Male Fischer Rats Research Articles

Ex vivo modulation of chemical-induced mutagenesis by subcellular liver fractions of rats treated with rooibos ( Aspalathus linearis) tea, honeybush ( Cyclopia intermedia) tea, as well as green and black ( Camellia sinensis) teas

Male Fischer rats were given unprocessed (not oxidized) and processed (oxidized) rooibos and honeybush teas as well as green and black teas as a sole source of drinking fluid for 10 weeks, and sub cellular liver fractions were prepared. Cytosolic fractions of rats consuming the unprocessed herbal teas, green and black teas significantly ( P<0.05) protected against 2-acetylaminofluorene (2-AAF)-induced mutagenesis in the Salmonella mutagenicity test with strain TA 98, using Aroclor 1254-induced microsomes. A marginal or no protection was obtained with the processed herbal teas. The mutagenic response of aflatoxin B 1 (AFB 1) against Salmonella strain TA 100 was significantly ( P<0.05) inhibited by cytosolic fractions from rats treated with processed and unprocessed herbal teas, while no effect was obtained with the green and black teas. Microsomal fractions prepared from livers of rats treated with both the processed and unprocessed rooibos teas and the unprocessed honeybush tea, significantly ( P<0.05) reduced the activation of AFB 1 while no protection was observed against 2-AAF-induced mutagenesis. In contrast, microsomal fractions from rats treated with the green, black and unprocessed honeybush teas significantly ( P<0.05) enhanced the mutagenic response of 2-AAF. None of the tea treatments significantly affected the concentration of the microsomal liver cytochrome P450.

The effect of age on P-glycoprotein expression and function in the Fischer-344 rat.

We investigated the effect of age on P-glycoprotein (P-gp) expression and function in rat liver, intestine, kidney, and endothelial cells of the blood-brain barrier (BBB) and lymphocytes. Flow cytometric analysis was used to examine P-gp expression in lymphocytes from male Fischer-344 rats from three age groups (young at 3-4 months, intermediate at 13-14 months, and old at 25-26 months). In addition, P-gp function in lymphocytes was assessed by measuring the ability of the P-gp inhibitor verapamil to limit the efflux of the fluorescent P-gp substrate rhodamine 123. P-gp expression was evaluated in the remaining four tissues by Western blot analysis. The effect of age on P-gp expression was tissue-specific. Although lymphocytic and hepatic P-gp expression increased with age, renal P-gp content was lower in the old kidneys. No statistical difference was observed in P-gp expression in intestinal microsomes or in BBB cell lysates among the three age groups. P-gp function was also increased by 6- to 8-fold in lymphocytes from the old rats. When P-gp expression was compared with CYP3A expression in these rats (reported elsewhere in this journal), we found that P-gp expression increased with age, whereas CYP3A expression and activity declined in the old livers. The converse pattern was observed in the kidney. Thus, age-related changes in P-gp expression and function are likely to be tissue-specific, and these changes may be inversely related to differences in CYP3A expression.

Species difference in the disposition of acrylonitrile: quantitative whole-body autoradiographic study in rats and mice

Previous studies from this and other laboratories have indicated the role of species difference in acrylonitrile (VCN) toxicity and its metabolism to cyanide. Our recent studies also indicated a more pronounced elimination of VCN following oral as compared to i.v. administration. To further characterize the mechanism of these differences on the distribution of VCN, quantitative whole-body autoradiographic distribution and elimination studies were conducted at various time points (0.08, 8, 24, 48 h) following the administration of an equivalent i.v. dose of 2-[14C]-VCN to male Fischer rats and male CD-1 mice. Whole-body autoradiographs obtained from freeze-dried and acid-extracted sections of rats and mice demonstrated a rapid uptake of 14C in liver, lungs, spleen and bone marrow at early time intervals. Quantitatively, the uptake, retention and covalent interaction of 14C were higher in organs of rats as compared to mice, over 48 h. Mice eliminated 74% of the total administered dose of 2-[14C]-VCN (expired air 4%, urine 16% and feces 54%), while rats eliminated only 26% of the dose (expired air 2%, urine 4% and feces 20%). Species differences in VCN toxicity seem to be correlated with its rate of elimination. The distribution and elimination data demonstrated that mice divest VCN more rapidly than rats. The study also demonstrated that administration of VCN in rats resulted in covalent interactions and retention of 2-[14C]-VCN/metabolites in the tissues thus exerting more chronic toxicity to rats than to mice.

