Growth hormone releasing factor in human cerebrospinal fluid

Biomarkers in cerebrospinal fluid of patients with bipolar disorder versus healthy individuals: A systematic review

BACKGROUND

The pathophysiological processes of bipolar disorder (BD) may be detectable by the use of cerebrospinal fluid (CSF) biomarkers.

AIM

We aimed for the first time to review studies of CSF biomarkers in patients with BD compared to healthy control individuals (HC). We investigated the effect of diagnosis, age, gender, clinical state, medication, technical characteristics of tests, fasting state and, cognitive function if applicable.

METHOD

We did a systematic review according to the PRISMA Statement based on comprehensive database searches for studies on cerebrospinal biomarkers in patients with bipolar disorder versus HC. Risk of bias was systematically assessed.

RESULTS

The search strategy identified 410 studies of which thirty-four fulfilled the inclusion criteria. A total of 117 unique biomarkers were investigated, out of which 11 were evaluated in more than one study. Forty biomarkers showed statistically significant differences between BD and HC in single studies. Only the findings of elevated homovanillic acid and 5-hydroxy-indoleacetic acid were replicated across studies. Most studies had a cross sectional design and were influenced by risk of bias mainly due to small sample size, lack of data on mood state at the time of the CSF puncture and not considering potential confounders including age, gender, diagnoses, BMI, life style factors such as smoking, and psychotropic medication.

CONCLUSION

Specific monoamine CSF biomarkers may be related to the pathophysiology of BD. Future studies must aim at increasing the level of evidence by validating the positive findings in prospective studies with stringent methodology.

The adrenergic-cholinergic imbalance hypothesis of depression: a review and a perspective

The catecholamine deficiency hypothesis of depression was essentially based on the incidental detection of iproniazide and imipramine. However, current findings favor noradrenergic overactivity, at least in the periphery. The incidental observation of acute behavioral inhibition by centrally active cholinomimetics like physostigmine suggested a cholinergic-adrenergic balance involved in the regulation of drive and mood. Indeed, cholinomimetics seem to have acute depressiogenic and antimanic properties and, conversely, anticholinergics some acute euphoriant activity. However, time course and dose-response relationships of drugs influencing mood and drive do not favor simple concepts of too much or too little activity of one or the other transmitter system. Cholinomimetics and psychostimulants show an acute mutual antagonism, the mechanism of which is obscure. In healthy volunteers clonidine and the putative antidepressant brofaromine did not influence the effects of physostigmine. Patients with mood disorders respond supersensitively to a cholinergic challenge in terms of behavior, neuroendocrine regulation and REM sleep induction. Thus, the anticholinergic properties of tricyclics might be relevant to their antidepressant activity. However, adjunctive treatment with the cholinolytic biperiden as compared to placebo did not enhance the antidepressant efficacy of mianserin or viloxazine. This is incompatible with cholinergic overactivity contributing to the depressive state. Physostigmine induces autonomous and endocrine responses reminiscent of stress reactions. Findings in healthy volunteers suggest relationships between the sensitivity to physostigmine and personality traits like irritability and emotional lability and passive stress coping strategies. Thus, the cholinergic supersensitivity in mood disorders might be related to some personality dimension like stress intolerance rather than the depressive state itself.

Cerebrospinal fluid variables among alcoholics lack seasonal variation

Seasonal influences on indices of serotonergic function, including cerebrospinal fluid (CSF) concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), have been reported in psychiatric patients and healthy volunteers. We examined seasonal differences in CSF concentrations of 5-HIAA among 135 alcoholics admitted to a research ward who had a lumbar puncture. No significant seasonal differences were found for either CSF concentrations of 5-HIAA or CSF concentrations of other monoamine metabolites or peptides. The possible explanations for these negative findings are discussed.

Growth hormone response to growth hormone releasing hormone in depression and schizophrenia

Growth hormone releasing hormone, a 44-amino acid peptide (GHRH-44), was administered (1 micrograms/kg i.v.) to 6 normal controls, 10 schizophrenic subjects, and 7 depressed subjects. A significantly lower growth hormone (GH) response was found in the schizophrenic and depressed groups. Two molecular forms of GH, 22K GH and 20K GH, were also measured but did not further differentiate the three groups of subjects.

