Baclofen-induced growth hormone secretion is blunted in chronic schizophrenics: neuroendocrine evidence for a GABA disturbance in schizophrenia

Low-dose baclofen therapy raised plasma insulin-like growth factor-1 concentrations, but not into the normal range in a predictable and sustained manner in men with chronic spinal cord injury

OBJECTIVE

To evaluate, whether once-daily oral baclofen administration increases and/or sustains plasma insulin-like growth factor-1 (IGF-1) concentration in 11 men with chronic spinal cord injury (SCI) and IGF-1 deficiency (i.e. <250 ng/ml).

DESIGN

Prospective, open-label, dose titration study. Baclofen was administered at 20 mg/day for 8 weeks; then increased to 40 mg/day for another 8 weeks. Plasma IGF-1 and self-reported side effects were measured at baseline and every other week for the duration of the study.

RESULTS

The subjects were 43 ± 12 years old, had duration of injury of 20 ± 12 years; eight subjects had a complete motor injury, and eight had paraplegia. Nine of 11 subjects completed the 20 mg/day treatment and 5 subjects completed the 40 mg/day treatment. Plasma IGF-1 levels improved with each baclofen dose; however, only one subject increased from baseline and remained above the targeted physiological range of 250 ng/ml throughout treatment. A significant increase in IGF-1concentration was observed between baseline and week 2 (154 ± 63 vs. 217 ± 69 ng/ml; P < 0.05), weeks 8 and 10 (188 ± 95 vs. 228 ± 93 ng/ml; P < 0.05), and weeks 8 and 16 (188 ± 95 vs. 259 ± 92 ng/ml; P < 0.05). No serious side effects were observed at 20 mg/day; the 40 mg/day dose was less well tolerated.

CONCLUSION

Baclofen was not effective at sustaining plasma IGF-1 concentrations in the physiological range in men with chronic SCI.

Immunohistochemical and immunoblot analysis of gamma-aminobutyric acid B receptor in the prefrontal cortex of subjects with schizophrenia and bipolar disorder

Immunohistochemical and immunoblot techniques were employed to examine the distribution and expression of GABA(B) receptors in the prefrontal cortex of postmortem subjects with schizophrenia and bipolar disorder. GABA(B)R1a/b immunoreactivity was observed in the neuronal soma and dendrites as well as in the neuropil in the control subjects. GABA(B)R1a/b immunolabeling in neurons from the subjects with schizophrenia and bipolar disorder was less intense than in those from the control subjects. In control subjects, the distribution of GABA(B)R2 immunoreactivity was found to be similar to that of GABA(B)R1a/b. GABA(B)R2 immunolabeling in neurons from the bipolar disorder group appeared less intense than that of the normal controls as well as that in schizophrenic groups. Immunoblot analysis demonstrated a significant decrease in GABA(B)R1a levels in schizophrenic subjects, while there was a significant decrease in GABA(B)R1a, GABA(B)R1b, and GABA(B)R2 levels in bipolar subjects compared with the controls. The present study suggests that the GABA(B) receptor is involved in the pathophysiology of schizophrenia and bipolar disorder, and further suggests that the patterns of changes in GABA(B) receptor subtypes are different between these two disorders.

A preliminary study of baclofen-induced growth hormone release in generalised social phobia

OBJECTIVE

The authors sought to examine central GABA(B) receptor responses in patients with generalised social phobia using the growth hormone (GH) response to baclofen.

METHOD

Baclofen 20 mg was administered to 15 patients and 15 healthy matched controls and plasma growth hormone was monitored over a 3 h period.

RESULTS

The GH response in patients was significantly reduced in comparison to that of controls when calculated as both area under the curve (AUC) and delta (Delta) response.

CONCLUSIONS

The results suggest an abnormality of central GABA(B) receptor function in this disorder.

