphyses.

Hypertension: cation transport and the physical properties of erythrocytes.

In recent years, many reports have appeared describing altered Na+ and K+ transport in erythrocytes of individuals with essential hypertension. Collectively, the interpretation of these results has been unclear. Our studies revealed that the active ouabain-sensitive K+ influx, the furosemide-sensitive K+ influx and the residual passive K+ influx in both human and rat erythrocytes can vary considerably among individual persons or rats and that these measurements alone can not be used to distinguish normotensive from hypertensive individuals. The only consistent cation transport difference observed was an increased Na+ permeability in spontaneously hypertensive rat (SHR) erythrocytes. We have also examined certain physical properties (equilibrium density distribution and sedimentation velocity) of erythrocytes from normotensive Wistar-Kyoto (WKY) and SHR rats, since these characteristics may be altered in response to abnormalities of ion transport. It was found that the erythrocytes from geographically, environmentally, and age-matched littermates of WKY and SHR rats have identical equilibrium density distributions. It was also found that the density distribution of erythrocytes can vary among geographically dispersed colonies of the same strain of rat, and even among successive litters of the same rat colony. However, the sedimentation time required for erythrocytes to reach their equilibrium density was always shorter in the normotensive WKY samples than in the matched SHR. Utilizing a simple centrifugation method, we were able to clearly show that for any population of erythrocytes with the same upper limit of cell density, normotensive WKY cells always sediment at a faster rate than those of the hypertensive SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

MECHANISM OF DAMAGE TO THE CONTRALATERAL TESTIS IN RATS WITH AN ISCHAEMIC TESTIS

A degenerating ischaemic rat testis produces damage to its contralateral testis. When ischaemic testes were grafted or injected as a homogenate for a week into littermate rats there was considerable damage to host testes. This damage was caused by an immunological response, demonstrated as an increase in cytotoxicity of host serum which increased immunofluorescence, particularly of the membrana propria, which had become thickened. Manipulation of the testis and its blood supply was sufficient to cause spermatogenic damage and initiate an immunological response. These results indicate that viable early torted testes must have their torsion corrected and be anchored in the scrotum, but if the testis is ischaemic and non-viable it should be removed to avoid damage to the contralateral testis.

Enhanced pulmonary and intestinal activation of procarcinogens and mutagens after chronic ethanol consumption in the rat.

Recent epidemiological surveys have indicated that alcoholics exhibit increased incidences of a variety of cancers. We have investigated, as a possible contributing factor to carcinogenesis in this population, the effect of chronic ethanol consumption on metabolic activation of procarcinogens by microsomes isolated from lungs and small intestine. These tissues are major sites through which procarcinogens enter the body and are also potential sites of procarcinogen metabolism. Rat litter-mates were pair-fed nutritionally adequate liquid diets which contained either ethanol as 36% of total energy or an equivalent energy content of carbohydrates in place of ethanol. Chronic ethanol consumption produced significant increases in pulmonary microsomal cytochrome P-450 and microsomal ethanol oxidation. The ethanol diet also enhanced the capacity of pulmonary microsomes to activate compounds present in tobacco pyrolyzates to mutagens detectable in the Ames Salmonella auxotroph reversion assay. The ethanol diet did not alter the capacity of pulmonary microsomes to hydroxylate benzo(a)pyrene (BaP) or to activate BaP to a mutagen. In contrast, microsomes from the upper small intestine of ethanol-fed rats did exhibit both higher levels of BaP hydroxylase activity and enhanced activation of BaP to a mutagen. The ethanol feeding also enhanced the capacity of the intestinal microsomes to activate to mutagens both tryptophan pyrolyzate and 2-aminofluorene but did not influence the metabolic activation of these promutagens by pulmonary microsomes. Chronic ethanol consumption thus influences carcinogen metabolism in the intestine and lung in a manner which varies with respect to both carcinogen and tissue.

Effects of age and sex on microsomal heme oxygenase and cytochrome P-450 content in liver of rats.

