Genetic analysis of behavioural responses to novelty in mice

Chronic immobilization stress induces anxiety-related behaviors and affects brain essential minerals in male rats

Alterations of essential elements in the brain are associated with the pathophysiology of many neuropsychiatric disorders. It is known that chronic/overwhelming stress may cause some anxiety and/or depression. We aimed to investigate the effects of two different chronic immobilization stress protocols on anxiety-related behaviors and brain minerals. Adult male Wistar rats were divided into 3 groups as follows (n = 10/group): control, immobilization stress-1 (45 minutes daily for 7-day) and immobilization stress-2 (45 minutes twice a day for 7-day). Stress-related behaviors were evaluated by open field test and forced swimming test. In the immobilization stress-1 and immobilization stress-2 groups, percentage of time spent in the central area (6.38 ± 0.41% and 6.28 ± 1.03% respectively, p < 0.05) and rearing frequency (2.75 ± 0.41 and 3.85 ± 0.46, p < 0.01 and p < 0.05, respectively) were lower, latency to center area (49.11 ± 5.87 s and 44.92 ± 8.04 s, p < 0.01 and p < 0.01, respectively), were higher than the control group (8.65 ± 0.49%, 5.37 ± 0.44 and 15.3 ± 3.32 s, respectively). In the immobilization stress-1 group, zinc (12.65 ± 0.1 ppm, p < 0.001), magnesium (170.4 ± 1.7 ppm, p < 0.005) and phosphate (2.76 ± 0.1 ppm, p < 0.05) levels were lower than the control group (13.87 ± 0.16 ppm, 179.31 ± 1.87 ppm and 3.11 ± 0.06 ppm, respectively). In the immobilization stress-2 group, magnesium (171.56 ± 1.87 ppm, p < 0.05), phosphate (2.44 ± 0.07 ppm, p < 0.001) levels were lower, and manganese (373.68 ± 5.76 ppb, p < 0.001) and copper (2.79 ± 0.15 ppm, p < 0.05) levels were higher than the control group (179.31 ± 1.87 ppm, 3.11 ± 0.06 ppm, 327.25 ± 8.35 ppb and 2.45 ± 0.05 ppm, respectively). Our results indicated that 7-day chronic immobilization stress increased anxiety-related behaviors in both stress groups. Zinc, magnesium, phosphate, copper and manganese levels were affected in the brain.

Transgenic overexpression of polysialyltransferase ST8SiaIV under the control of a neuron-specific promoter does not affect brain development but impairs exploratory behavior

A large body of the literature has demonstrated that the polysialic acid (polySia) modification of the neural cell adhesion molecule (NCAM) is a key regulator of cellular interactions during brain development, maintenance and plasticity. To properly fulfill these functions, polySia concentration has to be carefully controlled. This is done by the regulation of the expression of the two polySia-synthesizing enzymes ST8SiaII and ST8SiaIV. From this point of view we and others have demonstrated that downregulation of ST8SiaIV during oligodendrocyte differentiation is a prerequisite for efficient myelin formation and maintenance. Here, we addressed the question whether the prevention of polySia downregulation in neurons affects brain and particularly myelin development and functioning. For this purpose, we developed transgenic (tg) mouse lines overexpressing the polysialyltransferase ST8SiaIV in neurons. tg expression of ST8SiaIV prevented the postnatal downregulation of polySia, and most of the polySias in the forebrain and brain stem of adult tg mice were associated with NCAM-140 and NCAM-180 isoforms. Structural examination of the brain revealed no overt abnormalities of axons and myelin. In addition, ultrastructural and western blot analyses indicated normal myelin development. However, behavioral studies revealed reduced rearing activity, a measure for exploratory behavior, while parameters of motor activity were not affected in tg mice. Taken together, these results suggest that a persisting presence of polySia in neurons has no major effect on brain structure, myelination and myelin maintenance, but causes mild behavioral changes.

