Amphetamine Induced Selective Stimulation of Certain Behaviour Items With Concurrent Inhibition of Others in an Open-Field Test With Rats

Rats were treated with 5 mg/kg bodyweight d-amphetamine sulphate (N = 13) or placebo (N = 10) and the following six items of behaviour were studied quantitatively with an open-field test: forward locomotion (FL), rearing at wall (RW), rearing in free air (RF), grooming with forelegs (GFL), Grooming with head (GH) and grooming with hind legs (GHL). Three phases were observed during the action of amphetamine. The pre-phase (lasting from time of injection to average 46 minutes post injection) : in the beginning some behavioural items are decreased while others are concurrently increased but later all the behavioural items observed are reduced and finally disappear altogether. The stereotypy-phase (from average 46 min. p.i. to average 138 min. p.i.): all behaviour items mentioned above are absent. Only continuous sniffing and licking with head movements from side to side are performed (= the classical amphetamine-induced stereotypy). The after-phase (from average 138 minutes p.i.) : The normal behaviour items and the normal patterns reappear successively until total normalization and sleep. In the beginning of the afterphase some behavioural items are increased much above normal, while others are still suppressed. Six behaviour items were studied and the following influence of amphetamine was found : Forward locomotion (FL) was significantly increased by amphetamine according to the number of lines crossed, while distribution of the locomotion in the cage was restricted to routes (unvaried locomotion) or had in other respects a stereotyped character. These data will be published separately. Rearing at wall (RW) was significantly increased and in two rats combined with rearing in free air (RF) to a highly stereotyped pattern. Rearing in free air (RF) was significantly increased but less than RW and decreased earlier to zero than RW in the pre-phase. Grooming with forelegs (GFL) was quickly after the injection significantly decreased and disruption of the normal pattern GFL followed by grooming with head (GH) was observed. Grooming with head (GH) was significantly decreased. Grooming with hind legs (GHL) was significantly decreased and disappeared earlier (or was totally absent) in the pre-phase than GFL and GH, and appeared later in the after-phase also. The main conclusions of the experiments are: I) Amphetamine (5 mg/kg s.c.) cannot be characterized as a general stimulant. According to the overt behaviour studied the drug has a selective stimulating action with concomitant selective inhibition, as some behaviour items increase while other simultaneously decrease. 2) Amphetamine causes disruption of behaviour patterns as well as development of new combinations of items, which are not associated in normal subjects. 3) Amphetamine can induce changes in locomotion activity: a) Increase in the pre-phase, zero in the stereotypy-phase and increase (with later normalization) in the after-phase b) the locomotion was abnormally persevering or stereotyped; several rats followed a restricted route and other types of fixed locomotion patterns (These data will be published separately). The possible relation from the animal data to the study of stereotyped behaviour found in the psychopathology of humans, including amphetamine-addiction and the underlying brain mechanisms is discussed.