Low levels of somatostatin in human CSF mark depressive episodes

Somatostatin in neuropsychiatric disorders

1. Somatostatin is a peptide that is widely and discretely distributed throughout the central nervous system. 2. Its relevance to neuropsychiatric disorders is suggested both by the existence of disease-related alterations in somatostatin content in brain and cerebrospinal fluid as well as by the manifold neuroregulatory capabilities of somatostatin and related peptides. 3. This article will summarize the central nervous system effects of somatostatin, identify those neuropsychiatric disorders that are characterized by changes in somatostatin, and review the evidence for and potential significance of decreases in cerebrospinal fluid somatostatin in depression.

TRH: behavioral and endocrine effects in man

1. The tripeptide TRH exerts a spectrum of biological activities in both animals and man. Some of these activities have been extensively studied, particularly in psychiatric patients. 2. Behaviorally, TRH appears to increase the sense of well-being, motivation, relaxation, and coping capacity in both normal subjects and patients with psychiatric and neurologic disease. These effects are not disease-specific; attempts to use TRH as a treatment tool have thus been disappointing. 3. Endocrinologically, administration of TRH stimulates the response of TSH; this response has been reported to be blunted in approximately 30% of patients with major depression. However, TSH blunting is not specific for depression, it has also been observed in a variety of other psychiatric conditions. 4. The relevance of these effects for psychiatry in general, and for psychoneuroendocrinology especially, is discussed in this review.

Lack of effect of chronic carbamazepine on brain somatostatin in the rat

We investigated the effects of chronic carbamazepine treatment in rats on brain somatostatin. Following 12 days of carbamazepine treatment, no changes in somatostatin levels were found in any of the brain areas examined which included: amygdala, hippocampus, caudate-putamen, median eminence, arcuate nucleus, nucleus accumbens, nucleus interstitialis of the stria terminalis, nucleus periventricularis, parietal cortex, and occipital cortex. Thus, carbamazepine in low doses does not affect basal levels of brain somatostatin in the rat, in contrast to the previous reports of decreased somatostatin in the cerebrospinal fluid of affectively ill patients.

Serial DST, TRH test, and TRH-like immunoreactivity measurements in major affective disorders

Neuroendocrine functions in depressed patients with major affective disorders were serially investigated by the Dexamethasone Suppression Test (DST), the thyrotropin-releasing hormone (TRH) stimulation test, and the plasma TRH-like immunoreactivity (TRH-LI) measurement. Prior to antidepressant therapy, the sensitivity for nonsuppression to the DST was 36.0%, whereas that for blunted thyroid-stimulating hormone (TSH) response to TRH was 28.0%. Both DST nonsuppression and TSH blunting appeared to be state-related markers for depressed patients. Specifically, a significant increase of maximum TSH response to TRH after 4 weeks of antidepressant therapy was associated with clinical improvement. Plasma TRH-LI in depressed patients was significantly lower than that of healthy controls. It is possible that the lower plasma TRH-LI level is related to the pathophysiology of some depressed patients with major affective disorders.

Decreased somatostatin-like immunoreactivity in cerebral cortex and cerebrospinal fluid in Alzheimer's disease

To investigate changes in the somatostatinergic neurons of patients with Alzheimer's disease (AD), we determined the somatostatin-like immunoreactivity (SLI) in post-mortem brain tissue of histopathologically confirmed AD patients and in CSF of probable AD patients (according to DSM III). The CSF values were then correlated with psychological test scores. In 6 AD patients the SLI values were decreased 42% (P less than 0.005) in the frontal cortex, 28% (P less than 0.05) in the temporal cortex and 42% (P less than 0.01) in the parietal cortex but not in the thalamus and putamen compared to 11 control patients. In some brain areas there were statistical correlations between SLI values and cholinergic markers, choline acetyltransferase and acetylcholine esterase activities, suggesting a relationship between these two neurotransmitter systems. In the CSF among 75 AD patients SLI was 35% lower (P less than 0.001) than in controls. Severely demented power (P less than 0.001) than in controls. Severely demented patients showed lower SLI values than moderately demented individuals, but this difference was not significant. There was a weak but statistically significant correlation between SLI values in CSF and neuropsychological test scores. This study further confirms the involvement of somatostatinergic neurons in AD and suggests that this involvement may be related to the progression of dementia symptoms.

