The use of sudden darkness in mice: a behavioural and pharmacological approach

Sudden darkness is a non-invasive behavioural analysis tool which increases motor activity and decreases anxiety in rats. It has been shown in previous studies that in rats, dark test conditions can also modify behavioural responses to drugs acting on the dopaminergic system. The increasing use of transgenic mice in behavioural research has raised interest in developing new tests for phenotyping mice. Hence, the aim of the present study was to adapt the sudden darkness paradigm for mice. In the first part of this study, effects of sudden darkness on the performance of mice in the elevated plus maze test were evaluated. Both genders of two mouse strains (Swiss and Balb/c) were tested either in high light intensity conditions or were exposed to sudden darkness. In the second part, responses to the 5-HT_1A receptor agonist 8-OH-DPAT (0.5 and 1.0 mg/kg) and 5-HT_2C receptor agonist mCPP (1.0 and 2.0 mg/kg) were investigated in male Swiss mice. Sudden darkness induced a clear anxiolytic effect in male and female Swiss mice. In Balb/c mice, anxiety-related behaviour was only decreased in females, whereas in males the anxiety state remained unchanged. An increase in motor activity was only observed in male Swiss mice; in the other groups, sudden darkness did not affect locomotion. Depending on the light conditions used, the behavioural response to receptor agonists was more evident: 8-OH-DPAT (1.0 mg/kg) only significantly decreased the anxiety state when mice were tested under high levels of illumination, whereas the anxiogenic effect of mCPP (1.0 and 2.0 mg/kg) was only evident in the dark. This study suggests that the sudden darkness paradigm is also a useful tool for the analysis of mice and can be used to modulate the anxiety level without administering drugs. Depending on the mouse strain tested, the same effects on anxiety and motor activity were observed as have been shown for rats.     

The role of hippocampal cholinergic mechanisms in the aquisition of a barpress response.

The role of hippocampal cholinergic mechanisms in learning a bar-press response reinforced with food was investigated. Firstly, an interstrain comparison showed that mice having a low choline acetyltransferase activity in the dorsal hippocampus were quicker to associate the barpress with reinforcement. Secondly, when the activity of this enzyme was reduced by a subseizure electrical stimulation of the hippocampus learning was accelerated. It is suggested that acetylcholine availability at the hippocampal synapses slowed the apparition of these learned responses.     

Differences in developing the lever-pressing behavior in two strains of rats.

Learning to lever-press for food in rats may be experimentally analyzed according to (a) association of lever-pressing with food reinforcement; (b) development of the behavior of lever-pressing. The latter was studied in two strains of rats with a high or low level of 2,3-diphosphoglycerate (DPG) in erythrocytes. Twelve males from each strain, previously trained to lever-press, were used. The rate of responding increased faster with repeated training-testing sessions in the High Strain than in the Low-Strain under the CRF and the FR 10 schedule. The genetic difference in the DPG level in erythrocytes and the resultant long term difference in oxygen transport capability may be a significant factor contributing to the behavioral differences in these two strains.     

The Valsalva manoeuvre--cardiovascular effects and performance technique: a critical review

Variations in the technique of the Valsalva manoeuvre (VM) have been shown to greatly influence the pattern of cardiovascular response (CVR) to the test. Intra-strain tachycardia, post-strain bradycardia, Valsalva ratio, and baroreflex sensitivity decrease in proportion to an increase in lung volume and a decrease in strain pressure at VM. In conditions of completely expanded lungs and low strain pressure many subjects reveal an intra-strain bradycardic response to VM instead of the usual tachycardic one. Intra-strain arterial hypotension and post-strain hypertension decrease with decrease in strain pressure. The changes in heart rate and blood pressure during an expiratory VM are greater than the responses observed during completition of an inspiratory VM. The rate of the deep inspiration prior to strain has an impact particularly on phase I of the VM. The magnitude of the CVR correlates with the strain duration, particularly at high levels of strain pressure, and depends on the baseline level of the cardiovascular parameters and their variations. The paper discusses the possible mechanisms of different CVRs to variations in the technique of the VM. Some practical recommendations are suggested.     

