Schizophrenia dopaminergic neurotransmission

A number of azetidine-based compounds have been disclosed in patent applications from Aventis Pharma for CBi-modulated treatment of diseases such as obesity, Parkinson s disease, schizophrenia, respiratory and neurological diseases [330-334]. Compound (556) was specifically claimed for use in two formulation patent applications [330, 331] for a stable semi-solid composition and oral emulsion composition, respectively. The optional coadministration of an agent that activates norepinephrinergic and se-rotoninergic neurotransmission (for example, sibutramine) or dopaminergic neurotransmission was also claimed for the treatment of obesity. The optional use of a dopamine agonist (for example, levodopa) was claimed... 

The D2 antagonist activity of current antipsychotics led to the "dopamine hypothesis," which states that the pathophysiology of schizophrenia is due to excessive dopaminergic neurotransmission and dysfunctional D2 signaling [6]. This hypothesis has prevailed for nearly 60 years however, it falls short as a complete explanation due to the deficiencies current antipsychotics exhibit against negative and cognitive symptoms. 

In schizophrenia the dopaminergic neurotransmission is thought to be exaggerated. All known antipsychotic drugs are blockers of the dopamine... 

A principal interest in our laboratory is the molecular characterization of CNS receptor sites of the neurotransmitter dopamine (DA, 5). These sites are strongly implicated in the biochemical etiology of schizophrenia and Parkinson s Disease, as well as other diseases of the CNS (50,51). Thus, the rank order of clinical potency of antipsychotic drugs (neuroleptics) correlates with the affinity of these drugs for dopaminergic sites (52,53), It is also well established that Parkinson s disease is directly related to deterioration in dopaminergic neurotransmission in the corpus striatum, which is a brain region rich in dopamine receptor sites (54). The use of L-DOPA, the biosynthetic precursor of dopamine, in treatment of patients with Parkinson s disease is one of the best examples of biochemically directed medical treatment. 

The discovery that the first antipsychotic drugs in the early 1950s, such as chlorpromazine, work in vitro by blocking dopamine receptors led to the hypothesis that schizophrenia was the result of excessive dopaminergic neurotransmission (54, 55). Supporting this hypothesis, dmgs that enhance dopamine action (e.g., cocaine, amphetamines, and L-DOPA) worsen the symptoms of schizophrenia. However, it is clear that 1) not all patients respond to neuroleptic treatment and 2) not all symptoms are reversed by the medication. 

A disturbance in the dopaminergic neurotransmission plays a key-role in the pathogenesis of schizophrenia (Carlsson, 1988). Most di ugs amedoradng psychodc symptoms act as dopamine receptor blockers, in pardcular D2 receptor blockers. In light... 

Mesolimbic and mesocortical. These are dopaminergic neurons that project from the ventral tegmental area (VTA) to frontal and other cortical areas (mesocortical pathway) and to limbic structures such as the nucleus accumbens, the amygdala, and the olfactory tubercle (mesolimbic pathway). It is assumed that in schizophrenia, there is increased dopaminergic neurotransmission in the mesolimbic pathway and decreased transmission in the mesocortical region (see Section 4.1 for details). 

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