Long-Evans Hooded Rats Research Articles

Deficiency of Vitamin E and Selenium Enhances Calcium-Independent Phospholipase A2 Activity in Rat Lung and Liver

Conditions promoting oxidative stress, which is implicated in many diseases, activate phospholipases A2, a family of enzymes central to phospholipid metabolism and signal transduction. Little is known about isozyme specificity with respect to this activation process. Accordingly, a dietary deficiency model known to induce oxidative stress was used to investigate phospholipase A2 isozyme activity in rat tissues. Long-Evans hooded rats were fed purified diets for 6 wk with or without the addition of vitamin E and selenium in a 2 ՠ2 factorial design. Phospholipase A2 activity was assessed in lung, liver, kidney and heart cytosol and microsomes in the presence (5 mmol/L CaCl2) or absence (5 mmol/L EGTA) of calcium with dipalmitoylphosphatidylcholine at pH 6.5. Lung phospholipase A2 activity was also assessed with 1-stearoyl-2-arachidonoylphosphatidylcholine as substrate at pH 8.5. Organ samples from rats deficient in both nutrients showed two- to tenfold higher calcium-independent phospholipase A2 activity in lung cytosol and microsomes, and in liver cytosol compared with samples from control and single nutrient-deficient rats. In contrast, the calcium-dependent activity was affected only slightly. The malondialdehyde concentration of the organs was measured and the pattern obtained mirrored that of enhanced phospholipase A2 activity for lung but not for liver. The enhanced phospholipase A2 activity in the lung cytosol and microsomes from rats deficient in both nutrients was partially blocked by p-bromophenacylbromide, further enhanced by dithiothreitol and unaffected by treatment with diisopropylfluorophosphate. These results suggest that deficiency of both vitamin E and selenium activates and/or induces unique calcium-independent forms of phospholipase A2 markedly in rat lung, and to a lesser extent in liver.

Early-Onset albuminuria and Associated Renal Pathology in Leucine-Rich Repeat Kinase 2 Knockout Rats.

Activating mutations of the leucine-rich repeat kinase 2 (LRRK2) gene are associated with Parkinson disease (PD), prompting development of LRRK2 inhibitors as potential treatment for PD. However, kidney safety concerns have surfaced from LRRK2 knockout (KO) mice and rats and from repeat-dose studies in rodents administered LRRK2 inhibitors. To support drug development of this therapeutic target, we conducted a study of 26 weeks' duration in 2-month-old wild-type and LRRK2 KO Long-Evans Hooded rats to systematically examine the performance of urinary safety biomarkers and to characterize the nature of the morphological changes in the kidneys by light microscopy and by ultrastructural evaluation. Our data reveal the time course of early-onset albuminuria at 3 and 4 months in LRRK2 KO female and male rats, respectively. The increases in urine albumin were not accompanied by concurrent increases in serum creatinine, blood urea nitrogen, or renal safety biomarkers such as kidney injury molecule 1 or clusterin, although morphological alterations in both glomerular and tubular structure were identified by light and transmission electron microscopy at 8 months of age. Diet optimization with controlled food intake attenuated the progression of albuminuria and associated renal changes.

Taurine-Derived Compounds Produce Anxiolytic Effects in Rats Following Developmental Lead Exposure.

Lead (Pb2+) is a developmental neurotoxicant that disrupts the GABA-shift and subsequently causes alterations in the brain's excitation-to-inhibition (E/I) balance. Taurine is a well-established neuroprotective and inhibitory compound for regulating brain excitability. Since mechanistically taurine can facilitate neuronal inhibition through the GABA-AR, the present study examined the anxiolytic potential of taurine derivatives. Treatment groups consisted of the following developmental Pb2+-exposures: Control (0 ppm) and Perinatal (150 ppm or 1,000 ppm lead acetate in the drinking water). Rats were scheduled for behavioral tests between postnatal days (PND) 36-45 with random drug assignments to either saline, taurine, or taurine-derived compound (TD-101, TD-102, or TD-103) to assess the rats' responsivity to each drug in mitigating the developmental Pb2+-exposure and anxiety-like behaviors through the GABAergic system. Long-Evans hooded rats were assessed using an open field (OF) test for preliminary locomotor assessment. Twenty-four hours later, the same rats were exposed to the elevated plus maze (EPM) and were given an i.p. injection of 43mg/Kg of the saline, taurine, or TD drugs 15 min prior to testing. Each rat was tested using the triple-blind random assignment method for each drug condition. The OF data revealed that Control female rats had increased locomotor activity over Control male rats, and the Pb2+-exposed males and females had increased locomotor activity when compared to the Control male and female rats. However, in the EPM, the Control female rats exhibited more anxiety-like behaviors over Control male rats, and the Pb2+-exposed male and female rats showed selective responsivity to TD drugs when compared to taurine. For Pb2+-exposed males, TD-101 showed consistent recovery of anxiety-like behaviors similar to that of taurine regardless of Pb2+ dose, whereas in Pb2+-exposed females TD-101 and TD-103 showed greater anxiolytic responses in the EPM. The results from the present psychopharmacological study suggests that taurine and its derivatives are interesting drug candidates to explore sex-specific mechanisms and actions of taurine and the associated GABAergic receptor properties by which these compounds alleviate anxiety as a potential behavioral pharmacotherapy for neurodevelopmental Pb2+ exposure.

