Male Hatano high-avoidance rats show high avoidance and high anxiety-like behaviors as compared with male low-avoidance rats

A review of behavioral methods for the evaluation of cognitive performance in animal models: Current techniques and links to human cognition

INTRODUCTION

Memory is defined as the ability to store, maintain and retrieve information. Learning is the acquisition of information that changes behavior and memory. Stress, dementia, head trauma, amnesia, Alzheimer's, Huntington, Parkinson's, Wernicke-Korsakoff syndrome (WKS) may be mentioned among the diseases in which memory and learning are affected. The task of understanding deficits in memory and learning in humans is daunting due to the complexity of neural and cognitive mechanisms in the nervous system. This job is made more difficult for clinicians and researchers by the fact that many techniques used to research memory are not ethically acceptable or technically feasible for use in humans. Thus, animal models have been necessary alternative for studying normal and disordered learning and memory. This review attempts to bridge these domains to allow biomedical researchers to have a firm grasp of "memory" and "learning" as constructs in humans whereby they may then select the proper animal cognitive test.

RESULTS AND CONCLUSION

Various tests (open field habituation test, Y-maze test, passive avoidance test, step-down inhibitory avoidance test, active avoidance test, 8-arms radial maze test, Morris water maze test, radial arm water maze, novel object recognition test and gait function test) have been designed to evaluate different kinds of memory. Each of these tests has their strengths and limits. Abnormal results obtained using these tasks in non-human animals indicate malfunctions in memory which may be due to several physiological and psychological diseases of nervous system. Further studies by using the discussed tests can be very beneficial for achieving a therapeutic answer to these diseases.

Alterations between high and low-avoidance lines of Hatano rats in learning behaviors, ultrasonic vocalizations, and histological characteristics in hippocampus and amygdala

Growing evidence supports interactions between anxiety and cognitive function. The primary object of this study was to elucidate whether high-avoidance (HAA) and low-avoidance (LAA) strains of Hatano rats are suitable for the analysis of interactions between the formation of long-term memory and emotional reactivity. The learning/memory ability of Hatano rats and their Sprague-Dawley (SD) ancestors was evaluated using contextual fear conditioning, Y-maze, and Barnes maze tests from 8 weeks of age. Ultrasonic vocalizations were recorded and analyzed during contextual fear conditioning. In a separate experiment, rat brains were sampled 90 min after the first context test and subjected to Nissl staining and c-fos immunostaining. The duration of freezing and number of 22 kHz ultrasonic vocalizations were decreased in LAA compared with HAA and SD rats during the first and second context tests of contextual fear conditioning. The HAA rats did not show preferences for quadrants during the Barnes maze probe test, whereas the SD and LAA rats spent significantly more time in the quadrant where the goals had been placed. There was no difference among the strains in short-term spatial memory as shown by the Y-maze test. Decreases were found in the number of c-fos⁺ cells as well as the volume of some hippocampal regions in the HAA rats compared to SD and LAA rats. By contrast, the volume of the basolateral amygdala was bigger in the HAA than the other strains. On the basis of the 22 kHz ultrasonic calls and literature regarding Syracuse rats, the possibility that emotional reactivity influences contextual memory in Hatano strains was discussed. This emotional difference may be derived from structural and/or functional divergence in the hippocampus and amygdala between the strains. The cause of strain-related differences in long-term spatial learning was difficult to elucidate because there are several possible explanations, including differences in memory and/or the interference of hyperactivity during the Barnes maze test.

Maternal traits during lactation period reduce the anxiety-related behavior in male offspring: Results from a fostering study in Hatano rats

The Hatano strains of the Sprague Dawley rats have been selectively bred to create high- (HAA) and low- (LAA) active avoidance variants. We previously reported that HAA rats display more anxiety-related behavior than LAA rats, but whether this strain difference is affected by postnatal environmental factors remains unclear. In this study, we performed in- and cross-fostering between the HAA and LAA strains and investigated the effect of postnatal maternal traits on the emotional responses in each strain of the male offspring. We evaluated the effect of the fostering treatment on the emotional responses of the male offspring using the elevated plus maze test. The male LAA offspring reared by HAA dam showed higher anxiety-related behavior than those reared by LAA dam. Next, we quantified and typed various maternal behavior under the in- and cross-fostering conditions during the lactation period using a snapshot sampling method. This method allowed us to evaluate potential maternal traits that may influence the emotional responses of the offspring observed in our first experiment. We found that HAA dams showed long-term resting without offspring and offspring arrangement compared with LAA dams. These findings suggest that postnatal environmental factors may alter anxiety-related behavior in the male LAA offspring and that less direct contact with their offspring during the lactation period may induce anxiety-related behavior in male offspring.