Age-related differences in CYP3A expression and activity in the rat liver, intestine, and kidney.

We evaluated the effect of age on CYP3A expression and function in the liver, intestine, and kidney from young (3-4 months), intermediate (13-14 months), and old (25-26 months) male Fischer-344 rats. The biotransformation of triazolam to its primary hydroxylated products, 4-OH-TRZ (triazolam) and alpha-OH-TRZ, was used as a marker of CYP3A activity in rat liver and intestine. Immunoactive CYP3A expression was evaluated by Western blot analysis in the rat intestine, liver, and kidney. Since testosterone and NADPH reductase levels may modulate CYP3A activity, we also examined free plasma testosterone concentrations and NADPH reductase expression in these rats. The effect of age on CYP3A expression was tissue-specific. Although both CYP3A activity and expression were reduced by approximately 50 to 70% in the old livers compared with the young animals, intestinal CYP3A activity and expression did not change significantly with age. The expression of one CYP3A isoform was increased by 1.5-fold in the old kidneys. NADPH reductase expression was reduced by 23 to 36% with age in all tissues; this reached statistical significance only in the liver. Plasma testosterone levels declined by 74% in the old animals. This study suggests that the effect of age on CYP3A expression and function is tissue-specific. In addition, changes in testosterone levels and NADPH reductase expression may contribute to age-related differences in hepatic CYP3A activity.

Behavioral and antioxidant activity of a tosylbenz[g]indolamine derivative. A proposed better profile for a potential antipsychotic agent

BackgroundTardive dyskinesia (TD) is a major limitation of older antipsychotics. Newer antipsychotics have various other side effects such as weight gain, hyperglycemia, etc. In a previous study we have shown that an indolamine molecule expresses a moderate binding affinity at the dopamine D2 and serotonin 5-HT1A receptors in in vitro competition binding assays. In the present work, we tested its p-toluenesulfonyl derivative (TPBIA) for behavioral effects in rats, related to interactions with central dopamine receptors and its antioxidant activity.MethodsAdult male Fischer-344 rats grouped as: i) Untreated rats: TPBIA was administered i.p. in various doses ii) Apomorphine-treated rats: were treated with apomorphine (1 mg kg-1, i.p.) 10 min after the administration of TPBIA. Afterwards the rats were placed individually in the activity cage and their motor behaviour was recorded for the next 30 min The antioxidant potential of TPBIA was investigated in the model of in vitro non enzymatic lipid peroxidation.Resultsi) In non-pretreated rats, TPBIA reduces the activity by 39 and 82% respectively, ii) In apomorphine pretreated rats, TPBIA reverses the hyperactivity and stereotype behaviour induced by apomorphine. Also TPBIA completely inhibits the peroxidation of rat liver microsome preparations at concentrations of 0.5, 0.25 and 0.1 mM.ConclusionTPBIA exerts dopamine antagonistic activity in the central nervous system. In addition, its antioxidant effect is a desirable property, since TD has been partially attributed, to oxidative stress. Further research is needed to test whether TPBIA may be used as an antipsychotic agent.

Central AII evokes a normal sodium appetite in the Fischer rat, but its low spontaneous sodium intake may be related to reduced excitation and increased inhibition in septo-preoptic AII neurons

Fischer rats show a low or absent basal salt appetite and a reduced intake of salt solutions in response to peripherally administered angiotensin II (AII) when compared to other strains. We investigated spontaneous sodium intake, and sodium intake after intracerebroventricular (i.c.v.) AII and losartan, and septo-preoptic neuronal responses to AII and losartan, in age-matched male Fischer and Wistar rats. Spontaneous intake of 1.8% NaCl was lower in Fischers, but i.c.v. injection of 10 pmol AII produced similar 2 h intakes in a 2 h test period. Iontophoretic application of AII and losartan onto neurons in the septo-preoptic continuum revealed differences between the two strains of rat. In the Fischer rats only 11% of the spontaneously active neurons were sensitive to locally applied AII compared to approximately 30% in the Wistar. Local application of losartan produced neuronal inhibition in Fischer rats but neuronal excitation in Wistars. The central AII system appears to be regulated differently in these two strains, and may be related to the differences in their spontaneous sodium intake, but not to AII aroused sodium appetite.