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.

Effects of rat strain and method of inducing ethanol drinking on Pavlovian-Instrumental-Transfer with ethanol-paired conditioned stimuli.

Ethanol-paired conditioned stimuli (CSs) are widely thought to invigorate ethanol responding, and thus, precipitate relapse to drinking. However, preclinical studies investigating this issue using Pavlovian-Instrumental-Transfer (PIT) procedures have had mixed results, with some studies finding PIT while others did not. The studies failing to show PIT used Lewis rats and induced ethanol drinking using a post-prandial drinking procedure. The present experiments examined whether either of these two variables influenced the magnitude of PIT observed. In the first experiment, ethanol drinking in Lewis rats was induced using either sucrose fading or post-prandial drinking. In the second experiment, ethanol drinking was induced using post-prandial drinking in either Long-Evans Hooded or Lewis rats. In both experiments, rats were trained to respond for ethanol under a random interval schedule. Subsequently with the lever removed, 2-min light presentations were paired with ethanol deliveries. Finally, with the lever returned, the effect of light presentations on responding was tested while responding was in extinction. Light presentations similarly affected responding in Lewis rats regardless of the method of drinking induction. Likewise, light presentations similarly affected responding in both Lewis and Long-Evans Hooded rats. Neither ethanol induction method nor rat strain affected the magnitude of PIT observed, and thus, neither likely explains previous failures to observe PIT with ethanol-maintained behavior.

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.

Noise Induced DNA Damage Within the Auditory Nerve.

An understanding of the molecular pathology that underlies noise induced neurotoxicity is a prerequisite to the design of targeted therapies. The objective of the current experiment was to determine whether or not DNA damage is part of the pathophysiologic sequela of noise induced neurotoxicity. The experiment consisted of 41 hooded Long-Evans rats (2 month old males) that were randomized into control and noise exposed groups. Both the control and the noise group followed the same time schedule and therefore started and ended the experiment together. The noise dose consisted of a 6000 Hz noise band at 105 dB SPL. Temporal bones from both groups were harvested, and immunohistochemistry was used to identify neurons with DNA damage. Quantitative morphometric analyses was then employed to determine the level of DNA damage. Neural action potentials were recorded to assess the functional impact of noise induced DNA damage. Immunohistochemical reactions revealed that the noise exposure precipitated DNA damage within the nucleus of auditory neurons. Quantitative morphometry confirmed the noise induced increase in DNA damage levels and the precipitation of DNA damage was associated with a significant loss of nerve sensitivity. Therefore, DNA damage is part of the molecular pathology that drives noise induced neurotoxicity. Anat Rec, 300:520-526, 2017. © 2016 Wiley Periodicals, Inc.

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.

The role of sensory modality in prepulse inhibition: An ontogenetic study.

Deficits in prepulse inhibition (PPI), a measure of sensorimotor gating, are observed in neurodevelopmental and neuropsychiatric disorders. Despite the large PPI literature, the majority of studies characteristically employ tests with one interstimulus interval (ISI), of one modality, at one age. In the context of the auditory startle response (ASR), the present study examined (1) the profile for the ontogeny of PPI through adulthood in Long-Evans hooded rats with a reasonably comprehensive ISI function, (2) whether the ontogenetic profile for PPI is sensitive to modality of the prepulse stimulus, as a within-session variable, and (3) whether the maturation of PPI differs for males and females. Despite the basic effect of more pronounced PPI in adult relative to preweanling animals, each sensory modality displayed a unique ontogenetic profile for PPI, without any compelling evidence for major differences between males and females, in accordance with the known temporal course of peripheral and central maturational profiles of sensory systems in the rat. The context for assessing auditory PPI (auditory and tactile vs. auditory and visual prepulses) influenced the overall startle response, i.e., a shift in the height of the entire profile, but did not significantly impact the auditory PPI profile per se. The translational relevance of preclinical sensorimotor assessments to patients with neurodevelopmental and/or neuropsychiatric disorders depends partly on an understanding of the ontogeny of sensorimotor gating in different sensory systems, and can be strengthened with the use of a reasonably comprehensive number of ISIs to provide relatively precise and defined response functions.

