Postsynaptic serotonergic blockade following chronic antidepressive treatment with trazodone in an animal model of depression

The Roles of Endogenous Opioids in Placebo and Nocebo Effects: From Pain to Performance to Prozac

Placebo and nocebo effects have been well documented for nearly two centuries. However, research has only relatively recently begun to explicate the neurobiological underpinnings of these phenomena. Similarly, research on the broader social implications of placebo/nocebo effects, especially within healthcare delivery settings, is in a nascent stage. Biological and psychosocial outcomes of placebo/nocebo effects are of equal relevance. A common pathway for such outcomes is the endogenous opioid system. This chapter describes the history of placebo/nocebo in medicine; delineates the current state of the literature related to placebo/nocebo in relation to pain modulation; summarizes research findings related to human performance in sports and exercise; discusses the implications of placebo/nocebo effects among diverse patient populations; and describes placebo/nocebo influences in research related to psychopharmacology, including the relevance of endogenous opioids to new lines of research on antidepressant pharmacotherapies.

[Multimodal serotonergic antidepressants]

Based on the original literature, the author for the first time describes a history of selective serotonergic antidepressants simultaneously inhibiting the serotonin reuptake and directly interacting with serotonin receptors. A history of creation and introduction of their main representatives is presented. A history of investigation of their neurochemical activity is analyzed in details. The history of the evolution of their classifications is systemized. The data presented suggest the rationale for unifying all selective serotonergic antidepressants, simultaneously inhibiting the serotonin reuptake and directly interacting with serotonin receptors (trazodone, etoperidone, nefazodone, vilazodone, vortioxetine), in one group of 'multimodal serotonergic antidepressants'. The expediency to include this group in the modern neurochemical classification of nootropic drugs is substantiated.

Confirmation of the neurophysiologically predicted therapeutic effects of trazodone on its target symptoms depression, anxiety and insomnia by postmarketing clinical studies with a controlled-release formulation in depressed outpatients

Early human pharmaco-EEG and subsequent sleep laboratory studies identified trazodone, a 5-HT(2) antagonist and 5-HT reuptake inhibitor (SARI), as an antidepressant with therapeutic effects on its target symptoms depressed mood, anxiety and insomnia. On the occasion of the introduction of a controlled-release (CR) formulation (Trittico 150 mg retard, marketed in Austria by CSC Pharmaceuticals Handels GmbH, Vienna, Austria) in Austria in July 2000, a multi-center, open, clinical post-marketing study on the therapeutic effects, safety and target symptoms of trazodone CR in depression was carried out at 80 offices of Austrian neuropsychiatrists. 549 outpatients (63% females) of all age groups suffering from five different subtypes of depression were enrolled in the study. After a 2-week fixed dose-titration regimen up to 150 mg and a 4-week adjustment period to the optimum dose, 66% of the patients remained on 150 mg, 20% increased the dose and 11% decreased it. Only 3.7% discontinued treatment. Rating by the neuropsychiatrists based on the Clinical Global Impression showed very much to much improvement in 78.3% of the patients, and no change or a deterioration in only 3.6%. In the Hamilton Depression Scale (HAMD) a statistically significant improvement from a baseline score of 21 to a score of 14 after 2 weeks was found, and a normalization to a score of 8 after 6 weeks. Therapeutic effects were similar in the five groups suffering from different subtypes of depression and in patients with and without comedication. Self-rating by the patients based on the Zung Self-Rating Depression Scale (SDS) and Zung Self-Rating Anxiety Scale (SAS) also showed a significant improvement in the 2nd and 6th week of therapy. Evaluation of the target symptoms of trazodone by ranking the most improved symptoms identified insomnia as the most improved psychopathological item in all three scales. While in the observer ratings also suicidal tendencies and weight loss were found much improved, in the self-rated Zung SDS sadness and loss of drive came second and third in the improvement ranking, in the self-rated Zung SAS anxiety and the feeling of falling apart. Tolerability was very good. In the 2nd week only 16.9% and in the 6th week only 7.6% of the patients reported side effects, mostly characterized by tiredness and rarely by nausea and vertigo. The present clinical study is in agreement with previous studies identifying trazodone as a safe and effective antidepressant, specifically regarding its target symptoms insomnia, depression and anxiety. It also confirms our own early predictions based on neurophysiological investigations concerning the mode of action of the drug.

Inhibition of K(+)-evoked release of rat striatal 5-hydroxytryptamine by an atypical antidepressant: trazodone

Using microdialysis, extracellular concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the striatum of rats. In rats given trazodone, m-chlorophenylpiperazine dihydrochloride, or imipramine, the concentrations of 5-HT were unchanged. 5-HIAA in trazodone- or imipramine-treated rats, however, was respectively, decreased to 80 or 65% of preinjections levels. When the potassium concentration (K(+)) was increased up to 150 mmol/l in the perfusate, the concentrations of 5-HT increased to about ten times the basal levels in the rats given saline. In rats treated with trazodone, K(+)-evoked elevations of 5-HT were less than five times the basal level. Multiple trazodone administrations prolonged the duration of inhibition of 5-HT release. In rats treated with other drugs, the K(+)-evoked 5-HT release was not affected. These observations suggest that trazodone itself might reduce 5-HT neural transmission.