Cerebrospinal fluid somatostatin and psychiatric illness

Somatostatin is a tetradecapeptide that is assuming increasing importance as a regulator of central nervous system activity. Originally identified as the hypothalamic growth hormone release-inhibiting factor, somatostatin has subsequently been shown to be extensively and selectively distributed throughout the central nervous system, to alter neuron excitability, to regulate and be regulated by the activity of classical neurotransmitters and neuropeptides, to exert a number of direct behavioral actions, and to display neuropsychiatric disorder-related alterations. In this article, a three-part study of cerebral spinal fluid (CSF) somatostatin in affective illness and schizophrenia is presented. In part 1, significant reductions in CSF somatostatin were observed in 49 bipolar and unipolar depressed patients relative to 47 controls. Values during depression were also significantly lower than those observed in affective disorder during the improved state or in schizophrenia. Diurnal studies involving paired AM and PM lumbar punctures revealed that depressed patients and normal volunteers had similar somatostatin values in the evening, despite having significantly different values in the morning. In part 2, the effects of several psychopharmacological agents on CSF somatostatin were examined, particularly the tricyclic anticonvulsant carbamazepine. A significant reduction of CSF somatostatin during treatment with carbamazepine was observed. The effect of carbamazepine on somatostatin could be related to its anticonvulsant, analgesic, or psychotropic effects. Part 3 deals with somatostatin as a major regulator of hypothalamic-pituitary-adrenal (HPA) axis activity. Somatostatin affects HPA activity by inhibiting, at a number of cellular levels, the stimulated release of adrenocorticotrophic hormone (ACTH) from the pituitary. A significant negative relationship between CSF somatostatin and the postdexamethasone plasma cortisol level in 22 depressed and 16 schizophrenic patients was observed. This relationship between low CSF somatostatin and escape from dexamethasone suppression was observed irrespective of diagnosis (i.e., depression or schizophrenia). Thus, there is indirect supporting evidence for a role for somatostatin dysregulation in the most consistently observed biological abnormality in depression, escape from dexamethasone suppression. Further study of somatostatin in neuropsychiatric disorders, and particularly depressive illness, offers great promise for better understanding their underlying affective, vegetative, cognitive, and physiological dysregulations.

Effects of haloperidol on somatostatin-like immunoreactivity in the CSF of Schizophrenic patients

The levels of somatostatin-like immunoreactivity (SLI) were determined in the cerebrospinal fluid (CSF) of 14 schizophrenic patients before and after 3 weeks on haloperidol treatment. Baseline levels of SLI correlated negatively with psychopathological items on the Brief Psychiatric Rating Scale related to psychotic productivity. SLI levels increased after haloperidol treatment, but this increase did not correlate with psychopathological improvement. A difference in the ratio of larger and smaller molecular forms of the peptide was found before and after treatment. The drug-free samples showed a preponderance of the larger molecular forms, resulting in a ratio of 4:1, whereas the haloperidol-treated samples showed an equal distribution of both species.

Influence of free thyroid hormone levels on the TSH response to TRH in endogenous depression

The TSH response to TRH (delta max TSH) and the serum concentrations of free thyroxine (FT4), 3,5,3'-, and 3,3',5'-triiodothyronine (FT3 and FrT3) were studied in two groups of patients with endogenous depression before and after clinical recovery following electroconvulsive treatment (ECT). Before ECT, the patients from group 1 (n = 17) had a reduced delta max TSH (p less than 0.01), which after ECT rose to values not different from those found in controls. FT4 levels were elevated before ECT (p less than 0.01), and they decreased after ECT (p less than 0.05) to levels similar to those found in controls. FT3 and FrT3 levels were not different from the control values, but FrT3 decreased during ECT (p less than 0.01). In group 2 (n = 19), delta max TSH was reduced both before (p less than 0.02) and after (p less than 0.01) ECT. FT4 levels were increased both before and after ECT (p less than 0.02). Both parameters were unaffected by ECT. The data are compatible with the assumption that the decreased TSH response to TRH found in patients with endogenous depression is secondary to an increase in circulating FT4.