Differences in forebrain activation in two strains of rat at rest and after spinal cord injury

Forebrain activation patterns in normal and spinal-injured Sprague-Dawley (SD) rats were determined by measuring regional cerebral blood flow as an indicator of neuronal activity. Data are compared to our previously published findings from normal and spinal-injured Long-Evans (LE) rats and reveal a striking degree of overlap, as well as differences, between strains in the basal (unstimulated) forebrain activation in normal animals. Specifically, 81% of the structures sampled showed similar activation in both strains, suggesting a consistent and identifiable pattern of basal cerebral activation in the rat. LE controls showed significantly greater basal activation in the remaining structures compared to SD control group, including the anterior dorsal thalamus, basolateral amygdala, SII cortex, and the hypothalamic paraventricular nucleus. In contrast, spinal cord injury (SCI) resulted in strain-specific changes in forebrain activation categorized by structures that showed significant increases in: (1) only LE SCI rats (posterior, ventrolateral, and ventroposterolateral thalamic nuclei); (2) only SD SCI rats (anterior-dorsal and medial thalamus, basolateral amygdala, cingulate and retrosplenial cortex, habenula, interpeduncular nucleus, hypothalamic paraventricular nucleus, periaqueductal gray); or (3) both strains (arcuate nucleus, ventroposteromedial thalamus, SI and SII somatosensory cortex). These results provide information related to the remote, i.e. supraspinal, effects of spinal cord injury and suggest that genetic differences play an important part in the forebrain response to such injury. Brain activation studies therefore provide a useful tool in understanding the full extent of secondary consequences following spinal injury and for identifying potential central mechanism responsible for the development of pain.     

Biomechanical analysis and quantitative analysis of bone scintigraphy on thrust plate hip prosthesis

Introduction To study the load distribution of the thrust plate hip prosthesis (TPP, Sulzer Medica, Baar, Switzerland) on femoral bone, a TPP insertion group and intramedullary cemented stem insertion group were prepared with the use of embalmed femoral anatomic specimens, and strain on the femoral bone induced by loading was measured.Materials and methods Bone scintigraphy was performed in 26 joints which underwent total hip arthroplasty with the use of TPP, to enable quantitative evaluation of postoperative remodeling of the bone.Results In the TPP insertion group, the strain was almost equivalent to that in the untreated femoral control group. On the other hand, compared with the control group and TPP insertion group, strain in the proximal portion of the femoral bone (medial side of the femoral neck) was significantly smaller in the cemented stem group (control group versus cemented stem insertion group, p=0.0062; cemented stem insertion group versus TPP 130° insertion group, p=0.0005; cemented stem insertion group versus TPP 140° insertion group, p=0.0031). Bone scintigrams revealed decreased uptake at 12 weeks after operation compared with 6 weeks after operation, indicating that TPP allows earlier implant stabilization than the conventional stem.Conclusion Compared with the conventional stem, TPP is a prosthesis that can perform physiological load transmission.     

Anxiolytic-like profile in Wistar, but not Sprague–Dawley rats in the social interaction test

Rationale The social interaction test is a valuable behavioural model for testing anxiolytic drugs in rodents, quantifying the level of social behaviour between pairs of rats.Objective The aim of the present study was to assess the appropriateness of the social interaction test for use with a Sprague–Dawley rat line, because of increasing use of this strain in targeted mutagenesis research.Methods Sprague–Dawley and Wistar rats received either diazepam or mCPP or were exposed to different environmental conditions (lighting, social isolation prior testing, habituation, testing-time). General anxiety-related parameters measured were: duration of active social contact, frequency of active social contact, latency to first contact. Different forms of active social contact were recorded: number of crawls, follows and sniffs. Secondly, aversion-induced hippocampal serotonin release and serotonin content in brain regions were measured.Results In Wistar rats habituation to the test substantially increased the time of social contact, an effect comparable with treatment with diazepam (1 mg/kg), whereas changes in the lighting level had less impact. Latency to the first contact increased under anxiety-reducing conditions, the frequency of contacts did not change consistently. Sprague–Dawley rats behaviour did not change under varying environmental conditions, and treatment with diazepam had only sedating effects at higher doses (5 mg/kg). Anxiogenic doses of mCPP caused reduced social interaction in both strains. Serotonin release and serotonin content were higher in the anxious Wistar rats.Conclusions Different rat strains as well as differing test conditions have a major impact on the outcome of this animal test for anxiety.     

