A method of quantitating aggressive behaviour revealing possible dissociation of motor activity and aggression

Behavioral profiling of NPY in aggression and neuropsychiatric diseases

The abundantly expressed neuropeptide Y (NPY) has potent effects on feeding, body weight, and blood pressure, and exhibits important functions in various behavioral domains such as motor activity and anxiety. The potent neurotransmitter exerts its biological effects through at least five G-protein coupled receptors termed Y(1), Y(2), Y(4), Y(5), and y(6). The behavioral profile of NPY function has been extensively studied using traditional pharmacological and classic genetic animal models. Based on these studies, variations in the profile of NPY and its receptors have been found. To limit the variability and inconsistencies in the behavioral profile of NPY and to clarify its effects on certain domains in further detail, it is important to design a rational standardized strategy for behavioral testing, using a complement of different well-established and reproducible tests. This strategy can minimize the risk that false positive or false negative results lead to a contradictory and inconsistent behavioral characterization of NPY function. Ideally, such screening should be composed of an initial monitoring of general health, sensory functions, and motor abilities, before specific behavioral domains such as anxiety or aggression are investigated using a multi-tiered phenotyping approach. In this review, we will focus on a brief description of the latest insights into the behavioral profile of NPY in the selective lesser investigated domains such as aggression and depression-schizophrenia-related behaviors. We will combine this information with possible strategies to evaluate the different specific phenotypes in more detail.

Y1 receptors regulate aggressive behavior by modulating serotonin pathways

Neuropeptide Y (NPY) is pivotal in the coordinated regulation of food intake, growth, and reproduction, ensuring that procreation and growth occur only when food is abundant and allowing for energy conservation when food is scant. Although emotional and behavioral responses from the higher brain are known to be involved in all of these functions, understanding of the coordinated regulation of emotion/behavior and physiological functions is lacking. Here, we show that the NPY system plays a central role in this process because ablation of the Y1 receptor gene leads to a strong increase in territorial aggressive behavior. After exposure to the resident-intruder test, expression of c-fos mRNA in Y1-knockout mice is significantly increased in the medial amygdala, consistent with the activation of centers known to be important in regulating aggressive behavior. Expression of the serotonin [5-hydroxytryptamine (5-HT)] synthesis enzyme tryptophan hydroxylase is significantly reduced in Y1-deficient mice. Importantly, treatment with a 5-HT-1A agonist, (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide, abolished the aggressive behavior in Y1-knockout mice. These results suggest that NPY acting through Y1 receptors regulates the 5-HT system, thereby coordinately linking physiological survival mechanisms such as food intake with enabling territorial aggressive behavior.

Measuring behaviour: the tools and the strategies

Animal behaviour can be viewed as a stream of elements, which, once accurately described, can be counted and timed. Data acquisition techniques and tools are reviewed, and some strategies for collection and analysis of data using PC computers are suggested. Automated instruments are not satisfactory for the study of complex behaviour and as such systemic observation remains irreplaceable. IBM PC-type computers, with a wide range of analytical software (e.g., spreadsheets, statistical packages, technical graphics), are practical for data acquisition. Several systems which can satisfy different applications are reviewed. Some systems can communicate with a videorecorder, a facility which remarkably increases the accuracy of measurement; this is essential for meaningful analyses of the internal structure of behavioural streams (sequences, time patterns) or communication processes. The power of new tools enables behavioural measurement with the necessary complexity to allow a whole new set of questions to be addressed. However, it also increases demands for meaningful content and analysis of data.

Automated method for measuring fighting behavior and locomotor activity of mice

A multiunit apparatus for automatic quantification of intermale fighting behavior and locomotor activity of mice is described. The method uses static charge sensitive beds (SCSB) to detect movement, and appropriate hard- and software for data acquisition and analysis. The data obtained with the SCSB-method correlated well with those observed from video-recordings of the same 60 aggression trials for determining both the total fighting times (r = .967) and the latencies to first fighting (r = .982). d-Amphetamine significantly increased locomotor activity counts on the SCSBs, and this increase was blocked by haloperidol. It is concluded, that the SCSB-method is an accurate and flexible technique for quantifying intermale fighting behavior and locomotor activity of mice.

Growth hormone and isolation-induced aggression in wild male mice

Aggressive behavior, motor activity and defecation were examined simultaneously in wild male mice following daily growth hormone (GH) administration. GH was found to increase isolation-induced aggression by increasing fighting duration and decreasing latency to fight. There was no influence on non-aggressive motor activity nor on the defecation rate, a presumed parameter of emotionality. The results provide evidence of behavioral properties of GH. The mechanism of this action is discussed in terms of a possible direct central action of GH, not mediated by glucagon, insulin, secretin and gastrin.

An automated device for screening the effects of psychotropic drugs on aggression and motor activity in mice

An automated technique for measuring simultaneously aggressive behavior and motor activity in mice is described. This technique allows measure of aggressive behavior and motor activity continuously throughout long-lasting periods without disturbing the animals except for feeding, watering and cleaning the cages. The effects of n-D-propylacetate, a drug which affects aggression without affecting motor activity, were also tested.

Dietary tryptophan modulation and aggressive behavior in mice

The effects of a tryptophan-free diet on isolation-induced fighting and predatory cricket killing in mice were examined. The results demonstrated that consumption of a tryptophan-free diet for 18-20 days decreased both the number of fighters and duration of isolation-induced fighting; increased the number of cricket-killing mice and decreased the latencies to attack and the latencies to kill crickets; reduced brain serotonin 27%; increased water intake 38%; and decreased body weight 27% without affecting food intake. To determine if these effects were due specifically to the lack of dietary tryptophan, other groups of mice were fed a 5% tryptophan load in the standard chow; a 0.15% tryptophan supplement in the tryptophan-free diet; or a 3 grams/day restricted chow diet. The lack of tryptophan in the diet produced the marked inhibition in isolation-induced fighting, the reduction in brain serotonin, and the large decrease in body weight. The other non-specific effects appeared to be related to general factors such as dietary need for the cricket killing or diet composition (other than the lack of tryptophan) for the water intake.