Developmental social isolation affects adult behavior,social interaction,and dopamine metabolite levels in zebrafish

The zebrafish is a social vertebrate and an excellent translational model for a variety of human disorders. Abnormal social behavior is a hallmark of several human brain disorders. Social behavioral problems can arise as a result of adverse early social environment. Little is known about the effects of early social isolation in adult zebrafish. We compared zebrafish that were isolated for either short (7 days) or long duration (180 days) to socially housed zebrafish, testing their behavior across ontogenesis (ages 10, 30, 60, 90, 120, 180 days), and shoal cohesion and whole‐brain monoamines and their metabolites in adulthood. Long social isolation increased locomotion and decreased shoal cohesion and anxiety in the open‐field in adult. Additionally, both short and long social isolation reduced dopamine metabolite levels in response to social stimuli. Thus, early social isolation has lasting effects in zebrafish, and may be employed to generate zebrafish models of human neuropsychiatric conditions.     

Working memory training decreases hippocampal neurogenesis

The relationship between adult hippocampal neurogenesis and cognition appears more complex than suggested by early reports. We aimed to determine if the duration and task demands of spatial memory training differentially affect hippocampal neurogenesis. Adult male rats were trained in the Morris water maze in a reference memory task for 4 days, or alternatively working memory for either 4 or 14 days. Four days of maze training did not impact neurogenesis regardless of whether reference or working memory paradigms were used. Interestingly, 2 weeks of working memory training using a hidden platform resulted in fewer newborn hippocampal neurons compared with controls that received either cue training or no maze exposure. Stress is a well-established negative regulator of hippocampal neurogenesis. We found that maze training in general, and a working memory task in particular, increased levels of circulating corticosterone after 4 days of training. Our study indicates that working memory training over a prolonged period of time reduces neurogenesis, and this reduction may partially be mediated by increased stress.     

Behavioral effects of intracerebroventricular microinfusion of agmatine in adult rats

The present study investigated the behavioral effects of intracerebroventricular microinfusion of agmatine. Rats with low dose (10 microg), but not high dose (100 microg), of agmatine spent significantly less time in the enclosed arm and more time in the open arm in the elevated plus maze. In the water maze task, the high dose group displayed a transient impairment in searching for a hidden platform, whereas the low dose group had reduced latency in the first probe test. In the object recognition task, all groups could detect the novel object, but the low dose group spent significantly more time exploring displaced objects. Furthermore, the low dose group made significantly fewer errors in the working, but not the reference, memory version of the radial arm maze task. These results suggest that the behavioral effects of agmatine are task- and dose-dependent, and agmatine may be an anxiolytic and memory modulator.     

Prefrontal serotonin depletion impairs egocentric, but not allocentric working memory in rats

Working memory is a cognitive ability chiefly organized by the prefrontal cortex. Working memory tests may be resolved based on allocentric or egocentric spatial strategies. Serotonergic neurotransmission is closely involved in working memory, but its role in spatial strategies for working memory performance is unknown. To address this issue, prefrontal serotonin depletion was induced to adult male rats, and three days after the behavioral expression of both allocentric and egocentric strategies were evaluated in the "Y" maze and in a crossed-arm maze, respectively. Serotonin depletion caused no effects on allocentric-related behavioral performance, but lesioned rats performed deficiently when the egocentric working memory was evaluated. These results suggest that serotonin may be more closely related with the organization of working memory that uses own movement-guided responses than with that involving the use of external visuospatial signals. Further neurochemical studies are needed to elucidate possible interactions between serotonergic activity and other neurotransmitter systems in the organization of working memory-related allocentric and egocentric strategies.     

