Effects of alprazolam on increases in hormonal and anxiety levels induced by meta-chlorophenylpiperazine

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Human pharmacology of positive GABA-A subtype-selective receptor modulators for the treatment of anxiety

Anxiety disorders arise from disruptions among the highly interconnected circuits that normally serve to process the streams of potentially threatening stimuli. The resulting imbalance among these circuits can cause a fundamental misinterpretation of neural sensory information as threatening and can lead to the inappropriate emotional and behavioral responses observed in anxiety disorders. There is considerable preclinical evidence that the GABAergic system, in general, and its α2- and/or α5-subunit-containing GABA(A) receptor subtypes, in particular, are involved in the pathophysiology of anxiety disorders. However, the clinical efficacy of GABA-A α2-selective agonists for the treatment of anxiety disorders has not been unequivocally demonstrated. In this review, we present several human pharmacological studies that have been performed with the aim of identifying the pharmacologically active doses/exposure levels of several GABA-A subtype-selective novel compounds with potential anxiolytic effects. The pharmacological selectivity of novel α2-subtype-selective GABA(A) receptor partial agonists has been demonstrated by their distinct effect profiles on the neurophysiological and neuropsychological measurements that reflect the functions of multiple CNS domains compared with those of benzodiazepines, which are nonselective, full GABA(A) agonists. Normalizing the undesired pharmacodynamic side effects against the desired on-target effects on the saccadic peak velocity is a useful approach for presenting the pharmacological features of GABA(A)-ergic modulators. Moreover, combining the anxiogenic symptom provocation paradigm with validated neurophysiological and neuropsychological biomarkers may provide further construct validity for the clinical effects of novel anxiolytic agents. In addition, the observed drug effects on serum prolactin levels support the use of serum prolactin levels as a complementary neuroendocrine biomarker to further validate the pharmacodynamic measurements used during the clinical pharmacological study of novel anxiolytic agents.

A short history of the 5-HT2C receptor: from the choroid plexus to depression, obesity and addiction treatment

This paper is a personal account on the discovery and characterization of the 5-HT_2C receptor (first known as the 5-HT_1C receptor) over 30 years ago and how it translated into a number of unsuspected features for a G protein-coupled receptor (GPCR) and a diversity of clinical applications. The 5-HT_2C receptor is one of the most intriguing members of the GPCR superfamily. Initially referred to as 5-HT_1CR, the 5-HT_2CR was discovered while studying the pharmacological features and the distribution of [³H]mesulergine-labelled sites, primarily in the brain using radioligand binding and slice autoradiography. Mesulergine (SDZ CU-085), was, at the time, best defined as a ligand with serotonergic and dopaminergic properties. Autoradiographic studies showed remarkably strong [³H]mesulergine-labelling to the rat choroid plexus. [³H]mesulergine-labelled sites had pharmacological properties different from, at the time, known or purported 5-HT receptors. In spite of similarities with 5-HT₂ binding, the new binding site was called 5-HT_1C because of its very high affinity for 5-HT itself. Within the following 10 years, the 5-HT_1CR (later named 5-HT_2C) was extensively characterised pharmacologically, anatomically and functionally: it was one of the first 5-HT receptors to be sequenced and cloned. The 5-HT_2CR is a GPCR, with a very complex gene structure. It constitutes a rarity in the GPCR family: many 5-HT_2CR variants exist, especially in humans, due to RNA editing, in addition to a few 5-HT_2CR splice variants. Intense research led to therapeutically active 5-HT_2C receptor ligands, both antagonists (or inverse agonists) and agonists: keeping in mind that a number of antidepressants and antipsychotics are 5-HT_2CR antagonists/inverse agonists. Agomelatine, a 5-HT_2CR antagonist is registered for the treatment of major depression. The agonist Lorcaserin is registered for the treatment of aspects of obesity and has further potential in addiction, especially nicotine/ smoking. There is good evidence that the 5-HT_2CR is involved in spinal cord injury-induced spasms of the lower limbs, which can be treated with 5-HT_2CR antagonists/inverse agonists such as cyproheptadine or SB206553. The 5-HT_2CR may play a role in schizophrenia and epilepsy. Vabicaserin, a 5-HT_2CR agonist has been in development for the treatment of schizophrenia and obesity, but was stopped. As is common, there is potential for further indications for 5-HT_2CR ligands, as suggested by a number of preclinical and/or genome-wide association studies (GWAS) on depression, suicide, sexual dysfunction, addictions and obesity. The 5-HT_2CR is clearly affected by a number of established antidepressants/antipsychotics and may be one of the culprits in antipsychotic-induced weight gain.

