Approach, avoidance, and contact behavior of individually recognized animals automatically quantified with an imaging technique

Emerging Role of Translational Digital Biomarkers Within Home Cage Monitoring Technologies in Preclinical Drug Discovery and Development

In drug discovery and development, traditional assessment of human patients and preclinical subjects occurs at limited time points in potentially stressful surroundings (i.e., the clinic or a test arena), which can impact data quality and welfare. However, recent advances in remote digital monitoring technologies enable the assessment of human patients and preclinical subjects across multiple time points in familiar surroundings. The ability to monitor a patient throughout disease progression provides an opportunity for more relevant and efficient diagnosis as well as improved assessment of drug efficacy and safety. In preclinical in vivo animal models, these digital technologies allow for continuous, longitudinal, and non-invasive monitoring in the home environment. This manuscript provides an overview of digital monitoring technologies for use in preclinical studies including their history and evolution, current engagement through use cases, and impact of digital biomarkers (DBs) on drug discovery and the 3Rs. We also discuss barriers to implementation and strategies to overcome them. Finally, we address data consistency and technology standards from the perspective of technology providers, end-users, and subject matter experts. Overall, this review establishes an improved understanding of the value and implementation of digital biomarker (DB) technologies in preclinical research.

Neurotoxic effects of sublethal concentrations of cyanobacterial extract containing anatoxin-a(s) on Nauphoeta cinerea cockroaches

The detection of cyanotoxins, such as the anatoxin-a(s), is essential to ensure the biological safety of water environments. Here, we propose the use of Nauphoeta cinerea cockroaches as an alternative biological model for the biomonitoring of the activity of anatoxin-a(s) in aquatic systems. In order to validate our proposed model, we compared the effects of a cyanobacterial extract containing anatoxin-a(s) (CECA) with those of the organophosphate trichlorfon (Tn) on biochemical and physiological parameters of the nervous system of Nauphoeta cinerea cockroaches. In brain homogenates from cockroaches, CECA (5 and 50 μg/g) inhibited acetylcholinesterase (AChE) activity by 53 ± 2% and 51 ± 7%, respectively, while Tn (5 and 50 μg/g) inhibited AChE activity by 35 ± 4% and 80 ± 9%, respectively (p < 0.05; n = 6). Moreover, CECA at concentrations of 5, 25, and 50 µg/g decreased the locomotor activity of the cockroaches, diminishing the distance travelled and increasing the frequency and duration of immobile episodes similarly to Tn (0.3 μg/g) (p < 0.05, n = 40, respectively). CECA (5, 25 and 50 μg/g) induced an increase in the leg grooming behavior, but not in the movement of antennae, similarly to the effect of Tn (0.3 μg/g). In addition, both CECA (50 µg/200 μl) and Tn (0.3 µg/200 μl) induced a negative chronotropism in the insect heart (37 ± 1 and 47 ± 8 beats/min in 30 min, respectively) (n = 9, p > 0.05). Finally, CECA (50 µg/g), Tn (0.3 µg/g) and neostigmine (50 µg/g) caused significant neuromuscular failure, as indicated by the monitoring of the in vivo neuromuscular function of the cockroaches, during 100 min (n = 6, p < 0.05, respectively). In conclusion, sublethal doses of CECA provoked entomotoxicity. The Tn-like effects of CECA on Nauphoeta cinerea cockroaches encompass both the central and peripheral nervous systems in our insect model. The inhibitory activity of CECA on AChE boosts a cascade of signaling events involving octopaminergic/dopaminergic neurotransmission. Therefore, this study indicates that this insect model could potentially be used as a powerful, practical, and inexpensive tool to understand the impacts of eutrophication and for orientating decontamination processes.

Jaburetox, a natural insecticide derived from Jack Bean Urease, activates voltage-gated sodium channels to modulate insect behavior

Jaburetox (Jbtx) is an insecticidal peptide derived from Canavalia ensiformis urease, whose mechanism of action is not completely elucidated. We employed behavioral, electromyographical and electrophysiological protocols to identify the cellular and molecular targets involved in the Jbtx entomotoxicity in cockroaches and locusts. In Nauphoeta cinerea, Jbtx (32 μg/g) altered the locomotory behaviour inducing a significative decrease in the distance travelled followed by a significant increase in stopped time (52 ± 85 cm and 2573 ± 89 s, p < .05, n = 40). Jbtx (8 to 32 μg/g body weight, respectively) also increased the leg and antennae grooming activities (p < .05, n = 40, respectively). Jbtx (8 to 16 μg/g) induced a maximum neuromuscular blockade of 80.72% (n = 6, p < .05) and was cardiotoxic, decreasing the cockroach heart rate. The electrophysiological profiles of both muscle and nerve of L. migratoria showed that Jbtx (2.5 × 10^-7 and 2.5 × 10^-3 μg/ body weight) induced a significant increase in the amplitude of nerve action potentials (n = 5, p < .05). Voltage clamp analysis of Jbtx (200 nM) applied in Xenopus laevis oocytes heterologously expressed with Nav 1.1 channels showed a significant increase in the sodium currents. In conclusion, this work revealed that the entomotoxic activity of Jbtx involves complex behavioral alterations that begins with an initial activation of voltage-gated sodium channels.

