Behavioural and motor excitation and inhibition induced by the administration of small and large doses of somatostatin into the amygdala

The administration of lower (0.01, 0.1 μg) and higher (1.0, 10.0 μg) doses of somatostatin (SRIF) into the amygdaloid complex revealed a dose-dependent dissociation of effects on behaviour and motor control. While the lower doses generally induced a behavioural excitation accompanied by a variety of tremors and stereotyped movements, the higher doses prevented the expression of a normal behavioural pattern due to the severity of disturbances in motor control. The sleep-waking cycle was also affected; the duration of REM sleep showed a consistent dose-related reduction although the total sleeping time was not considerably altered. This was due to a paradoxical dose-related prolongation of shallow slow wave sleep (drowsiness) which typically accompanied the periods of immobilization caused by motor control difficulties. Electrophysiologically, this phenomenon was often reflected in a paradoxical pattern characterized by a dissociation of EEG from behaviour. The specificity of SRIF effects was tested by administration of some endocrinologically active and inactive analogues of SRIF via the same route. None of the analogues tested induced effects comparable to those observed after the administration of the same dose of the native hormone.