Genetic factors regulate processes related to anxiety in mice

Inter- and transgenerational heritability of preconception chronic stress or alcohol exposure: Translational outcomes in brain and behavior

Chronic stress and alcohol (ethanol) use are highly interrelated and can change an individual's behavior through molecular adaptations that do not change the DNA sequence, but instead change gene expression. A recent wealth of research has found that these nongenomic changes can be transmitted across generations, which could partially account for the "missing heritability" observed in genome-wide association studies of alcohol use disorder and other stress-related neuropsychiatric disorders. In this review, we summarize the molecular and behavioral outcomes of nongenomic inheritance of chronic stress and ethanol exposure and the germline mechanisms that could give rise to this heritability. In doing so, we outline the need for further research to: (1) Investigate individual germline mechanisms of paternal, maternal, and biparental nongenomic chronic stress- and ethanol-related inheritance; (2) Synthesize and dissect cross-generational chronic stress and ethanol exposure; (3) Determine cross-generational molecular outcomes of preconception ethanol exposure that contribute to alcohol-related disease risk, using cancer as an example. A detailed understanding of the cross-generational nongenomic effects of stress and/or ethanol will yield novel insight into the impact of ancestral perturbations on disease risk across generations and uncover actionable targets to improve human health.

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.

Gabra5-gene haplotype block associated with behavioral properties of the full agonist benzodiazepine chlordiazepoxide

The gabra5 gene is associated with pharmacological properties (myorelaxant, amnesic, anxiolytic) of benzodiazepines. It is tightly located (0.5 cM) close to the pink-eyed dilution (p) locus which encodes for fur color on mouse chromosome 7. We tested the putative role of the gabra5 gene in pharmacological properties of the full non specific agonist chlordiazepoxide (CDP), using behavioral and molecular approaches in mutated p/p mice and wild type F2 from crosses between two multiple markers inbred strain ABP/Le and C57BL/6By strain. From our results, using rotarod, light-dark box, elevated maze and radial arm maze tests, we demonstrate that p/p mice are more sensitive than WT to the sensory motor, anxiolytic and amnesic effect of CDP. This is associated with the presence of a haplotypic block on the murine chromosome 7 and with an up regulation of gabra5 mRNAs in hippocampi of p/p F2 mice.

Pharmacological alterations of anxious behaviour in mice depending on both strain and the behavioural situation

A previous study comparing non-emotive mice from the strain C57BL/6/ByJ with ABP/Le mice showed ABP/Le to be more anxious in an open-field situation. In the present study, several compounds affecting anxiety were assayed on ABP/Le and C57BL/6/ByJ mice using three behavioural models of anxiety: the elevated plus-maze, the light-dark discrimination test and the free exploratory paradigm. The compounds used were the full benzodiazepine receptor agonist, chlordiazepoxide, and the antagonist, flumazenil, the GABA(A) antagonist, bicuculline, the full 5-HT(1A) agonist 8-OH-DPAT, and the mixed 5-HT(1A)/5-HT(1B) agonist, RU 24969. Results showed the effect of the compounds to be dependent on both the strain and the behavioural task. Several compounds found to be anxiolytic in ABP/Le mice had an anxiogenic effect on C57BL/6/ByJ mice. More behavioural changes were observed for ABP/Le in the elevated plus-maze, but the clearest findings for C57BL/6/ByJ mice were observed in the light-dark discrimination apparatus. These data demonstrate that anxious behaviour is a complex phenomenon which cannot be described by a single behavioural task nor by the action of a single compound.

van der Mark M, de Kloet ER, S. Oitzl M. Differential MR/GR activation in mice results in emotional states beneficial or impairing for cognition

Corticosteroids regulate stress response and influence emotion, learning, and memory via two receptors in the brain, the high-affinity mineralocorticoid (MR) and low-affinity glucocorticoid receptor (GR). We test the hypothesis that MR- and GR-mediated effects interact in emotion and cognition when a novel situation is encountered that is relevant for a learning process. By adrenalectomy and additional constant corticosterone supplement we obtained four groups of male C57BL/6J mice with differential chronic MR and GR activations. Using a hole board task, we found that mice with continuous predominant MR and moderate GR activations were fast learners that displayed low anxiety and arousal together with high directed explorative behavior. Progressive corticosterone concentrations with predominant action via GR induced strong emotional arousal at the expense of cognitive performance. These findings underline the importance of a balanced MR/GR system for emotional and cognitive functioning that is critical for mental health.