Effects of electroacupuncture on stress and anxiety-related responses in rats

The aim of this work was to investigate if eletroacupuncture at PC6 would modulate the stress-induced anxiety-like behavior and the level of activation of several brain areas. Rats were distributed in groups: control; submitted to immobilization; submitted to immobilization and eletroacupuncture at PC6 or at the tail. Immobilization increased grooming and decreased stretched attend postures and the time spent in the open arms of the ele-vated plus-maze. Eletroacupuncture at PC6 or tail canceled the effect of immobilization on grooming and attenuated the stretched attend posture. Immobilization increased Fos-immunoreactivity in the prefrontal cortex, medial and central amygdala, paraventricular and dorsomedial nuclei of the hypothalamus, lateral hypothalamus, dentate gyrus, CA1, CA2 and CA3 hippocampal areas. The activation of paraventricular, dorsomedial nuclei and prefrontal cortex by immobilization was canceled by electroacupuncture at PC6 and attenuated by electroacupuncture in the tail. The activation of the other areas was canceled by electroacupuncture in PC6 or the tail. It is concluded that immobilization induced anxiety-like behavior that was moderately attenuated by eletroacupuncture with difference between the stimulation in PC6 or the rat tail. Eletroacupuncture showed specificity concerning to the attenuation of the effects of immobilization in the CNS areas related to the stress response, anxiety and cardiovascular system.

Short- and long-term behavioral analysis of social interaction, ultrasonic vocalizations and social motivation in a chronic phencyclidine model

Phencyclidine (PCP) has been suggested to induce symptoms of schizophrenia. However, animal models using PCP administration have produced ambiguous results thus far. It seems that acute effects are similar to symptoms of schizophrenia, however, it is not clear if PCP can induce permanent behavioral changes that reflect schizophrenic-like symptoms. Therefore, we assessed the ability of chronic PCP administration (3mg/kg, 14 days) to induce short or long lasting behavioral changes in rats. Social behavior, including ultrasonic vocalizations and motivation for social contact were investigated at different time points, up to 29-36 days, after cessation of PCP treatment. During a social separation test, performed at 5 and 36 days, PCP treated rats spent less time near the divider that separates them from their familiar cage mate compared with saline (SAL) treated rats. Further, at short term, PCP was able to induce a decrease in social behavior. In contrast, at long-term, PCP treated animals spent more time in contact when exposed to an unfamiliar partner as compared to SAL treated rats. But, this difference was not observed when exposed to a familiar partner. We did not find any difference in ultrasonic vocalizations at all time points. The results of our study indicate that PCP is unable to induce overt long term deficits in social interaction behavior. Rather, it seems that PCP diminishes motivation for social contact. The long-term consequences of chronic PCP administration on social behavior in rodent models remain complex, and future studies addressing this are still needed.

Social behavior in deer mice as a novel interactive paradigm of relevance for obsessive-compulsive disorder (OCD)

Greater obsessive-compulsive (OC) symptom severity may be associated with poor social adjustment. Rather than possessing deficits in social skill per se, OCD patients may be more socially isolative in the presence of normal controls. We aimed to apply a novel social interaction challenge (SIC) to an established animal model of OCD, viz., the deer mouse, to assess complex social behavior in animals by investigating group sociability and its response to chronic escitalopram treatment (50 mg/kg/day × 28 days), both within and between non (N)- (viz., normal) and high (H)- (viz., OCD-like) stereotypical cohorts. Using automated screening, we scored approach behavior, episodes of proximity, duration of proximity, and relative net weighted movement. H animals socialized more with one another within cohort in all of the above parameters compared to the within-cohort behavior of N animals. Furthermore, the social behavior of H animals toward one another, both within and between cohort demonstrated significant improvements following chronic escitalopram treatment. However, the study also demonstrates that the social interaction between H and N animals remain poor even after chronic escitalopram treatment. To conclude, findings from the current investigation support clinical data demonstrating altered sociability in patients with OCD.

