Diffuse traumatic axonal injury in mice induces complex behavioural alterations that are normalized by neutralization of interleukin-1ß.

Widespread traumatic axonal injury (TAI) results in brain network dysfunction, which commonly leads to persisting cognitive and behavioural impairments following traumatic brain injury (TBI). TBI induces a complex neuroinflammatory response, frequently located at sites of axonal pathology. The role of the pro-inflammatory cytokine interleukin (IL)-1ß has not been established in TAI. An IL-1ß-neutralizing or a control antibody was administered intraperitoneally at 30 min following central fluid percussion injury (cFPI), a mouse model of widespread TAI. Mice subjected to moderate cFPI (n = 41) were compared with sham-injured controls (n = 20) and untreated, naive mice (n = 9). The anti-IL-1ß antibody reached the target brain regions in adequate therapeutic concentrations (up to ~30 µg/brain tissue) at 24 h post-injury in both cFPI (n = 5) and sham-injured (n = 3) mice, with lower concentrations at 72 h post-injury (up to ~18 µg/g brain tissue in three cFPI mice). Functional outcome was analysed with the multivariate concentric square field (MCSF) test at 2 and 9 days post-injury, and the Morris water maze (MWM) at 14-21 days post-injury. Following TAI, the IL-1ß-neutralizing antibody resulted in an improved behavioural outcome, including normalized behavioural profiles in the MCSF test. The performance in the MWM probe (memory) trial was improved, although not in the learning trials. The IL-1ß-neutralizing treatment did not influence cerebral ventricle size or the number of microglia/macrophages. These findings support the hypothesis that IL-1ß is an important contributor to the processes causing complex cognitive and behavioural disturbances following TAI.

Traumatic axonal injury in the mouse is accompanied by a dynamic inflammatory response, astroglial reactivity and complex behavioral changes.

BACKGROUND: Diffuse traumatic axonal injury (TAI), a common consequence of traumatic brain injury, is associated with high morbidity and mortality. Inflammatory processes may play an important role in the pathophysiology of TAI. In the central fluid percussion injury (cFPI) TAI model in mice, the neuroinflammatory and astroglial response and behavioral changes are unknown. METHODS: Twenty cFPI-injured and nine sham-injured mice were used, and the neuroinflammatory and astroglial response was evaluated by immunohistochemistry at 1, 3 and 7 days post-injury. The multivariate concentric square field test (MCSF) was used to compare complex behavioral changes in mice subjected to cFPI (n = 16) or sham injury (n = 10). Data was analyzed using non-parametric statistics and principal component analysis (MCSF data). RESULTS: At all post-injury time points, ß-amyloid precursor protein (ß-APP) immunoreactivity revealed widespread bilateral axonal injury and IgG immunostaining showed increased blood-brain barrier permeability. Using vimentin and glial fibrillary acidic protein (GFAP) immunohistochemistry, glial cell reactivity was observed in cortical regions and important white matter tracts peaking at three days post-injury. Only vimentin was increased post-injury in the internal capsule and only GFAP in the thalamus. Compared to sham-injured controls, an increased number of activated microglia (MAC-2), infiltrating neutrophils (GR-1) and T-cells (CD3) appearing one day after TAI (P<0.05 for all cell types) was observed in subcortical white matter. In the MCSF, the behavioral patterns including general activity and exploratory behavior differed between cFPI mice and sham-injured controls. CONCLUSIONS: Traumatic axonal injury TAI resulted in marked bilateral astroglial and neuroinflammatory responses and complex behavioral changes. The cFPI model in mice appears suitable for the study of injury mechanisms, including neuroinflammation, and the development of treatments targeting TAI.

The influence of social subordinate housing on the withdrawal effects from progesterone and estradiol in male rats.

Chronic stress and its concomitant neurobiological consequences are, in all probability, provocateurs of mental disease in humans. To gain some insight into the provocative effects of stress on hormonally dependent conditions, we developed a rat model that combines social subordinate housing (SSH) with withdrawal from combined progesterone (P) and estradiol (E) treatment (PEWD). At the start of the experiment, male Wistar rats were housed in triads consisting of one younger rat (35 days old) and two older rats (55 days old), with the intent of producing subordination stress in the younger animals. Triads containing three 35-day-old rats were used as age controls. Subordination stress was assessed with the elevated plus maze (EPM) and by corticosterone (CORT) analysis. Social rank within the triads was determined using a food competition test (FCT) and a tube test (TT). The younger rats (subordinate) and the dominant rats were assigned to 10 days of treatment with 5mg/kg P combined with 10 µg/kg E, or placebo (vehicle). Twenty-four hours after the last injection, the subordinate and dominant animals were tested in an open-field test (OFT) and a social challenge test (SCT). The SCT consisted of a 10-min exposure to three unfamiliar rats. SSH increased baseline CORT levels and reduced EPM open-arm time and post-EPM CORT levels compared to age-control rats. Only in the subordinate animals did PEWD increase locomotor activity and digging behavior, and reduce wrestling and pinning behavior. The behavioral results indicate an interaction between the effects of the lasting social subordinate stress and PEWD.

