Physiological studies of neuroendocrine regulation confirm that aggressive behavior patterns are nearly universal in the animal kingdom. Different species of fish (e.g. Zebra Fish and Siamese Fighting Fish) are used as models for studies of animal behavior, including aggression. Despite an increased risk of injury or death, aggression frequently offers considerable benefits. It is mainly related with competition for limited resources, for example, competition for food or a mate, the establishment of territory and dominance hierarchies (a higher social status). Aggression is a kind of aversive drive to limit the freedom of other animals of the same or other species or to injure or kill them. Territorial behavior is a significant problem in farm and companion animals, not only causing economic losses but also threatening animal health and welfare. The following systems are involved in the regulation of aggressive behavior: the hypothalamo-pituitary-adrenocortical (HPA), sympathetico-medullary-adrenal (SAM), hypothalamo-pituitary-interrenal, serotonin, somatostatin, dopamine, histamine and nitric oxide pathways, as well as brain structures responsible for motivation. The aim of this article is to review the present state of knowledge concerning the neuro-endocrine modulation of aggressive behavior in animals.
Verapamil is a L-type voltage gated calcium channels inhibitor (VGCCI), which is a highly prescribed drug used in the treatment of hypertension, angina pectoris, cardiac arrhythmia and cluster headaches. Its common use caused its appearance in water environment. VGCC inhibit epinephrine release and cause many neuro-hormonal changes influencing also fish behavior. Siamese fighting fish was chosen to study the influence of verapamil given to the water on the beginning of experiment in 3 different concentrations of 0 (control), 8 and 160 μg • L-1, on aggressive behavior in these fish. The experimental fish were placed in individual glass containers for 3 weeks and the mirror test was used. The highest concentration led to a significant modulation of fish behavior after 1 week and the lower dose caused statistically significant behavioral changes after 2 weeks of verapamil treatment. Siamese fighting fish males exposed to verapamil had longer latencies to the first chase - 12.6 s (8 μg- L-1 of verapamil) and 18.8 s (160 μg • L-1 of verapamil) compared to 5.6 s in the control group, decreased attack frequency and shorter duration of these attacks. The number of attacks within 10 min was decreased from 38.3 in the control group to 27.1 and 16.1, respectively. Also the total duration of these attacks decreased from 354.8 (control) to 326.4 (decrease statistically insignificant) and to 194.8 s in verapamil treated groups. It was shown, that even relatively low concentrations of verapamil in water may have adverse effects on fish and probably other living organisms.