Partial cardiopulmonary bypass in rats using a hollow fibre oxygenator

Despite new minimally invasive techniques, cardiopulmonary bypass (CPB) is still necessary for many major operations in the field of cardiac surgery. Unwanted side effects of CPB are well known but poorly understood. We therefore developed a rodent model to study the pathophysiology of these potential complications. Male Fischer rats were anaesthetized, intubated and ventilated. The carotid artery and jugular vein were cannulated. The blood was actively drained from the venous circulation and further transferred by a miniaturized roller pump to a hollow fibre oxygenator and back to the animal via the carotid artery. The roller pump produces a pulsatile blood flow between 5 and 40 ml/min. The surface of the hollow fibre oxygenator is 0.025 m2. The priming volume (Ringer solution) of the whole system is 12 ml. Animals were catheterized and brought in partial bypass for a mean of 50+/-15 min. Normal cardiac function after successful weaning was confirmed by electrocardiography and blood pressure measurements. This technical study demonstrates the feasibility of a small animal model of CPB. The main improvement over existing techniques is the use of a highly effective hollow fibre oxygenator with a minimized priming volume. Therefore, no additional animals are needed as blood donors.

Enhanced potential for oxidative stress in livers of senescent rats by the peroxisome proliferator-activated receptor alpha agonist perfluorooctanoic acid

Aging sensitizes the liver to the hepatocarcinogenic effect of PPARα agonists via unknown mechanisms. This study was designed to investigate age-dependent, hepatic effects of the non-metabolizable PPARα agonist perfluorooctanoic acid (PFOA) on the delicate balance between activities of pathways involved in H 2O 2 production and elimination. Male Fischer-344 rats, ranging in age from juvenile (4 weeks old), post puberty (10 weeks old), mature adulthood (20 weeks old), middle age (50 weeks old), to senescence (100 weeks old), were treated intragastrically with either 150 mg PFOA/kg in 0.5 ml corn oil, or with corn oil alone. Animals were sacrificed at predetermined time-points ranging from 0–28 days post PFOA or oil administration. Hepatic peroxisomal β-oxidizing activities were significantly elevated (four- to six-fold) in all age groups by PFOA. While levels declined to near basal values within 3–7 days in 4 and 10, they remained elevated for an additional week in 20-, 50- and 100-week-old rats. However, catalase activity was significantly lower in senescent livers compared with all other groups. In conclusion, aging does not appear to hinder the capacity of the liver to produce excess H 2O 2 through peroxisomal β-oxidation upon exposure to PPAR agonists. However, the reduced ability of the senescent liver to recover from PFOA-induced potential increase in H 2O 2 production, coupled with the apparent diminished capacity of this liver to decompose H 2O 2, enhances the potential for hepatic oxidative damage in aged animals. This may explain the enhanced susceptibility of the senescent liver to the hepatocarcinogenic effect of PPAR agonists.

Aging and lifelong calorie restriction result in adaptations of skeletal muscle apoptosis repressor, apoptosis-inducing factor, X-linked inhibitor of apoptosis, caspase-3, and caspase-12