Progesterone withdrawal effects in the open field test can be predicted by elevated plus maze performance

Allopregnanolone (3alpha-hydroxy-5alpha-pregnane-20-one) is a ring-A-reduced metabolite of progesterone, which is naturally produced during the luteal phase of the menstrual cycle, during pregnancy and by stressful events. The steroid hormone inhibits neural functions through increased chloride ion flux through the GABA(A) receptor. The effects and subsequent withdrawal symptoms are similar to those caused by alcohol, benzodiazepines and barbiturates. This study examined the withdrawal effects of progesterone with regards to the influence of individual baseline exploration and risk taking. Rats were tested on the elevated plus maze (EPM) before hormonal treatment, in order to evaluate differences in risk taking and exploration of open and elevated areas. Treatment consisted of ten consecutive once a day progesterone or vehicle s.c. injections. On the last day of treatment, estradiol was injected in addition to progesterone, followed by a 24-h withdrawal before testing in the open field test (OF). Progesterone-treated rats showed a withdrawal effect of open area avoidance in the OF. The vehicle-treated control rats showed strong correlations between the EPM and OF parameters. This relationship was not found for the progesterone group at withdrawal. Rats with greater numbers of open arm entrance in the EPM pretest showed an increased sensitivity to progesterone withdrawal (PWD) compared to rats with low exploration and risk taking. The results indicate that the effects of PWD relate to individual exploration and risk taking. Furthermore, the possible analogy of PWD and PMS/PMDD in relation to individual traits is discussed.

Animal models of anxiety

Animal models for anxiety-related behavior are based on the assumption that anxiety in animals is comparable to anxiety in humans. Being anxious is an adaptive response to an unfamiliar environment, especially when confronted with danger or threat. However, pathological variants of anxiety can strongly impede the daily life of those affected. To unravel neurobiological mechanisms underlying normal anxiety as well as its pathologi- cal variations, animal models are indispensable tools. What are the characteristics of an ideal animal model? First, it should display reduced anxiety when treated with anxiolytics (predictive validity). Second, the behavioral response of an animal model to a threatening stimulus should be comparable to the response known for humans (face validity). And third, the mechanisms underlying anxiety as well as the psychological causes should be identical (construct validity). Meeting these three requirements is difficult for any animal model. Since both the physiological and the behavioral response to aversive (threatening) stimuli are similar in humans and animals, it can be assumed that animal models can serve at least two distinct purposes: as (1) behavioral tests to screen for potential anxiolytic and antidepressant effects of new drugs and (2) tools to investigate specific pathogenetic aspects of cardinal symptoms of anxiety disorders. The examples presented in this chapter have been selected to illustrate the potential as well as the caveats of current models and the emerging possibilities offered by gene technology. The main concepts in generating animal models for anxiety-that is, selective breeding of rat lines, experience-related models, genetically engineered mice, and phenotype-driven approaches-are concisely introduced and discussed. Independent of the animal model used, one major challenge remains, which is to reliably identify animal behavioral characteristics. Therefore, a description of behavioral expressions of anxiety in rodents as well as tests assays to measure anxiety-related behavior in these animals is also included in this chapter.

Behavioral phenotype of pre-proenkephalin-deficient mice on diverse congenic backgrounds

RATIONALE

The phenotype of genetically modified animals is thought to result from an interaction of gene manipulation with the genetic background and environmental factors.

OBJECTIVES

To test the behavioral and drug responses of Penk1(-/-) mice on different genetic backgrounds.

METHODS

Congenic C57BL/6J and DBA/2J mouse strains with a targeted deletion of the Penk1 gene were generated. Behavior and drug effects were tested in models of pain and anxiety.

RESULTS

Penk1(-/-) mice showed exaggerated responses to painful or threatening environmental stimuli, but the expressivity of the mutant phenotype was strongly dependent on the behavioral paradigm and on the genetic background. For example, elevated levels of anxiety were readily detectable in C57BL/6J-Penk1(-/-) mice in the light-dark and startle response tests, but not in the social interaction test. In contrast, we found elevated levels of anxiety in DBA/2J-Penk1(-/-) mice only in the zero-maze and social interaction tests. In some cases, the idiosyncratic behavior masked the appearance of the knockout gene effect. The activity of the anxiogenic drug, m-chlorophenylpiperazine, but not the anxiolytic drug diazepam, was strain and genotype dependent. Mice with the Penk1 mutation on the DBA/2J, but not on other genetic backgrounds, showed an increased opioid-dependent stress-induced analgesia.