Double dissociation of function within the hippocampus: spatial memory and hyponeophagia

Complete and dorsal hippocampal lesions impaired spatial performance on 2 working memory tasks: rewarded alternation on the T maze and matching to position in the water maze. In contrast, ventral hippocampal lesions had no effect on these tasks, even when task difficulty was increased by the introduction of delays. Ventral lesions did resemble complete lesions in reducing anxiety in 3 commonly used tests of anxiety (social interaction, plus-maze, and hyponeophagia). Dorsal lesions also appeared to be anxiolytic in the social interaction and plus-maze tests, but they did not affect hyponeophagia. Complete- and dorsal-lesioned rats displayed hyperactivity, whereas ventral-lesioned rats did not. These results show a double dissociation between dorsal and ventral hippocampal lesions (hyponeophagia vs. spatial memory), suggesting differentiation of function along the septotemporal axis of this structure.     

Effects of P2, a peptide derived from a homophilic binding site in the neural cell adhesion molecule on learning and memory in rats

The neural cell adhesion molecule (NCAM) plays a pivotal role in neural development, regeneration, synaptic plasticity, and memory processes. P2 is a 12-amino-acid peptide derived from the second immunoglobulin-like (Ig) module of NCAM mediating cis-homophilic interactions between NCAM molecules present on the same cell. P2 is a potent NCAM agonist, capable of promoting neuronal differentiation and survival in vitro. The aim of this study was to assess the effect of P2 on learning and memory. Rats treated with P2 intracerebroventricularly (1 h prior to test) performed significantly better than controls in the reinforced T-maze, a test of spatial working memory. Further, rats treated with P2 exhibited decreased anxiety-like behavior while learning the T-maze task. In the social recognition test, both intracerebroventricular (1 h prior to test) and systemic (1 and 24 h prior to test) P2 treatment enhanced short-term social memory and counteracted (administration 24 h prior test) scopolamine-induced social memory impairment. In contrast, P2 (1 h prior to test) did not significantly improve long-term (24 h) retention of social memory, nor did it have any significant effects on long-term memory evaluated by the Morris water maze (administration between 2 days before training and 5.5 h posttraining). In the open field test, P2 (1 h prior to test) decreased general locomotion and rearing, but did not influence any other anxiety-related behaviors, indicating only a minimal influence on baseline anxiety levels. Taken together, these data indicate that in vivo P2 enhances short-term memory and protects against the amnestic effects of scopolamine, while modulating emotional behavior in a learning or novelty-related task.     

T‐maze learning in weanling lambs

A major advantage of sheep models in experimental studies of neurodevelopmental disorders (e.g., with prenatal neurotoxicant exposure) is that the equivalent of all three trimesters of human brain development occurs in sheep entirely in utero. However, studies of learning and memory in sheep are limited. The goal of this study was to extend the analysis of spatial learning and memory in adolescent sheep using several traditional T‐maze tasks. Both 9‐ and 14‐week‐old lambs acquired a delayed nonmatching‐to‐place task, but the older lambs learned the task significantly faster. In contrast, acquisition of a matching‐to‐place task was significantly more difficult. Lambs, like rodents, appear to have a predisposition toward learning “win‐shift” spatial problems in a T‐maze under appetitive motivation. Lambs also rapidly acquired a position habit and showed typical reversal learning curves. These findings support the use of T‐maze tasks to assess behavioral outcomes in various sheep models. © 2011 Wiley Periodicals,Inc. Dev Psychobiol 54: 785–797, 2012     

Reward‐related distracters and working memory filtering

Reward‐related stimuli capture attention, even when they are task irrelevant. A consequence of attentional prioritization of reward‐related stimuli is that they may also have preferential access to working memory like other forms of emotional information. However, whether reward‐related distracters leak into working memory remains unknown. Here, using a well‐validated change detection task of visual working memory capacity and filtering, we conducted two studies to directly assess the impact of reward‐related distracters on working memory. In both studies, the distracters consisted of colored bars or circles that were previously associated with monetary reward. In Experiment 1, results indicated that previously rewarded distracters did not impact behavioral measures of working memory filtering efficiency compared to neutral distracters. In Experiment 2, using ERPs, we measured the contralateral delay activity (CDA), a psychophysiological index of the number of items retained in working memory, to further assess filtering efficiency. We observed that the CDA for high reward distracters was similar to low reward and neutral distracters. However, in early trials, behavioral measures revealed that previously rewarded stimuli negatively impacted working memory capacity, an effect not observed with neutral distracters. This effect, though, was not found for the CDA in early trials. In summary, our findings across two studies suggest that attentional capture by task‐irrelevant reward may have minimal impact on visual working memory—findings that have important implications for delineating the boundaries of reward‐cognition interactions.     