The mechanisms of apoptosis in the loss of myocytes in skeletal muscle with age and the role of mitochondrial and sarcoplasmic reticulum-mediated pathways of apoptosis are unknown. Moreover, it is unknown whether lifelong calorie restriction prevents apoptosis in skeletal muscle and reverses age-related alterations in apoptosis signaling. We investigated key apoptotic regulatory proteins in the gastrocnemius muscle of 12 and 26 month old ad libitum fed and 26 month old calorie-restricted male Fischer-344 rats. We found that apoptosis increased with age and that calorie-restricted rats showed less apoptosis compared with their age-matched cohorts. Moreover, pro- and cleaved caspase-3 levels increased significantly with age and calorie-restricted rats had significantly lower levels than the aged ad libitum group. Neither age nor calorie restriction had any effect on muscle caspase-3 enzyme activity, but the levels of X-linked inhibitor of apoptosis, particularly an inhibitor of caspase-3, increased with age and were reduced significantly in the 26 month old calorie-restricted cohort. The apoptotic inhibitor apoptosis repressor with a caspase recruitment domain (ARC), which inhibits cytochrome c release, underwent an age-associated decline in the cytosol but increased with calorie restriction. In contrast, mitochondrial ARC levels increased with age and were lower in calorie-restricted rats than in age-matched controls, suggesting a translocation of this protein to attenuate oxidative stress. The translocation of ARC may explain the reduction in cytosolic cytochrome c levels observed with age and calorie restriction. Moreover, we found a striking ∼350% increase in the expression of procaspase-12 (caspase located at the sarcoplasmic reticulum) with age which was significantly lower in the 26 month old calorie-restricted group. The total protein level of apoptosis-inducing factor in the plantaris muscle increased with age and was reduced calorie-restricted rats compared with age-matched controls, but there were no significant changes in this pro-apoptotic protein in the isolated nuclei. Calorie restriction is able to lower the apoptotic potential in aged skeletal muscle by altering several key apoptotic proteins toward cellular survival, thereby reducing the potential for sarcopenia.

Fumonisin contamination of a corn sample associated with the induction of hepatocarcinogenesis in rats—role of dietary deficiencies

A corn sample associated with a field outbreak of equine leukoencephalomalacia in Pennsylvania, USA, during 1983/1984 and induced hepatotoxic and hepatocarcinogenic effects when fed to male Fischer rats was analyzed mycologically and chemically for the presence of fumonisins (FB), hydrolysed FB derivatives and aflatoxins (AFB). Fusarium verticillioides was found to be the predominant fungal contaminant in the corn sample but Aspergillus flavus was also present. Trace amounts (0.1 μg/kg) of AFB1 and AFB2 and a total FB level of 33.5 mg/kg (FB1:FB2:FB3 ratio of 9:2.3:1) were found. No hydrolysed FB derivatives or AFG1 and AFG2 were detected. Based on the chemical stability of the fumonisins in different corn cultures of F. verticillioides kept at 4 °C over a period of 13–20 years, a level of approximately 55 mg/kg of total FB is estimated in the original corn sample. A possible role of certain dietary constituents such as the high protein content and deficiencies in certain micronutrients is evaluated to address differences in the organ-specific toxicity of FB1 in rats using commercial, semi-purified, purified and corn-only diets.

Brain stem opioidergic and GABAergic neurons mediate the antinociceptive effect of nitrous oxide in Fischer rats.

Recent studies have revealed that N2O exerts its antinociceptive effect by inducing opioid peptide release in the brain stem, thereby activating the descending noradrenergic inhibitory neurons, which modulate pain processing in the spinal cord. However, the precise neuronal pathways that mediate these events remain to be determined. Using immunohistochemical and behavioral techniques in adult male Fischer rats, the authors studied the involvement of brain stem opioidergic and gamma-aminobutyric acid-mediated (GABAergic) neurons in the N2O-induced antinociceptive effect using discrete microinjections of an opioid receptor antagonist or GABAergic activator into the periaqueductal gray area and pontine noradrenergic nuclei. They used c-Fos expression as an immunohistochemical mark of neuronal activation induced by N2O and the plantar test as the behavioral paradigm for nociception. Microinjection of either naloxone (an opioid receptor antagonist) or muscimol (a gamma-aminobutyric acid receptor type A agonist) into the ventrolateral periaqueductal gray area inhibited N2O-induced c-Fos expression in the spinal cord and pontine noradrenergic nuclei, particularly in the A7. Microinjection of either naloxone or muscimol into the A7 nuclei also inhibited N2O-induced c-Fos expression in the spinal cord and the N2O-induced antinociceptive effect by the plantar test. These results support the hypothesis that both opioidergic and GABAergic neurons mediate the antinociceptive effect of N2O at the periaqueductal gray area and A7 in the brain stem. The authors postulate that N2O-induced opioid peptide release leads to inhibition of GABAergic neurons via opioid receptors. The descending noradrenergic inhibitory pathways, which are tonically inhibited by these gamma-aminobutyric acid neurons, are thereby activated (disinhibited) and modulate pain processing in the spinal cord.

Increased formic acid excretion and the development of kidney toxicity in rats following chronic dosing with trichloroethanol, a major metabolite of trichloroethylene.

