Overexpression of synphilin-1 promotes clearance of soluble and misfolded alpha-synuclein without restoring the motor phenotype in aged A30P transgenic mice.

Lewy bodies and neurites are the pathological hallmark of Parkinson's disease. These structures are composed of fibrillized and ubiquitinated alpha-synuclein suggesting that impaired protein clearance is an important event in aggregate formation. The A30P mutation is known for its fast oligomerization, but slow fibrillization rate. Despite its toxicity to neurons, mechanisms involved in either clearance or conversion of A30P alpha-synuclein from its soluble state into insoluble fibrils and their effects in vivo are poorly understood. Synphilin-1 is present in Lewy bodies, interacting with alpha-synuclein in vivo and in vitro and promotes its sequestration into aggresomes, which are thought to act as cytoprotective agents facilitating protein degradation. We therefore crossed animals overexpressing A30P alpha-synuclein with synphilin-1 transgenic mice to analyze its impact on aggregation, protein clearance and phenotype progression. We observed that co-expression of synphilin-1 mildly delayed the motor phenotype caused by A30P alpha-synuclein. Additionally, the presence of N- and C-terminal truncated alpha-synuclein species and fibrils were strongly reduced in double-transgenic mice when compared with single-transgenic A30P mice. Insolubility of mutant A30P and formation of aggresomes was still detectable in aged double-transgenic mice, paralleled by an increase of ubiquitinated proteins and high autophagic activity. Hence, this study supports the notion that co-expression of synphilin-1 promotes formation of autophagic-susceptible aggresomes and consecutively the degradation of human A30P alpha-synuclein. Notably, although synphilin-1 overexpression significantly reduced formation of fibrils and astrogliosis in aged animals, a similar phenotype is present in single- and double-transgenic mice suggesting additional neurotoxic processes in disease progression.

Male long-tailed macaques (Macaca fascicularis) understand the target of facial threat.

The cognitive demands of group living have resulted in the development of social competences in a wide range of animal species. Primates are well aware of the complex social structure within their group and infer information about social status by observing interactions of others. A capacity used to infer this information, Visual Perspective Taking (VPT), is present in apes and in monkeys. However, it is unclear whether monkeys really understand that another individual is looking at a specific target. We investigated whether monkeys understand the target of attention of conspecifics using a new paradigm, based on expectancy violation. Subjects were exposed to pictures of scenes involving group members. These pictures either represented congruent (agonistic signals consistent with the dominance hierarchy) or incongruent (signals contradict the dominance hierarchy) social situations. The only difference between scenes concerned the looking direction, that is, the target of attention, and facial expression of the central monkey in the picture. Female subjects did not differ in their looking times to incongruent and congruent scenes, but results may be confounded by their longer looking times at scenes involving kin than non-kin. Male subjects looked significantly longer at incongruent than congruent scenes, suggesting that they understand the target of attention of other individuals. Alternative explanations involving simpler cognitive capacities were excluded. This implies that monkey species share social cognitive capacities underlying VPT with apes and humans. Am. J. Primatol. 78:720-730, 2016. © 2016 Wiley Periodicals, Inc.

Orangutan (Pongo spp.) whistling and implications for the emergence of an open-ended call repertoire: a replication and extension.

One of the most apparent discontinuities between non-human primate (primate) call communication and human speech concerns repertoire size. The former is essentially fixed to a limited number of innate calls, while the latter essentially consists of numerous learned components. Consequently, primates are thought to lack laryngeal control required to produce learned voiced calls. However, whether they may produce learned voiceless calls awaits investigation. Here, a case of voiceless call learning in primates is investigated--orangutan (Pongo spp.) whistling. In this study, all known whistling orangutans are inventoried, whistling-matching tests (previously conducted with one individual) are replicated with another individual using original test paradigms, and articulatory and acoustic whistle characteristics are compared between three orangutans. Results show that whistling has been reported for ten captive orangutans. The test orangutan correctly matched human whistles with significantly high levels of performance. Whistle variation between individuals indicated voluntary control over the upper lip, lower lip, and respiratory musculature, allowing individuals to produce learned voiceless calls. Results are consistent with inter- and intra-specific social transmission in whistling orangutans. Voiceless call learning in orangutans implies that some important components of human speech learning and control were in place before the homininae-ponginae evolutionary split.

