Pretreatment Of Adult Rats Research Articles

Pre-treatment of adult rats with high doses of erythropoietin induces caspase-9 but prevents light-induced retinal injury

Erythropoietin (Epo) had been shown to have a neuroprotective effect independent from its erythropoietic properties. In this study, we tested whether Epo could protect the retina from damage induced by a long period of moderate light insult and how it protected. First, rats were injected intraperitoneally (i.p.) by human recombinant Epo at 5000 or 30,000 U/kg to assess Epo concentration in plasma and retina. Second, rats were untreated or injected i.p. with Epo at 30,000 U/kg, 1 or 4 h before being placed in constant light (24 h; 2200 lux). Electroretinograms (ERG) were recorded before treatment, 1 day and 15 days (D15) after light exposure. After the last ERG, eyes were taken for histology. In parallel, we tested Epo protection against oxidative stressors on isolated retinas and its effect on caspase-9 activity. Epo injected at 30,000 U/kg body weight, 4 h before exposure to the damaging light, protected retinal function and structure against light damage and induced an increase in caspase-9 activity and expression. Epo had no direct or indirect protective effect against free radicals-induced death on isolated retinas. Epo protected the retina from a long period of moderate light exposure through a mechanism independent from a free radical scavenging property or an antioxidant facilitating activity. The activation of caspase-9, 4 h after Epo injection, corresponding to the start of light exposure, suggests that caspase-9 plays a role in neuroprotection.

Habituation enhances auditory perceptual capacity in adult rats

We have already demonstrated that pretreatment of adult rats with a 48-h-long “repetitive non-reinforced sound exposure (SE)” improves performance in two-sound discriminative operant conditioning (sound exposure-modulated discrimination [SED]). This three-part study addressed the neural basis of SED by parametrically analyzing SED: effects of the SE using various sound signals were compared during the performance of a sound-discrimination task. Experiment 1 provided evidence that SED was due to the improvement of auditory perceptual capacity rather than due to a change in motivation or attention or interference with association process. Results of Experiment 2 made it likely that SED took place mainly in higher cortical auditory fields, which potentially integrate acoustic information beyond the cochleotopy. Results of Experiment 3 favored the idea that SED was based on a stimulus-specific decrease rather than a stimulus-specific increase in the responsivity of the auditory system. Collectively, it is suggested that auditory habituation plays an important role in SED, i.e., a certain form of auditory perceptual learning.

Mediation by bradykinin of rat paw oedema induced by collagenase from Clostridium histolyticum.

1. Collagenases are thought to play a major role in the pathology of gas gangrene caused by Clostridium histolyticum, because they can destroy the connective tissue barriers. We investigated possible mediators involved in the oedema formation and plasma protein extravasation which follow the injection of a collagenase (EC 3.4.24.3) from Clostridium histolyticum into one hind paw of anaesthetized rats. 2. The magnitude of the oedema following a subplantar injection was dependent on the dose of collagenase (30, 100 and 300 micrograms) injected. It reached its maximum within 30 min and remained unchanged for at least 5 h. Plasma protein extravasation into the paw was most pronounced within 20 min of the injection. Heat-inactivated collagenase was ineffective. 3. The B2 bradykinin (BK) antagonist icatibant (D-Arg-[Hyp3-Thi5-D-Tic7- Oic8] bradykinin, formerly named Hoe-140) reduced oedema formation in a dose-dependent manner with a maximal reduction of around 65% at a dose of 100 nmol kg-1 (s.c.). A significant effect could already be observed at a dose of 10 nmol kg-1. The duration of the effect of icatibant (100 nmol kg-1) was found to be at least 3 h. These results demonstrate the high potency and long duration of action of icatibant. Pretreatment of rats with the bradykinin B1 antagonist, des-Arg9-[Leu8]-BK did not affect collagenase-induced paw oedema. Thus, the observed collagenase-induced effects are mainly mediated by BK through activation of B2 receptors. 4. Pretreatment of adult rats with capsaicin (125 mg kg-1, s.c.) three weeks before the collagenase injection caused a significant attenuation of the paw oedema and of plasma extravasation but was significantly less effective than icatibant (100 nmol kg-1, s.c.). The non-peptide substance P antagonist,CP-96,345 (l0 micromol kg-1, i.v.) significantly reduced collagenase-induced oedema formation to a degree comparable with that seen after capsaicin pretreatment. The inhibition by the substance P antagonist was significantly smaller than that seen after icatibant. The inhibitory effect of icatibant in capsaicin pretreated rats, or of icatibant together with CP-96,345 in untreated rats, was not greater than that oficatibant alone in rats treated with the vehicle for either capsaicin or CP-96,345. CP-96,344(10 micromol kg-1, i.v.), the inactive enantiomer of CP-96,345, did not affect collagenase-induced paw oedema. In capsaicin-pretreated rats, CP-96,345 (10 micromol kg-1, i.v.) did not reduce collagenase-induced paw oedema.The subplantar injection of bradykinin (30 nmol) induced a paw oedema comparable with that induced by collagenase (100 microg). CP-96,345 (10 micromol kg-1, i.v.), but not CP-96,344 (1O micromol kg-1, i.v.),significantly reduced the bradykinin-induced paw oedema. These findings indicate that collagenase leads to the release of bradykinin; bradykinin then stimulates afferent C-fibre terminals and causes the release of substance P and probably also neurokinin A, which augment the oedema-inducing effect of bradykinin.5. Indomethacin or mepyramine plus cimetidine failed to inhibit collagenase-induced paw oedema.Thus, prostaglandins and histamine do not seem to be involved in collagenase-induced paw oedema.6. After subplantar injection of collagenase, the sensitivity scores in a modified formalin-test rapidly increased during the first 10 min. This increase was abolished by pretreatment with icatibant(100 nmol kg-1, s.c.) indicating that the stimulation of nociceptive afferent neurones following injection of collagenase is due to the action of released kinins.7. In conclusion, bradykinin appears to be the main mediator of inflammation induced by a collagenase from Clostridium histolyticum. As well as having direct relevance to a known pathological condition,collagenase-induced paw oedema could prove to be a useful model in inflammation research and in the investigation of bradykinin antagonists. The present results might provide an experimental basis for clinical investigations of the effects of icatibant in infectious diseases where the release of collagenases from bacteria causes rapid spreading of inflammation.

