Pyridostigmine-induced growth hormone responses in healthy and depressed subjects: evidence for cholinergic supersensitivity in depression

Clinical implications of mechanisms of action of antidepressants

The purpose of this review is briefly to consider the biological basis of depression and to attempt to illustrate how antidepressants produce their beneficial effects by correcting these abnormalities.

Studying brain receptor function: a neuroendocrine approach

A significant component of psychiatric practice relates to the management of patients with behavioural disturbance whose aetiology lies in the subtle alteration of brain biochemistry. The major handicap in assessing such patients, both from a clinical and a research point of view has been a lack of suitably sophisticated technology for studying brain function. Despite significant improvements in imaging technique and the development of positron emission tomography we are still lacking tools which assess brain receptor functioning. The neuroendocrine axis provides us with the means of assessing specific neurotransmitters in a safe and relatively inexpensive way. Such an approach is now widely used in research and has considerable potential within a clinical setting.

The fact that classic monoamine neurotransmitters are implicated both in affective disorders and schizophrenia and at the same time control hypothalmic-anterior pituitary function provides the basis for many psychoneuroendocrine investigations. The stimulation of certain central neurotransmitter systems results in the elevation of anterior pituitary hormones. If a pharmacologically selective drug is used, the rise in the anterior pituitary hormone gives some index of the integrity of the neurotransmitter pathway and the sensitivity of its receptor system. This approach is heavily dependent on the development of selective drugs for challenging specific receptor systems. As there are a myriad of potential confounding variables it is essential that there be rigorous control over such factors as gender, age, psychotropic drug exposure, weight loss etc.

The release of growth hormone (GH) from the anterior pituitary is under the control of 2 peptides, namely growth hormone releasing hormone (GHRH) and somatostatin (SS). Noradrenaline acting via the GHRH containing neurones stimulates the release of GH (1,2). We now know that the stimulated release of GH through this mechanism is significantly blunted in patients with major depression (3,4,5). When sone suppression and noradrenergic mediated GH release are both investigated in depressed patients, those subjects who show dexamethasone non-suppression are more likely to demonstrate blunted GH release than those with normal dexamethasone responses (5).

Acetylcholine (ACh) stimulates growth hormone release via the SS method (6). It is now clear that depressed patients show enhanced release when their cholinergic system is challenged with pyridostigmine (7). Overall therefore, depressed patients seem to have a downregulation or under activity of their NA receptors and an up-regulation or over-activity of their ACh receptors.

GH release is also under GABAergic control. In a study of patients with major depression baclofen the GABA-B agonist was used to induce GH release. Baclofen (20 mg) significantly elevated GH levels in all healthy subjects but a blunting of response was seen in those patients with major depressive illness. The finding indicates diminished responsivity of the GABA-B receptor system in depression (7a).

The release of prolactin from the anterior pituitary is under the inhibitory control of dopamine (DA) which acts directly on the lactotrophs of the pituitary. The release of prolactin is stimulated by serotonin (8,9). There is now unequivocal evidence to indicate that 5-HT mediated prolactin release is blunted in major depression (10,11). Such blunting has been demonstrated with a wide variety of probe drugs including 1-tryptophan and fenfluramine. The abnormality is however not entirely specific to depression as patients with obsessive compulsive disorder and sociopathic personality disorder also demonstrate such blunting even in the absence of mood disturbance (12,13).

The first evidence to emerge that central DA receptors might in some way control GH release was demonstrated by the administration of 1-dopa which led to an increase in GH levels (14). GH responses to the DA agonist apomorphine have been reported to be greater in patients with first rank symptoms of schizophrenia, but to be blunted in those patients with significant egative symptoms such as emotional flattening and social withdrawal (15,16).

The very complex neurotransmitter control of such hormones as GH and prolactin provides a window to the biology of neuro-behavioural disturbance. As a tool psychoneuroendocrinology is of relevance not just to the researcher but to the practicing psychiatrist as well.