Long-term metabolic cage housing increases anxiety/depression-related behaviours in adult male rats

There are several reports on unfavourable effects of metabolic cage housing on animal welfare mainly due to the characteristic structures of these cages such as single housing and grid flooring. This study was aimed to compare the effects of long-term metabolic cage housing and conventional housing (normal grouped housing in standard cages) on the anxiety/depression-like behaviours in male rats. Anxiety/depression-related behaviours were evaluated by use of forced swimming test and open field test. Swimming and climbing were significantly lower and immobility duration higher in the metabolic cage group. In the open field test, total distance, mean velocity, time spent in the central area, zone transition, grooming, and rearing scores were significantly lower in the metabolic cage. Moreover, serum corticosterone level was higher in the metabolic cage group. The results of the study indicate that long-term metabolic cage housing may cause an increase in the anxiety- and depression-related behaviours in male rats.

Prophylactic Ketamine Attenuates Learned Fear

Ketamine has been reported to be an efficacious antidepressant for major depressive disorder and posttraumatic stress disorder. Most recently, ketamine has also been shown to be prophylactic against stress-induced depressive-like behavior in mice. It remains unknown, however, when ketamine should be administered relative to a stressor in order to maximize its antidepressant and/or prophylactic effects. Moreover, it is unknown whether ketamine can be prophylactic against subsequent stressors. We systematically administered ketamine at different time points relative to a fear experience, in order to determine when ketamine is most effective at reducing fear expression or preventing fear reactivation. Using a contextual fear conditioning (CFC) paradigm, mice were administered a single dose of saline or ketamine (30 mg/kg) at varying time points before or after CFC. Mice administered prophylactic ketamine 1 week, but not 1 month or 1 h before CFC, exhibited reduced freezing behavior when compared with mice administered saline. In contrast, ketamine administration following CFC or during extinction did not alter subsequent fear expression. However, ketamine administered before reinstatement increased the number of rearing bouts in an open field, possibly suggesting an increase in attentiveness. These data indicate that ketamine can buffer a fear response when given a week before as prophylactic, but not when given immediately before or after a stress-inducing episode. Thus, ketamine may be most useful in the clinic if administered in a prophylactic manner 1 week before a stressor, in order to protect against heightened fear responses to aversive stimuli.

Relationship between ethanol-induced activity and anxiolysis in the open field, elevated plus maze, light-dark box, and ethanol intake in adolescent rats

It is yet unclear if ethanol-induced motor stimulation in the open field (OF) merely reflects psychomotor stimulating effects of the drug or if this stimulation is driven or modulated by ethanol's antianxiety properties. In the present study, adolescent rats were administered with different ethanol doses or remained untreated. They were sequentially assessed in the OF, elevated plus maze (EPM), and light-dark box (LDB) and then assessed for ethanol intake. The aims were to assess the relationship between measures of ethanol-induced activity and anxiolysis, analyze ethanol intake as a function of prior ethanol exposure, and associate behavioral responsiveness in these apparatus with ethanol intake during adolescence. The results suggested that the enhanced exploration of the OF observed after 2.5 and 3.25 g/kg ethanol reflected a motor-stimulating effect that appeared to be relatively independent of anxiolysis. The 1.25 g/kg dose induced motor stimulation in the OF and anti-anxiety effects in the EPM, but these effects were relatively independent. The 0.5 g/kg ethanol dose exerted significant anxiolytic effects in the EPM in the absence of stimulating effects in the OF. A multivariate regression analysis indicated that adolescents with a higher frequency of rearing behavior in the OF, higher percentage of open arm entries in the EPM, and lower propensity to enter the central area of the OF exhibited greater ethanol intake. These results indicate that the OF is a valid procedure for the measurement of ethanol-induced stimulation, and provide information toward characterizing subpopulations of adolescents at risk for initiating alcohol drinking.

High and low rearing subgroups of rats selected in the open field differ in the activity of K+-stimulated p-nitrophenylphosphatase in the hippocampus