Effects of age and sex on microsomal heme oxygenase activity and cytochrome P-450 content were investigated in Wister rats. Heme oxygenase activity declined with an increase in age, namely, its activity in 100 days old (young) rats was 58% in male and 72% in female rats as compared with respective 30 days old (immature) rats, and in 300 days old (old) rats it was 32% in male and 39% in female rats. In male rats, cytochrome P-450 content based on 100 g body weight decreased only in old rats as compared with immature rats, whereas a significant reduction was observed in female rats in the content based on mg microsomal protein as well as based on 100 g body weight in young and old animals. In littermate rats at the age of 56 days which obtained by in breeding in our laboratory, sex difference was apparent in heme oxygenase activity and cytochrome P-450 content, and further a good reciprocal correlation between that activity and content (r = 0.9730 in male, and r = -0.852 in female) was observed.

MATURATION OF RENAL TUBULAR TRANSPORT OF DIGOXIN

Previous data have suggested an age related increase in renal tubular secretion of digoxin in infants and children receiving long term digoxin therapy. This phenomenon could be the result of a maturational process or secondary to chronic substrate stimulation. To investigate this question two groups of 2 week old paired litter-mate rats received intraperitoneal injections of either digoxin or an equal volume of normal seline (control) an alternate days until sacrificed at 4, 6, and 8 weeks of age. An additional group of 12 week old rats were studied as controls. I125 digoxin uptake was measured in renal cortical slices as the CPM/mg wet tissue slice to medium ratio (S/M). Both digoxin treated and control rats demonstrated significant age related increment in digoxin uptake. S/M ratios at 4, 6, 8, and 12 weeks in the control group were (mean ± S.D) 1.34 ± 0.06, 1.39 ± 0.14, 1.62 ± 0.18 and 1.93 ± 0.25 respectively (r = 0.81, p < 0.001) but did not differ significantly at each age from those in the control group. I125 uptake was significantly reduced by both Dinitrophenol (DNP) and sodium azide, as well as by a 100% nitrogen atmosphere. These results indicate that renal tubular transport of digoxin is an age related energy dependent process, which probably is not subject to substrate stimulation.

Distribution of 14C-phenytoin in rat Purkinje cells, cerebellar and cerebral neuronal tissue after a single intraperitoneal injection.

10 adult female littermate rats were injected intraperitoneally with 7.9 µmol (2 mg) of 14C-labeled phenytoin. A perikaryon-enriched Purkinje cell fraction was isolated from the cerebellar

Increased hepatic cholesterol synthesis in normal rats by cross-circulation with ileal bypassed partners

Aortic cross-circulation between Holtzman rat littermates was employed to investigate the possible role of a blood-borne factor from the small intestine in the regulation of hepatic cholesterol synthesis. Experimental pairs, consisting of a normal rat and a distal 50% small bowel excluded partner, demonstrated significantly increased combined hepatic cholesterol synthesis when compared to control pairs, consisting of two normal rats, both at 3 and 5 days following parabiosis. This difference was accounted for by increased hepatic cholesterol synthesis in the normal rat in each experimental pair. Neither weight loss nor differences in dietary intake contributed to this effect. Whole blood cholesterol in the common circulation of both experimental and control pairs was lowered; while hepatic cholesterol content was transiently increased, at 3 but not 5 days following parabiosis. Thus, the intestinal bypassed rat stimulates, or releases inhibition of, hepatic cholesterol synthesis in a non-bypassed parabiotic partner. The mechanism for this phenomenon has yet to be defined.

Maze training alters brain weights and cortical RNA/DNA ratios

In order to test whether training leads to anatomical and chemical changes in the brain, individual rats were given self-paced trials in mazes, traversing the maze in order to get from a food station to a water station. In 30 days of this training, during which they had no social interaction, the rats developed significant increases in weight and RNA/DNA of standard samples of cerebral cortex, as compared with littermate rats in either of two control conditions: (a) rats confined to small individual cages ( N = 70 per condition); (b) rats that traversed the empty maze box with no maze barriers present ( N = 29 per condition). Whereas the rats who faced maze problems decreased average transit times through the maze on successive trials, the rats that traversed the empty box showed no regular trend in running times over trials. The cerebral effects of maze experience versus control conditions were similar in pattern but were smaller in magnitude than effects of experience in a social group in a multisensory complex environment. This clear evidence of cerebral changes as consequences of maze training adds further support to the indications that similar cerebral changes resulting from enriched experience are due to learning rather than to other factors. The changes that follow training or enriched experience can be linked with other evidence concerning the roles of RNA and of protein synthesis in the formation of long-term memory traces. The U.S. Government's right to retain a nonexclusive royalty-free license in and to the copyright covering this paper, for governmental purposes, is acknowledged.