A cholinergic hypothesis of the unconscious in affective disorders

The interactions between distinct pharmacological systems are proposed as a key dynamic in the formation of unconscious memories underlying rumination and mood disorder, but also reflect the plastic capacity of neural networks that can aid recovery. An inverse and reciprocal relationship is postulated between cholinergic and monoaminergic receptor subtypes. M1-type muscarinic receptor transduction facilitates encoding of unconscious, prepotent behavioral repertoires at the core of affective disorders and ADHD. Behavioral adaptation to new contingencies is mediated by the classic prototype receptor: 5-HT1A (Gi/o) and its modulation of M1-plasticity. Reversal of learning is dependent on increased phasic activation of midbrain monoaminergic nuclei and is a function of hippocampal theta. Acquired hippocampal dysfunction due to abnormal activation of the hypothalamic-pituitary-adrenal (HPA) axis predicts deficits in hippocampal-dependent memory and executive function and further impairments to cognitive inhibition. Encoding of explicit memories is mediated by Gq/11 and Gs signaling of monoamines only. A role is proposed for the phasic activation of the basal forebrain cholinergic nucleus by cortical projections from the complex consisting of the insula and claustrum. Although controversial, recent studies suggest a common ontogenetic origin of the two structures and a functional coupling. Lesions of the region result in loss of motivational behavior and familiarity based judgements. A major hypothesis of the paper is that these lost faculties result indirectly, from reduced cholinergic tone.

Depression and antidepressants: molecular and cellular aspects

Clinical depression is viewed as a physical and psychic disease process having a neuropathological basis, although a clear understanding of its ethiopathology is still missing. The observation that depressive symptoms are influenced by pharmacological manipulation of monoamines led to the hypothesis that depression results from reduced availability or functional deficiency of monoaminergic transmitters in some cerebral regions. However, there are limitations to current monoamine theories related to mood disorders. Recently, a growing body of experimental data has showed that other classes of endogenous compounds, such as neuropeptides and amino acids, may play a significant role in the pathophysiology of affective disorders. With the development of neuroscience, neuronal networks and intracellular pathways have been identified and characterized, describing the existence of the interaction between monoamines and receptors in turn able to modulate the expression of intracellular proteins and neurotrophic factors, suggesting that depression/antidepressants may be intermingled with neurogenesis/neurodegenerative processes.

Enhanced cholinergic-mediated increase in the pro-inflammatory cytokine IL-6 in irritable bowel syndrome: role of muscarinic receptors

OBJECTIVES

Irritable bowel syndrome (IBS) is a functional disorder, which has recently been linked to immune activation. We tested the hypothesis that the pro-inflammatory cytokine profile in IBS is driven by the cholinergic system and determined if the responses are mediated by muscarinic receptors.

METHODS

Eighty-eight subjects took part in two studies, 37 IBS patients (Rome II), 14 depressed patients, and 37 healthy volunteers. Eighteen IBS patients had diarrhea predominant IBS, 14 were alternators, and 5 were predominantly constipated. In study 1, blood was drawn for baseline measurement of growth hormone (GH) and cytokines IL-6, IL-8, and IL-10. Pyridostigmine 120 mg was administered orally and further blood sampling took place for 180 min. In study 2, patients with IBS, depressed patients, and healthy subjects underwent the pyridostigmine test on two separate occasions with procyclidine (antimuscarinic) pre-treatment on one test occasion. Both GH and IL-6 were monitored.

RESULTS

In study 1, baseline IL-6 (P= 0.003) and IL-8 levels (P= 0.001) were higher in IBS than in controls. Pyridostigmine stimulated the release of IL-6 and GH, but not IL-8 or IL-10; these responses were significantly augmented in IBS patients relative to controls. The IL-6 level following pyridostigmine administration correlated significantly with the symptom score (P < 0.01). In study 2, IL-6 rose following pyridostigmine in IBS but not depression and procyclidine blocked the rise. The GH response was abolished by procyclidine in all three groups.

CONCLUSIONS

IBS and major depression are characterized by a pro-inflammatory profile, whereas IBS patients alone exhibit an exaggerated muscarinic receptor-mediated IL-6 response.

Effects of long-term estrogen replacement therapy on growth hormone response to pyridostigmine in healthy postmenopausal women

OBJECTIVE

There is growing evidence that estrogen may protect against age-related cognitive decline and reduce the risk of developing Alzheimer's disease (AD) in healthy, postmenopausal women. The underlying biological basis for this is not known but may include preservation of cholinergic systems. Cholinergic dysfunction has been implicated in the aetiology of age-related memory impairment and AD. We studied the effect of prolonged use of estrogen replacement therapy (ERT) on central cholinergic tone in healthy postmenopausal women.