Na(+)/K(+)-adenosinetriphosphatase (Na(+)/K(+)-ATPase) is of paramount importance for the proper functioning of the organism. The enzyme is involved in several aspects of brain function, such as the repolarization of the neuronal membranes and neurotransmitters uptake/release. Therefore, individual differences in the activity of brain Na(+)/K(+)-ATPase may result in differences in the functioning of the brain, which, in consequence, could lead to behavioral divergences. Individual differences in rearing, an exploratory behavior, have been shown to be genetically determined. In rats, the inhibition of the activity of Na(+)/K(+)-ATPase was reported to induce changes in the exploratory behavior. The aim of this work was to verify if subgroups of rats selected according to the number of rearings (high and low rearing subgroups) in the open field test differ in the activity of Na(+)/K(+)-ATPase in brain regions. Adult, male outbred Wistar rats were selected in the open field test according to the number of rearings in subgroups of high (HR) and low (LR) rearing responders. After a rest of about 20 days after the open field session, HR and LR rats were sacrificed. In the first experiment, frontal cortex, striatum, brainstem, hippocampus and the amygdala (including the overlying limbic cortex) were dissected. The reaction of dephosphorylation of Na(+)/K(+)-ATPase (K(+) stimulated p-nitrophenylphosphatase) was assayed in homogenates rich in synaptosomes. The results obtained showed a statistically significant higher activity of K(+)p-nitrophenylphosphatase only in the hippocampus of HR subgroup of rats. This result was replicated in two other subsequent experiments with different HR and LR subgroups of rats selected at different times of the year. Our data suggest that the difference in the activity of Na(+)/K(+)-ATPase in the hippocampus is innate and is involved in the expression of the rearing behavior.

Prenatal elevation of endocannabinoids corrects the unbalance between dopamine systems and reduces activity in the Naples High Excitability rats

Several evidences suggest that endocannabinoids exert a neurotrophic effect on developing mesencephalic dopamine neurons. Since an altered mesocorticolimbic system seems to underlie hyperactivity and attention deficit in clinical and animal studies of attention deficit hyperactivity disorder (ADHD), prenatal elevation of anandamide has been induced in Naples high excitability (NHE) rats by inhibition of its reuptake. To this aim, pregnant NHE and random-bred females received a subcutaneous injection of AM-404 (1 mg/kg) or vehicle daily from E11 until E20. Young adult male offsprings were exposed to a spatial novelty (Làt-maze) for 30 min and the behavior was videotaped and analysed for indices of activity (travelled distance, rearing frequency) and attention (rearing duration). Moreover, morphological analysis of the brains was carried out that pertained to cytochrome oxydase as marker of metabolic activity and thyrosine hydroxylase as marker of the dopamine systems. The results indicate that prenatal AM-404 treatment significantly reduces activity by about 20% during the entire testing period and modifies the distribution of scanning times towards short duration episodes in the first part of the test only in NHE-treated rats. In addition, image analysis revealed a significant increase in relative optical density of TH+terminals in the dorsal striatum and substantia nigra of AM-404 treated NHE rats and minor changes in the dorsal cortex of AM-404 treated NRB rats. The data suggest a corrected unbalance between the two dopamine systems that apparently leads to reduced hyperactivity and modified scanning times in this animal model of ADHD. This, in turn, might open new strategies in the treatment of a subset of ADHD cases.

Towards a genetics of anxious temperament: from mice to men

An enduring question in the study of human personality is 'to what extent and how do genetic factors influence such personality constructs as "trait anxiety"?'. We selectively survey progress and obstacles in the genetic dissection of fear-like behavior, especially as it pertains to more constitutional forms of anxiety or anxious temperament. We emphasize the selection of phenotypic dimensions and the utility of 'temperament' and personality constructs as mediating variables for psychopathology. We summarize studies on the use of mouse models of 'anxious temperament' to map genetic loci, and briefly review recent genetic association studies of related phenotypes in humans utilizing candidate genes. We suggest that further progress in genetic research on 'trait anxiety' disorders may come from the following: (i) developing alternate constructs for investigating psychiatric illness focusing on dimensional scales, mediating variables and premorbid traits; (ii) examining 'at-risk' populations for protective genetic factors influencing 'resilience' or loci providing a reduced risk of a given trait or disorder; and (iii) utilizing lower animal models as a bridge to dissect the genetic factors contributing to related human phenotypes.