Immunohistochemical localization of GABAB receptor in the entorhinal cortex and inferior temporal cortex of schizophrenic brain

Immunocytochemical techniques were employed to examine the changes in immunolabeling of the gamma-aminobutyric acid (GABA)B receptor within the entorhinal cortex and inferior temporal isocortex of the schizophrenic brain. In the entorhinal cortex of the control subjects, an intense immunoreactivity was observed in the soma and processes of stellate cells in Layer II, in pyramidal cells in Layers II, III, and V, and in nonpyramidal interneurons. In subjects with schizophrenia, GABA(B) immunoreactivity was markedly reduced in pyramidal cells throughout the layers. In the inferior temporal cortex of the controls, both pyramidal cells and nonpyramidal interneurons demonstrated an intense immunoreactivity, while in the same region of the schizophrenic brain a marked reduction of the GABA(B) immunolabeling was observed in pyramidal cells in Layer V. These findings suggest that in the entorhinal cortex and the inferior temporal cortex of the schizophrenic brain, the expression of the GABA(B) receptor is reduced, and raise the possibility that GABA(B) receptor dysfunction is involved in the pathophysiology of schizophrenia.

Growth hormone secretion after baclofen administration in different phases of the menstrual cycle in healthy women

AIM

The aim of this study was to investigate the effect of baclofen administration on growth hormone (GH) secretion during different phases of the menstrual cycle.

METHODS

Twelve healthy women (33.6 +/- (SD) 2.8 years; range 23-40 years) with regular menstrual cycles were enrolled. The phases of the menstrual cycle were determined using transvaginal ultrasonography (TV-US) and detecting hormonal serum levels. Plasma GH levels were evaluated during the early follicular, periovulatory and luteal phases of the cycle before and after the baclofen challenge test.

RESULTS

After acute baclofen administration, GH levels increased significantly (p < 0.001) compared to basal values during the periovulatory and luteal phases, while no significant variation was detected during the early follicular phase. In addition, plasma GH levels resulted significantly (p < 0.001) higher during the luteal phase than during the periovulatory phase.

CONCLUSION

Acute baclofen administration induces a significant increase in plasma GH levels in healthy females during the periovulatory and luteal phases, but not during the early follicular phase. These data suggest a modulator role of plasma sex steroids levels on GH release induced by baclofen.

Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human

During the last decade, the GH axis has become the compelling focus of remarkably active and broad-ranging basic and clinical research. Molecular and genetic models, the discovery of human GHRH and its receptor, the cloning of the GHRP receptor, and the clinical availability of recombinant GH and IGF-I have allowed surprisingly rapid advances in our knowledge of the neuroregulation of the GH-IGF-I axis in many pathophysiological contexts. The complexity of the GHRH/somatostatin-GH-IGF-I axis thus commends itself to more formalized modeling (154, 155), since the multivalent feedback-control activities are difficult to assimilate fully on an intuitive scale. Understanding the dynamic neuroendocrine mechanisms that direct the pulsatile secretion of this fundamental growth-promoting and metabolic hormone remains a critical goal, the realization of which is challenged by the exponentially accumulating matrix of experimental and clinical data in this arena. To the above end, we review here the pathophysiology of the GHRH somatostatin-GH-IGF-I feedback axis consisting of corresponding key neurotransmitters, neuromodulators, and metabolic effectors, and their cloned receptors and signaling pathways. We propose that this system is best viewed as a multivalent feedback network that is exquisitely sensitive to an array of neuroregulators and environmental stressors and genetic restraints. Feedback and feedforward mechanisms acting within the intact somatotropic axis mediate homeostatic control throughout the human lifetime and are disrupted in disease. Novel effectors of the GH axis, such as GHRPs, also offer promise as investigative probes and possible therapeutic agents. Further understanding of the mechanisms of GH neuroregulation will likely allow development of progressively more specific molecular and clinical tools for the diagnosis and treatment of various conditions in which GH secretion is regulated abnormally. Thus, we predict that unexpected and enriching insights in the domain of the neuroendocrine pathophysiology of the GH axis are likely be achieved in the succeeding decades of basic and clinical research.