The performance of WKY rats on three tests of emotional behavior.

The behavior of Wistar, Fischer-344, and WKY male rats was observed on three tests of emotional behavior. These included the defensive-withdrawal test, the elevated plus maze, and the conditioned defensive-burying test. Rats were subsequently exposed to the water-restraint ulcerogenic procedure. Fischer-344 rats were more active in the defensive-withdrawal tests, but other behavioral measures in this test did not discriminate between the three strains. Scores reflecting anxiety in the elevated plus maze were lowest for Fischer-344 rats and highest for WKY rats, but the anxiety scores of WKY rats did not differ significantly from Wistar rats. The behavior of WKY rats was significantly different from the other two strains in the conditioned defensive burying test. While the degree of anxiety is measured by burying behavior, elicited by the novelty of prod shock, immobility was the prevalent response of WKY rats. WKY rats also revealed significantly higher ulcer severity scores when exposed to water-restraint stress after each behavioral test procedure. We propose that WKY rats are hyperresponsive to stress and that novelty stress elicits depression-like behavior, which is the prevalent behavioral stress response in WKY rats.     

Opposite behaviours in the forced swimming test are linked to differences in spatial working memory performances in the rat

Despite consistent evidence of an association between depression and impaired memory performance, only a few studies have investigated memory processes in animal models of depression. The aim of the present study was to determine if rats selected for marked differences in their immobility response in the forced swimming test (FST, i.e. high-immobility, [HI] and low-immobility [LI] rats) exhibit differences in spatial and non-spatial memory performances. In a classic radial maze elimination task, we observed that HI rats made significantly more errors than LI rats, and their first error appeared significantly earlier. In a delayed spatial win-shift procedure where rats have to hold spatially relevant information in working memory across a 30 min delay, HI rats tended initially to perform more poorly than LI rats. HI rats made more across-phase errors, the occurrence of the first error was earlier and by the end of the experiment the differences between the two groups disappeared. Thus, HI rats present more difficulties to learn the rules in a spatial task and show weaker performances in spatial working memory in comparison to LI rats. On the other hand, performances in the two groups of animals were similar in a non-spatial task, the object recognition task. Complementary behavioral data indicate that the differences observed between the two groups are not attributable to opposite locomotor activities or to different levels of anxiety. Overall we can conclude that opposite swimming behavior in the FST could parallel some differences in cognitive performances, more specifically linked to spatial working memory.     

The role of alpha7 and alpha4beta2 nicotinic receptors in the nicotine-induced anxiolytic effect in zebrafish

Zebrafish (Danio rerio) have been widely used to study the molecular mechanisms of development including neurodevelopment. More recently, they have begun to be used to study neuropharmacology and neurotoxicology. Critical for this line of research are methods to study behavioral function in zebrafish. Previous studies have compared zebrafish with mammalian models to determine similarities and differences in locomotor behavior, learning and memory. Relatively little research has been conducted on stress response and anxiety behavior as well as the pharmacologic response in zebrafish. We have developed a test for zebrafish to assess stress response and anxiety: the novel tank diving test. In this short test normally zebrafish dive to the bottom of a novel tank and then gradually over the 5-min test begin exploring higher levels of the tank. Nicotine, which has anxiolytic effects in rodents and humans was found to diminish this novel tank diving response in zebrafish. The current study examined the nicotinic receptor subtype selectivity involved in the actions of nicotine. Two nicotinic receptor subtype selective antagonists were used: MLA (an α7 antagonist) and DHβE (an α4β2 antagonist). We replicated our previous finding of the anxiolytic effect of nicotine with significantly less bottom dwelling by the fish after nicotine treatment. This nicotine-induced anxiolytic effect was reversed by both MLA and DHβE, indicating that both nicotinic α7 and α4β2 receptors are involved in the nicotinic effect on anxiety in zebrafish.     