New therapeutic opportunities for 5-HT2C receptor ligands in neuropsychiatric disorders

The 5-HT2C receptor (R) displays a widespread distribution in the CNS and is involved in the action of 5-HT in all brain areas. Knowledge of its functional role in the CNS pathophysiology has been impaired for many years due to the lack of drugs capable of discriminating among 5-HT2R subtypes, and to a lesser extent to the 5-HT1B, 5-HT5, 5-HT6 and 5-HT7Rs. The situation has changed since the mid-90s due to the increased availability of new and selective synthesized compounds, the creation of 5-HT2C knock out mice, and the progress made in molecular biology. Many pharmacological classes of drugs including antipsychotics, antidepressants and anxiolytics display affinities toward 5-HT2CRs and new 5-HT2C ligands have been developed for various neuropsychiatric disorders. The 5-HT2CR is presumed to mediate tonic/constitutive and phasic controls on the activity of different central neurobiological networks. Preclinical data illustrate this complexity to a point that pharmaceutical companies developed either agonists or antagonists for the same disease. In order to better comprehend this complexity, this review will briefly describe the molecular pharmacology of 5-HT2CRs, as well as their cellular impacts in general, before addressing its central distribution in the mammalian brain. Thereafter, we review the preclinical efficacy of 5-HT2C ligands in numerous behavioral tests modeling human diseases, highlighting the multiple and competing actions of the 5-HT2CRs in neurobiological networks and monoaminergic systems. Notably, we will focus this evidence in the context of the physiopathology of psychiatric and neurological disorders including Parkinson's disease, levodopa-induced dyskinesia, and epilepsy.

Hypothalamic-pituitary-adrenocortical axis: neuropsychiatric aspects

Evidence of aberrant hypothalamic-pituitary-adrenocortical (HPA) activity in many psychiatric disorders, although not universal, has sparked long-standing interest in HPA hormones as biomarkers of disease or treatment response. HPA activity may be chronically elevated in melancholic depression, panic disorder, obsessive-compulsive disorder, and schizophrenia. The HPA axis may be more reactive to stress in social anxiety disorder and autism spectrum disorders. In contrast, HPA activity is more likely to be low in PTSD and atypical depression. Antidepressants are widely considered to inhibit HPA activity, although inhibition is not unanimously reported in the literature. There is evidence, also uneven, that the mood stabilizers lithium and carbamazepine have the potential to augment HPA measures, while benzodiazepines, atypical antipsychotics, and to some extent, typical antipsychotics have the potential to inhibit HPA activity. Currently, the most reliable use of HPA measures in most disorders is to predict the likelihood of relapse, although changes in HPA activity have also been proposed to play a role in the clinical benefits of psychiatric treatments. Greater attention to patient heterogeneity and more consistent approaches to assessing treatment effects on HPA function may solidify the value of HPA measures in predicting treatment response or developing novel strategies to manage psychiatric disease.

Experimental panic provocation in healthy man-a translational role in anti-panic drug development?

Experimental neurochemical provocation of panic attacks in susceptible human subjects has considerably expanded our knowledge of the pathophysiology and psychopharmacology of panic disorder. Some panicogens also elicit short-lived panic-like states in healthy man. This offers the opportunity to assess the anti-panic action of drugs in proof-of-concept studies. However, from current data it is still unclear whether experimental panic in healthy man is a valid translational model. Most such studies in healthy volunteers have been performed using a cholecystokinin tetrapeptide (CCK-4) challenge. While CCK-4 panic was blocked by alprazolam pretreatment, escitalopram showed negative results in healthy man. Preliminary findings on novel investigational drugs and a few problematic results will be reviewed. Small sample sizes in many panic provocation studies, lack of dose-response aspects, and still-insufficient knowledge about the biological underpinning of experimental and spontaneous panic limit the interpretation of existing findings and should inspire further research.