Chemoarchitectonics of axonal and perikaryal acetylcholinesterase along information processing systems of the human cerebral cortex

The distribution of axonal and perikaryal acetylcholinesterase (AChE) was studied in whole-brain sections. All cytoarchitectonic sectors and cortical layers of the human cerebral cortex contained AChE-rich axons. These axons displayed multiple varicosities which appeared to come in contact with AChE-rich and AChE-poor cortical perikarya. The upper layers of cortex tended to contain the highest density of AChE-rich axons. The AChE-rich axons were more dense in limbic-paralimbic areas of cortex than in primary sensory-motor and association areas. Within unimodal sensory association areas, the parasensory (upstream) sectors had a slightly lesser density of AChE-rich axons than the downstream sectors. Within paralimbic areas, the nonisocortical sectors displayed a distinctly higher density of AChE-rich axons than the more differentiated isocortical sectors. These observations indicate that the distribution of AChE-rich axons displays orderly variations that obey the organization of information processing systems in the cerebral cortex.

A genetic-correlational study of hippocampal neurochemical variation and variation in exploratory activities of mice

Previously, we have demonstrated that hippocampal mossy fibers, containing the opioid peptide dynorphin B, are functionally connected with the gene-dependent exploratory behavior of mice. In order to seek further evidence of causal relationships between dynorphin B action and exploration, a quantitative-genetic method was chosen. For this purpose, mice from the inbred strains C57BL/6, DBA/2, BLN, and CPB-K were used. By means of radioimmunoassay, the hippocampal level of dynorphin B was monitored in mice that had been exposed to environmental novelty, as compared to naive animals. Clear evidence was obtained that novelty induces the release of hippocampal dynorphin B. Furthermore, low tissue content was found to be causally connected with high exploratory scores.

Genetic control of hippocampal cholinergic and dynorphinergic mechanisms regulating novelty-induced exploratory behavior in house mice

Neurobehavioral genetics endeavors to trace the pathways from genetic and environmental determinants to neuroanatomical and neurophysiological systems and, thence, to behavior. Exploiting genetic variation as a tool, the behavioral sequelae of manipulating these neuronal systems by drugs and antisera are analyzed. Apart from research in rats, this paper deals mainly with the genetically-influenced regulation in mice of exploratory behaviors that are adaptive in novel surroundings and are hippocampally-mediated. Special attention is paid to neuropeptidergic, GABAergic, and cholinergic synaptic functions in the mouse hippocampus. The behaviorally different inbred mouse strains C57BL/6 and DBA/2 show opposite reactions (reductions and increases, respectively, in exploration rates) to peripheral and intrahippocampal injections with agents that interfere with peptidergic, cholinergic, and GABAergic neurotransmission. These findings can be explained by an interdependent over-release of opioids, arrested GABA release, and excess acetylcholine in the hippocampal neuronal network of DBA/2 mice, as compared to C57BL/6 mice where these systems are functionally well balanced. Very similar results have been obtained with the lines SRH and SRL, derived from C57BL/6 and DBA/2, and genetically selected for rearing behavior. Most probably, the opioids act to disinhibit exploratory responses. An additional genetic approach is mentioned, in which four inbred mouse strains and one derived heterogeneous stock are used for estimating genetic correlations between structural properties of the hippocampal mossy fibers and levels of hippocampal dynorphin B, on the one hand, and frequencies of exploratory responses to environmental novelty, on the other.

Genetic selection for novelty-induced rearing behavior in mice produces changes in hippocampal mossy fiber distributions

Previous investigations in mice revealed the existence of a set of genes that influence variations in hippocampal anatomy as well as variations in behavioral responses to novelty. In particular, a positive genetic correlation was found between the size of the intra- and infrapyramidal mossy fiber (iip-MF) projection and rearing frequency in an open-field. On the basis of these findings, we hypothesized that genetic selection for rearing would entail correlated changes in hippocampal morphology. This was tested in the inbred selection lines SRH (selection for rearing: high) and SRL (selection for rearing: low). As expected, the SRH mice appeared to possess iip-MF terminal fields that were larger than those of the SRL mice. Because the behavioral difference between the two lines is most probably caused by a single genetic unit, these animals represent valuable material for molecular-genetic investigations into the mechanisms that control behavioral and neuroanatomical variation.

The genetic architecture of behavioural responses to novelty in mice

The genetic architectures of 12 behavioural variables measured in adult male mice placed in a novel environment were analysed in a replicated 4 X 4 diallel cross. The results were combined with those obtained in a classical cross involving two of the four strains. Based on the hypothesis of an evolutionary history of stabilising selection for mouse exploratory behaviour, we expected additive genetic effects and ambidirectional dominance. Such genetic architectures were actually found for those exploratory behaviours where epistatic effects were of minor importance. Similar findings emerged for some non-exploratory phenotypes. All behaviours analysed appeared to be polygenically controlled.