Repeated MDMA ("Ecstasy") exposure in adolescent male rats alters temperature regulation, spontaneous motor activity, attention, and serotonin transporter binding

Previous research in our laboratory found that repeated exposure of adolescent rats to 3,4-methylenedioxymethamphetamine (MDMA) impaired working memory and reduced anxiety. The present experiment extended these findings by investigating the physiological, behavioral, and neurotoxic effects of a modified MDMA treatment regimen. Male Sprague-Dawley rats received 5 mg/kg of MDMA hourly for a period of 4 hr on every fifth day from postnatal day 35-60. Acute effects of the MDMA treatment included hypothermia, serotonin syndrome behavior, and ejaculation. Body weight gain was attenuated by repeated drug administration. The animals completed anxiety and working memory tests beginning 4 days after the final MDMA dose. MDMA altered habituation to the open-field, increased locomotor activity in the elevated plus-maze, decreased attention in the novel object-recognition test, and reduced serotonin transporter binding in the neocortex. These results indicate that repeated exposure to a relatively moderate MDMA dose during adolescence produces later changes in behavior and neurochemistry.     

Maternal stress suppresses cell proliferation in the forebrain of zebrafish larvae

Exposure to early life stress (ELS) can increase vulnerability to various psychiatric disorders. Although ELS has been shown to alter structure and functions of the hippocampus, amygdala and prefrontal cortex in the adult mammalian brain, it remains largely unclear whether ELS also affects embryonic or early‐stage brain development. In this study, I investigated the effects of a maternal stress (maternal starvation for 4 days) of adult zebrafish on offspring's larval brain development. Although maternal starvation did not largely affect proliferation rate in the midbrain and hindbrain, it significantly decreased that in the forebrain of larvae at 5 days post‐fertilization (dpf). I also found that embryos at 10 hr post‐fertilization (hpf) born from a starved mother showed elevated cortisol levels compared to those born from a control mother. Furthermore, cortisol treatment was sufficient to decrease proliferating cells in the forebrain of 5 dpf larvae. Our findings thus demonstrate for the first time that maternal starvation induces neurodevelopmental changes in the forebrain of zebrafish larvae and points to a possible role of maternal cortisol in mediating this effect of maternal stress to offsprings.     

Maternal care affects male and female offspring working memory and stress reactivity

Variations in maternal care affect the development of individual differences in learning and memory and neuroendocrine responses to stress in adult male offspring, but it is not known how variations in maternal care affect adult female offspring. The present study investigated the performance of adult Sprague-Dawley male and female offspring exposed to either low or high levels of maternal licking/grooming on a spatial memory task (Experiment 1) and the effects of acute stress on corticosterone levels and spatial memory performance (Experiment 2). In Experiment 1 rats were trained for 24 days on the spatial working/reference memory version of the radial arm maze (RAM). In Experiment 2, rats were trained on the same RAM task, exposed to an acute stress, and the effect of stress on corticosterone levels and subsequent spatial memory was examined. In Experiment 1, adult female offspring of low licking/grooming dams had enhanced working memory compared to all other groups. In Experiment 2, all groups of male and female offspring had enhanced working memory 24 h after exposure to acute 2 h restraint stress while reference memory was enhanced after stress in male and female offspring of low licking/grooming dams. Furthermore, female offspring of low licking/grooming dams showed the largest corticosterone response to the acute restraint stress compared to all other groups. Male offspring of low licking/grooming dams showed a flattened corticosterone response to stress. Thus variations in maternal care differentially affect working memory and stress reactivity in male and female offspring.     

