*Medicinal Plants Used in the Management of Psychosis DOI: http://dx.doi.org/10.5772/intechopen.100224*

#### *Complementary Therapies*

Dopaminergic deregulation, hypofunction of NMDA receptors and GABAergic activity, diminished cholinergic firing, neuroinflammation and increased oxidative stress has been demonstrated to play a pathophysiological role in schizophrenia [67].

The dopamine and amphetamine animal models are basically used to study the typical antipsychotic effects of drugs, their action are similar to the conventional antipsychotics such as haloperidol, chlorpromazine, fluphenazine and thioridazine. The stereotypic behavior observed in animals following the administration of apomorphine a dopaminergic agonist, are attributed to stimulation of D1 and D2 receptors [74, 75]. Mesolimbic and nigrostriatal dopaminergic pathways play key roles in the mediation of locomotor activity and stereotyped behavior. Animal models used for assessing antipsychotic drugs are established on the neurochemical hypothesis of schizophrenia, which involve largely the neurotransmitters dopamine and glutamate [76]. The antagonism of dopamine D2 receptors in the mesolimbicmesocortical system is thought to be the basis of the therapeutic actions of the antipsychotic drugs, especially those active against hallucinations and delusions [77]. The dopamine-based models usually employ apomorphine, a direct agonist, or amphetamine, a drug that increases the release of this neurotransmitter and blocks its re-uptake.

The term atypical refers to the reduced propensity of the of an agent to cause undesirable motor side effects, but it is also used to describe agents with a different pharmacological profile from the typical antipsychotics; several of these newer antipsychotics improve the negative as well as the positive symptoms [78]. The atypical antipsychotics are categorized base on their pharmacological properties. These include serotonin–dopamine antagonists, multi-acting receptor- Targeted antipsychotics, and dopamine partial agonists. [79]. Examples include clozapine, quetiapine, risperidone, amisulpride, sertindole, zotepine and aripiprazole. The dopamine dysregulation with hyperfunction of the mesolimbic dopamine system was the original tenet theory underlying the basis of schizophrenia [80] and the earliest animal models were established on the basis of pharmacological manipulation in an endeavor to simulate this feature [81], which respond to agents that affect primarily the dopaminergic system, but does not demonstrate the negative or cognitive symptoms seen in schizophrenia [82]. In contrast, a widely used animal model of schizophrenia involves the acute or repeated administration of subanesthetic doses of ketamine [83]. In rodents, N-methyl-Daspartic acid receptor (NMDAR) blockade induces hyperactivity, stereotypy, deficits in prepulse inhibition [84], social interaction and memory (Becker and Grecksch [85]), which models the positive, negative and cognitive symptoms of schizophrenia, respectively [9]. Furthermore, studies have revealed that reactive oxygen species have a significant role in the pathogenesis of many illnesses, particularly neurological and psychiatric illnesses. [86] Oxidative stress may be a common pathogenic mechanism underlying many major psychiatric disorders as the brain is relatively susceptible to oxidative damage [87]. Previous study confirmed that oxidative stress damage occurs in patients with schizophrenia and one possible therapeutic solution is to use antioxidants [88]. Reports from some of the medicinal plants studied that delineate some of the animal models used and their molecular mechanism of action are highlighted.

#### **7.1** *Morinda citrifolia* **Linn (Rubiaceae)**

*Morinda citrifolia* (noni) is an evergreen tree that grows in open coastline areas at sea level and in forest regions. Four doses (1, 3, 5, 10 g/kg) of the fruit extract of noni were administered prior to apomorphine/ amphetamine administration and observed for climbing behavior and stereotypy. The extract significantly decreased

the apomorphine-induced cage climbing behavior and climbing time in mice in a dose dependent manner. Demonstrating the antidopaminergic effect of the plant. The plant was found to be rich in rutin and scopoletin which might have played a role in the antipsychotic mechanism [60].
