Long-Evans Hooded Research Articles

Male Long Evans rats reared with a Fischer-344 peer during the juvenile period show deficits in social competency: a role for play

ABSTRACTRats that are deprived of play during the juvenile period develop into adults that have a host of socio-cognitive impairments. Thus, it has been hypothesized that experiencing play fighting during the juvenile period refines executive functions. The present study assesses the social ability of adult, male Long-Evans hooded (LE) rats that have been reared with either a same age and sex LE rat or a Fischer-344 (F344), a low playing strain. As adults, their social skills were assessed. This was done by introducing each rat into a neutral arena with an unfamiliar partner. As predicted, rats from both conditions engaged the stranger in play, but the LE rats that had been reared with a F344 partner were more likely to escalate these playful interactions into aggressive ones. These findings support the hypothesis that play experience during the juvenile period is critical for the development of some executive functions.

Pharmacokinetics, Distribution, Metabolism, and Excretion of Omadacycline following a Single Intravenous or Oral Dose of 14C-Omadacycline in Rats.

ABSTRACTThe absorption, distribution, metabolism, and excretion (ADME) of omadacycline, a first-in-class aminomethylcycline antibiotic with a broad spectrum of activity against Gram-positive, Gram-negative, anaerobic, and atypical bacteria, were evaluated in rats. Tissue distribution was investigated by quantitative whole-body autoradiography in male Long-Evans Hooded (LEH) rats. Following an intravenous (i.v.) dose of 5 mg/kg of body weight, radioactivity widely and rapidly distributed into most tissues. The highest tissue-to-blood concentration ratios (t/b) were observed in bone mineral, thyroid gland, and Harderian gland at 24 h post-i.v. dose. There was no evidence of stable accumulation in uveal tract tissue, suggesting the absence of a stable binding interaction with melanin. Following a 90 mg/kg oral dose in LEH rats, the highest t/b were observed in bone mineral, Harderian gland, liver, spleen, and salivary gland. The plasma protein binding levels were 26% in the rat and 15% to 21% in other species. Omadacycline plasma clearance was 1.2 liters/h/kg, and its half-life was 4.6 h; the steady-state volume of distribution (Vss) was 6.89 liters/kg. Major circulating components in plasma were intact omadacycline and its epimer. Consistent with observations in human, approximately 80% of the dose was excreted into the feces as unchanged omadacycline after i.v. administration. Fecal excretion was primarily the result of biliary excretion (∼40%) and direct gastrointestinal secretion (∼30%). However, urinary excretion (∼30%) was equally prominent after i.v. dosing.

Pinning in the Play Fighting of Rats: A Comparative Perspective With Methodological Recommendations

During play fighting, rats attack and defend the nape and during the course of this competitive interaction, they may adopt a configuration in which one animal stands over its supine partner (i.e., pin). Because the pin configuration is typically frequent and relatively easy to identify, it has been widely used as a marker to detect the effects of experimental treatments. In the present study, the frequency of pinning during standardized, 10min trials in three strains of rats, Long Evans hooded (LE), Sprague-Dawley (SD) and wild (WWCPS), was compared. LE and SD had higher rates than WWCPS rats (#/min: 6.5, 5.5, 1.5, respectively). When adjusted for strain differences in the frequency of attacks, SD as well as WWCPS rats had lower rates of pinning compared to LE rats. Both SD and WWCPS rats were less likely to use tactics of defense that promote pinning. Moreover, while the majority of the pins achieved in LE rats arose from the defender actively rolling over onto its back, the majority of pins in WWCPS rats arose because one partner pushed the other onto its back. SD rats were intermediate in this regard. Finally, once they do adopt the pin configuration, SD rats are less likely to remain supine than LE and WWCPS rats. That is, both SD and WWCPS rats have significantly fewer pins than LE rats, but a different combination of factors account for this. These data highlight the need to use a battery of measures for ascertaining the effects of experimental manipulations on play. Some suggested guidelines are provided.