Coping with an acute psychosocial challenge: behavioral and physiological responses in young women

Despite the relevance of behavior in understanding individual differences in the strategies used to cope with stressors, behavioral responses and their relationships with psychobiological changes have received little attention. In this study on young women, we aimed at analyzing the associations among different components of the stress response and behavioral coping using a laboratory psychosocial stressor. The Ethological Coding System for Interviews, as well as neuroendocrine, autonomic and mood parameters, were used to measure the stress response in 34 young women (17 free-cycling women in their early follicular phase and 17 oral contraceptive users) subjected to the Trier Social Stress Test (TSST) and a control condition in a crossover design. No significant differences in cardiac autonomic, negative mood and anxiety responses to the stressor were observed between the two groups of women. However, women in the follicular phase showed a higher cortisol response and a larger decrease in positive mood during the social stress episode, as well as greater anxiety overall. Interestingly, the amount of displacement behavior exhibited during the speaking task of the TSST was positively related to anxiety levels preceding the test, but negatively related to baseline and stress response values of heart rate. Moreover, the amount of submissive behavior was negatively related to basal cortisol levels. Finally, eye contact and low-aggressiveness behaviors were associated with a worsening in mood. Overall, these findings emphasize the close relationship between coping behavior and psychobiological reactions, as well as the role of individual variations in the strategy of coping with a psychosocial stressor.

Modulation of dopaminergic neurotransmission induced by sublethal doses of the organophosphate trichlorfon in cockroaches

Organophosphate (OP) insecticides have been used indiscriminately, based on their high dissipation rates and low residual levels in the environment. Despite the toxicity of OPs to beneficial insects is principally devoted to the acetylcholinesterase (AChE) inhibition, the physiological mechanisms underlying this activity remain poorly understood. Here we showed the pharmacological pathways that might be involved in severe alterations in the insect locomotion and grooming behaviors following sublethal administration of the OP Trichlorfon (Tn) (0.25, 0.5 and 1 µM) in Phoetalia pallida. Tn inhibited the acetylcholinesterase activity (46±6, 38±3 and 24±6 nmol NADPH/min/mg protein, n=3, p<0.05), respectively. Tn (1 µM) also increased the walking maintenance of animals (46±5 s; n=27; p<0.05). Tn caused a high increase in the time spent for this behavior (344±18 s/30 min, 388±18 s/30 min and 228±12 s/30 min, n=29-30, p<0.05, respectively). The previous treatment of the animals with different cholinergic modulators showed that pirenzepine>atropine>oxotremorine>d-tubocurarine>tropicamide>methoctramine induced a decrease on Tn (0.5 µM)-induced grooming increase, respectively in order of potency. Metoclopramide (0.4 µM), a DA-D2 selective inhibitor decreased the Tn-induced grooming activity (158±12 s/30 min; n=29; p<0.05). Nevertheless, the effect of the selective DA-D1 receptor blocker SCH 23390 (1.85 µM) on the Tn (0.5 µM)-induced grooming increase was significative and more intense than that of metoclopramide (54±6 s/30 min; n=30; p<0.05). Taken together the results suggest that a cross-talking between cholinergic M1/M3 and dopaminergic D1 receptors at the insect nervous system may play a role in the OP-mediated behavioral alterations.

Real-Time Localization of Moving Dipole Sources for Tracking Multiple Free-Swimming Weakly Electric Fish

In order to survive, animals must quickly and accurately locate prey, predators, and conspecifics using the signals they generate. The signal source location can be estimated using multiple detectors and the inverse relationship between the received signal intensity (RSI) and the distance, but difficulty of the source localization increases if there is an additional dependence on the orientation of a signal source. In such cases, the signal source could be approximated as an ideal dipole for simplification. Based on a theoretical model, the RSI can be directly predicted from a known dipole location; but estimating a dipole location from RSIs has no direct analytical solution. Here, we propose an efficient solution to the dipole localization problem by using a lookup table (LUT) to store RSIs predicted by our theoretically derived dipole model at many possible dipole positions and orientations. For a given set of RSIs measured at multiple detectors, our algorithm found a dipole location having the closest matching normalized RSIs from the LUT, and further refined the location at higher resolution. Studying the natural behavior of weakly electric fish (WEF) requires efficiently computing their location and the temporal pattern of their electric signals over extended periods. Our dipole localization method was successfully applied to track single or multiple freely swimming WEF in shallow water in real-time, as each fish could be closely approximated by an ideal current dipole in two dimensions. Our optimized search algorithm found the animal’s positions, orientations, and tail-bending angles quickly and accurately under various conditions, without the need for calibrating individual-specific parameters. Our dipole localization method is directly applicable to studying the role of active sensing during spatial navigation, or social interactions between multiple WEF. Furthermore, our method could be extended to other application areas involving dipole source localization.

Dopamine receptor antagonism disrupts social preference in zebrafish: a strain comparison study

Zebrafish form shoals in nature and in the laboratory. The sight of conspecifics has been found reinforcing in zebrafish learning tasks. However, the mechanisms of shoaling, and those of its reinforcing properties, are not known. The dopaminergic system has been implicated in reward among other functions and it is also engaged by drugs of abuse as shown in a variety of vertebrates including zebrafish. The ontogenetic changes in dopamine levels and, to a lesser degree, in serotonin levels, have been found to accompany the maturation of shoaling in zebrafish. Thus, we hypothesized that the dopaminergic system may contribute to shoaling in zebrafish. To test this we employed a D1-receptor antagonist and quantified behavioral responses of our subjects using a social preference (shoaling) paradigm. We found significant reduction of social preference induced by the D1-R antagonist, SCH23390, in the AB strain of zebrafish, an alteration that was not accompanied by changes in motor function or vision. We also detected D1-R antagonist-induced changes in the level of dopamine, DOPAC, serotonin and 5HIAA, respectively, in the brain of AB zebrafish as quantified by HPLC with electrochemical detection. We found the antagonist-induced behavioral changes to be absent and the levels of these neurochemicals to be lower in another zebrafish population, SF, demonstrating naturally occurring genetic variability in these traits. We conclude that this variability may be utilized to unravel the mechanisms of social behavior in zebrafish, a line of research that may be extended to other vertebrates including our own species.