The multivariate concentric square field test reveals behavioral profiles of risk taking, exploration, and cognitive impairment in mice subjected to traumatic brain injury.

There is a need for more efficient tests to evaluate functional outcome following experimental traumatic brain injury (TBI), reflecting deficits in cognitive, sensory, and motor functions that are seen in TBI patients. The Multivariate Concentric Square Field (MCSF) test is a relatively new behavioral model that measures exploration, risk taking, risk assessment, and shelter seeking, all of which are evolutionarily-conserved strategies for survival. The multivariate design enables scoring of different functional domains in a single test situation, with a free choice of optional environmental settings. Furthermore, repeated trials permits cognitive effects to be measured. In the present study, 11 anesthetized C57BL6 mice received controlled cortical injury (CCI) (0.5 mm and 3.3 m/sec) over the right parietal cerebral cortex or sham surgery (n = 12). Naïve mice (n = 12) not subjected to any surgical procedure were also included. The animals were evaluated in the MCSF test at 2 and 7 days post-surgery, and behavioral profiles were analyzed. The results revealed differences in risk taking and explorative behavior between the sham animals and the animals subjected to trauma. Animals subjected to trauma were characterized by taking more risks and had a higher level of exploration activity, but they sought less shelter. Repeated exposure to the MCSF caused a general decrease in activity in the naïve and sham group, while a more specific behavioral impairment was seen in injured mice, suggesting cognitive dysfunction. We submit that the MCSF test is a useful complementary tool for functional outcome evaluation in experimental TBI.

Peripheral administration of pancreatic polypeptide inhibits components of food-intake behavior in dogs.

Pancreatic polypeptide (PP) belongs to the neuropeptide Y (NPY) family of peptides and is released from pancreatic F cells postprandially. PP functions as a peptide hormone and has been associated with decreased food intake in humans and rodents. Our study describes the effects of PP on feeding behavior in dogs, whose mammalian order (Carnivora) is more distantly related to primates and rodents than these are to each other. Furthermore, obesity is becoming more prevalent in dogs which makes knowledge about their appetite regulation highly relevant. Repeated peripheral administration of physiological doses of PP (three injections of 30 pmol/kg each that were administered within 30 min) to six male beagle dogs prolonged the median time spent eating three servings of food by 19% but resulted in no reduction of food intake. In addition, PP decreased the duration of food-seeking behavior after the first serving by 71%. Thus, a physiological dose of PP seems to decrease both the appetitive and the consummatory drive in dogs.

Withdrawal effects from progesterone and estradiol relate to individual risk-taking and explorative behavior in female rats.

Withdrawal from progesterone and estradiol has been used as an animal model of premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PMDD). In the clinical population individual sensitivity to sex steroid hormones, personality and heredity influence PMS/PMDD. Understanding the phenotypic risk factors of PMS/PMDD and drug development requires an animal model which incorporates individual steroid sensitivity. The main objective of this study was to investigate whether the individual trait of risk-taking and exploration influence the severity of PEWD in female rats. Thirty-two female Wistar rats in their diestrus phase were tested in the open field (OF) and divided into high responders (HR) and low responders (LR). Injections were given i.p. twice daily for 6 days, either 5 mg/kg progesterone combined with 10 microg/kg 17beta-estradiol, or vehicle (sesame oil). After a 24-hour withdrawal the animals were tested in the elevated plus maze (EPM). Blood samples for CORT analysis were collected after both behavioral tests. The HR rats withdrawn from progesterone and estradiol, spent less time on the EPM open arms and had lower CORT levels than the HR controls. The LR group showed no differences in EPM behavior and CORT levels during PEWD. The controls showed a stable trait of risk-taking and exploration, indicated by behavioral and CORT level correlations between the OF and EPM tests. These findings show that female rats with the trait of risk-taking and explorative behavior (HR) are more affected by PEWD.

The multivariate concentric square field test reveals different behavioural profiles in male AA and ANA rats with regard to risk taking and environmental reactivity.

