Monoaminergic Depletion and Changes in Aggressive Behavior in Cats and Rats

Abstract

The involvement of various neurotransmitters in aggressive behavior has been studied intensively for years. It is known that various neurotransmitter systems remain in anatomical and functional interactions and it seems that the changes in their dynamic balance might play an important role in the regulation of complex behaviors.

The purpose of our experiments was to study the behavioral and biochemical effects of the destruction of noradrenergic (NA) system in respect to various types of aggression in two different species.

In both, cats and rats the experimental paradigms were designed as close to the natural circumstances as it was possible in the laboratory, i.e. predatory behavior and predatory competition for cats, mouse-killing and intruder-resident with computerized ethological analysis for rats. The first series of tests allowed to describe the behavioral profile of all animals. Then submissive cats and rats were treated with selective noradrenergic neurotoxin DSP-4 preceded by zimelidine to protect 5HT neurons. After the completion of the experiments, concentration of NA, 5HT and DA (in case of rats also their metabolites) was measured in brain structures associated with emotional behavior. It has been found that DSP-4 treatment did not affect prey killing in either cats or rats. Also well established dominance-submissive order during predatory competition remained unchanged, except the situation when the stressful stimuli were presented to the pair of cats. In rats, marked decrease of defensive episodes and increase of offense during social interactions, were observed. Simultaneously it was found that DSP-4 treated rats explored more in stressogenic highly illuminated area than controls. Three possible hypotheses are discussed: 1. increase of aggression 2. fear reduction 3. inadequate responsiveness to environmental factors.

Biochemical analysis showed significant reduction of NA and some changes in 5HT and DA, which we consider as an effect secondary to NA depletion. In the neurochemical perspective the results obtained can be interpreted in terms of altered NA, 5HT and DA balance that reflects functional interactions within monoaminergic systems.