Effect of complete maternal and littermate deprivation on morphine-induced Fos-immunoreactivity in the adult male rat brain.

Previous research has demonstrated that rats reared in isolation from their dam and littermates show altered behavioral responsiveness to both natural and drug-mediated rewards. This study examined the effects of complete maternal deprivation through the use of artificial rearing on neural activation after acute morphine exposure in adulthood. Male rats were either artificially reared (AR) or maternally reared (MR) from postnatal day 5 to 21. In adulthood (4 mo old), rats received a single injection of morphine sulfate (10 mg/kg) or equivolume saline 2 h before perfusion and brain extraction. Neural activation was quantified using Fos immunohistochemistry. Analyses of several brain regions revealed a consistent pattern of differences between AR and MR rats. Specifically, relative to MR rats, AR rats showed significantly greater morphine-induced Fos-immunoreactivity in brain regions associated with the mesocorticolimbic "reward" pathway. These results support the hypothesis that functional activity in reward neurocircuitry can be altered by early life experience.

Advantages of mixed effects models over traditional ANOVA models in developmental studies: a worked example in a mouse model of fetal alcohol syndrome.

Developmental studies in animals often violate the assumption of statistical independence of observations due to the hierarchical nature of the data (i.e., pups cluster by litter, correlation of individual observations over time). Mixed effect modeling (MEM) provides a robust analytical approach for addressing problems associated with hierarchical data. This article compares the application of MEM to traditional ANOVA models within the context of a developmental study of prenatal ethanol exposure in mice. The results of the MEM analyses supported the ANOVA results in showing that a large proportion of the variability in both behavioral score and brain weight could be explained by ethanol. The MEM also identified that there were significant interactions between ethanol and litter size in relation to behavioral scores and brain weight. In addition, the longitudinal modeling approach using linear MEM allowed us to model for flexible weight gain over time, as well as to provide precise estimates of these effects, which would be difficult in repeated measures ANOVA.

Postnatal dietary supplementation with either gangliosides or choline: effects on spatial short-term memory in artificially-reared rats.

This study addressed the hypothesis that dietary supplementation with either gangliosides or choline during the brain growth spurt would enhance short-term spatial memory. Male Long-Evans rats were reared artificially from postnatal days (PD) 5-18 and were fed diets containing either (i) choline chloride 1250 mg/l (CHL), (ii) choline chloride 250 mg/l and GD3 24 mg/l (GNG) or (iii) choline chloride 250 mg/l (STD). A fourth group (SCK) was reared normally. Rats were weaned onto AIN 93G diet and on PD 35 were trained on a cued delayed- matching-to-place version of the Morris water maze. All groups learned to swim to the beacon that indicated the platform position on the first trial; similarly, on the second un-cued trial, the distance swam to reach the platform decreased to the same extent in all groups over the five days of training. The groups also responded in the same way to an increase in delay between the first and second trial from 1 min to 1 h, showing an increase in the distance swam, accompanied by a decrease in the number of direct swims to the platform. Thus, all rats were equally proficient at using spatial short-term memory, regardless of the choline or ganglioside content of the preweaning diet.

Nutrition and the development of cognitive functions: interpretation of behavioral studies in animals and human infants.

A rapidly accumulating body of evidence on the neural basis of cognition suggests that cognition is not a unitary function but rather depends on the functions of multiple and dissociable neural systems. The nonlinear interactions in the differing trajectories of these systems during development result in changing patterns of cognitive functions over time; they may also lead to paradoxical outcomes, for which enhancement of one function through dietary intervention may be at the expense of another. This emerging understanding has important implications for the design and interpretation of studies on the cognitive effects of specific nutrients during development. It is important that researchers move away from global tests of development and strive rather to ensure that their choice of behavioral task is based on specific hypotheses of the systems expected to be altered by a dietary manipulation and on an understanding of which behavioral tests are valid, sensitive, and reliable indicators of this disruption. Furthermore, to understand whether accelerated or delayed development related to a particular cognitive function is beneficial or problematic, it is important to study the entire behavioral profile over different time points, rather than relying on one outcome measured at one time point. It is also necessary to control for sensory or motivational differences that will affect performance on the behavioral tasks. Implementation of these methodologic recommendations may contribute to a deeper understanding of the mechanisms involved in the nutrition-associated changes in cognitive functions and thereby aid in the development of an appropriate population-based dietary policy.

Artificial rearing alters the response of rats to natural and drug-mediated rewards.

Artificial rearing (AR) of infant rats permits precise control over key features of the early environment without maternal influence. The present study examined the behavioral response of AR rats towards natural and drug-mediated rewards, as well as their exploratory and affective behaviors. Adolescent AR rats showed increased preference for sucrose consumption relative to chow and demonstrated greater activity in the open field and in the elevated plus-maze compared to maternally reared (MR) rats. With respect to measures of emotionality, AR rats showed enhanced avoidance of the open arms of the plus-maze, indicating increased anxiety, but they did not differ from MR rats in exploring the center of the open field. Adult AR rats displayed a stronger conditioned response to morphine in a place preference test. These findings support the potential of the AR model to contribute to understanding the role of early experience in the development of behavioral motivation.