B(a)P exposure in utero result in oxidative stress‐induced high blood pressure in LEH rat offspring

Cancer Biology, Meharry Medical College, Nashville, TN In utero exposure of fetuses to benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon, can result in the impairment of brain development and function. Although other developmental indices are thought to be affected, the true nature of the effect of B(a)P exposure in utero is relatively unclear. To investigate the effects of in utero B(a)P exposure on high blood pressure development in later life, timed‐pregnant Long Evans Hooded (LEH) rats were exposed to B(a)P (0, 600 and 1200 μg/kg BW) by oral gavage on embryonic (E) days 14–17. The results indicate that the blood pressure of the B(a)P exposed offspring was significantly elevated compared to the controls. Similarly, western blot analysis and quantitative real time PCR (qRT‐PCR) also showed an increase in the level of protein and mRNA expression for angiotensin (AGT), (6R)‐5,6,7,8‐tetrahydro‐L‐biopterin (BH4) and nitric oxide synthase (NOS). However, there were no significant effects of in utero B(a)P exposure on the number of pups born per litter, the initial and final heart to body weight ratios, or the pre‐weaning growth weights. These data suggest that in utero exposure to B(a)P predispose offspring to functional deficits in cardiovascular development which leads to cardiovascular dysfunction in later life.

In utero exposure to benzo(a)pyrene predisposes offspring to cardiovascular dysfunction in later-life

In utero exposure of the fetus to benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon, is thought to dysregulate cardiovascular development. To investigate the effects of in utero B(a)P exposure on cardiovascular development, timed-pregnant Long Evans Hooded (LEH) rats were exposed to diluent or B(a)P (150, 300, 600 and 1200μg/kg/BW) by oral gavage on embryonic (E) days E14 (the metamorphosing embryo stage) through E17 (the 1st fetal stage). There were no significant effects of in utero exposure to B(a)P on the number of pups born per litter or in pre-weaning growth curves. Pre-weaning profiles for B(a)P metabolite generation from cardiovascular tissue were shown to be dose-dependent and elimination of these metabolites was shown to be time-dependent in exposed offspring. Systolic blood pressure on postnatal day P53 in the middle and high exposure groups of offspring were significantly elevated as compared to controls. Microarray and quantitative real-time PCR results were directly relevant to a biological process pathway in animal models for “regulation of blood pressure”. Microarray and quantitative real-time PCR analysis revealed upregulation of mRNA expression for angiotensin (AngII), angiotensinogen (AGT) and endothelial nitric oxide synthase (eNOS) in exposed offspring. Biological network analysis and gene set enrichment analysis subsequently identified potential signaling mechanisms and molecular pathways that might explain the elevated systolic blood pressures observed in B(a)P-exposed offspring. Our findings suggest that in utero exposure to B(a)P predispose offspring to functional deficits in cardiovascular development that may contribute to cardiovascular dysfunction in later life.

Use of an M1/M4-selective muscarinic agonist in combination with a peripheral antagonist as a novel approach for the treatment of Alzheimer's disease