CSF neuropeptide Y in alcoholics and normal controls

Neuropeptide Y is found in brain tissue. In dogs it has been shown to enhance activation of the hypothalamic-pituitary-adrenal axis by corticotropin-releasing hormone. It is localized in certain catecholamine neurons and to some extent colocalized with somatostatin. Disturbances of the central noradrenergic system may underlie some forms of alcoholism. Therefore, we compared male alcoholics and normal controls on cerebrospinal fluid (CSF) levels of neuropeptide Y. There was no significant difference between the two groups for neuropeptide Y. There was also no significant difference for CSF levels of growth hormone releasing hormone. However, there were significant positive correlations between CSF levels of neuropeptide Y and CSF levels of corticotropin-releasing hormone, somatostatin, and growth hormone releasing hormone.

CSF GABA and neuropeptides in pathological gamblers and normal controls

We previously reported that pathological gamblers may have increased central noradrenergic activity. Neurons releasing gamma-aminobutyric acid (GABA) are known to be a part of an inhibitory system regulating the activity of central noradrenergic neurons. Therefore, we examined cerebrospinal fluid (CSF) levels of GABA in pathological gamblers and normal controls. There was no significant difference between the groups. Also, depressed and nondepressed gamblers did not differ significantly in their CSF levels of GABA. Among controls, however, there was a significant negative correlation between CSF levels of GABA and the norepinephrine metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) and a significant positive correlation between CSF levels of GABA and corticotropin releasing hormone (CRH). Also, CSF levels of CRH showed a significant positive correlation with CSF levels of adrenocorticotropic hormone in both pathological gamblers and controls.

Intravenous physostigmine increases cerebrospinal fluid neuropeptide-Y

The ability to measure directly central nervous system (CNS) neurotransmitter changes after an acute pharmacological challenge would be a useful clinical tool in psychiatric research. As one approach to this possibility, we attempted to measure cerebrospinal fluid (CSF) neuropeptide changes produced by an intravenous infusion of the indirect cholinergic agonist physostigmine. Six rhesus monkeys, with indwelling CSF catheters, had serial CSF samples removed before and after a 15 micrograms/kg physostigmine infusion. Five of six monkeys studied showed at least a 50% increase in CSF neuropeptide-Y (NPY) levels. Normal human subjects (n = 27) had CSF sampled before and 15, 30, and 45 min after an acute intravenous infusion of physostigmine (either 0, 5, or 15 micrograms/kg). An Analysis of Variance revealed a significant (p = 0.04) dose-time interaction, suggesting that physostigmine increased CSF NPY at the 15 micrograms/kg dose. CSF levels of seven other neuropeptides remained unchanged. These results suggest that the pharmacological challenge paradigm can be adapted to CSF neuropeptides, providing new measures of CNS stimulus-induced response beyond the peripheral plasma determinations usually employed.

Characteristics of cerebrospinal fluid neuropeptides relevant to clinical research

Studies of human cerebrospinal fluid (CSF) peptides were conducted in an attempt to broaden the utility of CSF peptide determinations in psychiatric research. Healthy volunteers had two lumbar punctures, at least 3 weeks apart, to assess reproducibility within subjects. CSF levels of eight peptides were reliably reproducible, indicating that longitudinal studies of these CSF neuropeptides are feasible. Levels of 10 peptides were determined in four sequential 8 ml aliquots of CSF. CSF rostrocaudal gradients were not found for any of these 10 peptides. Neuropeptide Y (NPY), growth hormone releasing factor (GHRF), and corticotropin releasing factor (CRF) were measured in CSF from twins and brothers. CSF NPY levels were heritable, while CRF and GHRF levels were influenced more by environment. CSF levels of CRF, beta-lipotropin, vasoactive intestinal peptide, adrenocorticotropic hormone, and somatostatin were highly correlated with one another, suggesting that a common factor is responsible for a significant proportion of the observed variance in their CSF levels. These results suggest that CSF peptide measurements may have a broad range of applicability to clinical psychiatric research.

Blunted response of growth hormone to clonidine and apomorphine in endogenous depression

We measured the growth hormone (GH) response to clonidine (an alpha-2-adrenergic agonist) and to apomorphine (a dopaminergic agonist) in 15 major endogenous and 15 minor depressive in-patients matched for gender and age. Results showed a significantly smaller GH response in the major depressives to both clonidine (P less than 0.01) and apomorphine (P less than 0.001). No significant difference existed between the two groups with regard to changes in blood pressure and pulse rate during either test. While major depressives showed a trend toward smaller sedative side-effects than minor depressives after clonidine, they showed significantly smaller sedative and gastro-intestinal side-effects after apomorphine. No significant correlation was present either in the major depressive or in the minor depressive group between the GH responses following clonidine and apomorphine challenges. These results support the hypothesis of both noradrenergic and dopaminergic neurotransmitter disturbances in major depression, with individual variability with regard to those biochemical anomalies.