Active- and passive-avoidance learning in inbred mice: Transfer of training effects

Role of preexisting inhibitory control deficits vs. drug use history in mediating insensitivity to aversive consequences in a rat model of polysubstance use

RATIONALE

The nature and predictors of insensitivity to aversive consequences of heroin + cocaine polysubstance use are not well characterized.

OBJECTIVES

Translational methods incorporating a tightly controlled animal model of drug self-administration and measures of inhibitory control and avoidance behavior might be helpful for clarifying this issue.

METHODS

The key approach for distinguishing potential contributions of pre-existing inhibitory control deficits vs. drug use history in meditating insensitivity to aversive consequences was comparison of two rat strains: Wistar (WIS/Crl), an outbred strain, and the spontaneously hypertensive rat (SHR/NCrl), an inbred strain shown previously to exhibit heightened cocaine and heroin self-administration and poor inhibitory control relative to WIS/Crl.

RESULTS

In separate tasks, SHR/NCrl displayed greater impulsive action and compulsive-like behavior than WIS/Crl prior to drug exposure. Under two different schedules of drug delivery, SHR/NCrl self-administered more cocaine than WIS/Crl, but self-administered a similar amount of heroin + cocaine as WIS/Crl. When half the session cycles were punished by random foot shock, SHR/NCrl initially were less sensitive to punishment than WIS/Crl when self-administering cocaine, but were similarly insensitive to punishment when self-administering heroin + cocaine. Based on correlation analyses, only trait impulsivity predicted avoidance capacity in rats self-administering cocaine and receiving yoked-saline. In contrast, only amount of drug use predicted avoidance capacity in rats self-administering heroin + cocaine. Additionally, baseline drug seeking and taking predicted punishment insensitivity in rats self-administering cocaine or heroin + cocaine.

CONCLUSIONS

Based on the findings revealed in this animal model, human laboratory research concerning the nature and predictors of insensitivity to aversive consequences in heroin and cocaine polysubstance vs. monosubstance users is warranted.

Lactobacillus plantarum GKM3 Promotes Longevity, Memory Retention, and Reduces Brain Oxidation Stress in SAMP8 Mice

(1) Background: An age-related cognitive decline is commonly affecting the life of elderly with symptoms involved in progressive impairments to memory and learning. It has been proposed that probiotics could modulate age-related neurological disorders via the gut-brain axis. (2) Methods: To investigate the anti-aging effect of probiotic Lactobacillus plantarum GKM3, both survival tests and cognitive experiments were conducted in the SAMP8 mice model. The six-month-old SAMP8 (n = 20 in each gender) were fed with probiotic GKM3 at a dosage of 5.1 × 109 and 1.0 × 109 cfu/ kg B.W./day until their natural death. Then, the life span was investigated. Three-month-old SAMP8 (n = 10 in each gender) were administered GKM3 for 14 weeks. Then, the behavior tests and oxidation parameters were recorded. (3) Results: GKM3 groups showed significantly increased latency in the passive avoidance test and time of successful avoidance in the active avoidance test. The TBARS and 8-OHdG from mice brains also showed a significant reduction in the groups treated with GKM3. In addition, lower accumulation of the amyloid-β protein was found in SAMP8 mice brains with the supplement of GKM3. (4) Conclusions: These results indicated that L. plantarum GKM3 delayed the process of aging, alleviated age-related cognitive impairment, and reduced oxidative stress.

Contextual and cued fear conditioning in C57BL/6J and DBA/2J mice: context discrimination and the effects of retention interval

Context discrimination and time course studies of contextual fear conditioning revealed strain differences between C57BL/6J (B6) and DBA/2J (D2) mice. Both strains discriminated contexts, but D2 mice exhibited less freezing in a shock-paired context. The strains did not differ immediately, or at 1 and 3 hr after contextual fear conditioning training. D2 mice showed less freezing at 15 min, 30 min, and 24 hr after training. B6 mice exhibited exaggerated generalized freezing and poor discrimination between the context and altered context 7-30 days after training. The acoustic startle response in B6 mice was also enhanced at 14 days after training. D2 mice did not show this pattern of generalized freezing. B6, but not D2, mice retained contextual memories for at least 60 days.

Effects of situational variables on performance of inbred mice in active- and passive-avoidance situations

A group of experiments were conducted to assess the interaction between environmental factors and specific genetic loci upon the performance of mice in avoidance learning situations. The performance of all mice was better in passive-avoidance than in active-avoidance situations. The performance of C57BL/6J mice was generally superior to that of DBA/2J mice. C57BL/6J mice usually avoided foot-shocks, while DBA/2J mice attempted to escape them. DBA/2J mice performed poorly in the presence of mild foot-shocks, while C57-BL/6J mice performed poorly in the presence of intense foot-shocks. Analysis of the data suggested that the loci involved probably exerted their influence by affecting the subject's response to its environment.

Avoidance learning, behavior genetics, and aging: a critical review and comment on methodology

Animal models of human aging problems are potentially of enormous value to gerontological research. Models of behavioral problems have not often lived up to their promise. This review examines one such model system, avoidance learning in aging rodents. This model system has become increasingly popular among behavioral gerontologists, yet it has not provided the unambiguous answers to experimental questions which investigators expected. Our effort has been to determine why the system has failed, and to provide useful suggestions for future research. At the same time we have tried to provide a comprehensive review of the relevant literature and to assess the strengths and weaknesses of studies which have been conducted in the last two decades.

Genetic analysis of active avoidance performance in mice

Mice of two inbred strains, C57BL/6J and DBA/2J, and the F1 hybrid of a cross between them were trained in an active avoidance jump-up task under distributed practice conditions. Significant differences in the performance of mice of the two strains were observed, with relatively poor performance by DBA/2J mice and relatively good performance by C57BL/6 mice. The performance of F1 hybrid mice did not differ significantly from DBA/2J mice. Crosses were made to produce segregating generations of mice. Their performance supported a single-locus model of inheritance for active avoidance jump-up behavior. Under these experimental conditions the dominant allelle (Aapd) was associated with poor performance while homozygosity for the recessive allele (Aapb) was associated with superior performance.