METHOD

Growth hormone (GH) responses to oral pyridostigmine (120 mg) were measured over a 3 h period in thirty healthy postmenopausal women, 15 on long-term ERT and 15 ERT naïve.

RESULTS

GH release following pyridostigmine was significantly larger in ERT treated women than in ERT naïve women. In addition within the ERT treated group there was a significant positive correlation between duration of estrogen treatment and GH response.

CONCLUSIONS

Long-term ERT can enhance cholinergic function in postmenopausal women and this may be related to duration of estrogen treatment. Modulation of central cholinergic function may be one mechanism by which long-term ERT could preserve cognitive function in healthy, postmenopausal women.

Role of the cholinergic muscarinic system in bipolar disorder and related mechanism of action of antipsychotic agents

The evidence for the involvement of cholinergic muscarinic receptors in mania and depression is reviewed. Small pilot trials with cholinesterase inhibitors and muscarinic agonists suggest that stimulation of muscarinic receptors may produce an antimanic effect, possibly by activation of muscarinic M(4) receptors. It is concluded that it is not likely that currently used mood stabilizers, such as lithium, valproic acid and carbamazepine, work directly through muscarinic receptor mechanisms. Furthermore, the evidence indicates that antipsychotic agents used for mania are working through the common mechanism of antagonism of dopamine D(2) receptors, and interactions with muscarinic receptors do not play a key role. Finally, it is hypothesized that olanzapine has robust antimanic activity, due to blockade of dopamine D(2) receptors and antagonism of other monoaminergic receptors. Olanzapine may normalize mood due to antidepressant-like activities, such as 5-HT(2A) receptor antagonism and increasing cortical norepinephrine and dopamine.

Altered hypothalamic cholinergic responses in patients with nonulcer dyspepsia: a study of pyridostigmine-stimulated growth hormone release

OBJECTIVE

Acetylcholine plays a central and peripheral role in regulating gastric motility. In the hypothalamus, it is a key neuroendocrine modulator; acting through somatostatin, it brings about the release of growth hormone (GH). We measured hypothalamic cholinergic receptor sensitivity in patients with nonulcer dyspepsia (NUD) by examining GH release in response to cholinergic challenge.

METHODS

Forty patients with NUD and 40 healthy comparison subjects were administered pyridostigmine (the acetylcholinesterase inhibitor, 120 mg), and GH release over a 3-h period was monitored.

RESULTS

Calculating response as the maximum GH relative to baseline (delta GH), the mean +/- SEM response in the patients was 11.9 +/- 1.9 U/L and in the healthy subjects 6.7 +/- 0.7 mU/L (t = 2.1, df = 78, p = 0.03). Helicobacter pylori status had no appreciable impact on GH response with H. pylori-positive patients having a mean response of 10.5 +/- 2.1 mU/L and negative patients a mean response of 13.2 +/- 3.4 mU/L. Overall, patients with NUD release more GH in response to pyridostigmine challenge than healthy subjects.

CONCLUSIONS

Patients with NUD may have a pathophysiological disturbance involving central cholinergic systems.

Association of depressiveness with blunted growth hormone response to maximal physical exercise in young healthy men

Blunted response of growth hormone secretion to several pharmacological challenges is present in depression, but much less is known about the relationship of depression and secretion of growth hormone elicited by physiological stimuli. Furthermore, it is not known whether blunted growth hormone response occurs in depressiveness as measured with psychometric scales. A total of 82 healthy male volunteers (age 18-26 years) exercised on a bicycle ergometer with incremental load to achieve their maximal performance. Before exercise, subjects filled in approbated versions of Beck Depression Inventory (BDI), Spielberger's State-Trait Anxiety Scale, Cohens Perceived Stress Scale, and Schwartzers Self-Efficacy Scale. Blood samples were collected before and after exercise, and growth hormone, cortisol, and testosterone were measured by chemiluminescence immunoassay. Median perceived stress score of the subjects was identical to our population-based database median value, but the subjects had higher self-efficacy and lower depressiveness as shown by median values. In the majority of subjects, physical exercise induced remarkable increases in blood levels of the hormones. Cortisol and testosterone levels were not associated with the scores of psychometric scales. However, growth hormone response was virtually absent in high scorers (above median population score, n = 24) in BDI total score and the negative attitude subcomponent. Hence, this study demonstrates that growth hormone response to physiological stimuli is reduced in psychometrically measured depressiveness.

