A comparison of the behavioral effects of oral versus intravenous mCPP administration in OCD patients and the effect of metergoline prior to i.v. mCPP

Pentagastrin has panic-inducing properties in obsessive compulsive disorder

The effects of the CCKB-receptor agonist pentagastrin, a synthetic analogue of the cholecystokinin tetrapeptide (CCK-4), were studied in seven patients suffering from obsessive compulsive disorder (OCD) and seven healthy controls. All subjects were challenged with an IV dose of 0.6 micrograms/kg pentagastrin or placebo under double blind placebo controlled conditions, on two separate occasions, with a minimum interval of 1 week. Six (86%) out of seven OCD patients experienced a panic-like reaction after pentagastrin administration, against only two (29%) in the control group. These differences failed to reach statistical significance, probably due to the small sample size. No increases were observed in obsessions or compulsive behaviors as assessed with the Yale-Brown Obsessive Compulsive Challenge Scale, neither in the pentagastrin, nor in the placebo condition. These findings suggest that pentagastrin has panic-inducing properties in OCD patients, without affecting the core symptoms. The panic-inducing properties of pentagastrin are not specific for panic disorder patients, which might be indicative of a common neurobiological dysfunction in panic disorder and OCD at the level of CCK-B receptors.

Neuroendocrine responses to serotonergic agonists as indices of the functional status of central serotonin neurotransmission in humans: a preliminary comparative analysis of neuroendocrine endpoints versus other endpoint measures

The status of central serotonergic neurotransmission and of specific serotonin (5-HT) receptor subtype sensitivity has been inferred from neuroendocrine and other endpoint responses to serotonergic agents given to humans. The question of whether changes in neuroendocrine responsivity to the 5-HT2C partial agonist, meta-chlorophenylpiperazine (m-CPP), are accompanied by similar changes in other endpoints (temperature, behavior) is addressed in this brief review of published studies. These studies were selected based on the following criteria: (1) neuroendocrine (cortisol, prolactin increases) and at least one other endpoint (behavior and/or temperature increases) were measured in the same populations, and (2) statistically significant changes were observed after m-CPP in the healthy volunteer control or pre-long-term-treatment subjects. Parenthetically, in the 13 of 14 studies that reported both prolactin and cortisol responses, the results were congruent for the two neuroendocrine measures in 12 of the 13 (92%). However, neuroendocrine versus behavioral results were in agreement in fewer (7 of the 13) studies (54%). Neuroendocrine vs. temperature results were non-concordant in all 4 of the studies which included temperature measurements. These generally disparate findings suggest that these different endpoints may reflect brain serotonin neuroanatomic and receptor subsystem complexity and/or m-CPP's complex pharmacological properties. Thus, these neuroendocrine response measures cannot at this time be considered a general index of the other response measures, nor necessarily an index of the functional status of central serotonergic neurotransmission until this is established by more direct experimental investigations.

m-Chlorophenylpiperazine in patients with obsessive-compulsive disorder: absence of symptom exacerbation

Oral administration of the serotonin mixed agonist-antagonist meta-chlorophenylpiperazine (mCPP) at 0.5 mg/kg has been reported to exacerbate symptoms of obsessive-compulsive disorder (OCD). In an attempt to replicate these findings, double-blind behavioral and biochemical measures were obtained in 12 drug-free patients (9 men, 3 women) with OCD who received either oral mCPP (0.5 mg/kg), intravenous (IV) mCPP (0.1 mg/kg over 20 min), or placebo in random order on 3 separate test days. Neither oral nor IV mCPP had significant effects on the severity of OCD symptoms. The magnitude of the mCPP-induced plasma prolactin response and plasma mCPP levels were similar to those values obtained in other published studies in which mCPP exacerbated OCD symptoms. In contrast, both oral and IV mCPP were associated with significant increases in ratings of anxiety. These findings suggest that mCPP, whether administered by an oral or intravenous route (as a slow infusion), may not be a reliable probe for investigating obsessive-compulsive symptoms. It is possible, however, that more reproducible behavioral findings might be obtained by identifying susceptible subgroups of OCD or by including a behavioral exposure condition.

Behavioral and neuroendocrine responses to metaCPP in anorexia nervosa

In response to the partial serotonin agonist meta-chlorophenylpiperazine (metaCPP), patients with obsessive-compulsive disorder have been reported to exhibit an increase in obsessive symptoms and a diminished release of prolactin and/or cortisol compared to controls. We examined the response to metaCPP of 10 patients with anorexia nervosa, before and after weight gain, and of eight healthy controls. Prior to weight gain, the patients exhibited a greater behavioral response to metaCPP than the controls and diminished prolactin and cortisol responses. Only the prolactin abnormality persisted after weight gain. These observations suggest that, in patients with anorexia nervosa, weight loss is associated with the development of neurobiological disturbances which are in some ways similar to those of obsessive-compulsive disorder.

5-Hydroxytryptamine-interacting drugs in animal models of anxiety disorders: more than 30 years of research

An overview of the behavioral data arising from the vast literature concerning the involvement of 5-hydroxytryptamine (5-HT) neurotransmission in the regulation of anxiety is presented. More than 1300 experiments were carried out in this area and they provide evidence that: (1) results obtained in ethologically based animal models of anxiety with drugs stimulating 5-HT transmission are most consistent with the classic 5-HT hypothesis of anxiety in that they show an increase in animals' emotional reactivity; (2) no category of anti-anxiety models are selectively sensitive to the anxiolytic-like effects of drugs targetting 5-HT1A, 5-HT2A or 5-HT2C receptor subtypes; (3) anxiolytic-like effects of 5-HT3 receptor antagonists, in the great part, are revealed by models based on spontaneous behaviors. Taken together, these observations lead to the conclusion that different 5-HT mechanisms, mediated by different receptor subtypes, are involved in the genesis of anxiety.

Neuroendocrine responses to intravenous L-tryptophan in obsessive compulsive disorder

We studied the neuroendocrine responses produced by intravenous L-tryptophan (TRP) in 16 untreated patients with obsessive compulsive disorder (OCD) and 16 matched healthy controls. The increase in plasma growth hormone seen following TRP was significantly greater in the OCD patients, while TRP-induced prolactin release did not differ from controls. Taken in conjunction with findings from other neuroendocrine studies the data suggest that some aspects of 5-HT1A neurotransmission may be increased in OCD. This increase may represent a compensatory change which promotes adaptation to stress in non-depressed OCD patients.

Timing of neuroendocrine responses and effect of m-CPP and fenfluramine plasma levels in OCD

The present study assesses the timing of and relationship between neuroendocrine response and metabolite blood levels following the partial serotonin (5-HT) agonist m-CPP and the 5-HT releaser/reuptake blocker fenfluramine. Cortisol levels peaked significantly earlier than did prolactin, m-CPP, fenfluramine, or norfenfluramine blood levels by time-to-peak analysis. This earlier cortisol response to both 5-HT agents raises the possibility that peripheral mechanisms may play a role in cortisol release. Since peak m-CPP level correlated even more closely to peak prolactin rise than did peak fenfluramine, this suggests that prolactin response to oral m-CPP challenge is useful in assessing 5-HT function.