Neonatal dexamethasone treatment affects social behaviour of rats in later life

Synthetic glucocorticoids, like dexamethasone (DEX), have been frequently administered to premature infants to prevent chronic lung disease. Major concern has arisen about the long-term neurodevelopmental sequelae of this DEX treatment. In the present study, we found that neonatal DEX treatment in rats, using a treatment protocol resembling the one used in the clinical situation, increased social play behaviour in juvenile life. Furthermore, neonatal DEX treatment increased sexual motivation and intromission behaviour in the bi-level chamber, decreased submissive behaviour during an aggressive encounter, and impaired social memory in adulthood. These changes in social behaviour are not due to a general behavioural impairment since anxiety behaviour in the elevated plus maze and exploratory activity in the open-field were not affected in DEX rats. In addition, DEX rats showed no alteration in the total duration of social interest or social activity during a social interaction test. These effects of neonatal DEX treatment on behaviour later in life likely result from neurodevelopmental actions of the hormone since we found no differences in received maternal care between DEX and SAL treated pups. Together these results indicate that neonatal treatment with DEX selectively alters aspects of the behavioural response to social challenges. Thus, neonatal DEX treatment may lead to inappropriate interactions with conspecifics later in life. These data therefore warrant investigation of lasting and potentially adverse effects of treatment of human neonates with DEX on social functioning.

Assessment of motor behavior using a video system and a clinical rating scale in parkinsonian monkeys lesioned by MPTP

The best current model of Parkinson's disease is the primate treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Quantification of animal movement is important for the study of severity of parkinsonian syndrome induced by MPTP and response to drug treatments. Both require clinical rating scales that measure motor behavior with well-defined objective items. However, evaluations using these scales depend on the observer scoring the different items, according to his/her experience. The video image analyzer system, which produces an activity curve in correlation with the visual study of animal motor behavior, offers an automatic evaluation method that is observer-independent and reproducible. Using such an system we defined items correlated with those used in clinical rating scales that are sensitive to animal motor changes, decrease in movements with MPTP intoxication and alleviation afforded by levodopa: global locomotor activity and specific activities (climbing, social interactions, eating and drinking behaviors).

The EthoVision video tracking system--a tool for behavioral phenotyping of transgenic mice

Video tracking systems enable behavior to be studied in a reliable and consistent way, and over longer time periods than if they are manually recorded. The system takes an analog video signal, digitizes each frame, and analyses the resultant pixels to determine the location of the tracked animals (as well as other data). Calculations are performed on a series of frames to derive a set of quantitative descriptors of the animal's movement. EthoVision (from Noldus Information Technology) is a specific example of such a system, and its functionality that is particularly relevant to transgenic mice studies is described. Key practical aspects of using the EthoVision system are also outlined, including tips about lighting, marking animals, the arena size, and sample rate. Four case studies are presented, illustrating various aspects of the system: (1) The effects of disabling the Munc 18-1 gene were clearly shown using the straightforward measure of how long the mice took to enter a zone in an open field. (2) Differences in exploratory behavior between short and long attack latency mice strains were quantified by measuring the time spent in inner and outer zones of an open field. (3) Mice with hypomorphic CREB alleles were shown to perform less well in a water maze, but this was only clear when a range of different variables were calculated from their tracks. (4) Mice with the trkB receptor knocked out in the forebrain also performed poorly in a water maze, and it was immediately apparent from examining plots of the tracks that this was due to thigmotaxis. Some of the latest technological developments and possible future directions for video tracking systems are briefly discussed.

EthoVision: a versatile video tracking system for automation of behavioral experiments

The need for automating behavioral observations and the evolution of systems developed for that purpose is outlined. Video tracking systems enable researchers to study behavior in a reliable and consistent way and over longer time periods than if they were using manual recording. To overcome limitations of currently available systems, we have designed EthoVision, an integrated system for automatic recording of activity, movement, and interactions of animals. The EthoVision software is presented, highlighting some key features that separate EthoVision from other systems: easy file management, independent variable definition, flexible arena and zone design, several methods of data acquisition allowing identification and tracking of multiple animals in multiple arenas, and tools for visualization of the tracks and calculation of a range of analysis parameters. A review of studies using EthoVision is presented, demonstrating the system's use in a wide variety of applications. Possible future directions for development are discussed.

