Effects of social defeat and of diazepam on behavior in a resident-intruder test in male DBA/2 mice

Social stress induces robust behavioral and physiological changes, some of which may alter the responsiveness to pharmacological agents, including diazepam (DZP). We used a resident-intruder paradigm to (1) develop a comprehensive ethogram of behavioral changes following social defeat (SD) in the socially reactive strain, DBA/2 male mice, (2) determine whether acute exposure of DBA/2 mice to low-dose DZP would induce flight or aggressive behavior, both of which have been observed in other rodent models and (3) to test whether prior social stress affects responses to DZP. Behavioral responses to a nonaggressive intruder (NAI) mouse 24 h post-SD were measured in resident subject mice exposed to DZP (0, 0.5, 2.0 mg/kg, ip) either prior to the resident-intruder test (Experiment 1) or immediately post-SD (Experiment 2); control mice were not defeated (NOSD). In general, SD mice displayed increased passive and active avoidance, defense, immobility, and risk assessment relative to NOSD mice. In Experiment 1, mice treated acutely with 0.5 mg/kg DZP had more approach and flight behavior, while those treated with 2.0 mg/kg DZP had more avoidance than vehicle-treated mice, independent of SD. In Experiment 2, acute DZP (2 mg/kg) induced effects 24 h later, possibly secondary to withdrawal. In a nonsocial context (Experiment 3), DZP increased exploratory activity.

Importance of species selection in drug toxicity testing

The development of efficacious and safe new human pharmaceuticals continues to be highly dependent on well-designed and carefully executed animal toxicology studies. Although the protocols of most toxicology studies now conform to a standard format, careful selection of the most appropriate and relevant laboratory species is essential. This selection is usually based on pilot toxicity and general pharmacology studies in rodent and non-rodent animals, together with supporting comparative drug disposition studies to determine bioavailability and metabolic profile. A knowledge of the human metabolic profile from early in vitro studies with liver preparations can be particularly valuable.

Modulation of transforming growth factor beta 1 effects on prostate cancer cell proliferation by growth factors and extracellular matrix

Poorly differentiated MATLyLu rat prostate cancer cells are resistant to the growth inhibitory effect of transforming growth factor (TGF) beta 1 in vivo, but are inhibited by TGF-beta 1 in vitro. However, TGF-beta 1 inhibited proliferation only when the cells were plated at low density in serum-free medium (concentration for 50% of maximum inhibition, 0.1 ng/ml). TGF-beta 1 was not growth inhibitory when cells were plated at high density, or at low density in 0.5% serum. At low cell density in serum-free medium, 0.5 ng/ml TGF-beta 1 caused maximum inhibition. In the presence of basic fibroblast growth factor (10 ng/ml), TGF-beta 1 did not inhibit proliferation. In the presence of epidermal growth factor (50 ng/ml), TGF-beta 1 inhibited proliferation by only 18%. Growth inhibition by TGF-beta 1 was less effective on extracellular matrix than on plastic. The ability of high cell density, serum, growth factors, or extracellular matrix to prevent or blunt the growth inhibitory effect of TGF-beta 1 in vitro probably explains why TGF-beta 1 does not inhibit tumor growth in vivo. Thus, prostate cancer cells express high levels of TGF-beta and retain exquisite sensitivity to the growth inhibitory effect of TGF-beta, but have devised a way to protect themselves from growth inhibition by TGF-beta in vivo. TGF-beta 1 stimulated MATLyLu cell motility even at high cell density, suggesting that TGF-beta 1 might affect motility even in vivo and contribute to the aggressiveness of the tumor, without affecting proliferation.