Glial cell modulators attenuate methamphetamine self-administration in therat

Neuroinflammation induced by activated microglia and astrocytes can be elicited by drugs of abuse. Methamphetamine administration activates glial cells and increases proinflammatory cytokine production, and there is recent evidence of a linkage between glial cell activation and drug abuse-related behavior. We have previously reported that ibudilast (AV411; 3-isobutyryl-2-isopropylpyrazolo-[1,5-a]pyridine), which inhibits phosphodiesterase (PDE) and pro-inflammatory activity, blocks reinstatement of methamphetamine-maintained responding in rats, and that ibudilast and AV1013, an amino analog of ibudilast, which has similar glial-attenuating properties but limited PDE activity, attenuate methamphetamine-induced locomotor activity and sensitization in mice. The present study's objective was to determine whether co-administered ibudilast, AV1013, or minocycline, which is a tetracycline derivative that also suppresses methamphetamine-induced glial activation, would attenuate active methamphetamine i.v. self-administration in Long-Evans hooded rats. Rats were initially trained to press a lever for 0.1mg/kg/inf methamphetamine according to a FR1 schedule during 2-h daily sessions. Once stable responding was obtained, twice daily ibudilast (1, 7.5, 10mg/kg), AV1013 (1, 10, 30mg/kg), or once daily minocycline (10, 30, 60mg/kg), or their corresponding vehicles, were given i.p. for three consecutive days during methamphetamine (0.001, 0.03, 0.1mg/kg/inf) self-administration. Ibudilast, AV1013, and minocycline all significantly (p<0.05) reduced responding maintained by 0.03mg/kg/inf methamphetamine that had maintained the highest level of infusions under vehicle conditions. These results suggest that targeting glial cells may provide a novel approach to pharmacotherapy for treating methamphetamineabuse.

Effects of Repeated 3,4-Methylenedioxymethamphetamine Administration on Neurotransmitter Efflux and Sensory-Evoked Discharge in the Ventral Posterior Medial Thalamus

3,4-Methylenedioxymethamphetamine (MDMA) is known to enhance tactile sensory perception, an effect that contributes to its popularity as a recreational drug. The neurophysiological basis for the effects of MDMA on somatosensation are unknown. However, MDMA interactions with the serotonin transporter (SERT) and subsequent enhancement of serotonin neurotransmission are well known. The rat trigeminal somatosensory system receives serotonergic afferents from the dorsal raphe nucleus. Because these fibers express SERT, they should be vulnerable to MDMA-induced effects. We found that administration of a challenge injection of MDMA (3 mg/kg i.p.) after repeated MDMA treatment (3 mg/kg per day for 4 days) elicits both serotonin and norepinephrine efflux in the ventral posterior medial (VPM) thalamus of Long-Evans hooded rats, the main relay along the lemniscal portion of the rodent trigeminal somatosensory pathway. We evaluated the potential for repeated MDMA administration to modulate whisker-evoked discharge of individual neurons in this region. After surgically implanting stainless steel eight-wire multichannel electrode bundles, we recorded spike train activity of single cells while activating the whisker pathway using a piezoelectric mechanical stimulator. We found that repeated MDMA administration increased the spontaneous firing rate but reduced both the magnitude and duration of whisker-evoked discharge in individual VPM thalamic neurons. The time course of drug action on neuronal firing patterns was generally consistent with fluctuations in neurotransmitter efflux as shown from our microdialysis studies. On the basis of these results, we propose that single use and repeated administration of MDMA may "distort," rather than enhance, tactile experiences in humans, in part, by disrupting normal spike firing patterns through somatosensory thalamic relay circuits.

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.

GABA receptor proteins within lipid rafts in the AY‐9944 model of atypical absence seizures

