Differential ethanol intake in Tryon maze-bright and Tryon maze-dull rats: implications for the validity of the animal model of selectively bred rats for high ethanol consumption

DNA Instability in Neurons: Lifespan Clock and Driver of Evolution

In the last ten years, the discovery of neuronal DNA postmitotic instability has changed the theoretical landscape in neuroscience and, more broadly, biology. In 2003, A. M. Olovnikov suggested that neuronal DNA is the "initial substrate of aging". Recent experimental data have significantly increased the likelihood of this hypothesis. How does neuronal DNA accumulate damage and in what genome regions? What factors contribute to this process and how are they associated with aging and lifespan? These questions will be discussed in the review. In the course of Metazoan evolution, the instability of neuronal DNA has been accompanied by searching for the pathways to reduce the biological cost of brain activity. Various processes and activities, such as sleep, evolutionary increase in the number of neurons in the vertebrate brain, adult neurogenesis, distribution of neuronal activity, somatic polyploidy, and RNA editing in cephalopods, can be reconsidered in the light of the trade-off between neuronal plasticity and DNA instability in neurons. This topic is of considerable importance for both fundamental neuroscience and translational medicine.

Inbred Strains Should Replace Outbred Stocks in Toxicology, Safety Testing, and Drug Development

Methods of toxicity testing, barely changed for several decades, need to be improved. One way forward would be to use a small battery of inbred strains instead of the single outbred stock currently used in toxicity screening. Inbred strains are more stable, more uniform, more repeatable, and better defined than outbred stocks. Genetic variation would be observed as the difference between strains. Safety could be based on the most susceptible strain. Sometimes it may be possible to identify the genes involved. Mechanisms could be explored using gene expression profiling of susceptible and resistant strains. Two committees of toxicologists have concluded that the use of inbred strains, by controlling interindividual variability, would reduce the number of animals needed in toxicity screening, although both “preferred” outbred stocks. This preference appears to have been based on intuition rather than scientific principles. Data from a previously published study on the response to chloramphenicol in an outbred stock and four inbred strains is used to explain the advantages of the multistrain design. Toxicologists, safety pharmacologists, regulatory authorities, and pharmaceutical companies should take a critical look at the types of animals they use if they want to reduce the attrition rate of new drugs.

Preferences of 14 rat strains for 17 taste compounds

Two-bottle choice tests were used to assess the taste preferences of 8 male and 8 female rats from 3 outbred strains (SD, LE, WI) and 11 inbred strains (BN, BUF, COP, DA, Dahl-S, F344, FHH, LEW, Noble, PVG, SHR). Each rat received a series of 109 48-h tests with a choice between water and a "taste solution". Four to eight concentrations of the following compounds were tested: NaCl, CaCl2, NH4Cl, KCl, MgCl2, saccharin, sucrose, ethanol, HCl, citric acid, quinine hydrochloride (QHCl), caffeine, denatonium, monosodium glutamate (MSG), Polycose, corn oil, and capsaicin. Strain differences (p<0.001) were observed in preferences for at least one concentration of all compounds tested except denatonium (p=0.0015). There were also strain differences in the following ancillary measures: fungiform papillae number, water intake, food intake, and body weight. There were sex differences in food intake and body weight but no concerted sex differences in any of the other measures, including preferences for any taste solution. This comprehensive source of information can be used to guide the choice of appropriate rat strains and taste solution concentrations for future genetic studies.

Modulation of high alcohol drinking in the inbred Fawn-Hooded (FH/Wjd) rat strain: implications for treatment

The Fawn-Hooded rat (FH/Wjd) is an inbred alcohol-preferring rat strain, unlike most of the other strains that were selectively bred for high alcohol intake and preference. It was chosen for study some 16 years ago because of a reported mutation that disrupted platelet serotonin function. Although the FH/Wjd rat has high alcohol intake (>5 g/kg/day) and preference (>65%), interbreeding with an alcohol-non-preferring inbred strain suggested that these measures are unrelated to the serotonin abnormality. Similarly, the exaggerated immobility of the FH/Wjd rats in the forced swim test did not correlate with the high alcohol intake. Many compounds have been tested in the FH/Wjd rats after both acute and chronic treatment and a substantial number of them have proved effective. However, as the case with opiate antagonists, tolerance to the effects of the drug can develop. An up-regulation of opioid receptors accompanied the chronic treatment and this mechanism may account for the development of tolerance. Tolerance to opiate antagonists has also been demonstrated in two of the selectively bred alcohol-preferring rat lines, but it is unknown whether this process may contribute to the relapses seen in individuals being treated with naltrexone. Other drugs that reliably decrease alcohol intake in the FH/Wjd rats include the 5-hydroxytryptamine-2A receptor antagonist, amperozide, the mGlu5 receptor antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) and herbal derivatives such as ibogaine, St. John's wort and kudzu extract. Thus, studies in the FH/Wjd rat have led to the discovery of a wide variety of targets for the development of novel agents to treat alcoholism. The fact that several of these drugs were shown to reduce alcohol intake in some of the selectively bred alcohol-preferring rat lines and/or alcohol-preferring vervet monkeys increases our confidence that they are good candidates for further development.