Regulation of motility and cytoskeletal organization of rat bladder carcinoma cells by cyclic AMP

Cyclic AMP (cAMP) has been implicated in the regulation of movement of certain cultured cell types. We have studied the effects of cAMP on epithelial cell motility using serum-free NBT-II cells, derived from a rat bladder carcinoma. The random movement of these cells on type I collagen was reduced upon elevation of intracellular cAMP by several means and this effect was reversible. Alterations in the organization of the cytoskeletal proteins F-actin and alpha-actinin occurred concurrently with the reduction in motility, and the arrangement of these proteins resembled that seen in non-motile cells on glass. In addition, pretreatment of cells with KT5720, a cAMP-dependent protein kinase (PKA)-specific inhibitor, prevented the dibutyryl cAMP-induced reduction in cell movement as well as the associated cytoskeletal changes. These results suggest that elevation of PKA is responsible for the observed effects on cell motility and cytoskeletal reorganization and demonstrate a role for PKA in the regulation of cell motility in this system.

Carcinogenicity studies of fluoxetine hydrochloride in rats and mice

The antidepressant drug fluoxetine HCl was tested for carcinogenicity in three well designed and controlled studies in Fischer rats and C57BL/6 x C3H F1 mice. The compound was administered to the animals for 24 months at dietary doses of approximately 0, 0.5, 2.0, or 10.0 mg/kg body weight in rats and 1.0, 5.0, or 10.0 mg/kg in mice. The highest dose tested was a maximum tolerated dose for both species as evidenced by clinical signs (rats and mice) and some mortality (mice) referable to central nervous system pharmacological effects, decreased weight gain (rats), and histopathological changes of phospholipidosis (rats) and hepatic fatty change (mice). There was no evidence of an increased incidence of any type of unusual or commonly occurring spontaneous neoplasm in either rats or mice. There were statistically significant decreases in a few commonly occurring neoplasms. The data reported herein provide convincing evidence that fluoxetine is neither a complete carcinogen nor a tumor promoter.

Pharmacology and toxicology of nizatidine

In well-established animal models, nizatidine is a potent, specific, and competitive orally active H2-receptor antagonist. In rat and dog models, species in which the absorption, plasma half-life and routes of metabolism are similar to that of humans, nizatidine was three- to four-fold more active than cimetidine and was of similar potency to ranitidine. On repeated daily dosing in dogs for two weeks, no tolerance was developed to the pharmacological action. Following oral dosing to dogs, nizatidine reduced gastric acid secretion for up to 8 h suggesting that this compound could be used in humans with a once or twice daily dosage regime. Apart from its H2-antagonist activity on the gastric mucosa, nizatidine produced few effects on the cardiovascular, respiratory, or central nervous system of animals. Nizatidine was rapidly and well-absorbed orally in mice, rats, and dogs, was widely distributed in tissues and the majority of the dose was excreted in the urine within 24 h. A similar absorption and excretion profile has been seen in humans. The plasma half-life in each of the animal species was between 1 and 2 h and no accumulation of nizatidine or its metabolites was seen in rats or dogs after daily oral administration for long periods. Similarities in the pharmacokinetic profile of nizatidine in the laboratory animals and humans supported the selection of the mouse, rat, and dog for acute and chronic toxicity studies. Nizatidine was well-tolerated in animals after both intravenous and oral administration and following single or repeated administration.(ABSTRACT TRUNCATED AT 250 WORDS)

An evaluation of the toxicity of moxalactam in laboratory animals

The toxicity of moxalactam in laboratory animals was evaluated with six species. The acute toxicity of moxalactam was lower than that of cefazolin. The subchronic and chronic toxicity of moxalactam was studied for periods of one to six months at dosages of 100-3,500 mg/kg per day in rats, 100-1,600 mg/kg per day in dogs, and 100-500 mg/kg per day in monkeys. Treatment-related effects were limited to soft stool, cecal dilatation, and slight anemia resulting from local injury at the injection site in the higher dosage groups. All the effects were reversible and less severe than those caused by cefazolin. Studies of reproduction in rats, mice, and rabbits indicated that moxalactam had no teratogenicity and no adverse effects on fertility of parental animals and on gestation or growth and reproductive capacity of offspring. Comparative studies of nephrotoxiticity in rabbits demonstrated that moxalactam was considerably less nephrotoxic than cefazolin, cefotiam, and cefotaxime.