The inhibition of cholesterol synthesis with AY-9944 (AY) results in chronic recurrent atypical absence seizures in rodents. We hypothesized that cholesterol inhibition during the course of creating the AY model of atypical absence seizures results in an alteration of the entry of gamma-aminobutyric acid (GABA)(A) and GABA(B) receptors into lipid rafts that contributes to epileptogenesis in this model. The cholesterol synthesis inhibitor AY (7.5 mg/kg) was administered on postnatal day (P) 2, P8, P14, and P20 in Long-Evans hooded rats. The incorporation of GABA(A) and GABA(B) receptor proteins into lipid rafts of the brain was then determined. AY produced a shift of both GABA(A) and GABA(B) receptors in the examined detergent-resistant membranes (DRMs) and the soluble fractions. The percentage of the GABA(A) and GABA(B) receptors that shifted out of the DRMs varied between 17% and 50%, but the proportion of receptors in DRMs were decreased to levels around that of P5 animals or even lower. The shift observed in the AY-treated versus control animals was statistically significant (p < 0.01) for both GABA(A) and GABA(B) receptors. Cholesterol synthesis inhibition during rat brain development that is induced by AY leads to chronic atypical absence seizures and is associated with an alteration of GABA(A) and GABA(B) receptor proteins within lipid rafts. These data suggest a novel avenue of investigation into the epileptogenesis of experimental chronic atypical absence seizures.

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.

One hertz stimulation to the corpus callosum quenches seizure development and attenuates motor map expansion

Low-frequency stimulation applied through indwelling electrodes has been used to depress or depotentiate synaptic efficacy. Moreover it has been reported to inhibit seizure expression and progression when started either during or after seizures. We have recently shown that low-frequency stimulation can also reduce the size of seizure-enlarged movement representations (motor maps) when delivered after 30 afterdischarges that had propagated from the hippocampus to the neocortex. This study was designed to examine the effects of low-frequency stimulation delivered to the corpus callosum on motor map topography when applied during or after each elicited seizure. Specifically, 15 min of 1 Hz stimulation was applied to the corpus callosum either concurrent with or immediately following a neocortical afterdischarge that had propagated from the hippocampus. Long-Evans hooded rats were electrically stimulated twice daily in the right ventral hippocampus until the first neocortical afterdischarge was elicited. Rats then received low-frequency stimulation which began either with the afterdischarge or following each afterdischarge for 20 additional kindling sessions; a sham low-frequency stimulation group was also included. Afterdischarges were recorded from both hippocampal and neocortical sites, and seizure expression was documented. One to six days following the last stimulation session, forelimb movement representations were derived using high-resolution intracortical microstimulation in the left sensorimotor neocortex. Low-frequency stimulation following each kindled seizure, suppressed behavioral seizure severity and hippocampal afterdischarge duration, as well as attenuated kindling-induced motor map expansion.

Dose‐dependent anticonvulsant effects of linoleic and α‐linolenic polyunsaturated fatty acids on pentylenetetrazol induced seizures in rats

Linoleic and alpha-linolenic polyunsaturated fatty acids, derived from plant oils, have been reported to reduce neuronal excitability ex vivo and in cell culture. The evidence derived from animal seizure models, however, has been contradictory. The goal of the present study was to assess the dose-dependent anticonvulsant effects of a fatty acid mixture containing linoleic and alpha-linolenic acids in a 4 to 1 ratio (the "SR-3" compound). The maximal pentylenetetrazol seizure model and Long-Evans hooded rats were used. Daily intraperitoneal injection of SR-3 for 21 consecutive days raised omega-3 polyunsaturated fatty acid (n-3 PUFA) composition in the unesterified fatty acid fraction of brain lipids (p < 0.05), and increased latency to seizure onset when administered at 200 mg/kg (p < 0.05), but not at 40 mg/kg (p > 0.05). There were no significant effects of SR-3 on seizure occurrence or on seizure severity (p > 0.05). A toxic effect of the SR-3 compound on peristalsis was observed at a dose of 400 mg/kg and above. Linoleic and alpha-linolenic polyunsaturated fatty acids in a 4 to 1 ratio raises n-3 PUFA composition of unesterified fatty acids in the brain and increases resistance to pentylenetetrazol-induced seizures.

Perinatal exposure of female rats to 2,3,7,8-tetrachlorodibenzo-p-dioxin induces central precocious puberty in the offspring

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during the fetal and neonatal periods has been indicated to alter the development of the offspring later in life. In this study, we determined whether perinatal exposure to a low dose of TCDD affects the onset of puberty in the female offspring of Long-Evans hooded rats. On day 15 of gestation, pregnant female rats were administered TCDD by gavage at a single dose of 0 (vehicle), 200, or 800 ng/kg b.w. In the female offspring born to dams administered with TCDD at either 200 or 800 ng/kg b.w., the vaginal opening and first estrus occurred approximately 4-7 days earlier than in the offspring born to vehicle-treated animals. The ovarian weight gain was also accelerated following exposure to TCDD in a dose-dependent manner. We next examined the ovarian compensatory hypertrophy (OCH) as an indicator of the maturation of the LH/GnRH-generating system in the pituitary and the hypothalamus. Exposure to TCDD accelerated the onset of OCH in the female offspring in a dose-dependent manner. In particular, in the offspring born to the dams exposed to TCDD at 800 ng/kg b.w., hypertrophy, which is characterized by hyperovulation and a marked increase in the weight of the remaining ovary after hemi-ovariectomy, was observed on postnatal days 27-30, which was 10 days earlier than in the offspring born to the vehicle-treated dams. These results indicate that perinatal exposure to a low dose of TCDD induces precocious puberty, including early maturation of the hypothalamic-pituitary axis, the gonads and genitals, in female Long-Evans hooded rats.