In vivo effect of acetyl- l-carnitine on succinate oxidation, adenine nucleotide pool and lipid composition of synaptic and non-synaptic mitochondria from cerebral hemispheres of senescent rats

The effect of acetyl- l-carnitine on succinate oxidation, adenine nucleotide pool and lipid composition of synaptic and ‘free’, non-synaptic, mitochondria in cerebral hemispheres of senescent rats has been studied. Fisher rats (24- or 28-month-old) were treated with acetyl- l-carnitine (300 mg/kg body wt., intraperitoneally (i.p.)) 3 h before being killed. Oxygen consumption was measured using succinate as a substrate; adenine nucleotides and lipids were analyzed by high performance liquid chromatography (HPLC). Acetyl- l-carnitine reverses, in synaptic mitochondria, the age-related decrease in the respiratory control ratio due to a higher state 4 respiration rate. Administration of acetyl- l-carnitine to senescent rats does not affect the total adenine nucleotide pool of synaptic and non-synaptic mitochondria which was unchanged with age. Finally, pretreatment of senescent rats with acetyl- l-carnitine brings the cholesterol and phospholipid contents of synaptic mitochondria, reduced in senescent rats, to the adult level; pretreatment of adult rats has no such effect. Altogether these results suggest that acetyl- l-carnitine is able to reverse age-related deficits of brain mitochondria.

Naltrexone potentiates 4-aminopyridine seizures in the rat

The effects of a pharmacological blockade of the mu opiate receptors on the manifestation of tonic-clonic seizures were investigated in freely moving animals. 4-aminopyridine, a specific blocker of the neuronal K+ channels was used to produce generalized convulsions. After pretreatment of adult rats with 1 mg/kg naltrexone HCl, 3, 5, 7, 9, 14 mg/kg 4-aminopyridine was injected intraperitoneally, and the latencies of the symptoms generated by 4-aminopyridine were measured. Naltrexone HCl decreased these latencies and enhanced the seizures significantly. The experiments provided further evidence for the existence of a tonic anticonvulsant opioid system in the brain.

Interrelationship between RU38486 and the P450 activities in rat liver.