Effects of intrahippocampally-injected naloxone and morphine upon behavioural responses to novelty in mice from two selectively-bred lines

To examine the peptidergic regulation of behavioural responses to novelty, 5-month-old male mice from the inbred selection lines SRH (selected for rearing frequency: high) and SRL (selected for rearing frequency: low) were intrahippocampally micro-injected (0.5 microliter) with either the opiate antagonist naloxone (0.3 microgram), or the opiate agonist morphine (1.0 microgram), or saline vehicle alone, given 15 min prior to individual exposure to 20-min exploration tests in a novel environment. Naloxone exerted opposite effects upon various exploratory acts and locomotor activity in the two strains, that is, it decreased the scores in SRH and augmented them in SRL, while morphine depressed the scores in both. It is suggested that an excess of opioids in SRL, as compared to SRH, is attenuated by this dose of naloxone. In addition to previously obtained evidence of a genotype-dependent cholinergic mechanism in the mouse dorsal hippocampus controlling exploratory responses to novelty, these findings indicate that hippocampal opioid peptides are also involved in the genotype-dependent regulation of exploration.

Behavioral responses to novelty in mice: a reanalysis

A recently proposed searching procedure for scale transformations and models was applied to previously obtained data on rearing responses and locomotor activity in mice from two inbred selection lines (SRH and SRL) and four hybrid generations. Logarithmic transformation provided the most appropriate scale of measurement for both behaviors. For rearing, the simple additive model was adequate, thus validating the earlier findings. However, contrary to the previous conclusions, an additivity-dominance model fitted the locomotion data best. These results demonstrate the usefulness of the procedure described.

Inheritance of discrimination learning ability and retention in BA and DBA mice

Male house mice from two inbred strains, DBA/2 and BA, and their F1 and F2 crosses and backcrosses, B1 and B2, were tested for black-white discrimination learning and 24-hr response retention in a water maze. The BA strain exhibited an inferior learning performance. Nonparametric and biometrical genetic analyses provided only weak evidence of unifactorial inheritance of acquisitions, but somewhat stronger evidence in the case of retention.

Behavioural effects of (-)naloxone in mice from four inbred strains

To study the role of endogenous opioid peptides in the regulation of behavioural responses to novelty, male mice from the inbred strains SRH, SRL, C57BL/6, and DBA/2 were injected IP with either saline alone, or the opiate antagonist naloxone, dissolved in saline, in dosages of 4 or 8 mg/kg. After 10 min, the animals were placed individually for 20 min in a novel environment and some 12 behavioural components were recorded. Naloxone reduced grooming and incipient rearing in all four strains and it reduced sniffing, leaning against the wall, and locomotor activity in some of them. Object-sniffing, object-learning, defecation, freezing, and Straub tail elevation remained unaffected. The results for grooming and locomotor activity are largely in agreement with reports from others. Rather unexpectedly, the drug enhanced rearing responses in all strains. Although in several cases, a genotype-treatment interaction became apparent, the observed strain differences usually persisted and the correlations found between the behavioural components did not alter much. The naloxone-induced reductions in sniffing, leaning, locomotion, and grooming suggest endogenous opioid involvement in the control of behavioural activation in a novel situation. The increases in rearing possibly result from an additional agonist action of naloxone.

Ontogeny of behavior in two inbred lines of selected mice

The development over 11 ages of 14 reflex responses, 26 behavioral components, jumpiness, and left-right discrimination learning was studied in 2 strains of mice genetically selected for high (SRH) and low (SRL) rearing response frequency. Significant age-dependent differences between the strains were found mainly, but not exclusively, in the behavioral components, e.g., rearing, jumping, scratching, defecating. Two-week-old pups of both strains showed good acquisition and retention in learning tests without shock, but the "jumpy" behavior disturbed performance to a certain degree in the SRH strain. Although less active initially, SRH mice were ahead at later developmental stages. Whether these differences are determined by the gene controlling rearing frequency or by other genes remains undecided.