Psychoneuroendocrinology of schizophrenia

The study of psychoneuroendocrinology of schizophrenia has yielded an extensive but inconclusive body of data. Investigations to date have been limited by several factors, including the confounding effects of neuroleptic drugs, methodological limitations, and lack of appreciation for the heterogeneity of the illness. Previously, the focus of research has been on the measurement of anterior pituitary hormones, guided by the assumptions that these hormones are regulated by the central nervous system (CNS) to a significant degree and that the unique anatomic relationship of the pituitary gland to the hypothalamus and the CNS is potentially relevant. Patients with schizophrenia do appear to have distinct endocrinologic profiles. However, although the hormonal differences between patients with schizophrenia and the general population appear to be subtle in magnitude. Nonetheless, investigation, and the exploration of the possible effect of gonadal and posterior pituitary hormones merits particular attention.

GABAergic function in detoxified heroin addicts: relationship to anxiety disorders

The function of the GABAergic system was examined in 20 subjects with heroin dependence and abuse, 2 months after detoxification, and in 10 healthy volunteers, by measuring the growth hormone (GH) response to a challenge with the GABA B receptor agonist baclofen. Ten heroin addicts had comorbid anxiety disorder (Group A), while the other ten had heroin addiction uncomplicated by Axis I and II psychopathologies (Group B). GH responses to baclofen stimulation of Group A patients were significantly blunted, while those of Group B subjects did not differ from responses of healthy volunteers. Our data show that the function of the GABAergic system is impaired only in heroin addicts with comorbid anxiety disorders (anxious cluster), suggesting that the GABA system is not persistently influenced by prolonged exposure to opioid receptor stimulation.

Different control mechanisms of growth hormone (GH) secretion between gamma-amino- and gamma-hydroxy-butyric acid: neuroendocrine evidence in Parkinson's disease

The observation that baclofen stimulates growth hormone (GH) secretion in normal men, but not in parkinsonian patients led us to test the GH releasing effect of other gamma-amino-butyric acid (GABA)ergic agents with different mechanisms of action in Parkinson's disease. For this purpose 10 normal men and 10 de novo parkinsonian patients were tested with sodium valproate (800 mg PO), gamma-hydroxybutyric acid (GHB) (25 mg/kg body weight PO) and baclofen (10 mg PO). All drugs induced a significant increment in serum GH levels in the normal controls. On the other hand, GH secretion in parkinsonian patients did not change after baclofen or sodium valproate administration, whereas it showed normal responsiveness to GHB. These data suggest that the mechanism underlying the GH response to GHB is different from that (or those) mediating sodium valproate and/or baclofen action. In addition, the former, but not the latter mechanism appears to be preserved in the parkinsonian brain.

Enhanced GABAb receptor-mediated transmission in alcohol-dependence syndrome

We have studied the GABAb receptor-mediated neurotransmissions of alcoholic patients by administering baclofen 10 mg orally and measuring the growth hormone (GH) response. There was a minimal GH response to the baclofen in one of eight control subjects and a greater GH response in 11 of the 16 alcoholic patients. There is thus evidence for increased transmission at the GABAb receptor in detoxified patients with alcohol-dependence syndrome.

Growth hormone responses to pyridostigmine in schizophrenia: evidence for cholinergic dysfunction

The hypothesis that increased central cholinergic neurotransmitter function may be present in schizophrenic illness and may underlie negative symptoms was tested using a neuroendocrine challenge approach. The cholinergic challenge used was the anticholinesterase pyridostigmine, thought to cause the release of growth hormone (GH) from the anterior pituitary by diminishing inhibitory somatostatin tone. Eleven patients, six neuroleptic-naive and five neuroleptic-free, satisfying DSM-III-R criteria for schizophrenia and 11 matched controls took part. Subjects received pyridostigmine (120 mg orally) and blood was sampled at 0, 60, 90, 120, and 180 min for GH estimation. Peak GH responses were significantly increased in the schizophrenic group compared to controls. There was no relationship between individual peak GH values and negative symptom ratings (Scale for the Assessment of Negative Symptoms). Neither could a relationship be established between other aspects of psychopathology or dyskinesias and GH responses. An increased pyridostigmine/GH response is also found in affective disorders and could be related to nonspecific symptoms common to all these diagnostic groups. This study suggests that schizophrenia may be associated with increased cholinergic neurotransmitter function but the relationship between this cholinergic dysfunction and schizophrenia may involve psychopathology not specific to schizophrenia.

