[Biochemistry of depression]

Understanding the pathophysiology of depression: From monoamines to the neurogenesis hypothesis model - are we there yet?

A number of factors (biogenic amine deficiency, genetic, environmental, immunologic, endocrine factors and neurogenesis) have been identified as mechanisms which provide unitary explanations for the pathophysiology of depression. Rather than a unitary construct, the combination and linkage of these factors have been implicated in the pathogenesis of depression. That is, environmental stressors and heritable genetic factors acting through immunologic and endocrine responses initiate structural and functional changes in many brain regions, resulting in dysfunctional neurogenesis and neurotransmission which then manifest as a constellation of symptoms which present as depression.

Circadian rhythm hypotheses of mixed features, antidepressant treatment resistance, and manic switching in bipolar disorder

Numerous hypotheses have been put forth over the years to explain the development of bipolar disorder. Of these, circadian rhythm hypotheses have gained much importance of late. While the hypothalamus-pituitary-adrenal (HPA) axis hyperactivation hypothesis and the monoamine hypothesis somewhat explain the pathogenic mechanism of depression, they do not provide an explanation for the development of mania/hypomania. Interestingly, all patients with bipolar disorder display significant disruption of circadian rhythms and sleep/wake cycles throughout their mood cycles. Indeed, mice carrying the Clock gene mutation exhibit an overall behavioral profile that is similar to human mania, including hyperactivity, decreased sleep, lowered depression-like behavior, and lower anxiety. It was recently reported that monoamine signaling is in fact regulated by the circadian system. Thus, circadian rhythm instability, imposed on the dysregulation of HPA axis and monoamine system, may in turn increase individual susceptibility for switching from depression to mania/hypomania. In addition to addressing the pathophysiologic mechanism underlying the manic switch, circadian rhythm hypotheses can explain other bipolar disorder-related phenomena such as treatment resistant depression and mixed features.

Pathophysiology of depression and mechanisms of treatment

Major depression is a serious disorder of enormous sociological and clinical relevance. The discovery of antidepressant drugs in the 1950s led to the first biochemical hypothesis of depression, which suggested that an impairment in central monoaminergic function was the major lesion underlying the disorder. Basic research in all fields of neuroscience (including genetics) and the discovery of new antidepressant drugs have revolutionized our understanding of the mechanisms underlying depression and drug action. There is no doubt that the monoaminergic system is one of the cornerstones of these mechanisms, but multiple interactions with other brain systems and the regulation of central nervous system function must also be taken into account In spite of all the progress achieved so far, we must be aware that many open questions remain to be resolved in the future.

Angiotensin-converting enzyme inhibitors may cause renal dysfunction in patients on long-term lithium treatment

Anecdotal observations suggest that renal dysfunction may occur when unadjusted doses of angiotensin-converting enzyme inhibitors are administered to patients on long-term lithium treatment. Although no systematic experimental studies or controlled clinical observations are available, lithium is known to activate the renin angiotensin system through several mechanisms. In addition, direct interactions between lithium and angiotensin II may take place on a cellular level. We propose that (1) renal function should be closely monitored when patients on lithium treatment are given angiotensin-converting enzyme inhibitors and that (2) doses of both drugs should be chosen with caution to avoid serious drug interaction.

[The effect of the beta-adrenergic blocking agent propranolol in mania (author's transl)]

Six patients with the diagnosis of acute mania were treated with high doses of the beta-adrenergic blocking agent propranolol. One of these patients was treated during two manic phases. Psychopathologic change during treatment was rated daily by a psychiatrist not informed on the patients medication. The IMPS (Inpatient Multidimensional Psychiatric Scale) was used. Three cases were placebo-controlled under double blind conditions. Four times we had a second medication period, twice with propranolol and once with oxprenolol and dexpropranolol respectively. Propranolol was administered every 4 h (six times per day), starting with single doses of 20-40 mg. Doses were increased individually under control of pulse rate, blood pressure, and ECG. Augmentation of doses was continued until an effect on manic symptomatology was undoubtedly seen or until therapy had to be discontinued because of side-effects. In four patients definite improvement of manic symptomatology could be achieved during altogether five manic phases within usually two treatment periods of 5-15 days. Manic behavior disappeared completely in two of these patients. The effective dosage of propranolol varied between 280 and 2320 mg per day. All of the improved patients relapsed after discontinuation of the drug. In the only case on dexpropranolol (5 days up to 900 mg daily) the effect was questionable. No extrapyramidal side-effects were observed. In one patient treatment was discontinued because of lack of cooperation, in another because of extrasystoles. Gastrointestinal bleeding occurred in the patient who received dexpropranolol. This complication was possibly due to other medication. Other side-effects were insomnia, hypertension, precordial pain, abdominal pain as well as the expected hypotension and bradycardia. The significance of these results regarding the catecholamine hypothesis of manic-depressive illness is discussed.

Neurochemical and pharmacological studies on a new 5HT-uptake inhibitor, FG4963, with potential antidepressant properties

A new phenylpiperidine derivative, FG4963, and several tricyclic antidepressants were compared in various in vitro and in vivo tests for central 5HT- and NA-uptake inhibition. FG4963 was found to be a 5HT-pump blocker with activity similar to that of chlorimipramine. FG4963 inhibited NA-uptake less than the most potent tricyclic thymoleptics. In contrast to imipramine derivatives FG4963 was a weak inhibitor of peripheral NA-uptake. FG4963 seems to produce central 5HT-potentiation without affecting organ functions regulated by the autonomic nervous system as much as tricyclic antidepressants.