Norbert Sachser

Analyzing corticosterone metabolites in fecal samples of mice: a noninvasive technique to monitor stress hormones

In small animals like mice, the monitoring of endocrine functions over time is constrained seriously by the adverse effects of blood sampling. Therefore, noninvasive techniques to monitor, for example, stress hormones in these animals are highly demanded in laboratory as well as in field research. The aim of our study was to evaluate the biological relevance of a recently developed technique to monitor stress hormone metabolites in fecal samples of laboratory mice. In total, six experiments were performed using six male and six female mice each. Two adrenocorticotropic hormone (ACTH) challenge tests, two dexamethasone (Dex) suppression tests and two control experiments [investigating effects of the injection procedure itself and the diurnal variation (DV) of glucocorticoids (GCs), respectively] were conducted. The experiments clearly demonstrated that pharmacological stimulation and suppression of adrenocortical activity was reflected accurately by means of corticosterone metabolite (CM) measurements in the feces of males and females. Furthermore, the technique proved sensitive enough to detect dosage-dependent effects of the ACTH/Dex treatment and facilitated to reveal profound effects of the injection procedure itself. Even the naturally occurring DV of GCs could be monitored reliably. Thus, our results confirm that measurement of fecal CM with the recently established 5alpha-pregnane-3beta,11beta,21-triol-20-one enzyme immunoassay is a very powerful tool to monitor adrenocortical activity in laboratory mice. Since mice represent the vast majority of all rodents used for research worldwide and the number of transgenic and knockout mice utilized as animal models is still increasing, this noninvasive technique can open new perspectives in biomedical and behavioral science.

Emergence of individuality in genetically identical mice

Identical and Still Different Even in monozygotic twins reared together, there are always observable differences reflecting the influence of individual responses. Freund et al. (p. 756; see the Perspective by Bergmann and Frisén) developed an inbred mouse model for studying the environmental influences on genetically identical animals and examined their effects on behavioral and neural development. Over time, the brains and behaviors of inbred mice diversify. [Also see Perspective by Bergmann and Frisén] Brain plasticity as a neurobiological reflection of individuality is difficult to capture in animal models. Inspired by behavioral-genetic investigations of human monozygotic twins reared together, we obtained dense longitudinal activity data on 40 inbred mice living in one large enriched environment. The exploratory activity of the mice diverged over time, resulting in increasing individual differences with advancing age. Individual differences in cumulative roaming entropy, indicating the active coverage of territory, correlated positively with individual differences in adult hippocampal neurogenesis. Our results show that factors unfolding or emerging during development contribute to individual differences in structural brain plasticity and behavior. The paradigm introduced here serves as an animal model for identifying mechanisms of plasticity underlying nonshared environmental contributions to individual differences in behavior.

Baby schema modulates the brain reward system in nulliparous women

Ethologist Konrad Lorenz defined the baby schema (“Kindchenschema”) as a set of infantile physical features, such as round face and big eyes, that is perceived as cute and motivates caretaking behavior in the human, with the evolutionary function of enhancing offspring survival. The neural basis of this fundamental altruistic instinct is not well understood. Prior studies reported a pattern of brain response to pictures of children, but did not dissociate the brain response to baby schema from the response to children. Using functional magnetic resonance imaging and controlled manipulation of the baby schema in infant faces, we found that baby schema activates the nucleus accumbens, a key structure of the mesocorticolimbic system mediating reward processing and appetitive motivation, in nulliparous women. Our findings suggest that engagement of the mesocorticolimbic system is the neurophysiologic mechanism by which baby schema promotes human caregiving, regardless of kinship.

The Behavioral Endocrinology of Domestication: A Comparison between the Domestic Guinea Pig (Cavia apereaf.porcellus) and Its Wild Ancestor, the Cavy (Cavia aperea)