Avoidance deficits in rats after recovery from mild to moderate thiamin deficiency

Rat littermates (Sprague-Dawley) were administered either a thiamin-deficient diet or an equivalent amount of complete control diet (pair-fed controls) for 2, 3, or 4 weeks beginning at 28 days of age. At the end of treatment all groups were allowed 30 days of recovery on ad lib. normal diet prior to testing in a Y-maze for avoidance and brightness discrimination acquisition. Y-maze testing lasted for 20 days, 25 trials/day. All three thiamin-deficient groups showed avoidance acquisition deficits, none showed discrimination deficits. The data indicate that even mild to moderate degrees of thiamin deficiency that do not produce over neurological symptoms are capable of producing long-term changes in behavior.

Relative synthesis of myelin in different brain regions of postnatally undernourished rats

We used a double isotope procedure and starved and normal littermate rats to compare relative protein synthesis in the cerebellar nuclear, myelin, synaptosomal, mitochondrial, and microsomal subfractions of postnatally starved animals. The remaining brain tissue was dissected into 6 additional regions (cerebral cortex, medulla oblongata, midbrain, hippocampus, striatum, and hypothalamus) and these were frozen for similar subcellular fractionation and analysis at a later date. The microsomal fraction derived from frozen tissues was discarded. The results show that early postnatal starvation specifically depresses myelin synthesis to about the same extent in all major brain regions at 18 and 21 days of age.

Transplantation of a basicranial synchondrosis to a sutural area in the isogeneic rat

Summary In order to develop a method for characterizing the function of so-called growth cartilages the spheno-occipital synchondroses of 25-day-old, sex-matched littermate rats were transplanted to osseous environments. As a sham procedure sutures with some adjoining bone were similarly treated. The bony parts joined by the synchondroses generally became fused with the host bone within 25 days of the operation. When transplanted to the fronto-parietal sutural area the synchondroses retained their normal appearance for 75 days in some animals whereas in others they degenerated or became resorbed. Synchondroses transplanted into the central part of the parietal bone degenerated relatively soon after the operation. In sutures, exchanged with some adjoining bone between rats, the actual suture line was virtually indistinguishable from the control structure. In the present experiment the synchondroses seemed to become adapted to their new environment which did not permit all possible growth of the transplant to occur. The method seems potentially useful for its intended purpose.

Does anoxemia play a role in the effects of neonatal seizures on brain growth? An experimental study in the rat.

Groups of 4 Wistar rat littermates of matched sex and weight received the following daily treatment between the ages of 2 and 11 days: handling (untreated controls, UC), succinylcholine paralysis and ventilation with 100% O2 (respirator control, RC), electroconvulsive seizures (ECS) and ECS while paralyzed and ventilated with O2 (respirator seizures, RS). Analysis of heart blood O2 content showed that mechanical ventilation with 100% O2 effectively prevented the anoxemia observed during convulsive seizures. In the ECS and RS groups, several behavioral milestones (e.g. swimming) matured later than they did in either control group (UC, RC). No difference was observed between the two groups of seizure-treated rats. At the age of 30 days, both ECS and RS groups had smaller brains with a reduced DNA, RNA, protein and cholesterol content in both forebrain and hindbrain, suggesting that seizures curtailed the number of brain cells. The lack of any difference between the two seizure groups suggests that at least part of the adverse effects of experimental neonatal seizures on brain and behaviour are independent of anoxemia.