Inequity aversion in relation to effort and relationship quality in long-tailed Macaques (Macaca fascicularis).

Social animals may employ evolved implicit rules to maintain a balance between cooperation and competition. Inequity aversion (IA), the aversive reaction to an unequal distribution of resources, is considered such a rule to avoid exploitation between cooperating individuals. Recent studies have revealed the presence of IA in several nonhuman species. In addition, it has been shown that an effort is crucial for this behavior to occur in animals. Moreover, IA may well depend on the partner's identity. Although dominant individuals typically monopolize food, subordinate individuals obtain less preferred food and usually do not protest. Furthermore, "friends" may pay less attention to equity than "nonfriends." We tested whether long-tailed macaques show IA with different cost-benefit ratios. In addition, we determined whether IA depends on relationship quality (RQ). Dominant subjects expressed IA only when a small effort was required. At a very large effort, however, long-tailed macaques did not show IA, possibly owing to bottom effects on the number of rewards they aim to receive. Moreover, and contrary to our predictions, an individual's inequity response was similar when tested with a "friend" or a "nonfriend." Therefore, we conclude that long-tailed macaques show IA only in conditions of moderate effort, yet that IA seems independent of RQ. Furthermore, IA may not be domain specific. Altogether, IA may be a trait present in all species that habitually cooperate, independent of their social organization.

Long-lasting modulation of synaptic plasticity in rat hippocampus after early-life complex febrile seizures.

A small fraction of children with febrile seizures appears to develop cognitive impairments. Recent studies in a rat model of hyperthermia-induced febrile seizures indicate that prolonged febrile seizures early in life have long-lasting effects on the hippocampus and induce cognitive deficits. However, data on network plasticity and the nature of cognitive deficits are conflicting. We examined three specific measures of hippocampal plasticity in adult rats with a prior history of experimental febrile seizures: (i) activity-dependent synaptic plasticity (long-term potentiation and depression) by electrophysiological recordings of Schaffer collateral/commissural-evoked field excitatory synaptic potentials in CA1 of acute hippocampal slices; (ii) Morris water maze spatial learning and memory; and (iii) hippocampal mossy fiber plasticity by Timm histochemistry and quantification of terminal sprouting in CA3 and the dentate gyrus. We found enhanced hippocampal CA1 long-term potentiation and reduced long-term depression but normal spatial learning and memory in adult rats that were subjected to experimental febrile seizures on postnatal day 10. Furthermore, rats with experimental febrile seizures showed modest but significant sprouting of mossy fiber collaterals into the inner molecular layer of the dentate gyrus in adulthood. We conclude that enhanced CA1 long-term potentiation and mild mossy fiber sprouting occur after experimental febrile seizures, without affecting spatial learning and memory in the Morris water maze. These long-term functional and structural alterations in hippocampal plasticity are likely to play a role in the enhanced seizure susceptibility in this model of prolonged human febrile seizures but do not correlate with overt cognitive deficits.

Announced reward counteracts the effects of chronic social stress on anticipatory behavior and hippocampal synaptic plasticity in rats.

Chronic stress causes insensitivity to rewards (anhedonia) in rats, reflected by the absence of anticipatory behavior for a sucrose-reward, which can be reversed by antidepressant treatment or repeated announced transfer to an enriched cage. It was, however, not clear whether the highly rewarding properties of the enriched cage alone caused this reversal or whether the anticipation of this reward as such had an additional effect. Therefore, the present study compared the consequences of the announcement of a reward to the mere effect of a reward alone with respect to their efficacy to counteract the consequences of chronic stress. Two forms of synaptic plasticity, long-term potentiation and long-term depression were investigated in area CA1 of the hippocampus. This was done in socially stressed rats (induced by defeat and subsequent long-term individual housing), socially stressed rats that received a reward (short-term enriched housing) and socially stressed rats to which this reward was announced by means of a stimulus that was repeatedly paired to the reward. The results were compared to corresponding control rats. We show that announcement of enriched housing appeared to have had an additional effect compared to the enriched housing per se as indicated by a significant higher amount of LTP. In conclusion, announced short-term enriched housing has a high and long-lasting counteracting efficacy on stress-induced alterations of hippocampal synaptic plasticity. This information is important for counteracting the consequences of chronic stress in both human and captive rats.