Psychoneuroendocrinology of depression. Growth hormone

The release of growth hormone (GH) from the anterior pituitary is regulated by hypothalamic peptides especially GH-releasing hormone (GHRH) and somatostatin, which in turn are controlled by classic neurotransmitters such as noradrenaline, dopamine, and acetylcholine, as well as negative feedback from GH and insulin-like growth factor-1. There has been extensive investigation of this axis in patients with depression. The most consistently reported abnormality is in noradrenergic-mediated GH release, which probably occurs via GHRH containing neurones. ACh-induced GH release through the somatostatin system, GABA, and also GHRH-stimulated release are reported as abnormal by some researchers.

Specificity of the pyridostigmine/growth hormone challenge in the diagnosis of depression

Acetylcholine is a neurotransmitter that has been implicated in the pathophysiology of major depression. This is supported by the enhanced growth hormone (GH) release in response to pyridostigmine (PYD) challenge in depressed subjects relative to healthy comparison subjects. The aim of this study is to examine the specificity of the PYD/GH challenge in the diagnosis of depression. Pyridostigmine 120 mg orally, was administered to a total of 116 physically healthy subjects. Growth hormone responses were studied in 38 patients with (DSM-III-R) major depression, 13 subjects with panic disorder, 9 subjects with schizophrenia, 10 recently detoxified alcoholics, and a comparison group of 46 healthy volunteers. Mean delta GH (the difference between basal and maximal GH following PYD) was significantly greater than comparison subjects in patients with major depression. Responses observed in patients with schizophrenia and alcohol dependence syndrome did not differ from the comparison group. Those patients with panic disorder and a high Hamilton depression score had an enhanced delta GH. The sensitivity of the PYD/GH test was 63% for major depression. These results indicate that the PYD/GH test may help distinguish depression from schizophrenia, alcohol-dependence syndrome, or panic disorder with a low Hamilton depression score.

Enhanced growth hormone responses to pyridostigmine challenge in patients with panic disorder

BACKGROUND

Panic disorder is associated with neuroendocrinological abnormalities, some of which overlap with those seen in major depression. To date, there has been little assessment of the role of cholinergic mechanisms in this disorder.

METHOD

Sixteen patients with DSM-III-R panic disorder and an age and gender-matched comparison group were administered 120 mg of the acetylcholinesterase inhibitor pyridostigmine. Growth hormone (GH) responses over a three-hour period were monitored.

RESULTS

Mean delta GH, the difference between basal and the maximum pyridostigmine levels, was significantly greater in patients with panic disorder than in the comparison group.

CONCLUSIONS

This may reflect increased cholinergic responsivity in panic disorder.

Pre- and postprandial pyridostigmine and oxiracetam effects on growth hormone secretion in anorexia nervosa

Previous studies have shown that food ingestion is not capable of inhibiting the GHRH-induced GH release in anorexia nervosa, at variance with what is observed in normal subjects. Moreover, a cholinergic alteration has been hypothesized in this disorder. In a group of 24 anorectic patients in a stabilized phase of the illness, we tested, before and after a standard meal, the GH response to GHRH alone and after pre-treatment with pyridostigmine, an inhibitor of acetylcholinesterase, and, on a different day, with oxiracetam, which stimulates the central cholinergic neurones. The GH response to GHRH was significantly increased by both drugs in a fasting state. The postprandial response was not significantly modified by pyridostigmine nor by oxiracetam. Neither of these compounds was able to enhance the postprandial GH 'paradoxical' response to GHRH in anorectic patients. The lack of effect of both groups postprandially also suggests a suppression of somatostatinergic activity.

Are blunted dexamethasone-induced growth hormone responses unique to depression?