Postnatal development of resistance to short-term high-dose toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in TCDD-resistant and -semiresistant rats

Despite great interspecies differences in adult 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) sensitivity, the toxic potency of TCDD is similar across species in fetal mortality. Han/Wistar (Kuopio; H/W) rats are exceptionally resistant to acute toxicity of TCDD, but show sensitivity to embryotoxicity and teratogenicity. The resistance of adult H/W rats to acute TCDD toxicity is based on a point mutation in the transactivation domain of the aryl hydrocarbon receptor (AHR) and to an unknown gene “B”. This study investigated the time course of postnatal development of resistance to TCDD and the significance of genotypic variation in resistance development. H/W, line A (a new line with the H/W-type mutated AHR), and line B rats (a line with normal AHR but moderately resistant because of gene “B”) were exposed to a single dose of TCDD 2-56 days after birth. H/W and line A rats received 1000 μg/kg; male and female B rats received 200 and 100 μg/kg, respectively. Survival was monitored for 42 days. Interestingly, although TCDD ceased growth and weight gain in all TCDD groups, the younger dosed animals did not seem to reach the body weight of the older dosed animals even in 100 days. The survival results after 42 days showed that line A rats are fairly resistant to TCDD immediately after birth, and their full TCDD resistance develops during the first week of life. The moderate resistance of line B rats develops approximately at the time of weaning. This difference in the time course of resistance development suggests that there are basic differences in pathways mediating resistance in lines A and B rats.     

In vivo anterior cruciate ligament strain behaviour during a rapid deceleration movement: case report

The mechanism of anterior cruciate ligament (ACL) injury is still unclear. To gain this insight, knowledge of the mechanical behaviour of the healthy ACL during activities that may stress the ligament must be investigated in vivo. The goal of this research was to measure ACL strain in vivo during rapid deceleration, a sport type movement that has been previously shown to precede injuries to the ACL in healthy subjects. A young male subject with no previous knee joint injuries volunteered after informed consent. The strain gauge device (DVRT) was calibrated and surgically implanted in the antero-medial band of the intact ACL. The subject was then transported to the lab for data collection. The zero strain position of the ACL was determined using the slack-taut technique. The subject hopped as quickly as possible from a distance of 1.5 m to the target, an X taped at the centre of a force plate, landing with the instrumented left leg and stopping in the landed position. The entire collection window was five seconds at 1000 Hz. A total of three rapid deceleration trials were collected and averaged over the hop cycle. The slack-taut test was then repeated to ensure proper operation of the DVRT and the reliability of the results. The results showed an average peak strain of the ACL during the instrumented Lachman test of 2.00±0.17%. The average peak strain of the ACL during the rapid deceleration task was 5.47±0.28%. The data indicate that the RD task caused an increase in peak ACL strain that is much higher than during the instrumented Lachman test, and that the strain begins to increase during the flight phase, prior to landing, and reaches a peak that corresponds to the peak ground reaction force. This technique may be used in further sport-specific movements to gain insight into movement patterns associated with ACL injury mechanisms.     

Dose-response analysis of short-term effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in three differentially susceptible rat lines

Line A, B, and C rats were selectively bred from TCDD-resistant Han/Wistar (Kuopio; H/W) and TCDD-sensitive Long-Evans (Turku/AB; L-E) rats. Line A rats are the most resistant to TCDD acute lethality followed by line B and line C rats. The resistance in line A rats is associated with a mutated H/W-type aryl hydrocarbon receptor (Ahr) allele (Ahr(hw)) and in line B rats the resistance is associated with an allele of an unknown gene B (B(hw)), while line C rats are almost as sensitive to TCDD as L-E rats. The dose-responses of characteristic short-term effects (day 8 postexposure) of TCDD were used to evaluate the efficacy (magnitude of effect) and potency relationships between these lines. Line A rats showed similar efficacies as line C (line A:line C efficacy ratio more than 0.7) for thymus weight, EROD activity, and incisor tooth defects. In contrast, efficacies in line A were decreased (efficacy ratios 0.19-0.37) for body weight change, serum bilirubin, and FFA levels, and serum ASAT activity. For most endpoints the efficacies in line B rats seem to be lower than in line C rats. The potencies were close to each other in line A and B rats, but somewhat lower than in line C rats. The results support our previous concept of two different AHR-mediated signaling pathways leading to dioxin type I and type II endpoints. Rats with the Ahr(hw/hw) genotype show a markedly decreased efficacy for type II endpoints, but B(hw) allele had only a minor effect on efficacies for most endpoints. Both H/W-type resistance alleles also decreased the potency of TCDD. However, the potency differences in short-term toxicity seem not to explain, at least alone, the differences seen in acute lethality among the rat lines.