Prolonged Social Isolation, Started Early in Life, Impairs Cognitive Abilities in Rats Depending on Sex

Background: The chronic stress of social isolation is a valid predictor of cognitive pathology. This study aimed to compare the effects of long-term social isolation on female versus male Wistar rats’ learning and memory. We hypothesized that prolonged social isolation stress, which starts early in life, would affect learning in a sex-dependent manner. Methods: Social isolation started at the edge of early to mid-adolescence and lasted 9 months. The rat’s cognitive abilities were assessed by habituation and reactivity to novelty in the open field (OF) test, spatial memory in the Morris water maze (MWM), and the conditioned passive avoidance (PA) reflex. Basal serum corticosterone levels were assessed using an enzyme-linked immunosorbent assay. Results: Regardless of the housing conditions, females habituated to the OF under low illumination slower than males. Under bright light, the single-housed rats showed hyporeactivity to novelty. In the MWM, all the rats learned to locate the platform; however, on the first training day, the single-housed females’ speed was lower relative to other groups. Four months later, in the post-reminder probe trial, the single-housed rats reached the area around the platform site later, and only males, regardless of housing conditions, preferred the target quadrant. Single-housed rats, irrespective of sex, showed a PA deficit. There was a more pronounced conditioned fear in the single-housed males than in females. In both male and female rats, basal corticosterone levels in rat blood serum after 9 months of social isolation did not differ from that in the group-housed rats of the corresponding sex. Meanwhile, females’ basal corticosterone level was higher than in males, regardless of the housing conditions. The relative weight of the adrenal glands was increased only in single-housed females. Conclusions: Under long-term social isolation, started early in life, single-housed females compared with males showed more pronounced cognitive impairments in the MWM and PA paradigm, findings that specify their greater vulnerability to the stress of prolonged social isolation.

Hatano rats are a suitable metabolic syndrome model for studying feeding behavior, blood pressure levels, and percent body fat

Currently, metabolic syndrome is a worldwide concern. Thus, it is imperative to understand the mechanism of metabolic syndrome by establishing various metabolic syndrome models. In this study, we used Hatano high-avoidance animals (HAA) and low-avoidance animals (LAA), both derived from Sprague–Dawley rats by selective breeding to determine high- or low-avoidance rates in shuttle-box active avoidance tests. HAA and LAA rats have some strain differences related to eating and appetite. Therefore, we determined whether Hatano rats could be used as a metabolic syndrome model. We compared food intake, body weights, blood pressure levels, plasma component levels, and fat contents between HAA and LAA rats. The HAA rats showed more active eating, higher blood pressure, higher percentage fat, and higher triglyceride levels than the LAA rats—these features correspond to some of the risk factors associated with metabolic syndrome. Our study suggests that HAA rats can be considered as a metabolic syndrome model by focusing on their feeding behavior, blood pressure levels, and percent body fat.

Hatano rats selectively bred for high- and low-avoidance learning: an overview

This review compiles the results of a series of studies on Hatano high- and low-avoidance animals (HAA and LAA, respectively) established at the Hatano Research Institute, Food and Drug Safety Center, Japan. The HAA and LAA lines were selected and bred from Sprague Dawley rats for high and low avoidance learning, respectively, in a shuttlebox task since 1985. Although Hatano rats were selected only based on their behavioral traits in the active avoidance task, strain differences between the HAA and LAA lines were also observed in their stress responses and reproductive functions. However, the most noticeable finding of Hatano rats is a matched result in both active and passive avoidance tasks. The HAA and LAA lines are useful for next-generation toxicological studies, because the hereditary characters of behaviors or endocrine functions are well controlled.

Testing Animal Anxiety in Rats: Effects of Open Arm Ledges and Closed Arm Wall Transparency in Elevated Plus Maze Test

The elevated plus maze test is a behavioral test for assessing animal anxiety in rodents. Although this test is widely applied in the field of behavioral science, conflicting outcomes are often provided from different laboratories. To identify reasons for the different outcomes, we previously focused on arm features, which differ between laboratories, most notably the presence/absence of ledges at the sides of open arms and the transparency/opaqueness of closed arm walls. In a previous report, we used a custom designed container to compare rat behavior on different combinations of open and closed arm designs under otherwise identical experimental conditions, and showed that differences in arm features interfere with experimental outcomes. In brief, open arm ledges significantly increased anxiety-like behavior in rats, while transparent arms may also have decreased this behavior. Furthermore, we verified a higher detection sensitivity of the effect of an anxiolytic drug in a combination of no-ledged open arm + opaque walled closed arm compared with a combination of ledged open arm + transparent walled closed arm. In this report, we introduce our protocol for the elevated plus maze test, together with discussion of the key results from the previous report and our experimental experience. We believe this report will provide useful information for researchers who have employed or who plan to use the elevated plus maze in their studies.