Morphine attenuates the effects of juvenile isolation in rats

The acute effects of juvenile isolation on sucrose intake and its long-term consequences on adult social behavior were investigated. Additionally, the role of the endogenous opioid systems was studied. Juvenile rats were housed in one of three conditions: in groups or in isolation with (partial isolation, PI) or without 30 min of daily social contact from 22 to 35 days-of-age. During this period the rats were treated daily with saline or morphine. Juvenile isolated rats showed an increased sucrose intake as compared to non-isolated controls, with PI-rats somewhere in-between, suggesting a negative correlation between the amount of social contact and sucrose consumption. Morphine treatment during the isolation period enhanced the sucrose intake in non-isolated rats, whereas it decreased sucrose consumption in (partial) isolated rats. With regard to the long-term effects, (partial) isolated rats decreased social activity as compared to non-isolated controls which was reversed by morphine treatment during the isolation period. In non-isolated rats, morphine treatment caused an opposite effect: it decreased social activity as compared to the saline treated controls. The data suggest that stimulation of endogenous opioid systems in the juvenile phase may have an important modulatory role in the expression of adult social behavior. The results are discussed in relation to a possible function of morphine as a substitute for the release of endogenous opioid peptides during social play.

Body modeling and model-based tracking for neuroethology

The accurate tracking of an animal's movements and postures through time has broad applicability to questions in neuroethology and animal behavior. In this paper we describe methods for precision body modeling and model-based tracking of non-rigid animal movements without the use of external markers. We describe the process of obtaining high-fidelity urethane casts of a model organism, the weakly electric knifefish Apteronotus albifrons, and the use of a stylus-type 3-D digitizer to create a polygonal model of the animal from the cast. We describe the principles behind markerless model-based tracking software that allows the user to translate, rotate, and deform the polygon model to fit it to digitized video images of the animal. As an illustration of these methods, we discuss how we have used model-based tracking in the study of prey capture in nocturnal weakly electric fish to estimate sensory input during behavior. These methods may be useful for bridging between the analytical approaches of quantitative neurobiology and the synthetic approaches of integrative computer simulations and the building of biomimetic robots.

Classifying postures of freely moving rodents with the help of Fourier descriptors and a neural network

A computerized method for classifying the postures of freely moving rodents is presented. The behavior of the rats was recorded on videotape by means of a camera hanging perpendicular to an open field. An automatic tracking system (10 images/sec) was used to transform the video images of postures into a binary image, thereby providing silhouettes in a computer format. The contours of these silhouettes were used for determining their characteristic features with the help of a Fourier transformation. The resulting features were classified with the help of a Kohonen network composed of 32 neurons. The four best winning neurons, rather than the usual one, were used for the classification. The resolution (11,090 distinct classes of postures), reliability (96.9%), and validity of this method were determined. With the use of the same approach, the effectiveness of this method for classifying behaviors was illustrated by analyzing grooming (247 grooming images vs. 4,950 nongrooming images). We found 15.4% false positives and 2.5% false negatives.

Classification of rat behavior with an image-processing method and a neural network

Video recordings of 11 rats were digitized at five frames per second, and parameters describing the shape and the position of the rat were calculated. The behavior displayed by the rats was observed by an experienced observer. Separate neural networks were trained and validated, using the data for each individual rat. The neural networks correctly classified an average of 76.53% of the frames in the validation set and 98.18% of the frames in the training set. A single neural network was trained with 6 rats and validated with 5 rats. The neural network correctly classified 63.74% of the frames in the validation set and 82.85% of the frames in the training set.

Sequential analysis of juvenile isolation-induced decreased social behavior in the adult rat

The consequences of juvenile isolation on adult social behavior were studied in detail using two different analysis methods: frequency, duration, and latency of behavioral elements, and sequential analysis. Rats were either isolated or socially housed during weeks 4 and 5 of age, and after the isolation period housed in pairs with a rat of identical housing condition until the time of testing at 12 weeks of age. Juvenile isolation caused marked effects on the frequency, duration, and latency of various social behavioral elements, whereas the non-social activities such as ambulation, rearing, and self-grooming were hardly affected. Juvenile isolation reduced social exploration, anogenital sniffing, and approach/following and increased the latency to the first occurrence of these social behavioral elements. In contrast, the sequential analysis revealed that the structure of social behavior was barely affected by juvenile isolation. Some transitions were less pronounced in juvenile isolated rats compared to non-isolated rats, but no significant differences were observed in transitions between social elements. Thus, juvenile isolation bisected the time spent on adult social interactions, whereas it did not disrupt the sequential structure of social behavior. The present data suggest that juvenile isolation reduced the motivation for adult social behavior, but when social contact is initiated, a relatively normal social behavioral pattern is displayed.

