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The most often used method to induce stereotypic behaviour injecting some pharmaca in a specie, has been to use Amphetamine injections in Rats. Amphetamine increases the release of the neurotransmitter Dopamine (DA) pre-synaptic and is therefore considered a Dopamine-agonist. Other DA-agonists include Methamphetamine and Cocaine while a substance as Apomorphine is considers an indirect DA-agonist since this substance mimic Dopamine post-synaptic. The typical response from a rat which has received systemic (in the body) injections of amphetamine is an increased locomotive behaviour (low doses: up to a couple of mg/kg/day). At higher doses, stereotypies emerge in the form of oral-/head movements and sniffings. Below (Figure 4) is seen an outline of the connections to, and from, the two clusters in the brain which is particularly interesting when it comes to stereotypies and Dopamine. Figure 4
The two areas of special interest are both situated in a structure named Striatum. Caudatus putamen (sit. in the dorsal striatum) receives its innervation from Substantia nigra and form part of the Nigrostriatal Dopamine System. Nucleus accumbens (sit. in the ventral striatum) forms a part of the Mesolimbic Dopamine System and receives its innervations from the Ventral tegmental Area, which at the same time innervate three limbic structures. These are Amygdala; Hippocampus (especially important in this context) and the Prefrontal cortex. Two important features should be recognized in figure 4:
To give a couple of examples, it has been observed how hippocampoectomy (removal of H.) induces more head- and limb movements subsequent to injections with amphetamine. Prefrontal lesions cause oral stereotypies in rats and pacing in monkeys. Next topic: Tests with amphetamine and neurotoxins. |