Spatial learning in pigs: effects of environmental enrichment and individual characteristics on behaviour and performance.

This study investigated the effects of both environmental enrichment and individual behavioural characteristics on spatial cognitive capabilities of pigs, using a novel latent spatial learning paradigm based on Tolman's detour experiments (1948). Pigs were housed either in 'barren' pens or in pens enriched with straw bedding from birth. Pigs were restrained in a Backtest at 10 and 17 days postpartum. Based on their escape behaviour in this test, which has been shown to reflect their behavioural style, six 'high-resisting'(HR) and six 'low-resisting' (LR) pigs were selected from each housing environment (n = 24 in total). At 12 weeks of age, pairs of pen mates (LR and HR) were exposed to a maze three times (exploration trials). Pigs were then placed individually in the maze, and social reinstatement proved to be a strong incentive to find the exit leading to the home pen. We subsequently blocked the direct route to the exit, forcing animals to find a detour (memory test 1, MT1). This test was repeated once to investigate the relative improvement, i.e. detour learning (memory test 2, MT2). Housing condition and Backtest response strongly affected exploration patterns. In spite of this, no effects on performance during the subsequent memory tests were found. Performance was substantially improved in MT2, indicating that once a goal is apparent, pigs are able to solve a complex spatial memory task easily. In conclusion, social reinstatement provided a good incentive to complete a spatial task, and the substantial improvement in performance between MT1 and MT2 stresses the need for task complexity when testing spatial memory in pigs. Housing conditions or individual behavioural style did not affect spatial memory during MT1 or MT2. However, housing environment and behavioural style strongly affected explorative behaviour of pigs in an unfamiliar maze during both exploration trials and memory tests. This implicates that apparent effects of environmental enrichment on spatial learning and memory in pigs might reflect differences in explorative patterns rather than in cognitive processes.

Differential genetic regulation of motor activity and anxiety-related behaviors in mice using an automated home cage task.

Traditional behavioral tests, such as the open field test, measure an animal's responsiveness to a novel environment. However, it is generally difficult to assess whether the behavioral response obtained from these tests relates to the expression level of motor activity and/or to avoidance of anxiogenic areas. Here, an automated home cage environment for mice was designed to obtain independent measures of motor activity levels and of sheltered feeding preference during three consecutive days. Chronic treatment with the anxiolytic drug chlordiazepoxide (5 and 10 mg/kg/day) in C57BL/6J mice reduced sheltered feeding preference without altering motor activity levels. Furthermore, two distinct chromosome substitution strains, derived from C57BL/6J (host strain) and A/J (donor strain) inbred strains, expressed either increased sheltering preference in females (chromosome 15) or reduced motor activity levels in females and males (chromosome 1) when compared to C57BL/6J. Longitudinal behavioral monitoring revealed that these phenotypic differences maintained after adaptation to the home cage. Thus, by using new automated behavioral phenotyping approaches, behavior can be dissociated into distinct behavioral domains (e.g., anxiety-related and motor activity domains) with different underlying genetic origin and pharmacological responsiveness.

Effects of experience and context on 50-kHz vocalizations in rats.

Rats can emit ultrasonic 50-kHz vocalizations which are generally assumed to reflect the animals' positive emotional state. However, some aspects question the reliability of 50-kHz calls as indicators of positive affective states. Firstly, rats also emit them in novel environments containing scents of other rats, or even while being victims of intra-species aggression. Secondly, huge inter-individual variability in call production can be observed. The present two studies were conducted to further determine factors other than reward, which may influence or even induce calling. Experiment A showed that 50-kHz calls were emitted in relatively high numbers during short isolation in test cages, and, to a lesser extent, also during testing in an open field and an elevated plus maze. Despite inter-individual variability, calling behavior was individually stable over days and occurred irrespective of whether rats were tested in a cage with or without familiar rat scents. These data indicate that 50-kHz calling is not necessarily a response to the presence of pleasurable or social stimuli. Additionally, it was observed that call emission during isolation is strongly affected by prior experience. Rats that had been trained repeatedly in an appetitive discrimination task emitted only few calls during short isolation in test cages, whereas naïve rats emitted high numbers of 50-kHz calls which decreased over time. The most likely explanation is that rats call in response to separation from the cage mate, as the first group was trained before the recordings, while the naïve rats were recorded immediately after separation. This explanation was supported by Experiment B, which showed that the rats that remained alone in the home cage also called at 50 kHz after separation from the cage mates. In both experiments, most of the 50-kHz calls were not frequency modulated, which lend support for the suggestion that this subtype has a social-coordinating function. The present findings urge sophisticated spectrographic analysis of ultrasonic vocalizations and caution when interpreting 50-kHz vocalizations, since specific subtypes of these calls can occur in contexts that are not necessarily pleasurable to rats, and are affected by prior experience and huge individual differences.