In this study spontaneous behavior and endocrine parameters were compared between the domestic guinea pig (Cavia aperea f. porcellus) and its wild ancestor, the cavy (Cavia aperea), to elucidate the process of domestication in this species. In 120 h of observation time the behavior of five groups of wild and seven groups of domestic guinea pigs, each consisting of one adult male and two adult females, was analyzed quantitatively. To assess the activities of the pituitary-adrenocortical (PAC), the pituitary-gonadal (PG), and the sympathetic-adrenomedullary (SAM) systems, serum cortisol, testosterone, epinephrine, and norepinephrine concentrations, as well as adrenal tyrosine hydroxylase activities, were determined in males of both forms. The following significant differences between wild cavies and domestic guinea pigs were found: the domesticated animals displayed less aggressive but more sociopositive and more male courtship behavior than their wild ancestors. In addition, they were distinctly less attentive to their physical environment than the wild cavies. The basal activity of the SAM system, as well as the reactivity of the SAM and the PAC systems, was distinctly reduced in the domesticated animals. In contrast, the basal activity of the PAC system did not differ between both forms. The activity of the PG system was significantly higher in males of the domestic guinea pig than in male wild cavies. Thus, in guinea pigs the process of domestication has led to typical behavioral traits-reduced aggressiveness, increased social tolerance-which have also been found in comparisons between wild and domestic forms of other species. The decreased reactivity of the organisms stress axes can be regarded as a physiological mechanism which helps domesticated animals to adjust to man-made housing conditions.

Role of a neuronal small non-messenger RNA: behavioural alterations in BC1 RNA-deleted mice

BC1 RNA is a small non-messenger RNA common in dendritic microdomains of neurons in rodents. In order to investigate its possible role in learning and behaviour, we compared controls and knockout mice from three independent founder lines established from separate embryonic stem cells. Mutant mice were healthy with normal brain morphology and appeared to have no neurological deficits. A series of tests for exploration and spatial memory was carried out in three different laboratories. The tests were chosen as to ensure that different aspects of spatial memory and exploration could be separated and that possible effects of confounding variables could be minimised. Exploration was studied in a barrier test, in an open-field test, and in an elevated plus-maze test. Spatial memory was investigated in a Barnes maze and in a Morris water maze (memory for a single location), in a multiple T-maze and in a complex alley maze (route learning), and in a radial maze (working memory). In addition to these laboratory tasks, exploratory behaviour and spatial memory were assessed under semi-naturalistic conditions in a large outdoor pen. The combined results indicate that BC1 RNA-deficient animals show behavioural changes best interpreted in terms of reduced exploration and increased anxiety. In contrast, spatial memory was not affected. In the outdoor pen, the survival rates of BC1-depleted mice were lower than in controls. Thus, we conclude that the neuron-specific non-messenger BC1 RNA contributes to the aptive modulation of behaviour.

Environmental enrichment enhances cellular plasticity in transgenic mice with Alzheimer-like pathology

Alzheimers disease (AD) is accompanied by hippocampal neuronal loss and abnormal neurogenesis, both of which probably contributing to AD-related cognitive deficits. Mounting evidence indicates that cognitive and physical stimulation provided by environmental enrichment improves neurogenesis in healthy animals and counteracts beta-amyloid pathology in mouse models of AD. Here, we hypothesized that environmental enrichment has also an impact on hippocampal neurogenesis in mice with AD-like pathology. Therefore, TgCRND8 mice and wild type littermates were either housed under standard conditions or in an enriched environment for 4 months. Standard housed TgCRND8 mice revealed diminished hippocampal cell proliferation and reduced number of mature newborn neurons compared to wild type littermates under the same housing condition. However, environmental enrichment reversed this genotype effect. Here, we show that cognitive and physical stimulation is capable of increasing the number of newborn mature hippocampal neurons in transgenic mice to wild type levels. Moreover, the expression of various plasticity associated molecules was enhanced in transgenic mice due to enriched housing. This study identifies that environmental enrichment improves diminished cellular plasticity in AD brain, probably enhancing the brain capacity to better compensate for neurodegeneration.

Environmental bias? Effects of housing conditions, laboratory environment and experimenter on behavioral tests.

Behavioral testing does not always yield similar results when replicated in different laboratories, and it usually remains unclear whether the variability in results is caused by different laboratory environments or different experimenters conducting the tests. In our study, we applied a systematic variation of housing conditions, laboratories and experimenters in order to test the influence of these variables on the outcome of behavioral tests. We wanted to know whether known effects of different housing conditions on behavior can be demonstrated regardless of the respective laboratory and experimenters. In this study, we compared the behavior of mice kept under enriched housing conditions with mice kept in unstructured cages regarding their exploratory, locomotor and anxiety‐related behavior in the barrier test, in the open‐field test and in the elevated plus‐maze test. Experiments were conducted by six different persons in two different laboratories. In spite of an extensive protocol standardizing laboratory environment, animal maintenance and testing procedures, significant differences in absolute values between different laboratories as well as between different experimenters were noticed in the barrier test and in the elevated plus‐maze test but not in the open‐field test. However, with regard to the differences between enriched and unstructured housing conditions, overall consistent results were achieved by different experimenters in both laboratories. We conclude that the reliability of behavioral phenotyping is not challenged seriously by experimenter and laboratory environment as long as appropriate standardizations are met and suitable controls are involved.

