Since bipolar disorder involves cycling between two different states of mania and major depression, many different etiological factors come into play. The neurotransmitters involved in this illness are the serotonin, norepinephrine and dopamine. Preliminary research has also been conducted on glutamate. In patients with the depressive part of bipolar disorder, serotonin levels have been found to be lower than those of healthy, nondepressed patients (Young, Warsh, Kish, Shannak, & Hornykeiwicz, 1994). Young and. al. (1994) found reduced amounts of the serotonin metabolite 5-HIAA in the frontal and parietal lobes of deceased patients with bipolar disorder. Noradrenaline was also found to be lower. During the depressive state of bipolar disorder, the concentration of the norepinephrine-synthesizing enzyme tyrosine hydroxylase was lower in the locus coeruleus than in patients with only depression and not bipolar disorder (Wiste, Arango, Ellis , Mann and Underwood, 2008). . Although in the manic cycle of bipolar disorder, norepinephrine is elevated in the brain (Manji and Lenox, 2000). Additionally, it was found that dopamine was also lower in the brain during the depressive state of bipolar disorder. According to a study by Vawter, Freed, Kleinman (2000), the concentration of the dopamine metabolite homovanillic acid was found to be significantly lower in the parietal lobe of the brain. Dopamine agonists, although they can treat the depressive cycle of the disorder, can also cause the mania of the disorder; therefore, pharmacological treatment of bipolar disorder must be heavily regulated so that the treatment itself does not worsen the disorder instead of treating it (Manji et al. 2003). ...... middle of paper ...... & Lenox, R. (2000). The nature of bipolar disorder. Journal of Clinical Psychiatry, 61(13), 42-57. Sklar, P., Gabriel, SB, Craddock, N., DePaulo, JR, Lander, ES, McInnis, MG et al. (2002). Familial association study of 76 candidate genes in bipolar disorder: BDNF is a potential risk locus. Molecular Psychiatry, 7, 579-593. Vawter, MP, Freed, WJ, & Kleinman, JE (2000). Neuropathology of bipolar disorder. Biological Psychiatry, 48(6), 486-504. Wiste, AK, Arango, V., Ellis, SP, Mann, JJ, & Underwood, MD (2008). Imbalance of norepinephrine and serotonin in the locus coeruleus in bipolar disorder. Bipolar Disorders, 10 (3), 349-359. Young, L., Warsh, JJ, Kish, SJ, Shannak, K., & Hornykeiwicz, O. (1994). Reduced brain 5-HT and increased NE turnover and metabolites in bipolar affective disorder. Biological Psychiatry, 35(2), 121-127.