The neurochemistry of mania: a hypothesis of etiology and rationale for treatment

On the diagnostic and neurobiological origins of bipolar disorder

Psychiatry is constructed around a taxonomy of several hundred diagnoses differentiated by nuances in the timing, co-occurrence, and severity of symptoms. Bipolar disorder (BD) is notable among these diagnoses for manic, depressive, and psychotic symptoms all being core features. Here, we trace current understanding of the neurobiological origins of BD and related diagnoses. To provide context, we begin by exploring the historical origins of psychiatric taxonomy. We then illustrate how key discoveries in pharmacology and neuroscience gave rise to a generation of neurobiological hypotheses about the origins of these disorders that facilitated therapeutic innovation but failed to explain disease pathogenesis. Lastly, we examine the extent to which genetics has succeeded in filling this void and contributing to the construction of an objective classification of psychiatric disturbance.

Biological hypotheses and biomarkers of bipolar disorder

The most common mood disorders are major depressive disorders and bipolar disorders (BD). The pathophysiology of BD is complex, multifactorial, and not fully understood. Creation of new hypotheses in the field gives impetus for studies and for finding new biomarkers for BD. Conversely, new biomarkers facilitate not only diagnosis of a disorder and monitoring of biological effects of treatment, but also formulation of new hypotheses about the causes and pathophysiology of the BD. BD is characterized by multiple associations between disturbed brain development, neuroplasticity, and chronobiology, caused by: genetic and environmental factors; defects in apoptotic, immune-inflammatory, neurotransmitter, neurotrophin, and calcium-signaling pathways; oxidative and nitrosative stress; cellular bioenergetics; and membrane or vesicular transport. Current biological hypotheses of BD are summarized, including related pathophysiological processes and key biomarkers, which have been associated with changes in genetics, systems of neurotransmitter and neurotrophic factors, neuroinflammation, autoimmunity, cytokines, stress axis activity, chronobiology, oxidative stress, and mitochondrial dysfunctions. Here we also discuss the therapeutic hypotheses and mechanisms of the switch between depressive and manic state.

Switching to hypomania and mania: differential neurochemical, neuropsychological, and pharmacologic triggers and their mechanisms

Current data suggest that monoamines, acetylcholine, amino acids, cortisol, thyroid hormones, and melatonin may be involved in the pathophysiology of bipolar disorder (BPD). Any neuropsychological or pharmacologic factor causing a disturbance in these neurochemicals may trigger manic/hypomanic switching. Antidepressants, stimulants, anticholinergics, steroids, and thyroid hormone have been reported to cause treatment-emergent mania (TEM) in BPD, but only recently have the traditional antidepressants been systematically studied. Paroxetine, 20 mg/d, monotherapy in treatment of acute, relatively "pure" bipolar I and II depression, and fluoxetine monotherapy in bipolar II depression conferred a similar risk as placebo for TEM. Paroxetine or bupropion adjunctive therapy to mood stabilizer(s) had a similar risk as placebo for treatment of TEM in real world patients with bipolar depression during continuation treatment. Venlafaxine was shown to have an increased risk of TEM compared with bupropion and sertraline. The evolving literature continues to support the role of mood stabilizers in preventing future mood episodes of BPD.

Brain choline concentrations may not be altered in euthymic bipolar disorder patients chronically treated with either lithium or sodium valproate

Background

It has been suggested that lithium increases choline concentrations, although previous human studies examining this possibility using ¹H magnetic resonance spectroscopy (¹H MRS) have had mixed results: some found increases while most found no differences.

Methods

The present study utilized ¹H MRS, in a 3 T scanner to examine the effects of both lithium and sodium valproate upon choline concentrations in treated euthymic bipolar patients utilizing two different methodologies. In the first part of the study healthy controls (n = 18) were compared with euthymic Bipolar Disorder patients (Type I and Type II) who were taking either lithium (n = 14) or sodium valproate (n = 11), and temporal lobe choline/creatine (Cho/Cr) ratios were determined. In the second part we examined a separate group of euthymic Bipolar Disorder Type I patients taking sodium valproate (n = 9) and compared these to controls (n = 11). Here we measured the absolute concentrations of choline in both temporal and frontal lobes.

Results

The results from the first part of the study showed that bipolar patients chronically treated with both lithium and sodium valproate had significantly reduced temporal lobe Cho/Cr ratios. In contrast, in the second part of the study, there were no effects of sodium valproate on either absolute choline concentrations or on Cho/Cr ratios in either temporal or frontal lobes.