The MI 09-018 Series compounds are potential first-in-class drugs for Alzheimer's Disease (AD) that strongly activate brain signaling pathways known to enhance cognition and block putative AD disease mechanisms. Such drugs may also be useful in schizophrenia and other serious CNS conditions. These drug leads are subtype-selective muscarinic acetylcholine receptor (AChR) agonists. Approved cholinesterase inhibitor drugs show that increased brain acetylcholine may mitigate cognitive impairment in AD by partially restoring the cholinergic deficiency. An M1/M4 muscarinic acetylcholine receptor (AChR) agonist, xanomeline, showed interesting efficacy in AD and schizophrenia in Phase II clinical trials, but was abandoned due to poor tolerability. Furthermore, muscarinic AChR agonists improve cognition and inhibit putative AD disease processes in laboratory models. The 09-018 Series is targeted at selective activation of brain M1 and M4 AChR, while minimizing M2 and M3 activation, especially in the periphery. To complement the intrinsic selectivity of 09-018, further reduction of potential unwanted peripheral side effects has been demonstrated by combining 09-018 with peripheral muscarinic antagonists. Animals were dosed with 09-018 alone (0.01-3 mg/kg by subcutaneous injection) or in combination with a muscarinic antagonist (such as n-methylscopolamine or glycopyrrolate). Inositol phosphate (IP) signaling in the hippocampus (central M1 activation) and submaxillary glands (peripheral M3 activation) was measured in Long-Evans Hooded (LEH) rats. Peripheral side effects were assessed by quantifying the amount of saliva produced in anesthetized LEH rats. The apomorphine-induced climbing test was used to assess central M4 activation in CD-1 mice. Brain tissue and plasma were also collected to determine 09-018 and antagonist concentrations. Stimulation of IP signaling in the hippocampus was unaffected by the antagonist, while IP signaling in the salivary glands was blocked. The antagonist reduced the amount of saliva produced in a dose dependent manner. The antagonists did not reduce the effects of 09-018 on apomorphine-induced climbing. The use of a non-brain-penetrant muscarinic antagonist was shown to be effective at reducing the peripheral side effects of an M1/M4-selective muscarinic agonist while maintaining the desired central effects. This approach presents a promising therapeutic strategy for AD and schizophrenia.

Monoamine variability in the chronic model of atypical absence seizures

We studied the variability of the slow-spike-and-wave discharges (SSWDs) derived from AY-9944 (AY) treatment during brain development of Long-Evans hooded (LEh) rats. Although all LEh rats received the standard dose of AY (7.5 mg/kg), we have observed an intersubject variability of the total SSWD duration at postnatal day (P) 55. Therefore, we set out to investigate the underlying brain levels of norepinephrine (NE), dopamine (DA), and serotonin (5-HT) and its metabolite (5-HIAA), as determined by high-performance liquid chromatography (HPLC) analyses from four different brain regions: thalamus (Th), frontoparietal cortex (Cx), hippocampus (Hp), and brainstem (Bs). All brains were obtained after two baseline electrocorticographic (ECoG) recordings with characteristic chronic, recurrent, bilaterally synchronous 4-6 Hz SSWD, at P 55 (336.25 +/- 97.23 s/h) and P60 (494.50 +/- 150.36 s) (r = 0.951, r(2) = 0.904, p < 0.005, Pearson product). The thalamic NE levels and the brainstem NE, DA, and 5HT levels were all significantly correlated with baseline SSWD duration at P55 and P60 (p < 0.01, Pearson product). Our data indicate that brain monoamine levels may determine the intersubject variability of SSWD duration in AY rats with chronic atypical absence seizures.