Animal models for the comparative assessment of neurotoxicity following repeated administration of vinca alkaloids

Neurotoxicity is the major side effect occurring during the clinical use of vincristine (VCR). Animal models predictive of potential neurotoxicity would be very useful in the preclinical development of new vinca compounds. To simulate conditions in which neurotoxicity is produced during the clinical use of VCR, experimental animals (except the guinea pig) were given the test compounds by the iv route over a prolonged time period. Doses were selected based on the production of leukopenia. Vindesine (VDS), a chemically modified vinblastine (VBL) product, was compared with VCR and VBL in animal studies. Definite neurotoxic manifestations developed when VCR was given to chickens, cats, and monkeys. The administration of VDS or VBL did not produce neurotoxic signs in these species. The mouse, rat, dog, and guinea pig were not found to be useful models. Thus, it would appear the chicken, cat, and monkey would be appropriate animal models for the preclinical testing of new vinca compounds.

Toxicologic evaluation of cefamandole nafate in laboratory animals

The safety of cefamandole nafate in laboratory animals was evaluated in six species. The acute toxicity of cefamandole after intravenous or subcutaneous administration was similar to that of cephalothin sodium. The subacute and chronic toxicity of cefamandole was studied in rats and dogs for periods of two weeks to six months at doses of 250--1,000 mg/kg per day in rats and 125--1,500 mg/kg per day in dogs. No evidence of significant systemic toxicity was observed in these studies. There were, however, various degrees of local injury at the injection sites that resulted in slight decreases in hemoglobin, hematocrit, and red blood cell counts in the animals in which injury at the injection site was most severe. Studies of reproduction in rats and mice indicated that cefamandole nafate had no teratogenic effects and no adverse effects on fertility, gestation, or growth of offspring. Comparative studies of nephrotoxicity in rabbits demonstrated that the nephrotoxicity of cefamandole nafate was considerably less than that of cefazolin.

Metabolism of a new herbicide, tebuthiuron (1-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]- 1,3-dimethylurea), in mouse, rat, rabbit, dog, duck, and fish

Orally dosed tebuthiuron was readily absorbed in mice, rats, rabbits, dogs, and ducks. The compound was extensively metabolized and the metabolites were rapidly excreted in the urine of mice, rats, rabbits, and dogs and in the mixture of urine and feces in ducks. The major metabolites of tebuthiuron were formed by N-demthylation of the substituted urea side chain in each species examined, including fish. Oxidation of the dimethylethyl group occurred in mice, rats, dogs, rabbits, and ducks. The N-demethylation reaction at the 3-position of the urea proceded through an N-hydroxymethyl intermediate. No accumulation of tebuthiuron or its metabolites was observed in the animals, a finding consistent with the low order of toxicity observed in other studies.

Toxicology of vindesine (desacetyl vinblastine amide) in mice, rats, and dogs

Comparative acute intravenous toxicity studies of vinblastine sulfate (VLB), vincristine sulfate (VCR), and vindesine in mice and rats indicated that vindesine was more toxic than VLB and less toxic than VCR. Rats were able to tolerate larger repeated doses of vindesine than dogs. Rats given intravenous doses totaling 0.15 mg/kg-wk vindesine for 3 months developed no remarkable signs of toxicity. Doses of 0.3 mg/kg-wk or greater produced anorexia, depressed blood cell counts, atrophic intestinal mucosa, inhibition of spermatogenesis, extramedullary hematopoiesis, and infections. Dogs were given total weekly intravenous doses of 0.04, 0.08, 0.1, or 0.16 mg/kg vindesine for 3 months. The only observed effect in the two lower dose groups was inhibition of spermatogenesis. Groups receiving 0.1 or 0.16 mg/kg developed leukopenia, slight erythropenia, inhibition of spermatogenesis, focal skeletal muscle degeneration, elevated lactic dehydrogenase, and an increase in bone marrow myeloid: erythroid ratio. No evidence of functional or structural changes in neural tissues was found. The above effects are common to animals given VCR at lower doses and for a shorter test period. It is therefore concluded that vindesine is less toxic in animals than VCR.