Spontaneously hypertensive, Wistar-Kyoto and Sprague-Dawley rats differ in performance on a win-shift task in the water radial arm maze.

The spontaneously hypertensive rat (SHR) is a commonly used animal model of attention deficit hyperactivity disorder. Previous literature is inconclusive with respect to the exact nature of memory impairments in this strain. The objective of this study was to assess spatial memory as measured by performance of male SHR, Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats on a win-shift version of the water radial arm maze. On this task, all strains made more errors on Trial 4 when the mnemonic demand was highest, and showed a similar response when the delay was increased from 60s to 2h on Week 3. Both SHR and WKY rats made more reference memory errors than SD, however, SHR showed minimal improvement over weeks. The increase in errors may be due to a greater inclination of SHR and WKY to use a chaining strategy of entering consecutive arms than SD. Furthermore, the number of incomplete arm entries into reference memory arms decreased over weeks in WKY and SD, but increased in SHR, suggesting increased impulsivity of SHR at the later stages of testing. Although based on number of errors, the data indicate that SHR may have memory deficits, the data relating to arm entries suggest that the minimal improvement in SHR over weeks may have been due to greater impulsivity in the later weeks, rather than defective memory. Thus, these findings are consistent with SHR having impairments with selection of appropriate behavioural responses in a goal-directed task.

Short-term memory impairment and reduced hippocampal c-Fos expression in an animal model of fetal alcohol syndrome.

BACKGROUND: Previous work in our laboratory has shown that exposure to ethanol during the brain growth spurt impairs spatial short-term memory in rats on the delayed matching-to-place (DMP) version of the Morris water maze. The objectives of this study were to ascertain whether this impairment could: 1) be prevented by increasing the length of encoding time and 2) be related to hippocampal c-Fos expression. METHODS: Using an artificial rearing model, male Long-Evans rats were fed 6.5 g/Kg/day of ethanol from postnatal days 6-9, with controls fed an isocaloric amount of maltose dextrin. As adults, rats in each treatment condition were trained and subsequently tested on either the DMP version of the Morris water maze, or on a random platform version (RAN) that incorporated the same performance requirements, but disallowed spatial learning. Brains were processed for c-Fos expression. RESULTS: Ethanol-exposed rats showed longer search trials during training and took longer to learn the DMP task. When the delay between search and recall trials was increased from 60 sec to 120 min, the performance of ethanol-exposed rats was impaired compared with that of controls after a 10 sec, but not after a 45 sec, encoding time. Brain c-Fos expression was increased in hippocampus, prefrontal cortex and visual cortex in rats trained on the DMP compared to the RAN task. Furthermore, in the DMP-trained rats, hippocampal c-Fos expression was lower in ethanol-exposed rats. CONCLUSIONS: These results suggest that the short-term memory impairment of ethanol-exposed rats 1) can be improved slightly by an increase in encoding time and 2) is related to a decrease in c-Fos expression in the hippocampus.

Spontaneously hypertensive and Wistar Kyoto rats differ in delayed matching-to-place performance and response to dietary long-chain polyunsaturated fatty acids.

Spontaneously hypertensive rats (SHR) were used as an animal model of attention deficit hyperactivity disorder (ADHD). This study investigated whether, in comparison with its progenitor strain, Wistar-Kyoto rats (WKY), SHR would show deficits in spatial short-term memory in the delayed-matching-to-place (DMP) version of the Morris water maze and be more distracted by exposure to a novel stimulus during recall trials. It also addressed whether dietary supplementation with long-chain polyunsaturated fatty acids (LCPUFA) during development would increase brain docosahexaenoic acid (DHA) and improve SHR behavioral performance. Beginning at weaning (21 days), male SHR and WKY were fed either a control or LCPUFA supplemented diet [0.5% arachidonic acid (AA) and 0.9% DHA], and behavioral testing began at 8 weeks. The first three tasks comprised a series of problems, each consisting of an initial search trial and subsequent recall trials. The intertrial interval (ITI) between the search and recall trial was either 60 s or 60 min. Surprisingly, in contrast to SHR, WKY did not appear to use a spatial short-term memory strategy to solve the problem. Notwithstanding, the performance of both strains was affected by the delay, such that they showed longer path lengths at the long compared with the short ITI. There was no effect of dietary supplementation on DMP performance. SHR fed the control diet were less responsive to a novel stimulus introduced on the first recall trial than WKY, and this tended to increase with supplementation. Analysis of brain fatty acid composition indicated that supplementation did increase DHA in the phosphatidylethanolamine fraction in WKY; however, in SHR, there was either no change (phosphatidylethanolamine) or paradoxical decreases (phosphatidylcholine and phosphatidyserine/phosphatidylinositol). Further research is needed to determine whether SHR are an appropriate model for studying a possible relationship between dietary LCPUFA and the behavioral symptoms of ADHD.