In health, acute administration of glucocorticoids, such as dexamethasone (DEX), leads to growth hormone (GH) secretion. Depression is characterized by blunted DEX/GH responses. In order to determine the specificity of this test for depression we administered 4 mg of oral DEX, to patients with a DSM-III-R diagnosis of depression, schizophrenia, mania and alcohol dependency syndrome. Samples for GH estimation were taken at -15 min, 0 min, +60 min, +180 min, +240 min and +300 min. GH responses were attenuated to a similar degree in depression and mania. Less marked attenuation was seen in schizophrenia while those with alcohol dependency syndrome had GH responses indistinguishable from normal volunteers. Overall, we conclude that subnormal DEX/GH secretion is not specific to depression.

Potential animal model of multiple chemical sensitivity with cholinergic supersensitivity

Multiple Chemical Sensitivity (MCS) is a clinical phenomenon in which individuals, after acute or intermittent exposure to one or more chemicals, commonly organophosphate pesticides (OPs), become overly sensitive to a wide variety of chemically-unrelated compounds, which can include ethanol, caffeine and other psychotropic drugs. The Flinders Sensitive Line (FSL) rats were selectively bred to be more sensitive to the OP diisopropylfluorophosphate (DFP) compared to their control counterparts, the Flinders Resistant Line (FRL) rats. The present paper will summarize evidence which indicates that the FSL rats exhibit certain similarities to individuals with MCS. In addition to their greater sensitivity to DFP, the FSL rats are more sensitive to nicotine and the muscarinic agonists arecoline and oxotremorine, suggesting that the number of cholinergic receptors may be increased, a conclusion now supported by biochemical evidence. The FSL rats have also been found to exhibit enhanced responses to a variety of other drugs, including the serotonin agonists m-chlorophenylpiperazine and 8-OH-DPAT, the dopamine antagonist raclopride, the benzodiazepine diazepam, and ethanol. MCS patients report enhanced responses to many of these drugs, indicating some parallels between FSL rats and MCS patients. The FSL rats also exhibit reduced activity and appetite and increased REM sleep relative to their FRL controls. Because these behavioral features and the enhanced cholinergic responses are also observed in human depressives, the FSL rats have been proposed as a genetic animal model of depression. It has also been reported that MCS patients have a greater incidence of depression, both before and after onset of their chemical sensitivities, so cholinergic supersensitivity may be a state predisposing individuals to depressive disorders and/or MCS. Further exploration of the commonalities and differences between MCS patients, human depressives, and FSL rats will help to elucidate the mechanisms underlying MCS and could lead to diagnostic approaches and treatments beneficial to MCS patients.

Is cholinergic sensitivity a genetic marker for the affective disorders?

The recent literature on the involvement of cholinergic muscarinic mechanisms and adrenergic/cholinergic balance in affective disorders is reviewed and integrated with the older literature. There is strong evidence supporting the presence of exaggerated responses (behavioral, neuroendocrine, sleep) to cholinergic agents in affective disorder patients relative to normal controls and certain other psychiatric patients. There is also some, albeit less, conclusive evidence that these exaggerated responses may occur in euthymic individuals with a history of affective disorders, or in children at risk for development of affective disorders. Despite these promising results, suggesting a role for acetylcholine in the genetics of the affective disorders, further work in biochemistry and genetics is needed to link specific muscarinic receptors or other cholinergic variables to affective illness.

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.

Subnormal growth hormone responses to acutely administered dexamethasone in depression

OBJECTIVE

Acute oral administration of dexamethasone (DEX) stimulates growth hormone (GH) release at 3 hours in normal controls and provides us with a novel probe with which to study the somatotrophic axis. In affective illness GH release is subnormal in response to a number of stimuli. We decided to investigate the acute effects of DEX-induced GH release in depression.

DESIGN

A between subjects parallel group design was employed.

METHODS

Baseline levels of GH and cortisol were taken after which 4 mg of oral DEX was administered. Plasma samples for GH estimation were taken at +60, +180, +240 and +300 minutes.

PATIENTS

Sixteen normal subjects and 16 unipolar, nonpsychotic, melancholic DSM-111R major depressives were studied. Depressed subjects had to score over 17 on the Hamilton Depression Rating Scale; the mean +/- SEM scores were 27.4 +/- 1.0.

MEASUREMENTS

Plasma GH and cortisol levels were measured by radioimmunoassay.