Atrazine Disrupts the Hypothalamic Control of Pituitary-Ovarian Function

The chloro-S-triazine herbicides (i.e., atrazine, simazine, cyanazine) constitute the largest group of herbicides sold in the United States. Despite their extensive usage, relatively little is known about the possible human-health effects and mechanism(s) of action of these compounds. Previous studies in our laboratory have shown that the chlorotriazines disrupt the hormonal control of ovarian cycles. Results from these studies led us to hypothesize that these herbicides disrupt endocrine function primarily through their action on the central nervous system. To evaluate this hypothesis, we examined the estrogen-induced surges of luteinizing hormone (LH) and prolactin in ovariectomized Sprague-Dawley (SD) and Long-Evans hooded (LE) rats treated with atrazine (50-300 mg/kg/day, by gavage) for 1, 3, or 21 days. One dose of atrazine (300 mg/kg) suppressed the LH and prolactin surge in ovariectomized LE, but not SD female rats. Atrazine (300 mg/kg) administered to intact LE females on the day of vaginal proestrus was without effect on ovulation but did induce a pseudopregnancy in 7 of 9 females. Three daily doses of atrazine suppressed the estrogen-induced LH and prolactin surges in ovariectomized LE females in a dose-dependent manner, but this same treatment was without effect on serum LH and prolactin in SD females. The estrogen-induced surges of both pituitary hormones were suppressed by atrazine (75-300 mg/kg/day) in a dose-dependent manner in females of both strains evaluated after 21 days of treatment. Three experiments were then performed to determine whether the brain, pituitary, or both organs were the target sites for the chlorotriazines. These included examination of the ability of (1) the pituitary lactotrophs to secrete prolactin, using hypophyosectomized females bearing pituitary autotransplants (ectopic pituitaries); (2) the synthetic gonadotropin-releasing hormone (GnRH) to induce LH secretion in females treated with high concentrations of atrazine for 3 days; and (3) atrazine (administered in vivo or in vitro) to suppress LH and prolactin secretion from pituitaries, using a flow-through perifusion procedure. In conclusion, the results of these studies demonstrate that atrazine alters LH and prolactin serum levels in the LE and SD female rats by altering the hypothalamic control of these hormones. In this regard, the LE female appeared to be more sensitive to the hormone suppressive effects of atrazine, as indicated by the decreases observed on treatment-day 3. These experiments support the hypothesis that the effect of atrazine on LH and prolactin secretion is mediated via a hypothalamic site of action.

Rat strain and age differences in kainic acid induced seizures

This study reports comparative dose-response data for kainic acid (KA) induced seizures in juvenile (35-40 days old) and adult (70-90 days old) Wistar-Furth (WF), Fisher 344 (F344), Sprague-Dawley (SD) and Long-Evans Hooded (LEH) rats. Juvenile male WF (n = 51), F344 (n = 55), SD (n = 60), LEH (n = 50) and adult male WF (n = 48), F344 (n = 52), SD (n = 52), LEH (n = 53) rats were given KA 6, 8, 10, 12 or 14 mg/kg, sc. As previously demonstrated adult WF and F344 rats showed the greatest sensitivity and most reliable convulsant responses to kainic acid; SD and LEH rats were less sensitive and showed more variable convulsant responses. Regardless of strain, all juvenile rats exhibited greater sensitivity and less variable convulsant response to KA compared to adults. This was most evident in juvenile SD and LEH rats. Results suggest that while seizure sensitivity to KA decreases with age, genetic factors may regulate the expression of this resistance.

Strain differences between albino and pigmented rats in monoamine-synthesizing enzyme activities of brain, retina and adrenal gland

The present study compared the activities of some of the monoamine synthesizing enzymes in several brain regions, the retina as well as adrenal gland of albino Sprague-Dawley (SD) and Long-Evans hooded (LE) rats. Brainstem, hypothalamic and retinal tyrosine hydroxylase (TH) activity were significantly higher in LE than in SD. In addition to higher enzyme activity, a larger number of TH-immunoreactive perikarya as well as a higher concentration of TH-immunoreactive processess were observed in the retina of LE rats. There was no strain difference in TH activity of caudate nucleus (CN) and substantia nigra (SN). In contrast to brain regions and retina, adrenal TH activity was markedly higher in SD than in LE animals. Aromatic L-amino acid decar☐ylase (AADC) activity of both the brainstem and adrenal gland in the LE strain was lower than in SD animals. No differences in the AADC activity of hypothalamus, SN and CN were found between LE and SD strains. Phenylethanolamine N-methyltransferase (PNMT) activity of the hypothalamus, retina and adrenal gland of LE strains was significantly lower than in SD rats. In spite of the difference in the enzyme activity, there were no marked morphological changes observed in PNMT-immunostaining patterns between the retina of LE and SD rats. Tryptophan hydroxylase activity of both the brainstem and hypothalamus did not exhibit strain differences. Our results indicated that (1) there are significant differences in catecholamine synthesizing enzyme activities of various brain regions, retina and adrenal gland between pigmented and albino rat strains; (2) thus strain differences in TH enzyme activity paralleled the morphological changes in retinal TH staining; and (3) positively correlated with the presence of pigment.