Serotonin activates the hypothalamic-pituitary-adrenal axis via serotonin 2C receptor stimulation

The dynamic interplay between serotonin [5-hydroxytryptamine (5-HT)] neurotransmission and the hypothalamic-pituitary-adrenal (HPA) axis has been extensively studied over the past 30 years, but the underlying mechanism of this interaction has not been defined. A possibility receiving little attention is that 5-HT regulates upstream corticotropin-releasing hormone (CRH) signaling systems via activation of serotonin 2C receptors (5-HT(2C)Rs) in the paraventricular nucleus of the hypothalamus (PVH). Through complementary approaches in wild-type rodents and 5-HT(2C)R-deficient mice, we determined that 5-HT(2C)Rs are necessary for 5-HT-induced HPA axis activation. We used laser-capture PVH microdissection followed by microarray analysis to compare the expression of 13 5-HTRs. Only 5-HT(2C)R and 5-HT(1D)R transcripts were consistently identified as present in the PVH, and of these, the 5-HT(2C)R was expressed at a substantially higher level. The abundant expression of 5-HT(2C)Rs in the PVH was confirmed with in situ hybridization histochemistry. Dual-neurohistochemical labeling revealed that approximately one-half of PVH CRH-containing neurons coexpressed 5-HT(2C)R mRNA. We observed that PVH CRH neurons consistently depolarized in the presence of a high-affinity 5-HT(2C)R agonist, an effect blocked by a 5-HT(2C)R antagonist. Supporting the importance of 5-HT(2C)Rs in CRH neuronal activity, genetic inactivation of 5-HT(2C)Rs produced a downregulation of CRH mRNA and blunted CRH and corticosterone release after 5-HT compound administration. These findings thus provide a mechanistic explanation for the longstanding observation of HPA axis stimulation in response to 5-HT and thereby give insight into the neural circuitry mediating the complex neuroendocrine responses to stress.

Pharmacological models in healthy volunteers: their use in the clinical development of psychotropic drugs

Animal models of diseases are widely used in the preclinical phase of drug development. They have a place in early human clinical psychopharmacology as well, in order to get early clues that contribute to establish the proof of concept (POC) already in healthy volunteers (HV). Different types of models are available (pharmacological or non-pharmacological provocation, models based on age-related characteristics). This review is focused on pharmacological models in HV, with the aim to identify the main issues raised by their use in pharmaceutical trials. The available models unevenly fulfil the requirements of face validity, sufficient response rate, test-retest consistence and responsiveness to reference drugs. Most of them have been developed in the purpose of pathophysiology studies, using rating instruments validated for clinical practice. Substantial progress could be made by adapting models to the specific requirements of pharmaceutical trials, including wider use of biomarkers. Characteristics that make models, as well as biomarkers, suitabLe for use in drug development are proposed. Despite obvious limitations, human models can significantly enhance the way phase I studies contribute to establish the POC, provided they are integrated into adapted phase I development plans. Their use as industrial tools for drug evaluation requires specific, dedicated development.

gamma-Aminobutyric acid-serotonin interactions in healthy men: implications for network models of psychosis and dissociation

BACKGROUND

This study tested the hypothesis that deficits in gamma-aminobutyric acid type A (GABA(A)) receptor function might create a vulnerability to the psychotogenic and perceptual altering effects of serotonergic (5-HT(2A/2C)) receptor stimulation. The interactive effects of iomazenil, an antagonist and partial inverse agonist of the benzodiazepine site of the GABA(A) receptor complex, and m-chlorophenylpiperazine (m-CPP), a partial agonist of 5-HT(2A/2C) receptors, were studied in 23 healthy male subjects.

METHODS

Subjects underwent 4 days of testing, during which they received intravenous infusions of iomazenil/placebo followed by m-CPP/placebo in a double-blind, randomized crossover design. Behavioral, cognitive, and hormonal data were collected before drug infusions and periodically for 200 min after.

RESULTS

Iomazenil and m-CPP interacted in a synergistic manner to produce mild psychotic symptoms and perceptual disturbances without impairing cognition. Iomazenil and m-CPP increased anxiety in an additive fashion. Iomazenil and m-CPP interacted in a synergistic manner to increase serum cortisol.