Learning behavior in rat offspring after in utero and lactational exposure to either TCDD or PCB126

We studied and compared the possible effects of in utero and lactational exposure to 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) or 3, 3', 4, 4', 5-pentachlorobiphenyl (PCB126) on learning behavior in offspring. Pregnant Long-Evans Hooded rats were administered either TCDD (50, 200, or 800 ng/kg) or PCB126 (500, 2,000 or 8,000 ng/kg) on gestational day 15. A procedure of schedule-controlled operant behavior was applied to examine learning behavior in the male and female offspring at 11 weeks of age for 30 days. Three indices, namely, response rates in a fixed ratio (FR) and in a differential reinforcement of low rates (DRL), and reward rate in the DRL component in multiple FR 20 DRL 20 s (mult-FR 20 DRL 20-s) test sessions, were used for the evaluation of learning behavior. Toxic effects on learning behavior in male and female pups following in utero and lactational exposure to TCDD or PCB126 were observed mainly in the FR learning component. However, no linear dose-dependent effects of either of the two compounds were observed for the above three indices. The response rates of animals in the low-dose TCDD and PCB126 groups decreased and those in medium-dose TCDD and PCB126 groups appeared to induce hyperactive behavior. The high dose of PCB126 appeared to have a distinct toxicity from that of TCDD in terms of the acquisition of learning behavior. Toxicities of PCB126 and TCDD in learning behavior might be similar to each other and the current toxic equivalency factor (TEF) of 0.1 for PCB126 can be considered to be appropriate for this endpoint.

Lack of benefit of linoleic and α-linolenic polyunsaturated fatty acids on seizure latency, duration, severity or incidence in rats

Background Polyunsaturated fatty acids have been reported to increase seizure threshold and to reduce seizure duration and severity in rats. Objective The purpose of the present study was to test the anticonvulsant effects of an essential fatty acid mixture containing linoleic and α-linolenic acids at a 4:1 ratio (SR-3 compound), using the pentylenetetrazol seizure model in Long-Evans hooded rats. Results There were no significant effects of SR-3 on seizure latency, duration or severity ( P > 0.05). There were also no significant differences in the incidence of myoclonic jerks, forelimb and hindlimb clonus, forelimb and hindlimb tonus or running fits in rats that received SR-3, as compared to control rats ( P > 0.05). Conclusion Linoleic and α-linolenic polyunsaturated fatty acids have no beneficial effects on seizure latency, duration, average severity or incidence.

Denervation produces different single fiber phenotypes in fast- and slow-twitch hindlimb muscles of the rat

Using a single, mechanically skinned fiber approach, we tested the hypothesis that denervation (0 to 50 days) of skeletal muscles that do not overlap in fiber type composition [extensor digitorum longus (EDL) and soleus (SOL) muscles of Long-Evans hooded rats] leads to development of different fiber phenotypes. Denervation (50 day) was accompanied by 1) a marked increase in the proportion of hybrid IIB/D fibers (EDL) and I/IIA fibers (SOL) from 30% to >75% in both muscles, and a corresponding decrease in the proportion of pure fibers expressing only one myosin heavy chain (MHC) isoform; 2) complex muscle- and fiber-type specific changes in sarcoplasmic reticulum Ca(2+)-loading level at physiological pCa approximately 7.1, with EDL fibers displaying more consistent changes than SOL fibers; 3) decrease by approximately 50% in specific force of all fiber types; 4) decrease in sensitivity to Ca(2+), particularly for SOL fibers (by approximately 40%); 5) decrease in the maximum steepness of the force-pCa curves, particularly for the hybrid I/IIA SOL fibers (by approximately 35%); and 6) increased occurrence of biphasic behavior with respect to Sr(2+) activation in SOL fibers, indicating the presence of both slow and fast troponin C isoforms. No fiber types common to the two muscles were detected at any time points (day 7, 21, and 50) after denervation. The results provide strong evidence that not only neural factors, but also the intrinsic properties of a muscle fiber, influence the structural and functional properties of a particular muscle cell and explain important functional changes induced by denervation at both whole muscle and single cell levels.