Morphine treatment during juvenile isolation increases social activity and opioid peptides release in the adult rat

The consequences of juvenile isolation and morphine treatment on general activity, social activity and endogenous opioid release during a social interaction test were investigated in the adult rat. Rats were either isolated or socially housed during weeks 4 and 5 of age and treated daily during this isolation period subcutaneously with either saline or morphine. Directly after a social interaction test at 10 weeks of age, rats were injected with [3H]-diprenorphine and subsequently prepared for in vivo autoradiography. The autoradiographic technique was used to visualise neuroanatomical changes in opioid receptor occupancy, probably reflecting changes in opioid peptide release, as a result of social activity. Juvenile isolation increased general activity during the social interaction test, an effect which was accompanied by a reduction of opioid receptor occupancy in many brain areas, suggesting an increased opioid peptide release as a consequence of socially-induced general activity. Morphine treatment in isolated rats caused an increase in adult social activity and enhanced opioid peptide release in some cortical regions and the ventral tegmental area as compared to saline treated rats. Both social activity and opioid receptor occupancy were unaffected by morphine treatment in non-isolated rats. The present study underscores the role of opioid systems in adult social behaviors as a consequence of juvenile isolation. The results suggest a relationship between social activity and opioid peptide release during social contact. Increased social activity seems to be accompanied by elevated opioid peptide release in distinct brain areas after morphine treatment during juvenile isolation.

Isolation during the play period in infancy decreases adult social interactions in rats

The effects of 1 or 2 weeks of social isolation immediately after weaning on social activity in adulthood were investigated in rats. In addition, it was studied whether these effects were influenced by social experiences of the cagemate when rehoused after the isolation period. Isolation during weeks 4 and 5 of age caused a reduction of social activity as compared to non-isolated controls. Previous social experiences of the cagemate (isolated or non-isolated) did not affect this decreased social activity. Isolation during week 4 of age resulted in similar effects, but the reduced social activity was not present when the rats were rehoused with non-isolated rats. Isolation during week 5 of age did not influence social activity patterns in adulthood. These findings support the idea of a sensitive period in infancy for subsequent social behavior in rats. It is suggested that especially deprivation of acquiring play behavior underlies the social disturbances in adulthood.

Effects of vanadium on activity and learning in rats

The effects of vanadate administration on activity and learning were assessed in rats. Four groups of adult male rats were given by gavage 0, 4.1, 8.2, and 16.4 mg/kg/day of sodium metavanadate for eight consecutive weeks. Three weeks after the cessation of the treatment, general motor activity of all animals was measured in an open-field. Rats were also tested for two-way shock avoidance learning in an automatic reflex conditioner. At the end of the testing period, rats were killed and vanadium concentration was determined in a number of tissues. Vanadium exposure caused an observable but not significant effect on body weight gain, while a persistent presence of vanadium was observed in all tissues measured. The results of the behavioral testing show that oral vanadate administration resulted in significant reductions in both general activity and learning.

Recovery of function after sciatic nerve crush lesion in rats selected for diverging locomotor activity in the open field

The relation between recovery of function following a sciatic nerve crush lesion and an individual behavioural characteristic, the locomotor activity in an open field, was investigated in rats. Ten high-active (HA) and ten low-active (LA) rats were selected from a stock of sixty male, random-bred Wistar rats, by measuring travelled distance in an open field. Subsequently, both HA and LA rats underwent an unilateral sciatic nerve crush. Recovery of motor function revealed no significant differences between both groups, whereas recovery of sensory function in HA rats was significantly more rapid than in the LA rats (P < 0.01). These observations suggest the existence of a relationship between individual behavioural characteristics, and the sensory recovery of nerve function following crush lesion in rats.

Shift in the performance of 24-month-old Wistar rats in the Morris water escape task: a comparison across 36 experiments

Spatial discrimination learning in aged rats serves as an animal model of cognitive aging. We assessed the replicability of spatial discrimination performance in the standard Morris water escape task. To this end the learning curves and the performance in a probe trial of 24-month-old outbred Wistar (HsdWin:Wu) control rats from 36 experiments were compared. These experiments had been performed at our laboratory under strictly controlled conditions over a period of 71 weeks. There was a very high variability in the learning curves between experiments. The initial performance level, i.e. the performance during the first session, did not change systematically across the 36 experiments. In contrast, the final performance level, i.e. the level reached in the fifth training session, decreased over the 71 week period, when the platform escape latency and the distance swam to reach the platform, measured as number of line crossings, were considered. In the last experiments of the series, learning curves were no longer seen: the rats did not improve their performance across the acquisition sessions. By contrast, the swimming speed and, in the probe trial, the bias for the quadrant where the platform had been positioned during training, did not change. This indicates that a decrease across experiments occurred predominantly with respect to spatial orientation performance, whereas the motor performance appeared to be unchanged. Explanations for this observation, such as differences in viability between shipments and the possible occurrence of genetic drift, are discussed.