CONCLUSIONS

(1) The behavioral effects of the Penk1 gene deletion persists on different genetic backgrounds, but its detection sometimes requires the use of different behavioral paradigms. (2) The behavior of the background strain should be considered in the analysis of knockout mice to avoid floor and ceiling effects, which may mask the phenotype.

GENETIC APPROACHES TO THE STUDY OF ANXIETY

Anxiety and its disorders have long been known to be familial. Recently, genetic approaches have been used to clarify the role of heredity in the development of anxiety and to probe its neurobiological underpinnings. Twin studies have shown that a significant proportion of the liability to develop any given anxiety disorder is due to genetic factors. Ongoing efforts to map anxiety-related loci in both animals and humans are underway with limited success to date. Animal models have played a large role in furthering our understanding of the genetic basis of anxiety, demonstrating that the genetic factors underlying anxiety are complex and varied. Recent advances in molecular genetic techniques have allowed increasing specificity in the manipulation of gene expression within the central nervous system of the mouse. With this increasing specificity has come the ability to ask and answer precise questions about the mechanisms of anxiety and its treatment.

New replicable anxiety-related measures of wall vs. center behavior of mice in the open field

Anxiety is a widely studied psychiatric disorder and is thought to be a complex and multidimensional phenomenon. Sensitive behavioral discrimination of animal models of anxiety is crucial for the elucidation of the behavioral components of anxiety and the physiological processes that mediate them. Commonly used behavior paradigms of anxiety usually include only a few automatically collected measures; these do not exhaust the behavioral richness exhibited by animals, thus perhaps missing important differences between preparations. The aim of the present study was to expand the repertoire of automatically collected measures in a classical test of anxiety: behavior in relation to the wall in the open field. We present an algorithm, based on the Software for the Exploration of Exploration strategy, which automatically partitions the mouse path into intrinsically defined patterns of movement near the wall and in the center. These patterns are used to design new end points, which provide an articulated description of various aspects of behavior near the wall and in the center. Sixteen new end points were designed with data from C57BL/6J and DBA/2J mice tested in three laboratories. The strain differences in all end points were evaluated on another data set to assess their validity and were found to remain stable. Ten of the sixteen end points were found to discriminate between the two strains in a replicable manner. The entire set of end points can be used on various genetic and pharmacological models of anxiety with good prospects of providing fine discrimination in a replicable manner.

Emotional reactivity in mice may not be inherited but influenced by parents

Heredity is often assimilated to genetic transmission of traits. However, some traits may be socially inherited. This has been described for maternal behaviour as well as for emotional reactivity in rodents such as rats or mice. The aim of the present study was to investigate further this idea using two backcrosses between CB6 or B6C females and C57BL/6 males. Indeed, the experimental groups are genetically identical but may be exposed to very different mothering types. When adults, the offspring were subjected to rodent emotional reactivity tests such as elevated plus maze and free exploration paradigm. Results show that CB6xB6 males exhibit higher emotional reactivity than B6CxB6 and B6 males in all behavioural situations, but these effects are not seen in females. Contrarily to their offspring that show different reactivity even if sharing the same genetical background, CB6 and B6C females display quite identical emotional reactivity. A possible explanation is that emotional reactivity is induced by maternal behaviour rather than transmitted by the parents.

Behavioural screening in mutagenised mice—in search for novel animal models of psychiatric disorders

Complementary to the 'gene-driven' analysis of gene function, 'phenotype-driven' approaches can be performed and may be equally important. Despite the current availability of a long list of mouse mutants, there remains an appreciable need for behavioural phenotypes in mouse models permitting to learn more about the aetiology of psychiatric disorders. This lack can be compensated by phenotype-driven ethyl-nitrosourea (ENU)-mutagenesis programs which aim at identifying novel phenotypes without any a priori assumptions, thus, representing a unique possibility to create novel animal models which approximate the underlying genetic aetiology. The power of mouse mutagenesis critically depends on the phenotyping procedures performed. In the case of ENU-mutants, behavioural phenotyping is especially challenging, as behavioural profiles have to be identified in single individuals. For high-throughput screening, approaches have been made to establish standardised screening protocols including a combination of well-validated, easy to perform behavioural tests. Different strategies are being introduced, which are used in ENU-mutagenesis screens to identify behavioural mutants representing possible endophenotypes of psychiatric diseases.