Microsomal P450 monooxygenases contribute actively to the biotransformation of the antiglucocorticoid RU38486, an 11 beta-substituted nor-steroid. Pretreatment of adult rats by inducers of specific forms, belonging to different P450 subfamilies, affects the ability of liver microsomes to metabolize RU38486. Phenobarbital and pregnenolone 16 alpha-carbonitrile increase the metabolic activity of liver microsomes whereas methylcholanthrene decreases their capacity to oxidize the steroid. Thus P450 forms IIIA, IIB1,2 and IIC7 are good candidates to be involved in the degradation of this peculiar molecule. Our study has been completed by investigating whether RU38486 would influence the P450 spectrum. Whereas the treatment of rats with either a glucocorticoid (cortisol, dexamethasone) or an antiglucocorticoid (pregnenolone 16 alpha-carbonitrile) has been shown to induce the P450 activity by increasing the hepatic concentration of form IIIA, we observed a slight decrease of the P450 activity by treating the animals with RU38486. Moreover RU38486 was able to antagonize the P450 induction by the other steroids as well as it inhibits the synthesis of various liver enzymes induced by glucocorticoids (for instance tyrosine aminotransferase). These findings may be important for the therapeutic use of RU38486 since its inhibitory effect on P450 activity may be at the origin of drug interactions by modifying the endogenous hormonal status.

Capsaicin-induced excitation of locus coeruleus neurons.

The noradrenergic pontine nucleus locus coeruleus (LC) seems to be involved in sensory processing. In the present study, the effect of capsaicin, a drug which specifically interferes with chemosensitive primary afferents, on LC firing rate was analysed, utilizing electrophysiological techniques. In control rats, low doses of capsaicin (1-8 micrograms kg-1 i.v.) caused a marked excitation of LC units. The effect was instantaneous in onset but short-lasting and no signs of tachyphylaxis were observed. The excitation was maintained in adult rats treated as neonates with high doses of capsaicin (50 mg kg-1 s.c.) but almost totally prevented by pretreatment of adult rats with high doses of capsaicin (300 mg kg-1 s.c.). According to our histological data, using selective silver impregnation techniques, the LC seems not to receive innervation by sensory primary afferents. It is proposed that the capsaicin-induced excitation of LC neurons is a centrally mediated effect and might, in part, be involved in the analgetic effect induced by the drug.

Cholecystokinin-induced suppression of locomotion is attenuated in capsaicin pretreated rats

Cholecystokinin (CCK), a peptide found in both gastrointestinal endocrine cells and neurons, suppresses food intake and reduces locomotor behavior when injected systemically. Both the locomotor and ingestive effects of CCK are abolished by subdiaphragmatic vagotomy. Pretreatment of adult rats with capasaicin attenuates the reduced locomotor activity and reduced food intake which normally occurs following injection of exogenous cholecystokinin. Since capsaicin damages or destroys small-diameter, unmyelinated, sensory neurons, including vagal sensory fibers, these data support the interpretation that both CCK-induced suppression of food intake and CCK-induced reduction of locomotion are mediated by fine, unmyelinated sensory neurons.

CALCIUM CHANNEL BLOCKADE AS THE TREATMENT OF ENDOTOXIN SHOCK IN NEWBORN PUPPIES

Previous studies have shown that pretreatment of adult rats with the calcium channel blocker diltiazem(DZ) attenuates the Endotoxin(ET) induced decrease in cardiac output(CO). We have now measured the CO(cardio-green technique of Arcilla and Rowe), mean arterial pressure(MAP) and heart rate(HR) in 45 new born mongrel puppies. The animals were divided into 3 groups: I. ET (1.5 mg/kg IV) without DZ; II. DZ (600 μg/kg IV) 20 min. prior to ET; III. (1200 μg/kg IV) 20 min. prior to ET. MAP, CO and HR measurements (mean value± SE, no. of animals given in parentheses) at 1 and 2 hours post Endotoxin. There was no significant effect of ET or DZ (either dose) on HR. Although ET significantly (P< .05) decreased CO (Pre vs. post ET). DZ pretreatment produced no significant CO changes. However, MAP was significantly affected by DZ (DZ pretreatment vs ET alone). These results suggest that in newborn puppies ET shock, DZ causes early hypotension w/o affecting CO.

Protection from paraquat-induced lung damage and lethality in adult rats pretreated with clofibrate

Pretreatment of adult rats with the hypolipidemic agent clofibrate (60 mg/kg/day × 6 days) resulted in a marked degree of protection from paraquat-induced lung toxicity and lethality. The 10-day survival of treated rats was 39 56 (70%) compared to 21 76 (28%) (LT 50 = 2.8 days) for controls ( p < 0.001). Although clofibrate reportedly increases catalase activity in the liver, we found no increases in any of the antioxidant enzymes in the lung (catalase, superoxide dismutase, glutathione peroxidase, or G-6-PD) after clofibrate pretreatment. Lung lipid peroxidation at 24 and 48 hr post-paraquat was equivalent in both groups, although the clofibrate-pretreated rats showed significantly reduced lung edema and pathologic changes at these times. Blood paraquat levels were similar in both groups at 1, 3, and 24 hr postinjection. In two experiments, administration of clofibrate after paraquat injection afforded no protective effects. However, since pretreatment with clofibrate provided the best overall survival rate reported to date after a lethal dose of paraquat (35 mg/kg), further studies toward elucidating the mechanism(s) of action of this agent are warranted. Unraveling the protective mechanism(s) of the pretreatment regimen may still provide valuable clues to suggest effective post paraquat treatment approaches.