Prenatal exposure to morphine affects juvenile play behavior and adult social behavior in rats

The effects of morphine exposure in utero on play behavior and social behavior were investigated in a longitudinal study. Wistar rat dams were SC injected daily with saline (control) or 10 mg/kg morphine from day 8 to day 21 of gestation. Play behavior of the offspring was measured at 3 and 4 weeks of age and social behavior at 3 months of age. Pinning, a measure for play behavior and social grooming of the morphine-treated offspring were significantly elevated compared to saline controls, especially on day 21. The onset-latency of pinning behavior was not changed. Furthermore, prenatal morphine treatment resulted in more social approach and less social avoidance behavior in adulthood, whereas changes in general locomotor activity were not observed. The results are discussed in relation to the effects of in utero exposure of morphine on the development of incentive aspects of play and social behavior.

Effects of an electrolytic lesion of the prelimbic area on anxiety-related and cognitive tasks in the rat

The aim of this paper was to study the role of the prelimbic area of rats in response selection. A bilateral electrolytic lesion was made in the prelimbic area. The rats were tested in the Morris water-maze, the conditioned shock-prod burying test, the elevated plus-maze, a modified open field test, and the step-through passive avoidance test. In the water-maze during initial acquisition, the latency times of the lesioned rats were not different from those of the controls, but they found the platform faster than the sham operated rats after the platform was placed in a new position. The lesion did not affect performance in the shock-prod burying test. In the elevated plus-maze the lesioned rats were more active than the sham-operated rats and spent more time on the open arms. In the open field there was no difference between lesioned and sham-operated rats with regard to distance travelled or the time spent near the object in the center of the open field. In the passive avoidance test the lesioned rats had a shorter latency time to enter the shock compartment during the retention trial than the sham-operated rats did. The results were discussed in relation to those of similar studies. The extent and precise localisation of the lesion seems to be crucial for the outcome: lesions confined to the prelimbic area may have the opposite effects of larger lesions. Furthermore, it may well be that the prelimbic area is only involved in processing of stimuli of a specific sensory modality, as made probable by the results of different conditioned reinforcement tasks. Finally, it was stated that we still lack a hypothesis about the precise role of the prelimbic area in response selections.

Chronic administration of Org2766 and morphine counteracts isolation-induced increase in social interest: implication of endogenous opioid systems

In complex behaviors, like social behavior, the MSH/ACTH (4-9) analog Org2766 is found to counteract changes in social interest caused by preceding housing or test conditions. Previous studies have indicated an involvement of endogenous opioid systems in these outcomes. In the present study we have counteracted isolation-induced enhanced social interest by chronic treatment (7 x every 48 h) with Org2766 or with the opiate morphine. These effects were blocked by previous administration of naloxone. However, in group-housed animals, both Org2766 and morphine treatment did not result in changes in social activity as compared to saline-treated group-housed controls. Chronic administration of naloxone in group-housed rats resulted in an increase in social interest. These results are discussed in relation to possible function of Org2766 and morphine as a substitute for the release of endogenous opioids caused by social contact.

Long-term impoverished housing effects on Morris maze performance after a fimbria lesion

Male Wistar rats received bilateral Fimbria lesions and were postoperatively housed in either standard social conditions or in impoverished conditions (one rat per cage) for 2 weeks in experiment I, and for 7 months in experiment II. The effects of lesion and housing conditions were investigated in the Morris maze spatial orientation task. Fimbria lesions increased the latency to reach the platform during acquisition in both experiments, which indicates that functional recovery of the Morris maze impairment does not occur in 7 months time. Post-operative impoverishment for 2 weeks or for 7 months reduced the lesion induced deficit in Morris maze acquisition, while it had a more general effect in the trial without platform. Interestingly, the impoverishment effects were not more severe after 7 months, but even less easily detected. These findings are interpreted as if impoverishment effects the reactiveness of animals to external stimuli, which may help the animal to compensate for the lesion-induced-deficit in Morris maze learning.

The effect of corticosterone on reactivity to spatial novelty is mediated by central mineralocorticosteroid receptors

Corticosterone, secreted by the adrenal glands, binds to central mineralocorticoid receptors with high affinity and to glucocorticoid receptors with a tenfold lower affinity. In previous studies we have shown that the selective activation of either mineralocorticoid receptors or glucocorticoid receptors exerts distinctly different behavioural effects. In this study we examined in particular the mineralocorticoid receptor-mediated effect of corticosterone on the control of the behavioural response of male Wistar rats to spatial novelty. This analysis was based on our observation that in adrenal-intact rats the presence of an object in the centre of an open field alters the time spent and distance walked in the centre compared to the peripheral area, i.e. the pattern of reactive locomotor activity is changed. Using this paradigm we found that 1 day after removal of the adrenals the rats increased their behavioural reactivity towards the object. Treatment of adrenalectomized rats with a low dose of corticosterone (50 micrograms/kg s.c.) 1 h prior to testing restored the behavioural reactivity to the level of sham-operated, intact rats. Surprisingly, a high dose of corticosterone (1000 micrograms/kg s.c.) also increased the rat's reactivity towards the object. The same high dose of corticosterone given to adrenal-intact rats also increased behavioural reactivity. Pretreatment of these rats with an intracerebroventricular injection of the selective mineralocorticoid receptor antagonist RU28318 (100 ng/microliters) prevented the corticosterone-induced increase in behavioural reactivity, while the blockade of glucocorticoid receptors with the antagonist RU38486 (100 ng/microliters) was not effective. Administration of the mineralocorticoid receptor antagonist without corticosterone to adrenal-intact rats also increased behavioural reactivity, but this increase did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 beta, but not interleukin-6, impairs spatial navigation learning

