Differential effects of the enantiomers R(-) and S(+) oxaprotiline on major endogenous depression, the sleep EEG and neuroendocrine secretion: studies on depressed patients and normal controls

Depression and Sleep

Impaired sleep is both a risk factor and a symptom of depression. Objective sleep is assessed using the sleep electroencephalogram (EEG). Characteristic sleep-EEG changes in patients with depression include disinhibition of rapid eye movement (REM) sleep, changes of sleep continuity, and impaired non-REM sleep. Most antidepressants suppress REM sleep both in healthy volunteers and depressed patients. Various sleep-EEG variables may be suitable as biomarkers for diagnosis, prognosis, and prediction of therapy response in depression. In family studies of depression, enhanced REM density, a measure for frequency of rapid eye movements, is characteristic for an endophenotype. Cordance is an EEG measure distinctly correlated with regional brain perfusion. Prefrontal theta cordance, derived from REM sleep, appears to be a biomarker of antidepressant treatment response. Some predictive sleep-EEG markers of depression appear to be related to hypothalamo-pituitary-adrenocortical system activity.

Wake and sleep EEG provide biomarkers in depression

Both wake and sleep electroencephalogram (EEG) provide biomarkers of depression and antidepressive therapy, respectively. For a long time it is known that EEG activity is altered by drugs. Quantitative EEG analysis helps to delineate effects of antidepressants on brain activity. Cordance is an EEG measure with a superior correlation with regional brain perfusion. Prefrontal quantitative EEG cordance appears to be a predictor of the response to antidepressants. Sleep EEG shows characteristic changes in depression as impaired sleep continuity, desinhibition of REM sleep and changes of nonREM sleep. Elevated REM density (a measure for frequency of rapid eye movements) characterizes an endophenotype in family studies of depression. REM-sleep changes including a more distinct REM rebound after sleep deprivation are found in animal models of depression. Most antidepressants suppress REM sleep in depressed patients, normal controls and laboratory animals. REM suppression appears to be a distinct, but not an absolute requirement for antidepressive effects of a compound. Sleep-EEG variables like REM latency or certain clusters of variables were shown to predict the response to the treatment with a certain antidepressant or even the course of the disorder for several years. Some of these predictive sleep-EEG markers of the longterm course of depression appear to be closely related to hypothalamo-pituitary-adrenocortical system activity.

Amphetamine-type central nervous system stimulants release norepinephrine more potently than they release dopamine and serotonin

A large body of evidence supports the hypothesis that mesolimbic dopamine (DA) mediates, in animal models, the reinforcing effects of central nervous system stimulants such as cocaine and amphetamine. The role DA plays in mediating amphetamine-type subjective effects of stimulants in humans remains to be established. Both amphetamine and cocaine increase norepinephrine (NE) via stimulation of release and inhibition of reuptake, respectively. If increases in NE mediate amphetamine-type subjective effects of stimulants in humans, then one would predict that stimulant medications that produce amphetamine-type subjective effects in humans should share the ability to increase NE. To test this hypothesis, we determined, using in vitro methods, the neurochemical mechanism of action of amphetamine, 3,4-methylenedioxymethamphetamine (MDMA), (+)-methamphetamine, ephedrine, phentermine, and aminorex. As expected, their rank order of potency for DA release was similar to their rank order of potency in published self-administration studies. Interestingly, the results demonstrated that the most potent effect of these stimulants is to release NE. Importantly, the oral dose of these stimulants, which produce amphetamine-type subjective effects in humans, correlated with the their potency in releasing NE, not DA, and did not decrease plasma prolactin, an effect mediated by DA release. These results suggest that NE may contribute to the amphetamine-type subjective effects of stimulants in humans.

Glucocorticoids and depression

Depression has been associated with impaired mineralocorticoid receptor function, restrained glucocorticoid receptor feedback at the level of the hypothalamic-pituitary-adrenal (HPA) axis, raised cortisol level and increased corticotropin-releasing factor activity, which may act in concert to induce the signs and symptoms of the disorder. Pre-clinical and clinical evidence suggests that both genetic and environmental factors contribute to the development of these HPA axis abnormalities in depressed patients. Support for this view derives from models using genetically modified animals and/or chronic stress exposure at different developmental stages, although all of the current approaches have to be viewed within their limitations to model the disease. However, both animal and human studies challenging the HPA system show at least some neuroendocrine and behavioural changes comparable to those seen in depression, suggesting that some of the depressive symptoms can be attributed to HPA axis hyperactivity. Moreover, normalization of the neuroendocrine function following chronic antidepressant drug treatment seems to be a prerequisite for stable remission of depressive psychopathology, i.e. that normalization of HPA function is critical for relief of the clinical symptomatology of this disorder.

Differential effect of desipramine and 2-hydroxydesipramine on depolarization-induced calcium uptake in synaptosomes from rat limbic sites

This study was conducted to investigate the inhibition of synaptosomal 45Ca uptake by desipramine and its major metabolite 2-hydroxydesipramine in the rat hippocampus and cingulate cortex, areas associated with emotional control. A concentration-dependent inhibition of net depolarization-induced 45Ca uptake was observed for desipramine (20-200 microM) in synaptosomes from both sites. However, 20 microM 2-hydroxydesipramine failed to inhibit calcium channel function in either of the two limbic sites; higher concentrations (60 or 200 microM) did produce a minor degree of inhibition in hippocampus synaptosomes. Others have shown that the clinically encountered plasma concentrations of 2-hydroxydesipramine are lower than those of desipramine, and the brain concentration of 2-hydroxydesipramine is therefore not expected to surpass or even reach 20 microM. In view of the previously observed clinical activity of 2-hydroxydesipramine, the present results indicate that calcium channel antagonism may not be the basis for the therapeutic effect of tricyclic antidepressants.