The aim of the present investigation was to compare the behavioural profiles in alcohol-preferring AA (Alko, alcohol) and alcohol-avoiding ANA (Alko, non-alcohol) rats. Twelve adult, alcohol-naïve male AA and ANA rats were tested in the recently established multivariate concentric square field (MCSF) test. The more traditional open field and elevated plus-maze tests were used as reference tests. Six weeks after the initial MCSF test, a repeated testing was used to explore differences in acquired recognition after a previous experience. The results revealed distinct differences between the two lines. The ANA rats were generally more active in the three tests. In the MCSF, parameters of risk taking and shelter seeking indicated differences between the two lines. The ANA rats had higher shelter seeking behaviour and less risk taking behaviour than the AA rats. Repeated exposure to the MCSF caused a general decrease in activity and reduction in the number of visits to the various zones, especially evident in the ANA rats. The ANA rats showed more shelter seeking than the AA rats and also more shelter seeking than in the first trial, supporting an "anxiety-like" profile in these rats. In conclusion, the parameters related to risk taking and shelter seeking revealed obvious differences between AA and ANA rats. The higher risk taking behaviour seen in the AA rats might relate to their innate propensity for high voluntary alcohol intake. The results are discussed in relation to the reported neurobiological differences and in relation to other alcohol-preferring and alcohol-avoiding rat lines.

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.

Growth hormone replacement in hypophysectomized rats affects spatial performance and hippocampal levels of NMDA receptor subunit and PSD-95 gene transcript levels.

Clinical studies have demonstrated that growth hormone (GH) promotes learning and memory processes in GH-deficient (GHD) patients. In animal studies, GH also influences the N-methyl-D-aspartate (NMDA) receptor system in the hippocampus, an essential component of long-term potentiation (LTP), which is highly involved in memory acquisition. This study was designed to examine the beneficial effects of recombinant human GH (rhGH) on cognitive function in male rats with multiple hormone deficiencies resulting from hypophysectomy (Hx). The performance of an rhGH-treated group and an untreated control group was appraised in the Morris water maze (MWM). The rhGH-treated group performed significantly better in the spatial memory task than the control animals on the second and third trial days. Further training eliminated this difference between the groups. Hippocampal mRNA expression of the NMDA subunits NR1, NR2A and NR2B, insulin-like growth factor type 1 receptor (IGF-1R), and postsynaptic density protein-95 (PSD-95) was then measured in the animals by Northern blot analysis. The results suggest that there may be a relationship between the NMDA receptor subunit mRNA expression levels and learning ability, and that learning is improved by rhGH in Hx rats. Furthermore, a link between MWM performance and PSD-95 was also suggested by this study.

Variations in opioid peptide levels during the estrous cycle in Sprague-Dawley rats.

The estrous cycle, with its various hormonal conditions, may provide us with the means of understanding how endocrine states relate to opioid mechanisms. There has been increasing experimental support for interaction between sex steroids and opioid peptides in the central nervous system. Here, we describe fluctuations in endogenous brain immunoreactive (ir) peptide levels during various phases of the estrous cycle in the female Sprague-Dawley rat. Ir levels of dynorphin A, dynorphin B, Leu-enkephalin-Arg(6), Met-enkephalin-Arg(6)Phe(7) and nociceptin/orphanin FQ were measured in the pituitary gland and in 10 areas of the brain during the diestrus, proestrus and estrus phase. In several areas of the brain, basal levels of endogenous opioid peptides showed variation during the course of the estrous cycle. Significant differences were found between the diestrus state and the proestrus and/or estrus conditions, particularly in the nucleus accumbens, caudate putamen and the substantia nigra. The ir levels of the endogenous peptide nociceptin/orphanin FQ became altered in only one of the areas measured, indicating less variance during the estrous cycle. Correlation analyses revealed that significant associations between dynorphin A or dynorphin B and Leu-enkephalin-Arg(6) were found more often during estrus than during the diestrus and proestrus conditions. The ratio between the ir levels of Leu-enkephalin-Arg(6), a cleavage product of the enzymatic conversion of dynorphin peptides into shorter peptides in vivo, and dynorphin peptides was calculated. The significantly lower ratio between Leu-enkephalin-Arg(6) and dynorphin B in diestrus than in proestrus and estrus also indicates cyclic fluctuations in the enzymatic cleavage of dynorphin. These findings are discussed in relation to the possible role of interactions between sex steroids and opioid peptide mechanisms during the normal estrous cycle.

The Concentric Square Field: a multivariate test arena for analysis of explorative strategies.

In this study, we describe the behavior of laboratory rats in a recently developed observation arena, the Concentric Square Field (CSF). The CSF contains a number of areas designed to provoke exploration and behaviors associated with risk assessment, risk taking and security seeking in an environment not previously experienced. The model includes sheltered, open and elevated areas, a hole board device, areas with different light conditions, and wall-enclosed corridors. The rationale behind the CSF is to meet the demand for multivariate test situations that are not predictive in the sense of previous definition of a specific purpose of measuring a certain mental state. We define multivariate as being a free choice of where to stay in areas of different qualities. In the present study, identification of risky as opposed to safe areas is based on the retrieval behavior in lactating females and hoarding of food pellets in food-deprived males. Furthermore, we describe the effects of pre-trial food deprivation, immobilization, social stress, strain differences (Sprague-Dawley, Wistar and Lister Hooded males), sex differences (Sprague-Dawley) and repeated testing. Besides the conventional statistics, a principal component analysis (PCA) helped to discriminate between the various categories tested. Our conclusion is that the multivariate and non-predictive test situation (CSF) and the use of PCA provide a good tool for ethoexperimental analysis.