Bone Remodeling as an Expression of Altered Phenotype

The healing of tibial fractures was studied in 3 groups of young littermate rats; untreated osteopetrotic (ia/ia), normal littermates (ia/+) and osteopetrotic (ia/ia) cured of the disease 3 days earlier by transplanted normal spleen cells. The fracture site was completely remodeled in 4 weeks in normal rats, 6 weeks in transplanted (cured) osteopetrotic rats and 9 weeks in untreated osteopetrotic rats. The delayed healing in untreated osteopetrotic rats resulted from reduced resorption present in this mutation. Increased resorption brought about by transplantation of normal spleen cells accelerated healing in the transplanted osteopetrotic rats. Fracture repair took longer in the latter group than in normal littermates presumably because tibial fracture occurred before the 2 week interval required for skeletal transformation from osteopetrotic to normal phenotype following transplantation of normal spleen cells. These data show that alteration of the phenotype of osteopetrotic rats is reflected in fracture healing.

Social grouping cannot account for cerebral effects of enriched environments

Several experiments were conducted to test whether, as suggested by Welch et al. in this journal 20, mere group living (social stimulation) can account for the significant differences in measures of brain anatomy and brain chemistry that develop between rodents housed in groups in enriched environments and rodents housed singly in restricted environments; the alternative hypothesis was that features of the inanimate environment can significantly affect brain measures of animals living in a social group. Groups of 12 male rats were assigned for 30 days to several types of environment: (a) large cage without stimulus objects, (b) large cage containing varied stimulus objects, (c) large cage containing a maze whose pattern of barriers was changed daily, and (d) a seminatural outdoor environment; in each experiment, littermates of rats in the social conditions were housed in isolation in small colony cages. At the end of the 30-day period, measures were taken of weights of brain regions, RNA and DNA contents of regions of cerebral cortex, and acetylcholinesterase activities of brain regions. Although the number of rats housed together was constant for conditions a−d and cage size was constant for conditions a−c, the magnitudes of the cerebral measures varied significantly as a function of the inanimate stimulus conditions. The differences from isolation-housed littermates was greatest in condition d and smallest in condition a. Thus, social grouping alone is inadequate to explain the cerebral effects of enriched environments and the inanimate stimulus conditions must be taken into account.

Endocrine status of the testicular feminized male (TFM) rat

The plasma levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone (T), androstenedione (A), dihydrotestosterone (DHT), corticosterone and corticosterone binding globulin (CBG) were determined in 160- and 350-day testicular feminized male (tfm) and normal littermate (NL) rats. In the younger group the concentrations of T, A, DHT and 5α-androstan-3α,17β-diol (Adiol) were also determined in testis tissue. Tfm rats showed a greatly elevated plasma LH indicating lack of androgen feedback. Plasma FSH, however, was normal in both age groups, suggesting that inhibin production from tfm testes was relatively unaffected. Intratesticular concentrations of A were greatly elevated in the tfm animals at both ages whilst the testicular levels of T were highly reduced when compared to NL rats. This indicates a gonadal deficiency of the 17β-hydroxy steroid dehydrogenase (17β-HSD). Furthermore, the relatively low T: DHT ratio and high concentrations of Adiol in the tfm testes confirmed previous reports that the high 5α-reductase typical for the immature rat testis is maintained into adulthood in rats with the tfm condition. A considerable degree of peripheral conversion (A → T) probably helps to maintain normal or supranormal plasma levels of T. Gonadectomy rendered all plasma androgens undetectable, indicating that the adrenal contribution was negligible. Increasing age (350 days) was associated with a marked increase in circulating androgens in tfm rats. This is probably the reason for the observed significant reduction in circulating LH in this age group when compared to the 160-day animals. The aging tfm rat is predisposed to testicular tumors which, on the basis of histology, specific [ 125I]hLH binding and in vitro responsiveness to hCG, appear to be of Leydig cell origin. Microflow fluorometry (MFF) of tfm testis cell suspensions revealed the presence of haploid cells, suggesting that meiosis proceeds to a limited extent. Plasma corticosterone levels in the tfm rat were normal although plasma CBG levels were highly significantly elevated at both ages when compared to the levels in NL rats. We suggest that the adrenal hyperplasia observed in tfm rats is secondary to reduced corticosterone production and diminished free corticosterone in the circulation.