Anxiety-related behavior and densities of glutamate, GABAA, acetylcholine and serotonin receptors in the amygdala of seven inbred mouse strains

The amygdala is a brain region involved in the regulation of anxiety-related behavior. The purpose of this study was to correlate anxiety-related behavior of inbred mouse strains (BA//c, BALB/cJ, C3H/HeJ, C57BL/6J, CPB-K, DBA/2J, NMRI) to receptor binding in the amygdala. Binding site densities of receptors (NMDA, AMPA, kainate, GABA(A), serotonin, muscarinergic M(1)-M(2)) were measured with quantitative receptor autoradiography using tritiated ligands. Measurements of fear-sensitized acoustic startle response (ASR; induced by footshocks), elevated plus maze (EPM) behavior and receptor binding studies showed differences between the strains except for AMPA and muscarinergic M(2) receptors. Factor analysis revealed a Startle Factor with positive loadings of the density of serotonin and kainate receptors, and the amplitudes of the baseline and fear-sensitized ASRs. A second Anxiety-related Factor only correlated with the fear-sensitized ASR and anxiety parameters on the EPM but not receptor densities. There were also two General Activity Factors defined by (negative) correlations with entries to closed arms of the EPM. Because the density of NMDA and muscarinergic M(1) receptors also correlated negatively with the two factors, these receptors had a positive effect on general activity. In contrast, correlations of GABA(A), serotonin, and kainate receptors had the opposite sign as compared to closed arm entries. It is concluded that hereditary variations in the amygdala, particularly in kainate and serotonin receptors, play a role for the baseline and fear-sensitized ASR, whereas the general activity is influenced by many neurotransmitter receptor systems.

Genetic animal models of anxiety

The focus of this review is on progress achieved in identifying specific genes conferring risk for anxiety disorders through the use of genetic animal models. We discuss gene-finding studies as well as those manipulating a candidate gene. Both human and animal studies thus far support the genetic complexity of anxiety. Clinical manifestations of these diseases are likely related to multiple genes. While different anxiety disorders and anxiety-related traits all appear to be genetically influenced, it has been difficult to ascertain genetic influences in common. Mouse studies have provisionally mapped several loci harboring genes that affect anxiety-related behavior. The growing array of mutant mice is providing valuable information about how genes and environment interact to affect anxious behavior via multiple neuropharmacological pathways. Classical genetic methods such as artificial selection of rodents for high or low anxiety are being employed. Expression array technologies have as yet not been employed, but can be expected to implicate novel candidates and neurobiological pathways.

Genetic basis of anxiety-like behaviour: a critical review

The way genetic and/or environmental factors influence psychiatric disorders is an enduring question in the field of human psychiatric diseases. Anxiety-related disorders provide a relevant example of how such an interaction is involved in the aetiology of a psychiatric disease. In this paper we review the literature on that subject, reporting data derived from human and rodent studies. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of anxiety, including inbred mice, selected lines, multiple marker strains, or knockout mice and review data reporting environmental components influencing anxiety-related behaviours. We conclude that anxiety is a complex behaviour, underlined not only by genetic or environmental factors but also by multiple interactions between these two factors.

Unexpected absence of correlation between the genetic mechanisms regulating beta-carboline-induced seizures and anxiety manifested in an elevated plus-maze test

Among the ligands of the benzodiazepine site, one can mention the benzodiazepines as agonists and some beta-carbolines (e.g. methyl-beta-carboline-3-carboxylate, abbreviated hereafter beta-CCM) as inverse agonists. Most benzodiazepines and beta-carbolines act on processes involved in memory, anxiety, and convulsions with opposite physiological effects. Since these molecules have influences on both anxiety and convulsions, we predicted that there would exist a genetic correlation between anxiety evaluated in an elevated plus-maze and susceptibility to beta-CCM-induced seizures. Using inbred strains of mice, the genetic correlation was estimated with the Hegmann and Possidente model. An absence of genetic correlation was found, showing that the mechanisms responsible for basal anxiety measured with the elevated plus-maze test and those leading to susceptibility to beta-CCM-induced seizures do not share the same genetic pathways.

Emotional reactivity in mice, a case of nongenetic heredity?

Nongenetic heredity cases have been described in man, as well as in animals, and relationships between parents and offspring seem to play an important role in this transmission. In mice, mothering type could be nongenetically heritable by a latent learning close to mechanism. As mothering style clearly influences emotional reactivity, this reactivity could be nongenetically transmitted over generations. To clarify this question, the mother's influence on adult offspring reactivity must be established (whatever its basis, genetic, social or other). Thus, two reciprocal F1 hybrids (CB6 from a BALB/c mother and B6C from a C57BL/6 mother) have been compared using an ethological analysis in animal tests of emotional reactivity such as the free exploration paradigm and the light/dark box. First results show a sharp influence of the mother's strain and that suggests an effect of mothering style. The offspring from C57BL/6 mothers display less reactivity in the free exploration paradigm than the offspring from BALB/c mothers. In the light/dark box, no difference has been found between the two hybrids. Moreover, the mother's influence is greater in males than in females.

