Maudsley Reactive Strains Research Articles

Conflict behavior in maudsley reactive and nonreactive rats: Effects of noradrenergic neuronal destruction

The present studies were designed to examine the effects of treatment with the noradrenergic neurotoxin N-(2-chloroethyl)- n-ethyl-2-bromobenzylamine HCl (DSP4; 65 mg/kg, IP) on conflict behavior in the Maudsley reactive (MR) and nonreactive (MNRA) rat strains. In daily 10-min sessions, water-restricted rats were trained to drink water from a tube that was ocassionally electrified; electrification was signaled by the presence of a tone (7-s duration; ISI = 30 s). Consistent with previous reports, the number of shocks accepted by rats of the MR and MNRA strains did not differ initially, but MNRA rats exhibited a dramatic increase in punished responding relative to their MR counterparts over the course of several weeks of conflict testing. This MR vs. MNRA strain difference in punished responding did not exhibit extinction following discontinuation of CSD conflict behavior testing for a period of 6 weeks. Whether it was administered after conflict training or before, DSP4 treatment did not reduce the MR vs. MNRA strain difference in conflict behavior; rather, DSP4 treatment tended to increase the magnitude of the MR vs. MNRA difference in conflict behavior. The effects of DSP4 on norepinephrine (NE) and 5-hydroxytrypamine (5-HT) concentrations in the pons medulla region were determined in one group of conflict-experienced MR and MNRA rats (35 weeks after administration) and in a second group of naive MR and MNRA rats (3 weeks after administration). There were no MR vs. MNRA strain differences in NE or 5-HT concentrations in vehicle-treated rats. DSP4 treatment significantly reduced NE, but not 5-HT, concentrations when compared to control values; rats that were sacrificed 3 weeks following DSP4 administration exhibited a greater NE depletion than did rats sacrificed 35 weeks after DSP4 administration. Finally, there were no significant correlations between pons medulla region NE concentrations and conflict behavior in either strain alone or when the data from the two strains were combined. The present results are not consistent with the hypothesis that the MR vs. MNRA strain difference in conflict behavior is the result of strain differences in brain NE function.

Maudsley reactive and nonreactive rats in the forced swim test: Comparison in fresh water and solied water

Maudsley reactive (MR) and nonreactive (MNRA) and Sprague-Dawley (SD) male rats were tested for their immobility response in the forced swim test when the water was fresh or soiled by a rat of the same or other strain. For all strains, rats tested in soiled water were less immobile than rats in fresh water. The three strains did not differ as producers of soiling substance, but did differ in their response to it. The MR strain was least responsive, whereas the MNRA and SD did not differ from one another. These results support a previous study suggesting that MR rats are more immobile than MNRA rats in the forced swim test. The interpretation of these findings regarding the use of the Maudsley rat strains as an animal model for studying anxiety and/or depression is discussed.

Analysis of relative mRNA levels and protein patterns in brains of rat strains bred for differing levels of emotionality.

mRNA and protein populations were studied in the brains of Maudsley reactive (MR) and Maudsley nonreactive (MNR) rat strains, which exhibit differing levels of emotionality. Translational analysis of forebrain mRNA indicated that the relative levels of two translation products (42 kDA, pI 5.0; 30 kDa, pI 5.8) were increased in the MR compared to the MNR strain. In addition, a charge-shift variant of a 36 kDa protein was present in the MR strain. Analysis of brain protein patterns indicated that a protein of 39 kDa, pI 5.0, was found to be more abundant in MR compared with MNR strains in both frontal cortex and hippocampus and the relative level of one protein (40 kDa, pI 5.8) was decreased in the frontal cortex.

Brain adenosine receptors in Maudsley reactive and non-reactive rats

Previous work in our laboratory has shown that the Maudsley reactive (MR) strain of rats cannot be differentiated from the Maudsley non-reactive (MNR) strain regarding the number or affinity of their brain benzodiazepine binding sites. In the present study we show that the number of cerebellar adenosine receptors (as studied using [ 3H]cyclohexyladenosine, [ 3H]CHA, as the ligand) are increased by 15–30% in the MR strain. This alteration was corroborated by quantitative autoradiographic analysis and found to be localized to the molecular layer of the cerebellum where adenosine receptors are believed to reside on parallel fibers of cerebellar granule cells.

Effects of early handling on avoidance performance of Maudsley MR and MNR strains.

AbstractThis study investigated the effect of infantile handling on the emotionality and avoidance performance of the Maudsley reactive (MR) and nonreactive (MNR) strains of rats. The expected difference in emotionality was found (MR's had higher defecation scores than MNR's); however, this difference was unaffected by early handling. The avoidance behavior of the 2 strains was different in that MR's had shorter escape latencies; however, they did not differ with respect to CAR's. Handling had a significant effect on avoidance behavior, but this was not greater in one strain than another. The interaction of genetic differences and infantile stimulation on avoidance performance does not appear to be supported in females from these 2 strains.

Effects of trihexyphenidyl on schedule-induced alcohol drinking by rats

Three rats from the Maudsley reactive strains and three rats from the Maudsley nonreactive strain were trained to barpress with food reinforcement scheduled at fixed intervals of 1 min. With various alcohol concentrations, schedule-induced licking was higher in the nonreactive animals but there was little difference in intake between the strains. Injections of trihexyphenidyl attenuated alcohol consumption by all animals, with 3.0 mg/kg being the most effective dose.

The Maudsley strains: The evaluation of a possible artifact

Two experiments were carried out on the 31st and 32nd inbred generations of the Maudsley Reactive (MR) and Nonreactive (MNR) strains of rats to assess the contribution of the normal content of their digestive tract to their scores in the open-field test. It was found that the MR strain defecates a significantly greater weight of feces per 24 h than the MNR strain. The MNR strain, however, excretes a greater number of fecal boluses in the same period. Digestive transit time was then measured in the two strains. No differences emerged on this measure. The results together suggest that the differences in open-field defecation between the strains are the result of differential reactivity, rather than reflecting differences in the amount of fecal material in the rectum.

Consolidation and maze learning: the effects of post-trial injections of a depressant drug (pentobarbital sodium).

Subjects from the Maudsley Reactive and Non-Reactive strains were injected with either pentobarbital sodium or distilled water immediately after a daily trial on problem 4 of the Hebb Williams maze. The experimental group made more errors and took more time than their control groups, over a ten day period. Animals of the Maudsley Reactive strain were superior to those of the Non-Reactive strain. It was suggested that pentobarbital sodium disrupted learning by decreasing the rate of the consolidation process.