A relation between maze performance and increased ethanol intake in Long-Evans rats

In addition to the neurochemical and genetic basis of high ethanol consumption, there has been renewed interest in studying the role of behavioral variables and their relation to ethanol consumption. The present study was designed to assess whether a relation exists between a behavioral variable such as maze learning ability and ethanol consumption. Sixty, male, Long-Evans rats, exposed to food and water ad libitum, were given a daily trial in a complex, 16-arm T-maze for 19 consecutive days. The number of errors and time to complete the maze were monitored. Individual maze variable scores were transformed and then combined to allot each animal with an index of overall maze performance, with a smaller maze index score denoting good performance. After completion of maze testing, animals were given alternate-day, free-choice presentations of water and ascending doses of ethanol solutions (2%-10%), followed by a 10-day maintenance period with 10% ethanol. Animals were subsequently separated into two groups of high and low drinkers to examine any relation between differential ethanol intake and maze performance. A significant negative correlation between maze index and ethanol intake for the high drinkers group indicated that a smaller maze index was related to increased ethanol intake. No significant correlation was obtained for the low drinkers group. These results seem to indicate that individual variation in learning ability seems to be related to increased ethanol intake. Thus, innate learning processes may be a relevant trait when one attempts to understand the behaviors related to ethanol intake and preference.

Equal sensitivity to cocaine reward in addiction-prone and addiction-resistant rat genotypes

Rat genotypes tentatively identified as addiction-prone or addiction-resistant on the basis of alcohol preference and locomotor responsiveness to novelty--Lewis versus Fischer strains and Nijmegen high versus low responder lines--differed in time to develop intravenous cocaine self-administration habits, but did not differ in sensitivity to the ability of cocaine reward to summate with lateral hypothalamic brain stimulation reward. Moreover, rats from the Nijmegen low-responder line that initiated self-administration came to do so compulsively and to the same degree as did the Nijmegen high-responder rats. Thus the differences between both sets of genotypes appeared to reflect differences in reactions to the testing situation more than differences in reaction to the reinforcing drug per se.

Possible confounding influence of strain, age and gender on cognitive performance in rats

There are substantial differences in the performance of various rat strains in tasks of learning, memory and attention. Strain, age and sex differences are not consistent over procedures: poor performance in one paradigm does not predict poor performance in a different paradigm. Some strain differences are not readily apparent until a direct comparison is made between one or more strains. Moreover, large differences in nominally the same strain but obtained from different suppliers have been observed in behavioural, pharmacological and physiological parameters and can have important consequences for interpretation of drug effects. Longevity, and the effects of ageing can differ dramatically from one strain to another; drug effects can alter radically with increasing age and show strain (and individual) differences in their action. Sex can further complicate interpretation of results. Thus, non-cognitive factors may exert a major effect on results in cognitive testing, and strain-dependent effects may account for many conflicting results in the literature concerning mnemonic performance. Strain differences in particular must be identified and used to help identify fundamental effects on memory, rather than continue to be ignored and allowed to obscure interpretation of drug effects on cognitive processes.

Differential open field reactivity in HAS and LAS rats

To identify potential differences in emotional reactivity in high (HAS) and low (LAS) alcohol-sensitive rats in open field tests, 20 ethanol naive, 19th generation HAS and 20 LAS rats from the University of Colorado's Alcohol Research Center each received three consecutive daily 20-min exposures to a 1-sq m open field. The results of repeated-measures ANOVA and Keuls tests, performed on each of five concurrently recorded behaviors, indicated that, compared to HAS rats, LAS animals exhibited significantly greater latencies to begin ambulation, elevated ambulation, and rearing scores that failed to habituate over 3 days, and an increasing intersession bolus count. In addition, significant positive correlations occurred between days 2 + 3 (but not day 1) ambulation and bolus counts in LAS but not HAS rats, and between day 1 ambulation and (i) rearings and (ii) center square entries in HAS but not LAS rats. Together with other cited data, these results provide support for a hypothesis of relatively greater emotional reactivity in LAS rats and illustrate the need for multiple measures and sessions in evaluating open field behavior.