The effects of enriched environment on the behavioral and corticosterone response to methamphetamine in adolescent and adult mice

Methamphetamine alters behavior and the stress response system. Relatively little research has examined the effects of methamphetamine in adolescents and compared these effects to those in adults. Housing in enriched environments has been explored as one way to protect against the effects of methamphetamine, but the findings are conflicting and no study has examined how enriched environment may alter the behavioral and corticosterone responses to methamphetamine in adolescent and adult rodents. We examined the long‐term effects of methamphetamine exposure on anxiety, social behavior, behavioral despair, and corticosterone levels in adolescent and adult mice housed in enriched or isolated environments. Enriched environment did not alter the behavioral or corticosterone response to methamphetamine. Methamphetamine exposure decreased anxiety and increased behavioral despair in adult mice, but methamphetamine did not alter behavior in adolescent mice. There was no effect of methamphetamine on social behavior or corticosterone levels. Our findings demonstrate that the specific environmental enrichment paradigm used in this study was not sufficient to mitigate the behavioral effects of methamphetamine and that adolescent mice are relatively resistant to the effects of methamphetamine compared to adult mice.     

Maturation of shoaling behavior is accompanied by changes in the dopaminergic and serotoninergic systems in zebrafish

The zebrafish has been one of the preferred vertebrate model organisms of developmental biology, and is becoming an important research tool for behavioral neuroscience and behavior genetics. A prominent feature of zebrafish is their strong shoaling tendency. Most recently, the first study investigating the development of shoaling in zebrafish demonstrated that a few days after hatching zebrafish do not shoal, but that shoaling tendency gradually increases during development. The current study investigates this phenomenon using the nearest neighbor distance, a measure most frequently employed for the quantification of shoal cohesion in fish. We demonstrate that shoal cohesion increases with age, while thigmotaxis, "wall hugging," does not show a consistent age-dependent change. The mechanisms underlying the maturation of shoaling are unknown. HPLC analysis of whole brain extracts finds the concentration of dopamine, DOPAC, serotonin, and 5-HIAA normalized to total brain protein weight to increase with age. Although the behavioral and neurochemical results are only correlative at this point, they may open a new avenue into the investigation of the mechanisms and development of social behavior in zebrafish.     

Long-term effects of perinatal essential fatty acid deficiency on anxiety-related behavior in mice

Dietary essential fatty acids have been shown to regulate behavioral and cognitive functions in rodents. However, the long-term effect on behavior, besides memory and learning, of essential fatty acid deficiency (EFAD), i.e., lack of n-3 and n-6 fatty acids, during the perinatal period has not been investigated. Therefore, pregnant C57Bl/6 mice were given either an EFAD or an isoenergetic control diet from gestational day 16 and throughout lactation. The female offspring were given standard chow from 3 weeks of age, and at 12 to 14 weeks of age, open-field, object recognition, light-dark transition, elevated plus maze, and social interaction tests were performed. The brain glycerophospholipid fatty acid composition was investigated in 3-week-old and adult offspring by gas chromatography. The differences observed in behavior were indicative of lower anxiety in the EFAD mice compared to controls illustrated by more time spent in the open arms of the elevated plus maze (+ 41%, p < .05) and in the light compartment in the light-dark transition test (+ 63%, p < .05). The proportion of total n-3 fatty acids, especially 22:6n-3 in the brain, was lower with a compensatory increase in the proportion of total n-6 fatty acids, foremost 22:5n-6, in the EFAD mice compared to controls at 3 weeks of age. In the adult brains the fatty acid composition was normalized. In conclusion, our data show that EFAD during the perinatal period results in short-term alterations of fatty acid composition in brain and decreased anxiety in adult life.     

