Adrenergic and serotonergic receptor responsiveness in depression

Overtraining Syndrome as a Complex Systems Phenomenon

The phenomenon of reduced athletic performance following sustained, intense training (Overtraining Syndrome, and OTS) was first recognized more than 90 years ago. Although hundreds of scientific publications have focused on OTS, a definitive diagnosis, reliable biomarkers, and effective treatments remain unknown. The present review considers existing models of OTS, acknowledges the individualized and sport-specific nature of signs/symptoms, describes potential interacting predisposing factors, and proposes that OTS will be most effectively characterized and evaluated via the underlying complex biological systems. Complex systems in nature are not aptly characterized or successfully analyzed using the classic scientific method (i.e., simplifying complex problems into single variables in a search for cause-and-effect) because they result from myriad (often non-linear) concomitant interactions of multiple determinants. Thus, this review 1) proposes that OTS be viewed from the perspectives of complex systems and network physiology, 2) advocates for and recommends that techniques such as trans-omic analyses and machine learning be widely employed, and 3) proposes evidence-based areas for future OTS investigations, including concomitant multi-domain analyses incorporating brain neural networks, dysfunction of hypothalamic-pituitary-adrenal responses to training stress, the intestinal microbiota, immune factors, and low energy availability. Such an inclusive and modern approach will measurably help in prevention and management of OTS.

Serotonin and the prediction of response time to fluoxetine in patients with mild depression

Serotonin (5-HT) dysregulation has been associated with major depressive disorder (MDD); a blunted prolactin (PRL) response to D,L-fenfluramine (FEN) has been associated with MDD. Pharmacologic manipulation of the serotonin system with a selective serotonin reuptake inhibitor (SSRI) is effective in the treatment of depression. However, the relationship between pre-treatment 5-HT activity and response to SSRIs is not well understood. This study investigated the relationship between 5-HT dysregulation and response to fluoxetine (FLU). Twenty patients with MDD entered a double-blind placebo-controlled trial of fluoxetine preceded by D,L-fenfluramine stimulation. Patients were assigned randomly to either FLU, 20 mg QD, or placebo (PLA) for an 11-week trial. No relationship was found between the PRL response to FEN and response to FLU. Among the seven responding to FLU, there was a significant negative correlation between PRL response and the time until sustained response to FLU (r = -0.93, P < 0.001, n = 7). Although preliminary, this study suggests that low baseline serotonin activity may be associated with a slower response to FLU in depression.

5-HT brain function in affective disorder: d,l-fenfluramine-induced hormone release and clinical outcome in long-term lithium/carbamazepine prophylaxis

Prolactin (PRL) and Cortisol (CORT) responses to d,l-fenfluramine (FEN) challenge (60 mg) were examined in patients with affective disorders on two occasions under euthymic conditions: drug-free before admission to prophylactic treatment and after about 9 months of medication with lithium or carbamazepine. Response to treatment was assessed by a complex algorithm using continuous ratings in outpatient clinic over a period of 2 years. In general, treatment resulted in a delayed and diminished CORT release (n.s.); subgroup analysis revealed an attenuated CORT response (P < 0.05) in responders, whereas nonresponders showed no change in CORT secretion pattern except an enhanced CORT baseline value (P < 0.05). Cross-sectional comparison of responders with nonresponders under medication yielded a trend for greater CORT stimulation in nonresponders. This result was not affected by FEN/NorFEN or lithium/carbamazepine serum levels, baseline CORT values, age, sex, diagnostic distribution, number of appointments to the outpatient clinic or duration of medication at the time of FEN test session. Before onset of prophylactic medication responders and nonresponders could not be discriminated significantly regarding stimulated hormone release, probably due to the small sample size (n = 17). CORT response to FEN was increased in drugfree unipolar patients compared to bipolar (P < 0.05) and to schizoaffective patients (P < 0.1). In accordance with its well-documented presynaptic 5-HT-agonistic action lithium medication resulted in a significantly greater increase in CORT release than carbamazepine (P < 0.05). Evaluation of PRL stimulation showed patterns of secretion quite similar to those of CORT, without reaching statistical significance in most cases. Perhaps due to methodological differences in assessing treatment response, these data do not confirm former results, which supposed an enhanced 5-HT net activity in long-term prophylactic lithium treatment. Because of high interindividual variances of hormone parameters, the FEN-test procedure is not a useful tool for the prediction of therapeutical outcome in terms of clinical routine use. Relations of stimulated hormone response as a marker of central serotoninergic activity and clinical outcome are discussed.

Clonidine challenge testing of alpha-2-adrenoceptor function in man: the effects of mental illness and psychotropic medication

The clonidine challenge test is a means of assessing alpha-2-adrenoceptor sen sitivity in man. We review studies which have used this test to investigate central alpha-2- adrenoceptor changes in psychiatric illness, and to determine receptor changes after adminis tration and withdrawal of psychotropic treatments. Patients with severe depression show evidence of reduced alpha-2-adrenoceptor sensitivity, especially a reduced growth hormone response to clonidine. This may delineate a subgroup of patients with severe depressive illness from those with milder depression, and may even provide a trait marker for some depressed patients. Patients with panic disorder show evidence of subsensitivity to some and supersensitivity to other clonidine-induced responses. Other disorders, although less well investigated, may have abnormal test responses which may provide additional information about their cause and treatment. Changes in response after drug treatment have provided important information on the mode of action of antidepressants, and have suggested that noradrenergic function is altered by a variety of different antidepressants.

Growth hormone releasing factor in human cerebrospinal fluid

Growth hormone releasing factor (GHRF) was determined by radioimmunoassay in cerebrospinal fluid (CSF) from 37 unmedicated healthy volunteers (mean +/- SD = 23.4 +/- 7.2 pg/ml). A second lumbar puncture in 11 of these subjects suggested that the CSF GHRF levels were stable over time. High performance liquid chromatography revealed that the CSF immunoreactivity co-eluted with the 1-44NH2 and 1-4ONH2 forms of GHRF. Measurements of GHRF in sequential CSF aliquots revealed no evidence of a rostro-caudal gradient, an observation that is compatible with the hypothesis that GHRF has a long half-life in CSF. A significant negative correlation with body weight was found in the 37 subjects. Levels of CSF GHRF were determined in 24 lithium-treated euthymic bipolar patients, 13 of whom provided a second CSF sample during the unmedicated state. No group differences or effects of lithium were noted.