CONCLUSIONS

Gamma-aminobutyric acid-ergic deficits might increase the vulnerability to the psychotomimetic and perceptual altering effects of serotonergic agents. These data suggest that interactions between GABA(A) and 5-HT systems might contribute to the pathophysiology of psychosis and dissociative-like perceptual states.

Selective and nonselective serotonin antagonists block the aversive stimulus properties of MK212 and m-chlorophenylpiperazine (mCPP) in mice

Serotonin(2C) (5-HT(2C)) receptors have been implicated to treat mood disorders such as depression and anxiety. In the present study, the capacities of two 5-HT(2C) agonists, MK212 and mCPP, to produce conditioned taste aversions in mice were evaluated. On two training days, Swiss-Webster male mice (19-34g) were trained to associate the flavor of a novel solution with the injection of various doses of MK212 or mCPP. On two alternate training days, mice were trained to associate a different flavored solution with an injection of saline. For testing, both flavored solutions were presented simultaneously and an avoidance of the MK212 or mCPP-paired solution indicated conditioned taste aversion. Robust conditioned taste aversions were observed to solutions paired with 1.0 or 10mg/kg MK212 or mCPP. Acquisition of conditioned taste aversions was blocked by nonselective serotonin antagonists cyproheptadine, bromo-LSD, metergoline, methysergide and mianserin. Selective 5-HT(2B/2C) antagonist SB206,553 blocked both MK212- and mCPP-induced conditioned taste aversion although selective 5-HT(2B/2C) antagonist SB200,646 only blocked mCPP-induced conditioned taste aversion. In a single-bottle procedure, MK212, bromo-LSD, and mianserin failed to alter acquisition rate of a LiCl-induced conditioned taste aversion. Taken together, these data indicate that the serotonin agonists MK212 and mCPP produce conditioned taste aversion and that these effects are mediated predominantly through 5-HT(2C) receptors.

Cortisol response to diazepam: its relationship to age, dose, duration of treatment, and presence of generalized anxiety disorder

OBJECTIVE

Acute diazepam administration has been shown to decrease plasma cortisol levels consistent with decreased activity of the hypothalamic-pituitary-adrenal axis, especially in individuals experiencing stress. However, the effects of chronic diazepam treatment on cortisol have been less studied, and the relationship to age, anxiety, duration of treatment, and dose are not well understood.

METHOD

This double-blind placebo-controlled study examined acute and chronic effects of diazepam on plasma cortisol levels in young (19-35 years) and elderly (60-79 years) individuals with and without generalized anxiety disorder (GAD). Subjects received single oral challenges of placebo or diazepam (2.5 mg or 10 mg) in a placebo-controlled cross-over design, followed by 3 weeks of chronic daily treatment with 2.5 mg or 10 mg diazepam or placebo taken at 10 p.m., and then by a final acute challenge with a single oral dose of the same study medication received during chronic treatment.

RESULTS

The elderly experienced significant reductions in plasma cortisol levels compared to placebo both in the initial challenge and during chronic treatment, but the young did not. However, cortisol response to drug was comparable in both groups. Final challenge did not produce any significant cortisol effects in either group and the cortisol response in the elderly was significantly reduced compared to the initial challenge. GAD status was not a factor in plasma cortisol responses to diazepam.

CONCLUSIONS

Diazepam reduced cortisol both acutely and during chronic treatment, but not during final challenge, consistent with some tolerance development. This effect was most apparent in the elderly compared with the young adults and was not modulated by GAD status or dosage, and was not related to drug effects on performance and on self-ratings of sedation and tension.

Anxiogenic treatments do not increase fear-potentiated startle in mice

BACKGROUND

In rodents, the fear-potentiated startle paradigm (FPS; exaggerated startle as a measure of the conditioned fear response to cues associated with footshock) has demonstrated predictive validity for anxiolytic drugs. The predictive validity of the model for anxiogenic drugs, however, remains unclear. Therefore, we evaluated the bi-directionality of the FPS model for anxiety-modulating compounds in mice.