GABA and behavior: the role of receptor subtypes

The discovery of different GABA receptor subtypes has stimulated research relating this neurotransmitter to a variety of behavioral functions and clinical disorders. The development of new and specific GABAergic compounds has made it possible to try to identify the specific functions of these receptors. The purpose of the present review is to evaluate the data regarding the functions of the GABA receptor subtypes in different behaviors such as motor function, reproduction, learning and memory, and aggressive-defensive behaviors. A description of GABAergic functions (stress, peripheral effects, thermoregulation) that might directly or indirectly affect behavior is also included. The possible involvement of GABA in different neurological and psychiatric disorders is also discussed. Although much research has been done trying to identify the possible role of GABA in different behaviors, the role of receptor subtypes has only recently attracted attention, and only preliminary data are available at present. It is therefore evident that still much work has to be done before a clear picture of the behavioral significance of these receptor subtypes can be obtained. Nevertheless, existing data are sufficient to justify the prediction that GABAergic agents, in the near future, will be much used in the field of behavioral pharmacology. It is hoped that the present review will contribute to this. Some specific suggestions concerning the most efficient way to pursue future research are also made.

Reduction of GH response to the GABA-B agonist baclofen in patients with major depression

In order to establish whether alterations in the GABAergic control of GH secretion occur in male patients with major depression, the GH response to the GABAergic-B agonist baclofen (10 mg PO at 0830h) or to placebo was tested in 9 depressed men and in 10 age- and weight-matched male normal controls. The basal concentrations of GH were significantly lower in the depressed patients (0.87 +/- 0.69 ng/ml) than in the normal controls (1.57 +/- 0.33 ng/ml) (p = 0.011) and were not modified by the administration of placebo. The administration of baclofen induced a striking, significant increase in GH concentrations in the normal controls (mean peak at 90 min = 6.4 +/- 1.5 ng/ml). In contrast, a slight, nonsignificant GH increase occurred in the depressed patients after baclofen (mean peak at 90 min = 1.57 +/- 1.45 ng/ml). The GH response was significantly lower in the depressed than in the control subjects (p less than 0.001). These data indicate the presence of reduced GABAergic control of GH secretion in male depressed patients.

GABA, depression and the mechanism of action of antidepressant drugs: a neuroendocrine approach

Recent evidence has suggested the involvement of the GABAergic system in depression and in the mechanism of action of somatic antidepressant treatments. In particular, GABAB receptors have been found to be increased in the rat frontal cortex following chronic antidepressant therapies. In the present study, the sensitivity of GABAB binding sites was assessed in nine healthy men and 10 depressed patients via the plasma growth hormone (GH) response to acute baclofen administration (20 mg p.o.). Depressed subjects were tested before and after 15 and 35 days of treatment with amitriptyline (100 mg/day), imipramine (100 mg/day) and fluoxetine (20 mg/day). GH response to acute GABAB receptor activation did not differ between depressed subjects and healthy controls. Moreover, chronic antidepressant treatment did not significantly modify this response, even when a clear therapeutic effect was obtained. These results do not support the idea that GABAergic mechanisms are involved in the pathophysiology of depression and in the mechanism of action of antidepressant drugs.

Chronic antidepressant drug treatment does not affect GH response to baclofen in depressed subjects

The growth hormone (GH) response to baclofen, a specific GABAB agonist, was tested in 8 male depressed patients before and after chronic treatment with amitriptyline (100 mg/day). No difference was seen in plasma GH response before and 28 days after amitriptyline treatment, suggesting that chronic antidepressant drug treatment does not increase hypothalamic GABAB receptor sites in humans. These data suggest that further studies need to support the hypothesis of a GABA involvement in the mechanism of action of antidepressant drugs.