Tyrosine prevents effects of hyperthermia on behavior and increases norepinephrine

Tyrosine (TYR) is the precursor of the catecholamine (CA) neurotransmitters, dopamine (DA) and norepinephrine (NE). Catecholamines, especially NE, participate in the response of the brain to acute stress. When animals are acutely stressed, NE neurons become more active and tyrosine availability may be rate-limiting. Tyrosine administration, before exposure to physical and/or environmental stressors including cold, reduces the adverse behavioral, physiological and neurochemical consequences of the exposure. In this study, the effects of tyrosine (400 mg/kg) were examined on rats exposed to heat stress, for which its effects have not been examined. Coping behavior and memory were assessed using the Porsolt swim test and the Morris water maze. Release of hippocampal NE and DA was assessed with in vivo microdialysis. In vehicle-treated animals, heat impaired coping and memory, and increased release of NE, but not DA. In heated animals receiving tyrosine, coping was not impaired and NE release was sustained, thus demonstrating tyrosine protects against the adverse effects of heat, and suggesting these effects result from increased central NE release. This study indicates the effects of tyrosine generalize across dissimilar stressors and that tyrosine administration may mitigate the adverse behavioral effects of heat and other stressors on humans. In addition, it demonstrates that moderate heat stress impairs coping behavior, as well as working and reference memory.     

Working memory maintenance is sufficient to reduce state anxiety

According to the attentional control theory (ACT) proposed by Eysenck and colleagues, anxiety interferes with cognitive processing by prioritizing bottom‐up attentional processes over top‐down attentional processes, leading to competition for access to limited resources in working memory, particularly the central executive (Eysenck, Derakshan, Santos, & Calvo, 2007 ). However, previous research using the n‐back working memory task suggests that working memory load also reduces state anxiety. Assuming that similar mechanisms underlie the effect of anxiety on cognition, and the effect of cognition on anxiety, one possible implication of the ACT would suggest that the reduction of state anxiety with increasing working memory load is driven by activation of central executive attentional control processes. We tested this hypothesis using the Sternberg working memory paradigm, where maintenance processes can be isolated from central executive processes (Altamura et al., 2007 ; Sternberg, 1966 ). Consistent with the n‐back results, subjects showed decreased state anxiety during the maintenance period of high‐load trials relative to low‐load trials, suggesting that maintenance processes alone are sufficient to achieve this state anxiety reduction. Given that the Sternberg task does not require central executive engagement, these results are not consistent with an implication of the ACT where the cognition/anxiety relationship and anxiety/cognition relationship are mediated by similar central executive mechanisms. Instead, we propose an extension of the ACT such that engaging working memory maintenance suppresses state anxiety in a load‐dependent manner. Furthermore, we hypothesize that the efficacy of this effect may moderate the effect of trait anxiety on cognition.     

Neurobehavioral deficits in db/db diabetic mice

Recent clinical studies indicate neurobehavioral disturbances in type-2 diabetics. However, there is paucity of preclinical research to support this concept. The validity of db/db mouse as an animal model to study type-2 diabetes and related complications is known. The present study was designed to investigate comprehensively the db/db mouse behavior as preclinical evidence of type-2 diabetes related major neurobehavioral complications. We tested juvenile (5-6 weeks) and adult (10-11 weeks) db/db mice for behavioral depression in forced swim test (FST), psychosis-like symptoms using pre-pulse inhibition (PPI) test, anxiety behavior employing elevated plus maze (EPM) test, locomotor behavior and thigmotaxis using open field test and working memory deficits in Y-maze test. Both juvenile and adult group db/db mice displayed behavioral despair with increased immobility time in FST. There was an age-dependent progression of psychosis-like symptoms with disrupted PPI in adult db/db mice. In the EPM test, db/db mice were less anxious as observed by increased percent open arms time and entries. They were also hypo-locomotive as evident by a decrease in their basic and fine movements. There was no impairment of working memory in the Y-maze test in db/db mice. This is the first report of depression, psychosis-like symptoms and anxiolytic behavior of db/db mouse strain. It is tempting to speculate that this mouse strain can serve as useful preclinical model to study type-2 diabetes related neurobehavioral complications.