METHODS

The clinical anxiogenics FG-7142 (1-20 mg/kg), yohimbine (.1-10 mg/kg), and m-Chlorophenylpiperazine (mCPP; .3-3 mg/kg), and the putative anxiogenics atipamezole (.3-3 mg/kg) and corticotropin-releasing factor (h/r-CRF; .03-1 microg) were tested in DBA/1J mice trained for FPS.

RESULTS

Contrary to predictions, FG-7142 (10 and 20 mg/kg) and yohimbine (10 mg/kg) reduced FPS in mice without affecting baseline startle. Atipamezole (3 mg/kg), mCPP (3 mg/kg), and h/r-CRF (.3, 1 microg) did not affect FPS, but increased startle independently from the presence of the cue. FG-7142 and h/r-CRF had similar effects in 129SvEv mice.

CONCLUSIONS

Murine FPS is not bi-directionally predictive for anxiety-modulating compounds, although murine baseline startle may have some utility as a bi-directional model of anxiety. These data corroborate the recent hypothesis that systems mediating FPS are independent from systems mediating increased startle from unconditioned and putatively anxiogenic stimuli.

A preliminary open study of the tolerability and effectiveness of nefazodone in major depressive disorder: comparing patients who recently discontinued an SSRI with those on no recent antidepressant treatment

Anecdotal evidence suggests that the recent discontinuation of an SSRI may confound the tolerability of the initiation of nefazodone treatment. We sought to determine whether recent discontinuation of an SSRI interferes with effectiveness and/or tolerability of nefazodone. Twenty-six depressed subjects, 21-63 years old, were recruited at the Massachusetts General Hospital. Thirteen subjects (50%) had discontinued an SSRI within 1-4 weeks due to ineffectiveness and/or side effects. Thirteen subjects (50%) had not taken antidepressants for the previous 6 months. Subjects were administered open nefazodone 50 mg p.o. b.i.d., and doses were increased as tolerated to a maximum of 600 mg/day. Subjects were followed for 12 weeks and were assessed for response and side effects using HAM-D-6 and clinical interviews. Both groups improved significantly on nefazodone; however, there was no statistically significant difference in response (>or=50% decrease in HAM-D-6) rates between completers with prior SSRI treatment (80%) and completers without recent exposure to antidepressants (67%). Response rates based on intent-to-treat (ITT) analysis were 31% for both groups. Association between prior SSRI treatment and discontinuation of nefazodone due to side effects or non-response was not statistically significant. Our study suggests that the rate of negative outcomes with nefazodone is no different whether patients have recently failed an SSRI.

Interdose elevation in plasma cortisol during chronic treatment with alprazolam but not lorazepam in the elderly

Benzodiazepines (BZPs) have been shown to reduce hypothalamic-pituitary-adrenal (HPA) axis activity acutely in normal humans. In contrast, the effects of chronic BZP treatment on the HPA axis have not been well studied, especially in the geriatric population. This study examined the acute and chronic effects (3 weeks) of alprazolam and lorazepam on plasma cortisol in 68 subjects (60-83 years) who received 0.25 or 0.50 mg b.i.d. alprazolam, or 0.50 or 1.0 mg b.i.d. lorazepam, or placebo orally according to a randomized, double-blind, placebo-controlled parallel design. Memory assessment and blood samples for plasma cortisol were obtained prior to the morning dose on days 0, 7, 14, and 21, and at 1, 2.5, and 5 h postdrug on days 0 and 21. Assessments of anxiety and depression were carried out at days 0, 7, 14, and 21 before drug administration. Plasma cortisol was affected compared to placebo only by the 0.5 mg alprazolam dose. During the first and the last day of treatment, there was a significant drop in cortisol at 2.5 h after alprazolam compared to placebo. The predose cortisol levels increased significantly during chronic alprazolam treatment, and correlations were found between these cortisol changes and changes in depression, anxiety, and memory scores. These findings suggest that even a short period of chronic treatment with alprazolam, but not lorazepam, may result in interdose HPA axis activation in the elderly, consistent with drug withdrawal. If confirmed, this effect may contribute to an increased risk for drug escalation and dependence during chronic alprazolam treatment.