Exploration and risk assessment in female wild house mice (Mus musculus musculus) and two laboratory strains.

In an evolutionary prospective, it is possible that female mice have a differential perception of novel events than male mice and use a different behavioural strategy for risk assessment. However, female mice are less studied than male mice in behavioural tests of emotional reactivity. The aim of the present study was to investigate how wild-derived female house mice differ from domesticated female mice in their risk assessment strategy. A total of 46 adult female mice, 14 BALB/c, 16 C57BL/6 and 14 Wild mice were tested in the Concentric Square Field (CSF), Open Field (OF) and Elevated Plus Maze (EPM) at three consecutive days. Parameters from all three tests were categorized according to their relevance to activity, exploration, approach-avoidance and use of open areas-shelter. Principal Component Analysis (PCA-SIMCA) of the animals' behaviour in the CSF arena was performed both for females alone and in comparison with earlier findings in male mice under the same test conditions. The results clearly show that female wild mice had a higher avoidance of open areas than the laboratory strains. There was also a trend indicating differences in exploration and approach-avoidance between female Wild and the laboratory strains. The multivariate test, CSF, was able to detect differences between Wild and laboratory strains in three (exploration, approach-avoidance, open-shelter) of the four functional categories measured. Wild female mice also had a higher frequency of rearing and grooming and a lower duration in the corridors in the CSF. Clear strain differences were found between BALB and C57BL in all tests where BALB generally had higher risk assessment and lower risk taking than C57BL. No general sex differences were found, however the sex differences were greater in Wild mice compared to the laboratory strains.

Exploration and risk assessment: a comparative study of male house mice (Mus musculus musculus) and two laboratory strains.

The ability to gather information and assess risks in novel environments is crucial for survival and fitness in the wild. Our aim was to characterise behavioural strategies of exploration and risk assessment in novel environments and to investigate in what respects wild house mice differ from domesticated mice. A total of 39 adult male mice from three genetic backgrounds (Wild, BALB/c, and C57BL/6) were tested in three behavioural tests, the concentric square field (CSF), a modified open field (OF), and a conventional elevated plus maze (EPM). In addition to spatial measures, behavioural measures of exploration and risk assessment were registered. The parameters were categorised according to their relevance to activity, exploration, approach-avoidance, and use of open areas/shelter. Wild mice had lower activity and a higher avoidance of open areas than the laboratory strains. No differences were found in exploratory motivation. The BALB/c mice avoided risk areas and showed high risk assessment (SAP), whereas C57BL/6 mice were more explorative and risk taking and showed little risk assessment. Wild mice seemed to have a different behavioural strategy of risk assessment in being more cautious before entering a potentially dangerous zone but explored all zones after assessed as nonrisky. A principal component analysis (PCA) of the animals' behaviour in the CSF arena supported these findings by clearly separating the three strains on the basis of their behavioural performances. It is concluded that there are obvious differences in behavioural strategies related to risk assessment and risk taking among wild mice versus domesticated house mice and also among laboratory strains. The relationship between the animal's risk concern and adaptability is discussed and should be a matter of importance considering animal welfare as well as the experimental aim and protocol.

Functional evaluation of cerebral microembolization in the rat.

This study investigates the effects of cerebral microembolism on motor performance and risk assessment behavior in the rat. Cerebral infarcts were produced in rats by injecting small plastic beads into the left heart ventricle under short-acting anesthesia. The functional outcome was tested 24 h later by subjecting the animals to a series of consecutive behavioral tests. Thereafter, the rats were anesthetized and underwent magnetic resonance imaging. On average about seven infarcts per brain were found. The volume of the individual infarcts was largest in the hippocampus (mean=4.26 mm(3)) and smallest in the white matter (mean=0.83 mm(3)). Embolized animals performed spontaneous and evident locomotion. The activity was, however, significantly decreased compared to rats treated with vehicle. More specific tests for motor ability revealed reduced gait capacity and muscular strength. A significant relationship was found between behaviors reflecting motor ability and the total volume of infarcted tissue in the brain stem, cortex and cerebellum. Also the behavioral profile of risk and benefit assessment was found to be altered by the microembolization. It is concluded that the combination of the microembolization method and behavioral tests provides a valuable tool for further studies of the pathophysiology of, and potential treatment for, cerebral infarction.