Is a wild mammal kept and reared in captivity still a wild animal

This study compared domestic guinea pigs (Cavia aperea f. porcellus; DGP) and two different populations of the wild cavy (Cavia aperea), its ancestor, to examine whether rearing of wild mammals in captivity affects their behavior and physiological stress responses. One population of wild cavies consisted of wild-trapped animals and their first laboratory-reared offspring (WGP-1). The animals of the other population were reared in captivity for about 30 generations (WGP-30). The spontaneous behavior of each of six groups of WGP-1 and WGP-30 and nine groups of DGP, each consisting of one adult male and two adult females, was analyzed quantitatively. Blood samples of the males were taken to determine cortisol, epinephrine, and norepinephrine concentrations. In addition, the exploratory behavior of 60-day-old male WGP-1, WGP-30, and DGP was investigated in an exploration apparatus. The domesticated animals displayed significantly less aggression, but significantly more sociopositive and male courtship behavior than their wild ancestors. In addition, DGP were much less attentive to their physical environment. Surprisingly, no behavioral difference was found between WGP-1 and WGP-30. Basal cortisol concentrations did not differ between wild and domestic guinea pigs. Catecholamine concentrations, however, as well as the challenge values of cortisol, were distinctly reduced in the DGP. WGP-1 and WGP-30 did not differ with respect to their endocrine stress responses. In the exploration apparatus both forms of wild cavies were much more explorative than the domestic animals. These data suggest that the long-term breeding and rearing of wild guinea pigs in captivity do not result in significant changes in behavior and hormonal stress responses. It appears to take much longer periods of time and artificial selection by humans to bring about characters of domestication in wild animals.

Social stress in guinea pigs

Confrontation studies between eight pairs of two 7-8 months old male guinea pigs, each raised with one female from their 30th day of age, were conducted in an enclosure of 2 m2 in the presence of an unfamiliar female. The opponents were chronically kept together for up to 8 days. When they were not separated after 52 hr, one or (in 1 case) both males fell into a comatose state and died 5-8 days after the onset of the confrontation. Four hr after the onset of the confrontations both opponents showed significantly increased plasma glucocorticoid (CS) titers. At this time as well as 24 hr earlier, prospective winners (PW) and prospective losers (PL) did not yet differ in any physiological parameter measured. Forty-eight hr later, PW were characterized by a low body weight loss, low CS, high testosterone (T) and elevated plasma-catecholamine (CA) values. In contrast, PL showed a high body weight loss, very high CS titers, low T-titers and more elevated CA values than PW. Despite these highly significant differences in physiological parameters, PL and PW did not yet differ in the frequency of any agonistic behavioral element recorded. Seventy-two hr after the onset of the chronic cohabitation, losers began to behave more and more passive, they ceased feeding and drinking and were less and less involved in social interactions. The physiological differences between winners and losers intensified.(ABSTRACT TRUNCATED AT 250 WORDS)

Social experience, behavior, and stress in guinea pigs

This study examined the effect of varying rearing and testing conditions on guinea pig aggression, courting behavior, endocrine responses and body weight. Pairs of 7-8-month-old males were placed in chronic confrontations for 6-50 days in 2 m2 enclosures. Social behavior was recorded with a total of 882 h observation time. Body weight as well as plasma glucocorticoid, testosterone and norepinephrine titers were determined for each male 20 h before, and 4, 52 and 124 h after, the onset of the chronic encounters. Three experiments were conducted: in Experiment I, 7 pairs of males, each male raised singly with one female (FRM), were confronted in the presence of an unfamiliar female, in Experiment II, 6 pairs of FRM were confronted with no female present, and in Experiment III, 7 pairs of males which were raised in different large colonies were confronted in the presence of an unfamiliar female. In Experiment II and III low levels of aggression, no distinct endocrine changes and no indications of physical injury occurred in winners or losers, whereas in Experiment I high levels of aggression and courting behavior, extreme increases in glucocorticoid titers and distinct decreases in body weights were found in both males. Losers, however, were affected to a much greater extent than winners. These findings suggest that in guinea pigs a causal relationship exists between social rearing conditions, behavior as adults and degree of social stress in chronic encounters.