Between and within laboratory reliability of mouse behaviour recorded in home-cage and open-field.

BACKGROUND: Reproducibility of behavioural findings between laboratories is difficult due to behaviour being sensitive to environmental factors and interactions with genetics. The objective of this study was to investigate reproducibility of behavioural data between laboratories using the PhenoTyper home cage observation system and within laboratory reproducibility using different lighting regimes. NEW METHOD: The ambulatory activity of C57BL/6 and DBA/2 mice was tested in PhenoTypers in two laboratories under near identical housing and testing conditions (Exp. 1). Additionally activity and anxiety were also assessed in the open-field test. Furthermore, testing in either a normal or inverted light/dark cycle was used to determine effects of lighting regime in a within-laboratory comparison in Aberdeen (Exp. 2). RESULTS: Using the PhenoTyper similar circadian rhythms were observed across laboratories. Higher levels of baseline and novelty-induced activity were evident in Aberdeen compared to Utrecht although strain differences were consistent between laboratories. Open field activity was also similar across laboratories whereas strain differences in anxiety were different. Within laboratory analysis of different lighting regimes revealed that behaviour of the mice was sensitive to changes in lighting. COMPARISON WITH EXISTING METHODS: Utilisation of a home cage observation system facilitates the reproducibility of activity but not anxiety-related behaviours across laboratories by eliminating environmental factors known to influence reproducibility in standard behavioural tests. CONCLUSIONS: Standardisation of housing/test conditions resulted in reproducibility of home cage and open field activity but not anxiety-related phenotypes across laboratories with some behaviours more sensitive to environmental factors. Environmental factors include lighting and time of day.

Mu opioid receptor knockout mice in the Morris Water Maze: a learning or motivation deficit?

An earlier study done by Kas et al. [Kas MJ, van den Bos R, Baars AM, Lubbers M, Lesscher HM, Hillebrand JJ, et al. Mu-opioid receptor knockout mice show diminished food-anticipatory activity. Eur J Neurosci 2004;20(6):1624-32] suggested that mu opioid receptor (MOR) knockout mice have deficits in the motivational component rather than in the information processing component of learning. To substantiate this difference further, MOR knockout mice and wildtype littermates were tested in the Morris Water Maze (MWM), which allows for testing both components of learning. On traditional parameters for performance, no significant differences between genotypes were found. However, swimming velocity, indicative of motivation, decreased for MOR knockout mice during the course of training but not for wildtype mice. In contrast, probe trial performance was comparable between genotypes. Again, these results suggest normal information processing abilities but a decreased motivation in this MOR knockout mouse. Our conclusion is discussed in the light of other studies using MOR knockout mice that do find differences on information processing between genotypes in MWM performance.

Effects of genetic background and environmental novelty on wheel running as a rewarding behaviour in mice.

Recent studies suggest running wheel activity to be naturally rewarding and reinforcing; considering the shared neuro-behavioural characteristics with drug-induced reward situations, wheel running behaviour gains interest as a tool to study mechanisms underlying reward-sensitivity. Previously, we showed that wheel running has the potential to disrupt the daily organization of home cage behaviour in female C57BL/6 [de Visser L, van den Bos R, Spruijt BM. Automated home cage observations as a tool to measure the effects of wheel running on cage floor locomotion. Behav Brain Res 2005;160:382-8]. In the present study, we investigated the effects of novelty-induced stress on wheel running and its impact on home cage behaviour in male C57BL/6 and DBA/2 mice. Our aim was to determine whether wheel running may be used as a tool to study both genetic and environmentally induced differences in sensitivity to rewarding behaviour in mice. One group of male mice was placed in an automated home cage observation system for 2 weeks with a wheel integrated in the cage. A second group of mice was allowed to habituate to this cage for 1 week before a running wheel was introduced. Results showed a pronounced sensitising effect of novelty on the level of wheel running in C57Bl/6 mice but not in DBA mice. Overall levels of wheel running were higher in DBA/2 mice. Furthermore, wheel running affected circadian rhythmicity in DBA/2 mice but not in C57BL/6 mice. From these findings we tentatively suggest that wheel running behaviour could serve as a tool to study the interaction between genetic and environmental factors in sensitivity to rewarding behaviour in mice. As it is displayed spontaneously and easy to monitor, wheel running may be well suitable to be included in high-throughput phenotyping assays.