Male Hatano low-avoidance rats show more active sexual behavior with lower plasma testosterone than high-avoidance rats

Two inbred strains of Sprague-Dawley rats, known as the Hatano high- and low-avoidance animals (HAA and LAA respectively), have been selectively bred for high versus low rates of avoidance responses in a shuttle-box avoidance task. To investigate differences in the sexual behavior of Hatano rats, male HAA, LAA and SD rats were tested from 12 to 15 weeks of age. LAA rats exhibited more rapid and frequent sexual behavior than HAA or SD rats, and such differences increased with repeated sexual experience. Plasma testosterone levels tended to be lower in LAA rats than in HAA or SD rats, suggesting that active sexual behavior in LAA rats is not related to these levels. Strain differences in mating behavior between HAA and LAA rats may be caused by emotional responses to novelty.

A Window on the Study of Aversive Instrumental Learning: Strains, Performance, Neuroendocrine, and Immunologic Systems

The avoidance response is present in pathological anxiety and interferes with normal daily functions. The aim of this article is to shed light on performance markers of active avoidance (AA) using two different rat strains, Sprague-Dawley (SD) and Wistar. Specifically, good and poor performers were evaluated regarding anxiety traits exhibited in the elevated plus maze (EPM) and corticosterone levels and motor activity in the open field test. In addition, the plasma levels of Interleukin-6 (IL-6), Interleukin-1Beta (IL-1beta), Nerve Growth Factor Beta (NGF-beta), Tumor Necrosis Factor-Alpha (TNF-alpha) and cytokine-induced neutrophil chemoattractant 1 (CINC-1) were compared in the good and poor performers to better understand the role of the immunologic system in aversive learning. Behavioral criteria were employed to identify subpopulations of SD and Wistar rats based on their behavioral scores during a two-way AA test. The animals were tested for anxiety-like behavior in the EPM and motor activity in the open-field test. Plasma corticosterone levels were measured at the end of the avoidance test. Cytokine levels of IL-6, IL-1beta, NGF-beta, TNF-alpha, and CINC-1 were measured in the plasma of the Wistar rats. Sixty-six percent of the Wistar rats and 35% of the SD rats exhibited a poor performance. This feature was associated with a decrease in anxiety-like behavior in the EPM. The poor and good performers exhibited lower levels of corticosterone compared with the control animals, which suggests that training alters corticosterone levels, thereby leading to hypocortisolism, independent of the performance. The CINC-1 levels were increased in the poor performers, which reinforces the role of immunologic system activation in learning deficits. Our study provides a better understanding of the complex interactions that underlie neuroimmune consequences and their implications for performance.

Stress-reactive rats (high-avoidance female rats) have a shorter lifespan than stress-nonreactive rats (low-avoidance female rats)

Although Hatano high-avoidance and low-avoidance rats (HAA and LAA, respectively) have been selectively bred for good versus poor avoidance learning, HAA rats are known to be more reactive to stress than LAA rats. In this study, HAA and LAA female rats were compared during reproductive aging by observing estrous cycles from 8 to 11 months of age. Furthermore, these rats were allowed to live out their natural lifespans, that is, until 24 months of age, in order to compare their survival and to clarify the relationship between reproductive aging and tumor development. At eight months of age, 2 of 35 HAA rats and 20 of 35 LAA rats had abnormal estrous cycles. The median lifespan of the HAA rats (673 days) was shorter than that of the LAA rats (733 days). The incidence of pituitary neoplasia was higher in the HAA rats than in the LAA rats. These results suggest that HAA female rats (i.e., stress-reactive rats) have a shorter lifespan than LAA female rats (i.e., stress-nonreactive rats) and develop pituitary neoplasia, which was one of the causal factors in their accelerated mortality. However, the onset of an age-matched abnormal cycle did not correspond with their lifespan.

Higher detection sensitivity of anxiolytic effects of diazepam by ledge-free open arm with opaque walled closed arm elevated plus maze in male rats

The elevated plus maze (EPM) is an established method for testing animal anxiety. However, EPM apparatuses and their features can differ among laboratories, most notably in the presence/absence of ledges on the open arm and/or the transparency/opaqueness of walls on the closed arm. The combined effects of these variable arm features on EPM behavior are not yet fully understood. In the present study, we prepared four types of EPM apparatus - open arms with (0.5 cm) or without (0 cm) ledges×closed arms with transparent or opaque walls - and compared the maze-exploration behavior of male Sprague-Dawley rats. We found that the presence of open arm ledges significantly increased the incidence of open arm exploration. Furthermore, time spent in the distal segment of the open arm was shortest in the apparatus that had open arms with no ledges and opaque closed arms (No-Ledges/Opaque), and was longest in the apparatus that had open arms with ledges and transparent closed arms (Ledges/Transparent). Additionally, the No-Ledges/Opaque apparatus could detect the effect of 0.5mg/kg diazepam, an anxiolytic drug, whereas the Ledges/Transparent apparatus could not. These results indicate that arm structure (features of both open and closed arms) significantly influences maze-exploratory behavior in rats, and that No-Ledges/Opaque apparatuses have higher detection sensitivity for anxiolytic effects of diazepam than that of Ledges/Transparent apparatuses.