Different behavioural patterns induced by apomorphine: evidence that the method of administration determines the behavioural response to the drug.

The behavioural effects of s.c. injected apomorphine was studied on habituated rats in a test-box designed to measure 8 different components of behaviour. Apomorphine, 1 mg/kg, induced two different behaviours: The "G-type" of behaviour characterized by compulsive gnawing and the "LS-type" of behaviour characterized by increased locomotion, sniffing and repetitive head and limb movements. G-type behaviour was induced when apomorphine, dissolved by heating, was injected s.c. into the flank of the animal. LS-type behaviour was induced both when apomorphine, dissolved by heating, was injected s.c. into the neck and when it was dissolved by heating together with a high concentration of ascorbic acid (1 mg/ml) and injected s.c. into the flank. G-type behaviour could not be elicited by changing the dose which induced LS-type behaviour or vice versa. We therefore conclude that these different behavioural effects of apomorphine were not dose--response effects but were elicited by at least two different synaptic mechanisms in the brain. Experimentally induced changes from one of these apomorphine-induced behaviours to another can therefore not merely be interpreted as a change in the intensity of the behavioural response as is done in e.g. commonly used stereotypy rating scales.