Conclusions

These findings suggest that measuring Cho/Cr ratios may not accurately reflect brain choline concentrations. In addition, the results do not support previous suggestions that either lithium or valproate increases choline concentrations in bipolar patients.

Role of the cholinergic muscarinic system in bipolar disorder and related mechanism of action of antipsychotic agents

The evidence for the involvement of cholinergic muscarinic receptors in mania and depression is reviewed. Small pilot trials with cholinesterase inhibitors and muscarinic agonists suggest that stimulation of muscarinic receptors may produce an antimanic effect, possibly by activation of muscarinic M(4) receptors. It is concluded that it is not likely that currently used mood stabilizers, such as lithium, valproic acid and carbamazepine, work directly through muscarinic receptor mechanisms. Furthermore, the evidence indicates that antipsychotic agents used for mania are working through the common mechanism of antagonism of dopamine D(2) receptors, and interactions with muscarinic receptors do not play a key role. Finally, it is hypothesized that olanzapine has robust antimanic activity, due to blockade of dopamine D(2) receptors and antagonism of other monoaminergic receptors. Olanzapine may normalize mood due to antidepressant-like activities, such as 5-HT(2A) receptor antagonism and increasing cortical norepinephrine and dopamine.

Basal ganglia choline levels in depression and response to fluoxetine treatment: an in vivo proton magnetic resonance spectroscopy study

We have investigated proton magnetic resonance spectra of the basal ganglia in 41 medication-free outpatients with major depression, prior to starting an 8-week standardized trial of open-label fluoxetine, and 22 matched comparison subjects. Upon completing the trial, depressed subjects were classified as treatment responders (n = 18) or nonresponders (n = 23), based on changes in the Hamilton Depression Rating Scale. Depressed subjects had a lower area ratio of the choline resonance to the creatine resonance (Cho/Cr) than comparison subjects. This statistically significant difference between the depressed subjects and comparison subjects was more pronounced in the treatment responders than in the nonresponders. There were no differences in the relative volumes of gray matter or white matter in the voxel used for proton spectroscopy in depressed subjects relative to comparison subjects. These results are consistent with an alteration in the metabolism of cytosolic choline compounds in the basal ganglia of depressed subjects and, in particular, those who are responsive to fluoxetine.

Choline in the treatment of rapid-cycling bipolar disorder: clinical and neurochemical findings in lithium-treated patients

This study examined choline augmentation of lithium for rapid-cycling bipolar disorder. Choline bitartrate was given openly to 6 consecutive lithium-treated outpatients with rapid-cycling bipolar disorder. Five patients also underwent brain proton magnetic resonance spectroscopy. Five of 6 rapid-cycling patients had a substantial reduction in manic symptoms, and 4 patients had a marked reduction in all mood symptoms during choline therapy. The patients who responded to choline all exhibited a substantial rise in the basal ganglia concentration of choline-containing compounds. Choline was well tolerated in all cases. Choline, in the presence of lithium, was a safe and effective treatment for 4 of 6 rapid-cycling patients in our series. A hypothesis is suggested to explain both lithium refractoriness in patients with bipolar disorder and the action of choline in mania, which involves the interaction between phosphatidylinositol and phosphatidylcholine second-messenger systems.

1H magnetic resonance spectroscopy characterization of neuronal dysfunction in drug-naive, chronic schizophrenia

RATIONALE AND OBJECTIVES

We investigated the proton metabolism of right prefrontal white matter in drug-naive, chronic schizophrenic patients (n = 23), compared with healthy normal control subjects (n = 10), by using localized, water-suppressed in vivo 1H magnetic resonance (MR) spectroscopy.

METHODS

All 1H MR spectroscopy examinations were performed on a 1.5-T MR imaging/MR spectroscopy system by using a point-resolved spectroscopy pulse sequence for localized volumes of 2 x 2 x 2 cm3. Proton metabolite ratios relative to creatine (Cr) were obtained using a Marquart algorithm.

RESULTS

Drug-naive, chronic schizophrenic patients demonstrated a decrease in the N-acetylaspartate (NAA):Cr and choline (Cho):Cr ratios and an increase of the complex of gamma-aminobutyric acid (GABA) and glutamate (Glu)-containing ratio [(GABA + Glu):Cr] as compared with normal control subjects.

CONCLUSION

Results suggest that the reduction of NAA and Cho may indicate neuronal dysfunction and that the elevation of GABA and Glu may play a role in chronic schizophrenia. 1H MR spectroscopy may be a useful modality in research and in the clinical evaluation of chronic schizophrenic patients.