Assessment of positive emotions in animals to improve their welfare.

It is now widely accepted that good welfare is not simply the absence of negative experiences, but rather is primarily the presence of positive experiences such as pleasure. However scientific investigation of positive emotions has long been neglected. This paper addresses two main issues: first, it reviews the current state of scientific knowledge that supports the existence of positive affective states in animals and, second, it suggests possible applications of this knowledge that may enhance quality of life under animal management conditions. In the first part of the paper, recent advances in psychology and neuroscience are reviewed to provide pragmatic frameworks based on cognitive processes (such as positive anticipation, contrast and controllability) for further investigations of positive emotions in animals. Thereafter, the neurobiological bases of positive emotions are highlighted in order to identify behavioral and physiological expressions of positive experiences in animals. Monitoring both the autonomic nervous system (via heart rate and its variability) and the immune system could offer relevant tools to better assess emotional states in animals, complementary to classical adrenocortical measures. In the second part of the paper, useful strategies for enhancing positive experiences (such as physical, social and cognitive enrichment or putative genetic selection) are outlined. Then this paper emphasizes practical applications for assessing and promoting positive emotions that may help in providing animals with a better quality of life. Play, affiliative behaviors and some vocalizations appear to be the most promising convenient indicators for assessing positive experiences in laboratory and farm animals under commercial conditions.

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.

Rats assess costs and benefits according to an internal standard.

Variation in effort to obtain rewards is a fact of mammalian everyday life. In this study, we assess how rats scale variable costs and benefits. Different groups of rats were trained in a T-maze to discriminate a high (three or five sugar pellets) from a low reward (one sugar pellet) arm. Subsequently barriers were introduced at the high and low reward side such that the overall long-term pay-off of the high reward arm finally became lower than that of the low reward arm. The data show that under different regimes of costs (climbing barriers) and benefits (number of rewards) of the two arms rats appear to shift their behaviour towards the better side according to a constant relative cost-benefit ratio between the arms. Such a ratio allows them to deal with variation in the (physical appearance of) costs and benefits and choose the best long-term option.

The effect of reward magnitude differences on choosing disadvantageous decks in the Iowa Gambling Task.

In the Iowa Gambling Task, participants have to develop a long-term profitable monetary scenario in a situation of uncertainty and a conflict between the chance of encountering an immediate large reward (100 US dollars) in two long-term loosing decks (A and B; -250 US dollars per 10 cards) and the chance of encountering an immediate small reward (50 US dollars) in two long-term winning decks (C and D; +250 US dollars per 10 cards). The ratio of the immediate rewards in decks A/B and C/D is thus 2:1. Here, we manipulated these differences in reward magnitude between the advantageous (C/D) and disadvantageous (A/B) decks, while keeping the net gains and losses per 10 cards the same, to assess the impact of the conflict between immediate and distant pay-off on choice behaviour. Participants selected less cards from disadvantageous decks and won more money when the reward magnitude difference was decreased, A/B:C/D=1:1, while they selected more cards from disadvantageous decks and lost more money when reward magnitude differences were increased, A/B:C/D=4:1 and 6:1. This study shows that the outcome in the Iowa Gambling Task is sensitive to differences between the magnitude of immediate rewards in the advantageous and disadvantageous decks.

Advanced behavioural screening: automated home cage ethology.