RESULTS

Baseline mean +/- SEM GH levels (depressives 2.4 +/- 0.6 mU/l; controls 2.6 +/- 0.4 mU/l) did not differ significantly between the two groups (P < 0.28). DEX-induced GH secretion was subnormal in depressives as opposed to controls (2.1 +/- 0.7 vs 19.4 +/- 2.2 mU/l, P < 0.001). There were significant differences between the two groups at 60, 180 and 240 minutes (P < 0.05). Baseline cortisol values were significantly different between the two groups (depressives 303.3 +/- 31.5 nmol/l; controls 138 +/- 4.7 nmol/l). An analysis of covariance, with cortisol as a covariate, still found the depressives to have significantly subnormal GH responses as compared to the control group (P < 0.05).

CONCLUSION

Dexamethasone-induced GH release is subnormal in depression.

Time dependency of pyridostigmine-induced growth hormone response

Growth hormone (GH) plasma levels reflect a balance between stimulation via GH-releasing hormone (GHRH) and inhibition by somatostatin (SS). Steroids influence GH secretion by modulating SS tone. There is a correlation between the diurnal secretion of GH and cortisol (CORT). Pyridostigmine, the acetylcholinesterase inhibitor, increases cholinergic tone, inhibits SS release and increases the release of GH. We investigated the influence of CORT on pyridostigmine-induced GH responses by testing subjects at 9.00 and 14.00 h. Basal (mean +/- SEM) CORT levels at 9.00 and 14.00 h were 251.5 +/- 18.4 nmol/l and 142.7 +/- 6.7 nmol/l, respectively. Pyridostigmine-induced GH responses were greater at 9.00 h than at 14.00 h (8.7 +/- 1.5 mU/l; 3.0 +/- 1.0 mU/l, respectively, [ p < 0.001]). A positive correlation between CORT and delta GH values was demonstrated (p < 0.0004).

Glucocorticoids and the genesis of depressive illness. A psychobiological model

Abnormalities in the hypothalamic-pituitary-adrenal axis (HPA) have been the most consistently demonstrated biological markers in depressive illness. Numerous other neuroendocrine disturbances have also been described, including blunted clonidine-induced growth hormone release and blunted fenfluramine-induced prolactin release. These disturbances are generally interpreted in terms of monoaminergic receptor dysfunction. The theory presented here suggests that chronic stress which activates the HPA will in certain susceptible people produce changes in central monoamines. The high level of glucocorticoid receptors on such central neurons is postulated as mediating the alterations. Thus monoamine abnormalities, rather than being a core aetiological feature of depression, are seen as secondary to HPA overdrive.

Pyridostigmine induced growth hormone release in mania: focus on the cholinergic/somatostatin system

OBJECTIVE

The release of growth hormone (GH) from the anterior pituitary is partly under cholinergic control. Pyridostigmine, the acetylcholinesterase inhibitor, releases GH by this mechanism. Pyridostigmine/GH responses have been reported as enhanced in depression. The aim of the current study was to examine such responses during a manic episode.

DESIGN

A between subjects design was employed.

SUBJECTS

Seven male manic patients and seven male healthy controls were studied. They were matched in terms of age and body mass index.

MEASUREMENTS

GH response to pyridostigmine (120 mg) challenge was measured as the net increase above baseline. Cortisol levels were also measured.

RESULTS

Release of GH in the manic patients was significantly enhanced and their baseline cortisol levels were elevated.

CONCLUSIONS

These results demonstrate enhanced pyridostigmine/GH responsiveness in mania which may be due to enhanced somatostatin tone or increased cholinergic receptor responsivity.

BAP/SKB Young Psychopharmacologist Award Towards a neuroendocrinology of obsessive-compulsive disorder

Neuroendocrine research has made an important contribution to the understanding of psychiatric illness in vivo. This review is a summary of the recent neuroendocrine studies on obsessive-compulsive disorder (OCD) patients carried out at the Departments of Psychiatry at Trinity College Medical School and St. Patrick's Hospital, Dublin, Ireland. We found that both serotonergic and cholinergic abnormalities were present in OCD, while noradrenergic responsivity and hypothalmic-pituitary axis function were normal. The data suggests that OCD may have a unique neuroendocrinology.