Alprazolam (a benzodiazepine activating GABA receptor) reduces the neuroendocrine responses to insulin-induced hypoglycaemia in humans

OBJECTIVE

Alprazolam (ALP), a benzodiazepine-activating GABAergic receptor, possesses clear centrally mediated inhibitory effects on ACTH and cortisol secretion that could reflect an inhibitory influence on CRH- and/or AVP-secreting neurones. An inhibitory effect of ALP on catecholamine release has also been shown while its effect on GH secretion is unclear. To further clarify the neuroendocrine actions of ALP, we studied the ALP effects on the neurohormonal responses to hypoglycaemia in a group of normal subjects.

DESIGN

In eight normal subjects [four women and four men, 22-34 years old, body mass index (BMI) 20-25 kg/m2] the ACTH, cortisol, GH, adrenaline (A) and noradrenaline (NA) responses to insulin-induced hypoglycaemia [ITT, 0.1 UI/kg regular insulin intravenously (i.v.) at 0 min] preceded by placebo or ALP (0.02 mg/kg orally at -90 min) were studied in two sessions at least 10 days apart.

MEASUREMENTS

Blood samples were taken basely at -90 and 0 min and every 15 min up to +120 min. ACTH, cortisol, GH, A and NA level were assayed at each time point in both sessions.

RESULTS

All subjects experienced hypoglycaemia (plasma glucose levels below 2.2 mmol/l). After placebo ITT induced clear-cut increases in ACTH (peak vs. baseline, mean +/- SEM: 27.9 +/- 3.9 vs. 7.1 +/- 1.5 pmol/l), cortisol (438.1 +/- 32.0 vs. 237.7 +/- 19.3 nmol/l) and GH (38.1 +/- 9.7 vs. 5.7 +/- 2.0 micro g/l) levels (P < 0.05). Marked increase in A (6627.2 +/- 116.7 vs. 263.7 +/- 71.4 pmol/l) and NA (3.8 +/- 1.5 vs. 1.6 +/- 1.0 nmol/l) levels were also recorded (P < 0.05). Pretreatment with ALP significantly inhibited the ACTH peak response to ITT (17.8 +/- 5.0 pmol/l, P < 0.05), while the cortisol response showed a non significant reduction (342.1 +/- 38.7 nmol/l). ALP also significantly reduced the GH (21.7 +/- 4.7 micro g/l, P < 0.02) and A (3828.0 +/- 1400.7 pmol/l, P < 0.02) responses to ITT. On the contrary, ALP lowered basal NA levels (P < 0.05) but did not significantly affect its response to ITT (2.2 +/- 1.2 nmol/l). Glucose changes induced by ITT were not modified by ALP.

CONCLUSIONS

This study shows that GABAergic activation by alprazolam significantly inhibits the neuroendocrine and adrenomedullary responses to hypoglycaemia.

Discriminative stimulus effects of m-chlorophenylpiperazine as a model of the role of serotonin receptors in anxiety

Serotonin is known to play a role in anxiety. The roles of serotonin reuptake and 5-HT1A receptors have been well characterized, but the contribution of other serotonin receptor subtypes is not as clear. 1-(3-Chlorophenyl)-piperazine (mCPP), which binds non-selectively to a wide range of serotonin receptors, has often been used to produce anxiety in humans and in animal models. Because functional assays indicate that mCPP is significantly more potent at 5-HT2C receptors, it may serve as a tool to investigate the contribution of 5-HT2C receptors to anxiety. This paper reviews the results of behavioral tests using mCPP, including the drug discrimination assay, to model anxiety. Although the discriminative stimulus effects of mCPP do not seem to be a useful screen for general anxiolytics, they do seem to be useful for characterization of the contribution of 5-HT1B and 5-HT2C receptors to the mediation of anxiety-like behaviors.

