Behavioral consequences of agonistic experiences in the male S3 (Tryon Maze Dull) rat

Aggression occurring during an initial confrontation between two rats may result in significant behavioral changes in one or both animals. The present experiment was designed to study behavioral changes occurring in the course of an agonistic interaction and the consequences of winning or losing. In order to ensure winning, male CPB-S3 Tryon Maze Dull) rats were confronted with males of a more aggressive strain (Long Evans); and to ensure losing they were confronted with those of a less aggressive strain Wistar). Winners were tested against losers, this test being repeated after an interval of 17 days. Winners and losers were also tested with naive S3 opponents. Possible effects of winning and losing in nonagonistic behavioral tests were then examined. These measured open field activity, passive avoidance learning, and masculine sexual behavior. The results replicate and extend earlier findings using a different strain, indicating that significant and relatively permanent behavioral changes are induced in male winners and losers. Behavioral change is most prominent in the losers. Despite the behavioral differences between winners and losers in tests for agonistic behavior, no consistent differences were noted in any of the other behavioral tests.     

The decline of aggressiveness in male mice during group caging as determined by punishment delivered by the cage mates

Group-housed rodents are generally less aggressive than isolated counterparts. The present study examined the role of defeat by cage mates as a reason for this decline in aggressiveness. In Experiment I, highly aggressive isolated male mice were introduced into aggressive or nonaggressive resident groups. The intruder's level of aggressiveness directed toward a group-housed standard opponent declined more rapidly after daily exposure to the aggressive than to the nonaggressive groups. Intruders in the aggressive groups received more attacks from their cage mates, and delivered fewer attacks to them than did the intruders in the nonaggressive groups. In Experiment II, the intruders lived for seven days in small wire net cages in the middle of the group cages. Their level of aggressiveness toward standard opponents decreased little during the preexposure but after being put freely into the groups, their aggressiveness declined to a minimal level within a day. Experiment III showed that when the wire net protection in the middle of the cage was installed after the group caging experience, the aggressiveness of the intruders did not return to the isolation level as effectively as it did in isolation. This is explained by the aggression-inhibiting content that the cues from the cage mates have acquired during group caging. The decline of aggressiveness in male mice during group caging is determined by punishment delivered by the cage mates.     

Variable-ratio schedules as variable-interval schedules with linear feedback loops.

The mathematical theory of linear systems has been used successfully to describe responding on variable-interval (VI) schedules. In the simplest extension of the theory to the variable-ratio (VR) case, VR schedules are treated as if they were VI schedules with linear feedback loops. The assumption entailed by this approach, namely, that VR and VI-plus-linear-feedback schedules are equivalent, was tested by comparing responding on the two types of schedule. Four human subjects' lever pressing produced monetary reinforcers on five VR schedules, and on five VI schedules with linear feedback loops that reproduced the feedback properties of the VR schedules. Pressing was initiated by instructions in 2 subjects, and was shaped by successive approximation in the other 2. The different methods of response initiation did not have differential effects on behavior. For each of the 4 subjects, the VR and the comparable VI-plus-linear-feedback schedules generated similar average response rates and similar response patterns. The subjects' behavior on both types of schedule was similar to that of avian and rodent species on VR schedules. These results indicate that the assumption entailed by the VI-plus-linear-feedback approach to the VR case is valid and, consequently, that the approach is worth pursuing. The results also confute interresponse-time theories of schedule performance, which require interval and ratio contingencies to produce different response rates.     

Effects of reinforcement schedule on facilitation of operant extinction by chlordiazepoxide

Learning and memory are central topics in behavioral neuroscience, and inbred mice strains are widely investigated. However, operant conditioning techniques are not as extensively used in this field as they should be, given the effectiveness of the methodology of the experimental analysis of behavior. In the present study, male C57B1/6 mice, widely used as background for transgenic studies, were trained to lever press on discrete-trial fixed-ratio 5 or fixed-interval (11 s or 31 s) schedules of food reinforcement and then exposed to 15 extinction sessions following vehicle or chlordiazepoxide injections (15 mg/kg i.p., administered either prior to all extinction sessions, or prior to the final 10 extinction sessions). Extinction of operant behavior was facilitated by drug administration following training on either schedule, but this facilitation only occurred once a number of extinction sessions had taken place. The extinction process proceeded more rapidly following fixed-interval training. Resistance to extinction was equally high following training with either schedule type, and was reduced by drug administration in both cases. These phenomena were evident in individual cumulative records and in analyses of group data. Results are interpreted in terms of phenomena of operant extinction identified in Skinner's (1938) Behavior of Organisms, and by behavioral momentum theory. These procedures could be used to extend the contribution of operant conditioning to contemporary behavioral neuroscience.     