Electrophysiologic analysis of antidepressant drug effects on the GABA(A) receptor complex based upon antagonist-induced encephalographic power spectrum changes

To better understand antidepressant drug effects on the GABA(A) receptor complex (the GABA(A) receptor, chloride ionophore and benzodiazepine receptor), we investigated how antidepressants influenced power spectrum changes induced by pentylenetetrazol (PTZ), a chloride ionophore antagonist, in the rat hippocampal electroencephalogram (EEG). In control recording, PTZ (27.5 mg/kg i. p.) increased EEG power at frequencies under 12 Hz up to five times. After rats were pretreated with imipramine, fluoxetine or trazodone for 7 days (10 mg/kg i.p., twice a day), PTZ could not increase EEG power to more than three times the power before injection; this effect was not observed after pretreatment for 3 days. These three antidepressants inhibit serotonin uptake, while two other antidepressants, desipramine and nortriptyline, that inhibit norepinephrine uptake failed to counter the PTZ effect. We concluded that antidepressants with serotonergic effects enhanced the function of the GABA(A) receptor complex.

Ziprasidone in the short-term treatment of patients with schizoaffective disorder: results from two double- blind, placebo-controlled, multicenter studies

This study assessed the efficacy of ziprasidone for the treatment of schizoaffective disorder. Data were taken from subsets of patients with schizoaffective disorder, derived from two separate double-blind, placebo-controlled, parallel-group, multicenter studies. A total of 115 hospitalized patients with an acute episode of schizoaffective disorder were randomly assigned to receive either fixed oral doses of ziprasidone 40 mg/day (N = 16), 80 mg/day (N = 18), 120 mg/day (N = 22), 160 mg/day (N = 25), or placebo (N = 34) for 4 to 6 weeks. Mean baseline-to-endpoint changes in Brief Psychiatric Rating Scale (BPRS) total, BPRS Core, Clinical Global Impressions Severity scale (CGI-S), BPRS Depressive, BPRS Manic, and Montgomery-Asberg Depression Rating Scale total scores were compared between the placebo and ziprasidone groups. Neurological (Simpson-Angus, Barnes Akathisia, Abnormal Involuntary Movement Scale [AIMS]) and other side effects were also assessed. Significant dose-related improvements on all primary efficacy variables (BPRS total, BPRS Core, CGI-S) and for BPRS Manic items were observed with ziprasidone treatment in a combined analysis of data from both studies (p < or = 0.01). Ziprasidone 160 mg/day was significantly more effective than placebo in improving mean BPRS total, BPRS Core, BPRS Manic, and CGI-S scores (p < 0.05). At 120 mg/day, ziprasidone was significantly more effective than placebo in improving mean CGI-S scores (p < 0.05). The incidence of individual adverse events was generally low in all treatment groups and was not dose-related. In addition, no significant differences were observed between baseline-to-endpoint mean changes in Simpson-Angus and AIMS scores with placebo or ziprasidone 40 to 160 mg/day. These results suggest that ziprasidone may have efficacy in the treatment of affective as well as psychotic symptoms of schizoaffective disorder, with a low side-effect burden.

Operant response suppression induced with systemic administration of 5-hydroxytryptophan is centrally mediated

Intracerebroventricular (ICV) administration of selective serotonergic agents was used to examine the extent of central mediation of 5-HTP-induced operant response suppression in rats. ICV administration of LY53857 (1.0, 3.75, or 7.5 micrograms/5 microliters/5 min) dose dependently blocked response suppression induced with systemically administered 5-HTP (25 mg/kg, IP), whereas ICV 0.9% saline (5 microliters over 5 min) had no significant effect on 5-HTP-induced response suppression. ICV ketanserin (7.5 micrograms/5 microliters/5 min) also blocked response suppression induced with systemically administered 5-HTP. ICV administration of the 5-HT2A/2C receptor agonist DOI (80 micrograms/5 microliters/5 min) induced significant periods of response suppression in this model, which was blocked with LY53857 (1.0 mg/kg, IP) pretreatment. These data demonstrate that central administration of 5-HT2A/2C antagonists potently attenuate operant response suppression induced with systemically administered 5-HTP or DOI and are in agreement with previous findings suggesting central mediation of 5-HTP-induced operant response suppression.