The Wistar Furth rat: an animal model of hereditary macrothrombocytopenia

The mechanisms that determine and regulate platelet size are unknown. By phase microscopy, we observed that Wistar Furth (WF) rats had macrothrombocytopenia. In this study, we have characterized and compared platelets and megakaryocytes of WF rats with those of Wistar, Long-Evans hooded (LE), and Sprague-Dawley rats. In addition, we have examined the mode of inheritance of this WF rat platelet abnormality. The average platelet count of WF rats was only one-third that of the other three rat strains. In contrast, the mean platelet volume (MPV) of adult WF rats was twice that of the other rat strains; however, the average megakaryocyte diameter and DNA content distribution of WF rats were not significantly different from those of LE rats. The average megakaryocyte concentration was 30% lower in the WF strain compared with that of LE rats. Mazelike membrane formations were observed in WF platelets and megakaryocytes by electron microscopy. Reciprocal crosses of WF and LE rats resulted in offspring with MPVs and platelet counts like those of LE rats, indicating that the macrothrombocytopenic trait is recessive in its inheritance. Reciprocal marrow transplants between the WF and LE strains resulted in MPVs like those of the donor strain, demonstrating that the macrothrombocytopenia is an intrinsic marrow abnormality of the WF strain. Splenectomy did not alter the MPV of WF rats. The response of WF megakaryocytes and platelets to severe, acute thrombocytopenia was similar to that of LE rats except that the shift to higher megakaryocyte DNA contents was muted and platelet recovery was slower in the WF rats. In summary, the WF rat has a hereditary macrothrombocytopenia that is recessive in nature and not due to differences in megakaryocyte size or DNA content. These results suggest that the macrothrombocytopenia of WF rats results from the formation of fewer platelets per megakaryocyte, possibly resulting from a qualitative or quantitative defect in some component necessary for proper subdivision of megakaryocyte cytoplasm into platelets.

The Wistar Furth Rat: An Animal Model of Hereditary Macrothrombocytopenia

The mechanisms that determine and regulate platelet size are unknown. By phase microscopy, we observed that Wistar Furth (WF) rats had macrothrombocytopenia. In this study, we have characterized and compared platelets and megakaryocytes of WF rats with those of Wistar, Long-Evans hooded (LE), and Sprague-Dawley rats. In addition, we have examined the mode of inheritance of this WF rat platelet abnormality. The average platelet count of WF rats was only one-third that of the other three rat strains. In contrast, the mean platelet volume (MPV) of adult WF rats was twice that of the other rat strains; however, the average megakaryocyte diameter and DNA content distribution of WF rats were not significantly different from those of LE rats. The average megakaryocyte concentration was 30% lower in the WF strain compared with that of LE rats. Mazelike membrane formations were observed in WF platelets and megakaryocytes by electron microscopy. Reciprocal crosses of WF and LE rats resulted in offspring with MPVs and platelet counts like those of LE rats, indicating that the macrothrombocytopenic trait is recessive in its inheritance. Reciprocal marrow transplants between the WF and LE strains resulted in MPVs like those of the donor strain, demonstrating that the macrothrombocytopenia is an intrinsic marrow abnormality of the WF strain. Splenectomy did not alter the MPV of WF rats. The response of WF megakaryocytes and platelets to severe, acute thrombocytopenia was similar to that of LE rats except that the shift to higher megakaryocyte DNA contents was muted and platelet recovery was slower in the WF rats. In summary, the WF rat has a hereditary macrothrombocytopenia that is recessive in nature and not due to differences in megakaryocyte size or DNA content. These results suggest that the macrothrombocytopenia of WF rats results from the formation of fewer platelets per megakaryocyte, possibly resulting from a qualitative or quantitative defect in some component necessary for proper subdivision of megakaryocyte cytoplasm into platelets.