Subordinate male mice show long-lasting differences in spatial learning that persist when housed alone

In the wild, house mice live in social groups, whereas in the laboratory male mice are often singly housed. Environmental enrichment such as that provided by social housing has been argued to improve the cognitive performance of laboratory animals in experimental tests. The aim of the present study was to test the cost of aggressive social interactions on learning in male CD-1 mice. We found that subordinate mice from more aggressive dyads showed spatial learning impairment, measured as alternation on a T-maze. Learning impairments in subordinates have hitherto been presumed attributable to the animals' exposure to, and relative standing within, the social group. By contrast, the impairment we observed could not have been the result of recent social defeat because it persisted weeks later when the mice were housed alone. Elevated urinary corticosterone predicted later subordination, though paradoxically these abnormally high levels were reduced by pair housing.     

Newly observed microscopic planar defects on {111} in natural diamond

Abstract

Circular disc-crack-like defects randomly distributed on {111} planes have been discovered by 300kV transmission electron microscopy in diamond that had crystallized on non-faceted growth surfaces of mean orientation {100}. In a sample of ～ 100 defects, disc diameters were narrowly distributed about a mean of 1·2 μm and one in seven discs were located on a coplanar stacking fault of average diameter 2 μm. Discs totally enclosed within the specimen exhibit concentric moiré fringes covering their image areas when viewed obliquely, showing them to be dilated into thin lenticles. Internal pressures, deduced from moiré-fringe counts on six lenticles, were in the range 1·5 to 1·8 GPa.     

Fractal growth of graphite nodules in iron

It has been found from a large number of statistical tests that graphite nodules in malleable iron grow with time according to a power law. The growth of the nodules and their fractal dimension have been investigated experimentally as a function of annealing time. Based on the assumption of carbon-diffusion-controlled growth in the initial stage, the growth equation is R _G = K ₁ t ^1/(D-1), where R _G is the radius of the graphite nodules, t the time, D the fractal dimension and K ₁ a constant. Assuming cementite-dissolution-controlled growth in the later stages of growth, the relation is R _G = K ₃ t ^3/D , where K ₃ is a constant. The fractal dimension, or the aggregate state of the graphite nodules, strongly influences the growth process.     

On elastic–viscoplastic modeling of nanotwinned metals based on coupled intra-twin and twin-boundary-mediated deformation mechanisms

An elastic–viscoplastic model has been developed for nanotwinned (nt) metals based on coupled intra-twin and twin-boundary-mediated (TBM) deformation mechanisms. The grain-size dependence of intra-twin plasticity was incorporated in the proposed model to determine the transitional twin thickness corresponding to the maximum strength. In addition, the joint distribution of grain size and twin thickness was also taken into account to simulate the microstructure of nt metals. The results obtained show that the TBM deformation mechanism dominated at low strain rate and small twin thickness, and that the grain-size and twin-thickness distributions had significant influence on the macroscopic behavior of nt metals. A linear relation between the transitional twin thickness and grain size is predicted by the proposed model, which is in good agreement with the results obtained from three-dimensional molecular dynamics simulations and experiments.     

New insights on tensile plasticity of ultrafine-grained metallic materials

ABSTRACT

The tensile properties of TiNi_43.5Fe_6.5 alloy samples having different grain sizes (0.16, 0.35, 1.7, 2.3, and 3.9?μm) and fabricated by severe plastic deformation and annealing were investigated. It was observed that both the strength and the elongation of the alloy increase with a decrease in the grain size until the average size reaches 1.7?μm. However, for average grain sizes smaller than 1.7?μm, the elongation decreases continuously with further grain refinement. On the other hand, the strain-hardening rate does not decrease with the decrease in plasticity but instead increases slightly. The poor ductility of the ultrafine-grained TiNi_43.5Fe_6.5 alloy is accompanied by a high degree of strain hardening. This newly observed ductility behaviour of the ultrafine-grained TiNi_43.5Fe_6.5 alloy is elucidated by characterising the intragranular and grain boundaries.