In the 1950s the neurotransmitter dopamine was discovered in the brain by Katharine Montagu, and characterised as a neurotransmitter a year later by Arvid Carlsson, for which he would be awarded the Nobel Prize. A. N. Ernst then discovered in 1965 that apomorphine was a powerful stimulant of dopamine receptors. This, along with the use of sublingual apomorphine tablets, led to a renewed interest in the use of apomorphine as a treatment for alcoholism. A series of studies of non-emetic apomorphine in the treatment of alcoholism were published, with mostly positive results. However, there was little clinical consequence. Parkinsons disease
The use of apomorphine to treat "the shakes" was first suggested by Weil in France in 1884, although seemingly not pursued until 1951. Its clinical use was first reported in 1970 by Cotzias et al., although its emetic properties and short half-life made oral use impractical. A later study found that combining the drug with the antiemetic domperidone improved results significantly. The commercialization of apomorphine for Parkinsons disease followed its successful use in patients with refractory motor fluctuations using intermittent rescue injections and continuous infusions. Aversion therapy
Aversion therapy in alcoholism had its roots in Russia in the early 1930s, with early papers by Pavlov, Galant and Sluchevsky and Friken, and would remain a strain in the Soviet treatment of alcoholism well into the 1980s. In the US a particularly notable devotee was Dr Voegtlin, who attempted aversion therapy using apomorphine in the mid to late 1930s.
Shortage or excess of dopamine can prevent proper function and signaling of these receptors leading to disease states.Apomorphine improves motor function by activating dopamine receptors in the nigrostriatal pathway, the limbic system, the hypothalamus, and the pituitary gland. It also increases blood flow to the supplementary motor area and to the dorsolateral prefrontal cortex (stimulation of which has been found to reduce the tardive dyskinesia effects of L-DOPA). Parkinsons has also been found to have excess iron at the sites of neurodegeneration; both the (R)- and (S)-enantiomers of apomorphine are potent iron chelators and radical scavengers.Apomorphine also decreases the breakdown of dopamine in the brain (though it inhibits its synthesis as well). It is an upregulator of certain neural growth factors, in particular NGF but not BDNF, epigenetic downregulation of which has been associated with addictive behaviour in rats.Apomorphine causes vomiting by acting on dopamine receptors in the chemoreceptor trigger zone of the medulla; this activates the nearby vomiting center. Pharmacokinetics
While apomorphine has lower bioavailability when taken orally, due to not being absorbed well in the GI tract and undergoing heavy first-pass metabolism, it has a bioavailability of 100% when given subcutaneously. It reaches peak plasma concentration in 10–60 minutes. Ten to twenty minutes after that, it reaches its peak concentration in the cerebrospinal fluid.