Evaluation of the Teratogenic Effects of Tri-ortho-cresyl Phosphate in the Long-Evans Hooded Rat

Evaluation of the Teratogenic Effects of Tn-ortho-ciesyl Phosphate in the Long–Evans Hooded Rat. TOCCO, D. R., RANDALL, J. L., YORK, R. G., and SMITH, M. K. (1987). Fundam. Appl. Toxicol. 8, 291–297. The developmental toxicity of tri-ortho-cresyl phosphate (TOCP) was evaluated in Long–Evans rats. Pregnant rats were treated with 87.5, 175, and 350 mg/kg/day TOCP throughout organogenesis from gestation Days 6 through 18 (Day of sperm = Day 0). The highest dose tested (350 mg/kg) was lethal in 28% of the dams; no maternal deaths or toxicity were observed in the 87.5 or 175 mg/kg dose groups. There were no significant differences noted among the experimental and control groups for preimplantation loss or resorption. Fetal weights for both sexes in the TOCP groups were significantly greater than in the control group; however, no difference among the TOCP groups was observed. Malformation rates were too low to warrant statistical analysis. Numerous soft tissue and skeletal variations were observed in both control and TOCP-treated groups; there were no significant differences in the frequency of variations among the dose groups. The results of this study indicate that TOCP is not teratogenic in the Long–Evans rat.

Strain differences in susceptibility of normal and diabetic rats to acetaminophen hepatotoxicity

The effects of streptozotocin (STZ)-induced diabetes on acetaminophen metabolism and hepatotoxicity in male Sprague-Dawley (SD) and Long Evans Hooded (LEH) rats were compared. In agreement with earlier studies, normal SD rats were more resistant to acetaminophen-induced hepatic necrosis than normal LEH rats. In contrast to LEH rats, the diabetic state did not protect SD rats from liver injury. Pharmacokinetic studies revealed that normal SD rats eliminated acetaminophen faster than normal LEH rats, and that the diabetic state further enhanced elimination in both strains of rats; however, the effect was much greater in LEH rats. Normal SD rats had a greater capacity to metabolize acetaminophen to nontoxic glucuronide and sulfate conjugates than normal LEH rats. In LEH rats, the diabetic state enhanced acetaminophen glucuronidation and sulfation, whereas in SD rats the diabetic state increased only sulfation; glucuronidation was unaffected. Additional studies revealed that the difference in the glucuronidation capacities between normal LEH and normal SD rats was not due to differences in either the amount of the enzyme, glucuronyl transferase, or basal hepatic levels of the cofactor, UDPGA. Similarly, the diabetes-induced enhancement of glucuronidation in LEH rats was not due to differences in predrug levels of either glucuronyl transferase or UDPGA. Thus, the major difference in susceptibility of the two strains of normal rats to acetaminophen hepatotoxicity appears to be due to the capacity to clear the drug through nontoxic pathways. The greater glucuronidation capacity seen in diabetic LEH rats and in normal and diabetic SD rats as compared to normal LEH rats, appears to be due to a greater ability to produce UDPGA in response to the metabolic demand.

Open Field Behaviors Correlated with Reward Availability and Reward Shift in Three Rat Strains

Rats derived from Wistar (W), Sprague-Dawley (SD), and Long-Evans hooded (LE) strains were placed in an open field for 5 min per day under three conditions: habituation (4 days), preshift (10 days), in which half of each strain was given access to a 32% sucrose solution and half to 4% solution, and postshift (4 days) in which all rats received the 4% solution. Individual and multivariate analyses of 10 dependent variables indicated reliable strain differences in the way the animals allocated their time in various stages of the experiment. In particular, the availability of different sucrose solutions exerted the greatest effect on the response patterns of the SD rats and the least on the W rats, the SD rats tended to ambulate more when sucrose was not available, and the LE rats engaged in the most rearing behavior. Some behavioral categories were sensitive to the stage of the experiment but not to the strain differences. All strains responded similarly to a shift in sucrose solutions and to the availability of sucrose in novel locations during the postshift period. Implications of these data for strain differences and similarities, obtained in operant and other situations, were considered.