Effect of capsaicin on morphine analgesia--possible involvement of hypothalamic structures.

1. Rats were treated with 50 mg/kg capsaicin on the second day of life or at the age of 2--3 months. The effect of morphine on the nociceptive threshold, as determined by the reaction time in tail withdrawal test, was measured 3--4 and 1--2 months after capsaicin pretreatment, respectively. 2. The analgesic effect of morphine was markedly attenuated in rats treated with capsaicin in the adult age, while neonatal capsaicin treatment did not affect morphine analgesia. 3. Pretreatment of adult rats with capsaicin results in the impairment of certain hypothalamic preoptic neurones, while neonatal capsaicin treatment induces selective degeneration of chemosensitive primary sensory neurones without affecting hypothalamic neurones. Therefore, it is suggested that in the analgesic effect of morphine the capsaicin-sensitive neurones of the preoptic area are involved, and the contribution of spinal mechanisms might be of minor importance. Thus, the preoptic region may be an important link in endogenous pain controlling systems.

DL-ethionine treatment of adult pancreatic donors. Amelioration of diabetes in multiple recipients withe tissue from a single donor.

Transplantation of adult rat pancreatic islet tissue as a free graft requires the separation of islet from exocrine tissue to avoid host injury or graft destruction by digestive enzymes. The poor yield from islet isolation techniques currently necessitates the use of multiple donors to ameliorate diabetes in a single recipient. DL-ethionine (DLE) is an agent selectively toxic to the exocrine pancreas. We examined the effect of DLE administration on pancreatic digestive enzyme content and islet mass in adult Lewis rats and the ability of such pancreatic tissue dispersed by collagenase digestion without specific islet isolation to ameliorate diabetes when transplanted to the portal vein of syngeneic rats with streptozotocin induced diabetes. Rats fed normal chow supplemented with 0.5% DLE for 14-20 days showed a logarithmic loss of pancreatic mass. Total pancreatic amylase content declined to 0.3 + 0.1 mg, less than 3% of control values (14.3 +/- 1.0 mg). Total insulin content in DLE treated rats was 87 +/- 8 microg, not significantly different from control rats (101 +/- 7 microg). Histological examination confirmed the selective atrophy of exocrine tissue in DLE treated rats. Fresh pancreatic tissue prepared from a single DLE treated donor ameliorated diabetes 75% of the time when transplanted to one or two recipients and 65% of the time when divided between three of four recipients. Tissue prepared from a single DLE treated donor and stored for 24-48 hours ameliorated diabetes 91% of the time when divided between one or two recipients. Only four of 31 diabetic rats transplanted with fresh pancreatic tissue from untreated adult donors became normoglycemic. Pretreatment of adult rats with DLE induces selective exocrine atrophy, permits dispersed pancreatic tissue from a single donor to ameliorate experimental diabetes in up to four recipients, and allows tissue to be preserved by culture for up to 48 hours without specific islet isolation.

Perinatal development of, and effect of chemical pretreatment on, glycine N-acyltransferase activities in liver and kidney of rabbit and rat.

The ontogenic development of glycine N-acyltransferase activity was studied in preparations of hepatic and renal mitochondria from the New Zealand White rabbit and the Sprague-Dawley rat. Preparations of hepatic mitochondria from the rat and the rabbit attain adult glycine N-acyltransferase specific activities by birth and 4 weeks of age respectively, whereas mitochondrial preparations from rabbit kidney do not attain adult activity until 4 months of age. Pretreatment of adult rats or immature rabbits with salicylic acid, benzoic acid or phenobarbital had little effect on glycine N-acyltransferase activity in vitro in liver or kidney.

Effect of substrate pretreatment on renal organic ion transport in the adult rat.

The ability of renal cortical slices to accumulate PAH and NMN was not significantly affected by pretreatment of adult rats with large doses of PAH. Pretreatment of adult rats with THAM significantly increased PAH accumulation but had no effect on NMN. Inulin and PAH clearance and filtration fraction were significantly decreased by PAH pretreatment but unaffected by THAM pretreatment. The effects of pretreatment on transport are probably due to non-specific toxicity.