Benzodiazepines and anterior pituitary function

Benzodiazepines (BDZ) are one of the most prescribed classes of drugs because of their marked anxiolytic, anticonvulsant, muscle relaxant and hypnotic effects. The pharmacological actions of BDZ depend on the activation of 2 specific receptors. The central BDZ receptor, present in several areas of the central nervous system (CNS), is a component of the GABA-A receptor, the activation of which increases GABAergic neurotransmission and is followed by remarkable neuroendocrine effects. The peripheral benzodiazepine receptors (PBR), structurally and functionally different from the GABA-A receptor, have been shown in peripheral tissues but also in the CNS, in both neurones and glial cells, and in the pituitary gland. BDZ receptors bind to a family of natural peptides called endozepines, firstly isolated from neurons and glial cells in the brain and then in several peripheral tissues as well. Endozepines modulate several central and peripheral biological activities, including some neuroendocrine functions and synthetic BDZ are likely to mimic them, at least partially. BZD, especially alprazolam (AL), possess a clear inhibitory influence on the activity of the HPA axis in both animals and humans. This effect seems to be mediated at the hypothalamic and/or suprahypothalamic level via suppression of CRH. The strong negative influence of AL on hypothalamicpituitary-adrenal (HPA) axis agrees with its peculiar efficacy in the treatment of panic disorders and depression. BZD have also been shown to increase GH secretion via mechanisms mediated at the hypothalamic or supra-hypothalamic level, though a pituitary action cannot be ruled out. Besides the impact on HPA and somatotrope function, BDZ also significantly affect the secretion of other pituitary hormones, such as gonadotropins and PRL, probably acting through GABAergic mediation in the hypothalamus and/or in the pituitary gland. In all, BDZ are likely to represent a useful tool to investigate GABAergic activity and clarify its role in the neuroendocrine control of anterior pituitary function; their usefulness probably overrides what had been supposed before.

Serotonin syndrome after challenge with the 5-HT agonist meta-chlorophenylpiperazine

meta-Chlorophenylpiperazine (mCPP) is a non-selective 5-HT-receptor agonist/antagonist that is used extensively in psychiatry to assess central serotonergic function. We report on three patients who developed symptoms of the serotonin syndrome when they participated in an mCPP (0.5 mg/kg body weight p.o.) challenge test as part of a research protocol. They had relatively high plasma mCPP concentrations. The syndrome did not occur in normal volunteers who had comparable plasma concentrations of mCPP. Investigators should be aware of the possible occurrence of the serotonin syndrome after a single oral dose of mCPP.

Serotonin syndrome induced by venlafaxine and fluoxetine: a case study in polypharmacy and potential pharmacodynamic and pharmacokinetic mechanisms

OBJECTIVE

To document a case of serotonin syndrome associated with venlafaxine and fluoxetine that did not involve a monoamine oxidase inhibitor, and to examine the multiple factors, including pharmacodynamic and pharmacokinetic interactions, that likely caused this adverse drug reaction (ADR).

CASE SUMMARY

A 39-year-old white woman with depression and panic attacks was being treated with fluoxetine, trazodone, clonazepam, and cimetidine. After fluoxetine and clonazepam were abruptly discontinued, venlafaxine and lorazepam were started. Within 24 hours, she developed diaphoresis, tremors, slurred speech, myoclonus, restlessness, impaired thinking, and diarrhea. This constellation meets Sternbach's criteria for serotonin syndrome.

DISCUSSION

The possible contributors to this ADR are discussed, including a single drug effect (e.g., an idiosyncratic reaction to venlafaxine), a pharmacokinetic interaction, a pharmacodynamic interaction, a combined pharmacokinetic-pharmacodynamic interaction, and the patient' s panic disorder.

CONCLUSIONS

As more serotonergic drugs are developed and used for psychiatric disorders, frequently in combination or close temporal proximity, clinicians must be aware of and consider the factors that may increase the risk of patients experiencing serotonin syndrome.

Atrial natriuretic hormone in lactate-induced panic attacks: mode of release and endocrine and pathophysiological consequences