The chronic toxicity of trichloroethanol, a major metabolite of trichloroethylene, has been assessed in male Fischer rats (60 per group) given trichloroethanol in drinking water at concentrations of 0, 0.5 and 1.0 g/l for 52 weeks. The rats excreted large amounts of formic acid in urine reaching a maximum after 12 weeks ( approximately 65 mg/24 h at 1 g/l) and thereafter declining to reach an apparent steady state at 40 weeks (15-20 mg/24 h). Urine from treated rats was more acidic throughout the study and urinary methylmalonic acid and plasma N-methyltetrahydrofolate concentrations were increased, indicating an acidosis, vitamin B12 deficiency and impaired folate metabolism, respectively. The rats treated with trichloroethanol developed kidney damage over the duration of the study which was characterised by increased urinary NAG activity, protein excretion (from 4 weeks), increased basophilia, protein accumulation and tubular damage (from 12 to 40 weeks), increased cell replication (at week 28) and evidence in some rats of focal proliferation of abnormal tubules at 52 weeks. It was concluded that trichloroethanol, the major metabolite of trichloroethylene, induced nephrotoxicity in rats as a result of formic acid excretion and acidosis.

Evaluation of a short duration behaviour-based post-operative pain scoring system in rats

We have recently demonstrated dose-related analgesic-induced reductions in the occurrence of 7 behavioural activities following midline laparotomy in rats. For these behaviours to be useful in evaluating pain in laboratory rats they must be shown to occur after different types of surgery, and frequently enough to allow rapid scoring of animals. Here, the relevant behaviours were used to test the analgesic efficacy of meloxicam with a variation of our previous laparotomy model. As part of an unrelated project, 57 male Fischer rats were divided into groups to receive either saline (0.2 ml/100 g s/c), meloxicam (0.5, 1 or 2 mg/kg s/c) or carprofen (2.5, 5, or 10 mg/kg s/c) 1 h before surgery. Behaviour data were collected for 10 min following 25 min of recovery from isoflurane anaesthesia. The cumulative frequencies of back arching, fall/stagger, writhe and poor gait were used to compute a composite behaviour score. Irrespective of whether analyses included only 5 or all 10 min of the observation period, the relevant behaviours occurred significantly more often in rats given saline or low dose meloxicam than in those given 1 or 2 mg/kg of meloxicam, or any dose of carprofen. We conclude that this technique of quantifying post-surgery behaviour is an effective pain scoring method following abdominal surgery in rats, and that 1 mg/kg meloxicam significantly attenuates laparotomy induced pain. Since only a short observation period is required, this approach represents an important practical advance in assessing abdominal pain severity and clinical drug potency.

L-arginine levels in blood as a marker of nitric oxide-mediated brain damage in acute stroke: a clinical and experimental study.

There are no useful markers in blood of nitric oxide (NO)-mediated brain damage. Because l-arginine (l-arg) is the only known substrate for NO generation, the authors investigated the plasma profile of l-arg after cerebral ischemia, and the relationship of L-arg concentrations in blood with stroke outcome and infarct volume in a clinical and experimental study. l-Arg levels were determined with high-performance liquid chromatography in blood and CSF samples obtained on admission, and in blood 48 hours after inclusion, in 268 patients admitted with a hemispheric ischemic stroke lasting 8.2 +/- 5.9 hours. Infarct volume was measured by days 4 to 7 using computed tomography. Plasma l-arg profiles were analyzed in a separate group of 29 patients seen within 8 hours of onset (median, 4.5 hours) and in 24 male Fischer rats treated with subcutaneous vehicle or 20-mg/kg 1400W (a specific inducible NO synthase inhibitor) every 8 hours for 3 days after performing sham or permanent middle cerebral artery occlusion. Plasma l-arg concentrations decreased after the ischemic event, both in patients and rats, and peaked between 6 and 24 hours. In patients, there was a highly correlation between l-arg levels in CSF and plasma at 48 hours (r = 0.85, P<0.001). CSF and plasma l-arg concentrations negatively correlated with infarct volume (r = -0.40 and r = -0.35, respectively, P<0.001), and were significantly lower in patients with early neurologic deterioration and in those with poor outcome (Barthel index <85) at 90 days (P<0.001). In rats, the administration of 1400W resulted in a 55% significant reduction of infarct volume measured 72 hours after permanent middle cerebral artery occlusion, an effect that correlated with the inhibition caused by 1400W on the ischemia-induced decrease of plasma l-arg concentrations at 6 to 24 hours after the onset of the ischemia. Taken together, these data indicate that determination of l-arg levels in blood might be useful to evaluate the neurotoxic effects of NO generation. These findings might be helpful to guide future neuroprotective strategies in patients with ischemic stroke.