The effects of the cytokines interleukin-1 and -6 (IL1 beta, IL6; 100 ng) on spatial learning were examined in the Morris water maze. Intracerebroventricular injection of IL1 or IL6 before the training on day 1 did not influence the acquisition of spatial navigation. However, IL1 administered at 60 min, but not immediately before the training, resulted in impaired performance of spatial navigation the following day. In contrast, IL6 administered at both times had no effect. In a second experiment the same doses of IL1 and IL6 increased the body temperature of rats in a time-related fashion. The temperature effect of IL1 developed after a delay of 120 min, while the IL-6-effect was immediate. Comparable behavioral changes might accompany infections or inflammatory diseases and therapeutic cytokine administration.

An ACTH/MSH(4-9) analog counteracts the behavioral effects of a mineralocorticoid receptor antagonist

The ACTH/MSH(4-9) analog Org2766 has been demonstrated to counteract age-related behavioral and morphological parameters especially those related to hippocampal functioning. Hippocampal mineralocorticoid receptors (MRs) are known to decline in the senescent rat. This decrease can be also counteracted by a chronic treatment with an ACTH(4-9) analog. The apparent effect of the peptide on hippocampal functioning prompted us to study a possible interaction between ACTH and MRs at a behavioral level. A chronic treatment with the ACTH(4-9) analog prevented the behavioral alteration induced by a specific MR antagonist (RU28318; 100 ng/microliters, ICV) in the Morris water maze and a step-through avoidance task. A possible role for neuronal excitation, involving MR activation, in peptide-facilitated behavioral recovery as seen in lesion studies and aging is discussed.

Effects of haloperidol on the acquisition of a spatial learning task

The effects of systemic injections of the dopaminergic antagonist haloperidol on the acquisition of the Morris water maze with either a visible or an invisible platform (nonspatial vs. spatial learning) were investigated. An open field test was used for selecting a dosage (< or = 0.1 mg/kg), that (hardly) affected locomotor behaviour. Differential effects were found. At 0.1 mg/kg, haloperidol reduced locomotion in the open field, impaired acquisition in the Morris maze with a visible platform, and blocked escape onto an invisible one. Even though 0.07 mg/kg haloperidol reduced locomotion, both 0.04 and 0.07 mg/kg only impaired Morris maze performance in the spatial version. A large effect was found in the first trial of every day's training block. These results indicate that haloperidol at low doses can lead to a moderate but significant impairment of spatial learning. It is suggested that the effects found are related to the function of the striatal areas in cue- and noncue-directed behaviour.

Effects of the ACTH4-9 analog Org2766 on brain plasticity: modulation of excitatory neurotransmission?

ACTH-like neuropeptides have been investigated in various paradigms such as cognition, neuronal damage and neuronal excitation. All their effects may be collectively described as modulation of neural plasticity. However, the mechanism of action accounting for these effects remains to be demonstrated. This report is an overview of the data and has incorporated some additional findings of the influence of the ACTH4-9 analog, Org2766, on neuronal excitation, especially in the hippocampus. An interaction with NMDA receptors may account for the various aspects of plasticity. Based on recent findings demonstrating that the ACTH4-9 analog counteracts both the NMDA antagonist, AP5, and NMDA-induced explosive running behavior, the hypothesis is put forward that glutamatergic neurotransmission is involved in behavioral changes induced by the ACTH4-9 analog.

The MSH/ACTH(4-9) analog Org2766 counteracts isolation-induced enhanced social behavior via the amygdala

MSH/ACTH-like peptides influence social behavior induced by isolation It has been previously demonstrated that changes in locomotor activity as a result of isolation can be counteracted by Org2766 via the amygdala. The present study investigates whether isolation-induced changes in social behavior can also be affected by this peptide via the amygdala. A fully automated observation system was applied for detailed registration and analysis of movements of group-housed and 7-day isolated rats in a social interaction test. Administration of the MSH/ACTH(4-9) analog into the central nucleus of the amygdala elicited decreased locomotion, approach, and avoidance behaviors after isolation as compared to placebo-treated controls. However, general activity and social interest of group-housed rats were not affected by the MSH/ACTH(4-9) fragment. It is hypothesized that the amygdala is a site of action for neuropeptides in modulating social behavior.