Previous studies have shown unequivocally a lack of pituitary-adrenocortical stress hormone activation during lactate-induced panic attacks despite considerable psychopathological alterations, signs of arousal and several vegetative symptoms regularly occurring during stressful conditions. To study the possible inhibitory action of atrial natriuretic hormone (ANH) on adrenocorticotrophic hormone (ACTH) and cortisol release in humans, 10 patients with panic disorder (DSM-III-R) received sodium lactate and placebo (0.9% saline) infusions and ten healthy comparison subjects additionally received a 2.5% saline infusion and the response of ANH, vasopressin, ACTH, cortisol, and several biochemical and physiological cardiovascular parameters were measured. In comparison to placebo, lactate infusion led to enhanced ANH levels in both non-panicking comparison subjects and panickers. Importantly, panickers showed significantly lower baseline levels of ANH than comparison subjects followed by a faster release. No significant concomitant changes in vasopressin, ACTH, and cortisol were observed. During lactate infusion, heart rate was accelerated considerably in the two groups; in contrast, the reduction of pCO2 indicated an enhanced ventilation only in panickers. The pattern of ANH release cannot be attributed simply to either the volume load administered, the cardiac activation or an osmotic effect since neither 0.9 nor 2.5% saline resulted in comparable effects. Additional central nervous mechanisms must be considered for the increased ANH concentrations in lactate-induced panic attacks. We propose that the release of ANH is an intrinsic mechanism contributing to the apparent unresponsiveness of the pituitary-adrenocortical system in lactate-induced panic attacks. In addition, we surmise that ANH may also play a role in the yet unknown mechanisms for termination of panic attacks, e.g. either by inhibitory actions on the locus coeruleus or by bronchiorelaxation and consecutive decatastrophization.

Acute inositol does not attenuate m-CPP-induced anxiety, mydriasis and endocrine effects in panic disorder

Many anti-panic drugs, administered chronically, can block pharmacologically-induced "panic attacks"; acutely they often exacerbate panic disorder. Theories of action need to account for this biphasic effect. Chronic inositol had previously shown efficacy against panic disorder. The authors investigated the effect of a single dose of 20 g inositol on an m-CPP challenge in a double-blind placebo-controlled crossover trial in panic-disorder patients. Seven patients had robust psychological, physiological and endocrine responses to 0.08 mg m-CPP i.v.; inositol had virtually no effect on these responses, although it had some acute effects during the evening before the challenge. A similar trial involving chronic inositol would be of interest.

A comparative study of the effects of selective and non-selective 5-HT2 receptor subtype antagonists in rat and mouse models of anxiety

Although there is some evidence that compounds acting at 5-HT2 receptors show anxiolytic activity, little is known about the specific involvement of the different 5-HT2 receptor subtypes in the modulation of anxiety-related responses. In the present study, the behavioural effects of mianserin, a non-selective 5-HT2 receptor antagonist, MDL 100,907, a selective 5-HT2A receptor antagonist, and SB 206553, a selective 5-HT2B/2C receptor antagonist, were investigated in two rat (the Vogel drinking conflict and the elevated plus-maze tests) and two mouse (i.e. the mouse defense test battery (MDTB) and the light/dark choice test) models of anxiety. Diazepam was used as a positive control. In the Vogel drinking test, mianserin (10 mg/kg) and SB 206553 (3-30 mg/kg), but not MDL 100,907, increased punished responding. Similarly, mianserin (1 mg/kg) and SB 206553 (3-10 mg/kg), but not MDL 100,907, increased entries into the open arms of the elevated plus-maze. These effects are consistent with anxiolytic-like actions of mianserin and SB 206553, although the magnitude of the effects of these two compounds was less than those of diazepam. In addition, in the MDTB, the 5-HT2 antagonists did not clearly affect the defensive reactions of mice exposed to a rat stimulus and they failed to reverse the avoidance of the illuminated box in the light/dark choice test. These results indicate a lack of anxiolytic-like action of the compounds in mice. These behavioural profiles suggest that blockade of the 5-HT2A receptor may not reduce anxiety and demonstrate that 5-HT2B and/or 5-HT2C receptor subtypes may be primarily involved in the anxiolytic-like effects of mianserin and SB 206553 in rats.

Serotonin function in panic disorder: intravenous administration of meta-chlorophenylpiperazine

A placebo-controlled study of the direct serotonin receptor agonist meta-chlorophenylpiperazine (MCPP), intravenously infused over 90 s in a 0.06 mg/kg dose, was conducted in 10 patients with panic disorder and 9 normal control subjects. Cortisol, MCPP serum levels, and behavioral responses in both groups. Differences between intravenous and oral administration of MCPP are discussed, and the present findings are related to the serotonergic hypothesis of panic disorder.