Effect of route of administration on the disposition of acrylonitrile: quantitative whole-body autoradiographic study in rats

Previous studies on the effect of route of administration on acrylonitrile (VCN) toxicity in animal models indicated high rates of metabolism in rats that received an oral dose than those received an i.p. VCN dose. To evaluate the role of route of administration on the distribution of VCN, a quantitative whole-body autoradiography (QWBA) and elimination studies were conducted. Equimolar doses of 2-[ 14 C ]-VCN were administered i.v. or p.o. to male Fischer (F-344) rats. Time course of QWBA indicated a higher retention and covalent interaction of radioactivity in the liver, spleen and bone marrow of rats received an i.v. dose of 2- 14 C -VCN than those received a p.o. dose. Unlike rats that received an i.v. dose of VCN, the animals received an oral dose showed a high retention of 14 C in blood, stomach and gastric mucosa. Differences were also reflected in 14 C elimination in urine, feces and expired air. Animals treated orally with 2-[ 14 C ]-VCN excreted 61% of the administered radioactive dose (4% in expired air, 4% in urine and 53% in feces). Rats that received an i.v. dose of 2-[ 14 C ]-VCN, however, eliminated only 30% of the total radioactive dose (expired air 2%, urine 8% and feces 21%). The results indicate that metabolism, detoxication and elimination of VCN are more pronounced following oral administration as compared to i.v. route of administration. The study also demonstrates that the systemic administration of VCN enhances its covalent interaction and retention in the tissues thus cause more toxicity in these organs.

Effects of pico-tesla electromagnetic field treatment on wound healing in rats.

To evaluate the effects of a pico-tesla electromagnetic field (PTEF) on healing of sutured and open skin wounds and clinicopathologic variables in rats. 64 male Fischer-344 rats. An incision made in the dorsal aspect of the neck was sutured (n = 32) or left open to heal (32). In each group, 16 rats were not PTEF-treated (controls). Wound treatment consisted of exposure to a PTEF once daily. Rats in each group were euthanatized at days 2, 4, 7, and 14. Wounds were evaluated via tensiometry (sutured wounds), digital planimetry (open wounds), laser Doppler perfusion imaging, bacteriologic culture, and histologic examination. Blood samples were collected from all rats for analysis. At day 14, sutured wounds in PTEF-treated rats were stronger (ultimate stress) and tougher (strain energy) than were sutured wounds in control rats. Open wounds in PTEF-treated rats contracted more quickly at days 2 and 4 than did those in control rats. Compared with control wounds, histologic changes (indicative of improved healing) in sutured and open wounds in PTEF-treated rats were detected as early as day 4. Laser Doppler perfusion measurements, results of CBCs, serum biochemical analyses, and bacteriologic cultures were not different between groups. Exposure to the PTEF caused no adverse effects on clinicopathologic, histologic, or bacteriologic variables tested in this study. It appears that PTEF is a safe form of adjuvant treatment for wounds and improves strength of sutured wounds and speeds contraction of open wounds.

Age and attenuation of exercise-induced myocardial HSP72 accumulation.