An animal model for the study of the genetic bases of behaviour in men: the multiple marker strains (MMS)

Animal models are often used for preclinical research on the neurobiology of psychiatric disorders. Whereas many are employed to screen new therapeutic agents, few of them are used to study the genetic bases of psychiatric diseases, probably because of the complex genetic determinism underlying quantitative behavioral traits such as mood, personality or intelligence. The present article presents a short review introducing an analysis model using mice: the marker strains model. Using this model it is possible both to display genetic determinism data and to locate some of the chromosomal fragments involved in the regulation of anxiogenic processes. At present it cannot accurately determine the position of one or more genes, but it does provide a valuable means of 'scanning' the genome for an approximation. Through genetic analysis, using the model, an attempt will be made to identify autosomal fragments which may be involved in two behavioural traits: anxiety and chemical-induced seizures. In this paper, after reviewing theoretical aspects of looking for genes involved in behaviour, we will successively introduce studies in genetic topics in psychiatric human studies as well as appropriated behavioural animal studies. Then we will present a genetic model in mice which allows us to locate chromosomal fragments associated with a behavioural trait: multiple marker strains.

Strain differences in the anxiolytic effects of losartan in the mouse

Anxiolytic effects of the angiotensin AT(1) receptor antagonist losartan were studied in the elevated plus maze (EPM) and the light/dark test (LDT) in different mouse strains as were responses to angiotensin II and acetylcholine in isolated ascending colon. There were no significant strain differences in behaviour on the EPM, and diazepam was anxiolytic in C57BL/6, DBA/2 and BKW mice. Losartan was anxiolytic in BKW only. In the LDT, there were significant strain differences, with BKW mice exhibiting greatest anxiety-like behaviour; losartan was ineffective in this test. In vitro responses to angiotensin II and acetylcholine were significantly smaller in BKW than in C57BL/6 and DBA/2. These results indicate that the mouse strain exhibiting least angiotensin receptor function is the most responsive to the anxiolytic effects, suggesting a possible relationship between angiotensin receptor function and anxiolytic response to losartan.

Targeted genome screen of panic disorder and anxiety disorder proneness using homology to murine QTL regions

Family and twin studies have indicated that genes influence susceptibility to panic and phobic anxiety disorders, but the location of the genes involved remains unknown. Animal models can simplify gene-mapping efforts by overcoming problems that complicate human pedigree studies including genetic heterogeneity and high phenocopy rates. Homology between rodent and human genomes can be exploited to map human genes underlying complex traits. We used regions identified by quantitative trait locus (QTL)-mapping of anxiety phenotypes in mice to guide a linkage analysis of a large multiplex pedigree (99 members, 75 genotyped) segregating panic disorder/agoraphobia. Two phenotypes were studied: panic disorder/agoraphobia and a phenotype ("D-type") designed to capture early-onset susceptibility to anxiety disorders. A total of 99 markers across 11 chromosomal regions were typed. Parametric lod score analysis provided suggestive evidence of linkage (lod = 2.38) to a locus on chromosome 10q under a dominant model with reduced penetrance for the anxiety-proneness (D-type) phenotype. Nonparametric (NPL) analysis provided evidence of linkage for panic disorder/agoraphobia to a locus on chromosome 12q13 (NPL = 4.96, P = 0.006). Modest evidence of linkage by NPL analysis was also found for the D-type phenotype to a region of chromosome 1q (peak NPL = 2.05, P = 0.035). While these linkage results are merely suggestive, this study illustrates the potential advantages of using mouse gene-mapping results and exploring alternative phenotype definitions in linkage studies of anxiety disorder.

Divergent levels of anxiety in mice selected for differences in sensitivity to a convulsant agent

Spontaneous behavior patterns were assessed in eight different behavioral situations in two lines of mice, BR and BS, previously selected for their sensitivity to an anxiogenic benzodiazepine (BZ) receptor inverse agonist, Methyl beta-carboline-3-carboxylate (beta-CCM). BR is highly resistant, and BS, highly sensitive to beta-CCM-induced seizures. Tests used included an assessment of general locomotor activity, several situations classically used for measuring fear-motivated behaviors (open field, thigmotaxis, elevated plus-maze, light-dark discrimination, staircase), a test for measuring exploration (holeboard), and a test for measuring nociception (hot-plate). In the absence of beta-CCM, the results provide evidence of reduced motor activity and higher levels of anxiety in the BR line as compared to the BS line.

