Pharmacologic Theories Of Schizophrenia

Pharmacologic Models Current pharmacologic models were developed based on our understanding of the alterations in various neurotransmitter system found in schizophrenia. These models are largely based on the neurodegenerative theory of schizophrenia. In general, the predictive validity of these models is variable, but often fairly good because most pharmacologic models involve the administration of drugs that induce or exacerbate schizophrenic symptoms in humans (Steeds et al. 2014). The construct and face validity are also generally good, but quite limited given our poor understanding of the fundamental basis of thought and cognition.

Dopamine

The dopamine hypothesis of schizophrenia (Steeds et al., 2014, Peleg-Raibstein et al. 2008) attributes

PPI is impaired in schizophrenia, as well as in rats given a dopamine agonist like apomorphine or amphetamine (Geyer et al. 2001), strongly mimicking the PPI deficits seen in schizophrenia. Administration of antipsychotic drugs restores PPI function in these rats with response to the antipsychotic being strongly correlated with both clinical antipsychotic potency and D2 receptor affinity, as seen in human schizophrenia patients. These results suggest face validity in these models. Further, PPI can be disrupted in rats by the direct infusion of dopamine into the nucleus accumbens (NAC), an effect that can also be blocked by antipsychotics (Rio et al., 2014), suggesting some degree of predictive validity in this model as well. Although the dopamine hypothesis is the oldest and most established of the schizophrenia hypotheses, the underlying mechanism by which dopamine activity is altered is still unknown. There is little evidence that dopamine plays a primary causal role in the development of schizophrenia (Grace, 2000), as some patients with schizophrenia (specifically those with mostly negative symptoms) respond poorly or not at all to treatment with dopamine antagonists. Therefore, despite the emphasis placed on this model in literature, the construct validity of dopamine animal models of schizophrenia is quite

Polymorphisms of the 5-HT2a receptor gene have been implicated as a minor risk factor for developing schizophrenia (Steeds, 2015). Additionally, a loss of PFC 5-HT2a receptors accompanied by an increase in 5-HT1a receptors and a blunted neuroendocrine response to 5-HT2a agonists (Eggers, 2013, Millan, 2000) have been seen in schizophrenia. Finally, the high affinity of atypical antipsychotic medications such as clozapine for the 5-HT2a receptor further supports the role of the 5-HT serotonergic systems in schizophrenia (Eggers, 2013).

Psychedelic hallucinogenic drugs such as LSD and mescaline are believed to mediate their effects through 5-HT receptors (Harrison et al., 2000). As with dopaminergic and glutamatergic animal models, LSD has been shown to disrupt PPI and startle habituation in humans and rats (Millan, 2000), an effect that is mediated through direct stimulation of 5-HT2a receptors (Gu et al.,