Overexpression of heat shock protein (HSP)72 is associated with cardioprotection. Hyperthermia-induced HSP72 overexpression is attenuated with senescence. While exercise also increases myocardial HSP72 in young animals, it is unknown whether this effect is attenuated with aging. Therefore, we investigated the effect of aging on exercise-induced myocardial heat shock factor (HSF)-1 activation and HSP72 expression. Male Fischer-344 rats (6 or 24 mo) were randomized to control, exercise, and hyperthermic groups. Exercise consisted of 2 days of treadmill running (60 min/day, approximately 75% maximal oxygen consumption). Hyperthermia, 15 min at approximately 41 degrees C (colonic temperature), was achieved using a temperature-controlled heating blanket. Analyses included Western blotting for myocardial HSP72 and HSF-1, electromobility shift assays for HSF-1 activation, and Northern blotting for HSP72 mRNA. Exercise and hyperthermia increased (P < 0.05) myocardial HSP72 in both young (>3.5- and 2.5-fold, respectively) and aged (>3- and 1.5-fold, respectively) animals. Both exercise and hyperthermic induction of HSP72 was attenuated with age. Myocardial HSF-1 protein, HSF-1 activation, and HSP72 mRNA did not differ with age. These data demonstrate that aging is associated with diminished exercise-induced myocardial HSP72 expression. Mechanisms other than HSF-1 activation and transcription of HSP72 mRNA are responsible for this age-related impairment.

Effect of subacute and chronic immobilisation stress on the outcome of permanent focal cerebral ischaemia in rats

The aim of this study was to determine the effect of mood disorders, including psychological distress and depression, on stroke outcome. Male Fischer rats were exposed to immobilisation stress, an animal paradigm of psychological stress, major depression and post-traumatic stress disorder. Either a subacute (1 h for 7 days) or a chronic (6 h for 21 days) exposure to stress was applied 24 h before permanent middle cerebral artery occlusion (MCAO). Stroke outcome was assessed by measurement of infarct size and behavioural characterisation. Serum glutamate and brain ATP levels as well as brain glutamate transporter function and expression were studied in the search for the molecular mechanisms involved. Subacute stress exposure increased infarct size and decreased behavioural scores after stroke. On the contrary, chronic stress exposure decreased infarct size. Peak serum glutamate levels correlated with infarct size after MCAO. Expression of glutamate transporters was decreased by subacute stress, whereas the expression of EAAT1, a glial glutamate carrier, was increased after the chronic stress protocol. Our results indicate that distinct patterns of stress determine different stroke outcomes, and that expressional changes of brain glutamate transporters, able to affect glutamate release after stroke, are involved.

Reduced cortical noradrenergic neurotransmission is associated with increased neophobia and impaired spatial memory in aged rats

In the present study, young (5-month-old (mo)) and aged (24 mo) adult male Fischer-344 (F344) rats were assigned to experimental groups based upon their performance of a reference memory task in the Morris water maze and reactivity to a novel palatable taste in a gustatory neophobia task. Levels of norepinephrine (NE) and its metabolite 3-methoxy-4-hydroxy-phenylglycol (MHPG) were assayed via high performance liquid chromatography (HPLC) in brain regions associated with the locus coeruleus (LC)–hippocampus–cortex system and A1/A2-hypothalamic system. Binding of ligands specific for alpha-1, alpha-2, beta-1, and beta-2 receptors was assessed in hippocampus and cortex with receptor autoradiography. Impaired acquisition and retention of the water maze task and gustatory neophobia in aged rats was primarily associated with decreased NE activity in cingulate cortex (CC) as indicated by a significant reduction in the MHPG/NE ratio coupled with increased NE content. No significant changes in adrenergic receptor binding were detected in any region sampled. The results suggest that an aging-related reduction in cortical NE neurotransmission is associated with the expression of increased neophobia and deficits in spatial learning and memory performance occurring with advanced age in rats.

Synaptic plasticity preserved with arachidonic acid diet in aged rats

We examined whether synaptic plasticity was preserved in aged rats administered an arachidonic acid (AA) containing diet. Young male Fischer-344 rats (2 mo of age), and two groups of aged rats of the same strain (2 y of age) who consumed either a control diet or an AA ethyl ester-containing diet for at least 3 mo were used. In the Morris water maze task, aged rats on the AA diet had tendency to show better performance than aged rats on the control diet. Long-term potentiation induced by tetanic stimulation was recorded from a 300 μm thick hippocampal slice with a 36 multi-electrode-array positioned at the dendrites of CA1 pyramidal neurons. The degree of potentiation after 1 h in aged rats on the AA diet was comparable as that of young controls. Phospholipid analysis revealed that AA and docosahexaenoic acid were the major fatty acids in the hippocampus in aged rats. There was a correlation between the behavioral measure and the changes in excitatory postsynaptic potential slope and between the physiologic measure and the total amount of AA in hippocampus.