Biological Theories Applied to the Etiology of Bipolar And Related Disorders
Precise biological causes of bipolar and related disorders are still not known, but there are several biological theories applied to their etiology. The neural circuitry theory suggests that bipolar disorder (BD) is caused by structural and functional abnormalities in brain areas, such as grey matter reduction or overactivation of the thalamus and amygdala (Sigitova et al., 2017). Another theory suggests that BD is caused by genetic polymorphism of some candidate genes, such as 5-HTT, DAT, BDNF, TPH, and others, which makes some individuals be more susceptible to BD than others (Sigitova et al., 2017). According to the monoamine hypothesis, BD is associated with a lack of monoamine neurotransmitters, such as serotonin, dopamine, and norepinephrine (Sigitova et al., 2017). The inflammatory theory posits that in patients with BD, the immune system is constantly activated, which leads to producing inflammatory cytokines, changing the brain function, and causing mood disorders (Sigitova et al., 2017). These are some of the theories that try to explain the etiology of BD and related disorders.
Summary of the Assigned Medications
Lithium carbonate and carbamazepine are two medications used for treating patients with bipolar and related disorders. Lithium is used for treating BD during the maintenance phase; in the acute phase, lithium is more effective when combined with an antipsychotic or sodium valproate (Sani et al., 2017). Carbamazepine is prescribed for treating epilepsy but is also used as a second-line treatment for BD (Ayano, 2016). Both medications are used for the long-term treatment of BD.
The Mechanism of Action
The mechanism of action of lithium carbonate is based on its influence on transmitter receptors. Lithium affects adrenoceptors and serotonin, the phosphoinositide cycle, and the calcium-calmodulin systems, which has an impact on neurotransmission (Sani et al., 2017). As a result, it decreases apoptosis, i.e., the death of cells, thus increasing the cell viability (Sani et al., 2017). Carbamazepine also influences neurotransmission, namely, GABA neurotransmission, glutamate neurotransmission, and dopaminergic transmission (Ayano, 2016). As a consequence, it has antimanic and mood-stabilizing effects on patients with BD.
Possible Side Effects and Their Presence in Behavioral Symptoms
Both medications have such common side effects as nausea, diarrhea, and weight gain. The intake of lithium may lead patients to have subjective feelings of tremor, weight gain, or cognitive impairment (Sani et al., 2017). As a result, they can stop adhering to this medication. As for carbamazepine, patients have a good response to it, especially in the cases with various manias, history of alcoholism, and substance issues (Ayano, 2016). The presence of side effects of carbamazepine in behavioral symptoms is not reported in the literature.
Possible Interactions and Contraindications
Both medications should be administrated with caution to patients taking other drugs because interactions with some drugs may increase their toxicity. Lithium should not be used in patients with renal and cardiovascular diseases, while carbamazepine is contraindicated to patients with previous bone marrow problems.