Animal behaviour has been studied using two approaches, (1) well-controlled experiments focusing on specific responses and (2) those with natural - fuzzy - but biologically relevant conditions. Ideally, one behavioural test should be able to address both. The home cage provided with various stimuli is proposed as an all-in-one possibility. This, however, results in an exponential increase in complexity regarding observation and analysis tools. It seems difficult to accept that behavioural expressions need a mathematical approach to unravel its organisation and meaning. Developments in artificial intelligence and data mining are essential to accelerate this necessary evolution in behavioural sciences.:

Intermediate-term emotional bookkeeping is necessary for long-term reciprocal grooming partner preferences in an agent-based model of macaque groups.

Whether and how primates are able to maintain long-term affiliative relationships is still under debate. Emotional bookkeeping (EB), the partner-specific accumulation of emotional responses to earlier interactions, is a candidate mechanism that does not require high cognitive abilities. EB is difficult to study in real animals, due to the complexity of primate social life. Therefore, we developed an agent-based model based on macaque behavior, the EMO-model, that implements arousal and two emotional dimensions, anxiety-FEAR and satisfaction-LIKE, which regulate social behavior. To implement EB, model individuals assign dynamic LIKE attitudes towards their group members, integrating partner-specific emotional responses to earlier received grooming episodes. Two key parameters in the model were varied to explore their effects on long-term affiliative relationships: (1) the timeframe over which earlier affiliation is accumulated into the LIKE attitudes; and (2) the degree of partner selectivity. EB over short and long timeframes gave rise to low variation in LIKE attitudes, and grooming partner preferences were only maintained over one to two months. Only EB over intermediate-term timeframes resulted in enough variation in LIKE attitudes, which, in combination with high partner selectivity, enables individuals to differentiate between regular and incidental grooming partners. These specific settings resulted in a strong feedback between differentiated LIKE attitudes and the distribution of grooming, giving rise to strongly reciprocated partner preferences that could be maintained for longer periods, occasionally up to one or two years. Moreover, at these settings the individual's internal, socio-emotional memory of earlier affiliative episodes (LIKE attitudes) corresponded best to observable behavior (grooming partner preferences). In sum, our model suggests that intermediate-term LIKE dynamics and high partner selectivity seem most plausible for primates relying on emotional bookkeeping to maintain their social bonds.

Novel approach to automatically classify rat social behavior using a video tracking system.

BACKGROUND: In the past, studies in behavioral neuroscience and drug development have relied on simple and quick readout parameters of animal behavior to assess treatment efficacy or to understand underlying brain mechanisms. The predominant use of classical behavioral tests has been repeatedly criticized during the last decades because of their poor reproducibility, poor translational value and the limited explanatory power in functional terms. NEW METHOD: We present a new method to monitor social behavior of rats using automated video tracking. The velocity of moving and the distance between two rats were plotted in frequency distributions. In addition, behavior was manually annotated and related to the automatically obtained parameters for a validated interpretation. RESULTS: Inter-individual distance in combination with velocity of movement provided specific behavioral classes, such as moving with high velocity when "in contact" or "in proximity". Human observations showed that these classes coincide with following (chasing) behavior. In addition, when animals are "in contact", but at low velocity, behaviors such as allogrooming and social investigation were observed. Also, low dose treatment with morphine and short isolation increased the time animals spent in contact or in proximity at high velocity. COMPARISON WITH EXISTING METHODS: Current methods that involve the investigation of social rat behavior are mostly limited to short and relatively simple manual observations. CONCLUSION: A new and automated method for analyzing social behavior in a social interaction test is presented here and shows to be sensitive to drug treatment and housing conditions known to influence social behavior in rats.

Neonatal amygdala lesions affect appetitive motivational and consummatory aspects of social behavior in the rat.

In the present study, rats received amygdala lesions (AMX) on either Postnatal Day 7 (PD 7; immature brain) or PD 21 (almost mature brain), and adult social activity was studied after short-term isolation housing. Sham-operated rats demonstrated increased following and approaching behavior after 7 days of isolation compared with after 4 days of isolation, an effect that was absent in AMX-PD 7 and AMX-PD 21 rats. Furthermore, AMX-PD 7 rats, but not AMX-PD 21 rats, displayed a reduction in investigatory behavior after prolonged isolation. This indicates that in AMX-PD 21 rats, mainly appetitive motivational aspects of social behavior were affected, whereas in AMX-PD 7 rats both motivational and consummatory aspects were disturbed. Finally, the reported deficits in AMX-PD 7 rats may reflect neurodevelopmental deficits of structures connected with the amygdala.