Preoperative open field behavior predicts levels of neuropathic pain-related behavior in mice

Exploratory open field (OF) activity was assessed in seven different mouse strains and selection lines. We counted the number of beam interruptions made by three cagemate mice at a time. This assay tests reactivity to aversive stimuli, anxiety and emotionality. One hindlimb was then totally denervated by transecting the sciatic and saphenous nerves on one side, and autotomy, a behavior thought to be related to neuropathic pain, was quantified over 35 days. We report that OF activity and autotomy are highly variable across different strains/lines. These results reaffirm the genetic control of these behaviors. We also found that these behaviors are inversely and significantly correlated. We suggest that common genetically-determined neural mechanisms may underlie anxiety, emotionality and neuropathic pain in mice.

Effects of repeated fluoxetine on anxiety-related behaviours, central serotonergic systems, and the corticotropic axis axis in SHR and WKY rats

In keeping with the anxiolytic property of selective serotonin reuptake inhibitors (SSRIs) in humans, we have examined in the spontaneously hypertensive rat (SHR) and the Wistar-Kyoto (WKY) rat, which display low and high anxiety, respectively, some psychoneuroendocrine effects of a repeated treatment with the SSRI fluoxetine (5 or 10 mg/kg daily, for 3 weeks). Two days after the last injection, plasma levels of fluoxetine were not detectable whereas those of its metabolite, norfluoxetine, were present to similar extents in both strains. By means of the elevated plus-maze test (29-30 h after the 13th administration of fluoxetine) and an open field test (48 h after the last injection of fluoxetine), it was observed that fluoxetine pretreatment did not yield anxiolysis; hence, some, but not all, behaviours were indicative of anxiety and hypolocomotion (as assessed through principal component analyses and acute diazepam studies). In both strains, the 10 mg/kg dose of fluoxetine decreased hypothalamus 5-HT and 5-HIAA levels, and reduced midbrain and/or hippocampus [3H]citalopram binding at 5-HT transporters, but did not affect [3H]8-hydroxy-2-(di-N-propylamino)tetralin binding at hippocampal 5-HT1A receptors. However, the fluoxetine-elicited reduction in hippocampal 5-HT transporter binding was much more important in WKY than in SHR rats, this strain-dependent effect being associated in WKY rats with a reduction in cortical [3H]ketanserin binding at 5-HT2A receptors. Lastly, in WKY rats, repeated fluoxetine administration increased adrenal weights and the plasma corticosterone response to open field exposure, but did not affect the binding capacities of hippocampal mineralocorticoid and glucocorticoid receptors. These data show that key psychoneuroendocrine responses to repeated fluoxetine administration may be strain-dependent, and that repeated fluoxetine administration does not yield anxiolysis, as assessed by two standard tests of emotivity.

A genetic and multifactorial analysis of anxiety-related behaviours in Lewis and SHR intercrosses

Lewis (LEW) and spontaneously hypertensive rats (SHR) have been shown to differ in a series of fear-related behaviours measured in different anxiety/emotionality tests. In the present study, we have investigated some of the genetic mechanisms underlying these differences. To this end, male and female rats from the two inbred strains were crossed to produce two parental (LEW and SHR), two F1 (LEW or SHR mother), and two F2 (LEW or SHR grandmother) groups. All rats were tested in the elevated plus-maze and in the open field, besides being characterised for systolic blood pressure (BP). LEW rats approached the open arms of the plus-maze and the central area of the open field less than SHRs. The two strains also differed in their BP (SHR > LEW). LEW/SHR differences were found to be due to direct effects of the genes, rather than to indirect maternal and grand-maternal effects. Central locomotion in the open field was shown to be the most heritable of all the traits considered herein. A factor analysis on the segregating F2 population produced three independent factors. The first one was associated to measures of anxiety from the elevated plus-maze, and the second to measures of locomotion in novel environments. Factor scores revealed that the parental strains differ in relation to the first but not to the second factor. This study demonstrates the usefulness of coupling genetic and multifactorial methods to investigate behavioural traits and it confirms LEW and SHR strains as an interesting genetic tool for the study of anxiety.