Effects of high-gamma-linolenic acid canola oil compared with borage oil on reproduction, growth, and brain and behavioral development in mice.

Previous research in rats and mice has suggested that gamma-linolenic acid (GLA) derived from borage oil (BO: 23% GLA) may be an appropriate source for increasing levels of long-chain n-6 FA in the developing brain. Recently, transgenic technology has made available a highly enriched GLA seed oil from the canola plant (HGCO: 36% GLA). The first objective of this study was to compare the effects of diets containing equal levels of GLA (23%) from either BO or HGCO on reproduction, pup development, and pup brain FA composition in mice. The second objective was to compare the effects of the HGCO diluted to 23% GLA (GLA-23) with those of undiluted HGCO containing 36% GLA (GLA-36). The diets were fed to the dams prior to conception and throughout pregnancy and lactation, as well as to the pups after weaning. The behavioral development of the pups was measured 12 d after birth, and anxiety in the adult male offspring was assessed using the plus maze. The findings show that despite equivalent levels of GLA, GLA-23 differed from BO in that it reduced pup body weight and was associated with a slight increase in neonatal pup attrition. However, there were no significant effects on pup behavioral development or on performance in the plus maze. An increase in dietary GLA resulted in an increase in brain 20:4n-6 and 22:4n-6, with a corresponding decrease in 22:6n-3. Again, despite their similar levels of GLA, these effects tended to be larger in GLA-23 than in BO. In comparison with GLA-23, GLA-36 had larger effects on growth and brain FA composition but no differences with respect to effects on reproduction and behavioral development. These findings suggest that the HGCO can be used as an alternative source of GLA.

Testing the spatial- versus object-learning distinction: water-maze performance of male rats exposed to ethanol during the brain growth spurt.

This study investigated the effects of exposure to ethanol during the brain growth spurt on a visual-discrimination (VD) and a place-learning task (PL) using intra-maze cues in the water maze. Artificially reared male Long-Evans rats were exposed to ethanol (ET) in a binge pattern from postnatal days 6-9 (6.5 g kg(-1) x day(-1); BAC approximately 330 mg/dl) or an isocaloric maltose-dextrin solution (gastrostomy control). A third suckled control group was reared by lactating dams. In experiment 1, rats were trained to discriminate horizontal- (H) versus vertical-striped (V) cues, with the positive cue providing escape from water. Groups did not differ with V+, but ET rats made more errors with H+. In experiment 2, the ET group was impaired in learning the spatial location of a submerged platform relative to intra-maze cues. In both tasks, acquisition deficits among ET rats were characterized by impairment emerging at trial 2, with intact reference memory on trial 1, and the ET group reached a comparable level of performance to controls by the end of training. In summary, because impairment was related to task characteristics, a clear distinction between impaired spatial- versus cue-based learning was not supported. However, these findings do support an effect of exposure to ethanol during the brain growth spurt on recent event, but not reference, memory.

Dietary essential fatty acids and brain function: a developmental perspective on mechanisms.

Brain development is a complex interactive process in which early disruptive events can have long-lasting effects on later functional adaptation. It is a process that is dependent on the timely orchestration of external and internal inputs through sophisticated intra- and intercellular signalling pathways. Long-chain polyunsaturated fatty acids (LCPUFA), specifically arachidonic acid and docosahexaenoic acid (DHA), accrue rapidly in the grey matter of the brain during development, and brain fatty acid (FA) composition reflects dietary availability. Membrane lipid components can influence signal transduction cascades in various ways, which in the case of LCPUFA include the important regulatory functions mediated by the eicosanoids, and extend to long-term regulation through effects on gene transcription. Our work indicates that FA imbalance as well as specific FA deficiencies can affect development adversely, including the ability to respond to environmental stimulation. For example, although the impaired water-maze performance of mice fed a saturated-fat diet improved in response to early environmental enrichment, the brains of these animals showed less complex patterns of dendritic branching. Dietary n-3 FA deficiency influences specific neurotransmitter systems, particularly the dopamine systems of the frontal cortex. We showed that dietary deficiency of n-3 FA impaired the performance of rats on delayed matching-to-place in the water maze, a task of the type associated with prefrontal dopamine function. We did not, however, find an association over a wider range of brain DHA levels and performance on this task. Some, but not all, studies of human infants suggest that dietary DHA may play a role in cognitive development as well as in some neurodevelopmental disorders; this possibility has important implications for population health.