Structure-activity relationship studies of CNS agents, Part 22. A search for new trazodone-like antidepressants: synthesis and preliminary receptor binding studies

New 1-phenyl- and 1-(3-chlorophenyl)piperazines containing a 4-[3-(heterocyclic)propyl] fragment were synthesized. It was found that of all the investigated compounds 11b (Ki = 13 +/- 2 nM) and 8b (Ki = 38 +/- 2 nM) were the most active 5-HT1A and 5-HT2A ligands, respectively. Several derivatives (3a, 4a, 8b, 11b, 12b, 13a, and 13b) were selected as good candidates for new, potential antidepressants on the basis of their 5-HT1A/5-HT2A receptor binding profiles.

Comparison of the action of the 5-HT2 antagonists amperozide and trazodone on preference for alcohol in rats

Previous studies in the rat demonstrated that the 5-hydroxytryptamine2 (5-HT2) antagonist amperozide attenuates the volitional intake of both alcohol and cocaine solutions in a free-choice situation. However, another 5-HT2 antagonist, ritanserin, has not been found to reduce alcohol drinking consistently in the rat. In this study, trazodone was compared to amperozide for its effect on the volitional consumption of alcohol because, like amperozide, trazodone is a potent 5-HT2 receptor antagonist but a weak inhibitor of 5-HT reuptake. Male Sprague-Dawley rats were induced to drink alcohol by 10 mg/kg cyanamide injected for 3 days b.i.d. One week later the rats were offered a choice of water and increasing concentrations of alcohol solutions ranging from 3% to 30% v/v in a three-bottle two-choice paradigm. After the concentration of alcohol that produced maximal daily intake was determined for each rat, trazodone or amperozide was injected b.i.d. SC in doses of 1.0 mg/kg or 2.5 mg/kg for three days. Whereas the higher dose of amperozide produced a significant, 55.6% decrease from pretreatment baseline of alcohol intake, trazodone did not alter alcohol preference at either the 1.0- or 2.5-mg/kg dose. These results are discussed in terms of whether the antagonism of 5-HT2 receptors by amperozide is critical to its attenuating effect on preference for alcohol solutions.

Pharmacologic treatment of schizoaffective disorder

In contrast to the considerable systematic study of the pharmacologic treatment of schizophrenia and mood disorders, the pharmacologic treatment of schizoaffective disorder has been relatively ignored. The authors reviewed the available literature regarding the pharmacologic treatment of schizoaffective disorder. The total number of controlled studies of the acute and prophylactic treatment of schizoaffective disorder was small and few used modern criteria to define the disorder. In studies of schizoaffective disorder, bipolar type (manic), lithium and antipsychotics produced comparable albeit incomplete responses, except in highly agitated patients when antipsychotics exerted superior efficacy. The combination of lithium and antipsychotics appeared to be superior to antipsychotics alone for schizoaffective, bipolar type patients. In the only controlled study of schizoaffective disorder, depressed type, the presumed superiority of combined antidepressant and antipsychotic treatment to antipsychotic alone was not found. Although combined antipsychotic and thymoleptic treatment represents common prophylactic management of schizoaffective disorder in clinical practice, the efficacy of this strategy has not been studied in controlled trials. Advances in the nosology of schizoaffective disorder, emerging epidemiologic data demonstrating large numbers of patients with this disorder in clinical populations, and preliminary evidence that clozapine may have combined antipsychotic and thymoleptic properties as well as efficacy in both the psychotic and affective components of schizoaffective disorder, suggest that renewed interest in the diagnosis and treatment of this disorder may lead to improved delivery of care for this understudied but seriously ill group of patients.

Effects of bulbectomy and subsequent antidepressant treatment on brain 5-HT2 and 5-HT1A receptors in mice

The effects of bilateral olfactory bulbectomy on serotonergic 5-HT2 and 5-HT1A receptor binding were studied in the frontal cortex (FC), limbic structures (LS), including the hippocampus, amygdala, olfactory tubercule, and piriform cortex, and hypothalamus (HTH) in mice. Bulbectomy resulted in the increase of Bmax for [3H]spiperone binding with 5-HT2 receptors in FC in C57Bl/6j. The receptors in LS and HTH remained unchanged. Subchronic treatment of the bulbectomized mice with antidepressant trazodone (20 mg/kg/day, IP, 14 days) induced downregulation of 5-HT2 receptors in FC and LS. The other two antidepressants used, amitriptyline (20 mg/kg/day, IP, 14 days) and imipramine (10 mg/kg/day, IP, 14 days), did not alter these receptors. [3H]8-OH-DPAT binding with 5-HT1A receptors was not altered by bulbectomy in any brain area in C57Bl/6j mice. Amitriptyline and trazodone decreased Bmax for these receptors in FC in the bulbectomized mice while imipramine was ineffective. Amitriptyline and imipramine significantly increased Bmax and decreased Kd in HTH, and trazodone displayed the same tendency. Bulbectomy did not alter 5-HT2 receptors in DBA/2j mice. Amitriptyline increased Kd in the all brain areas without changing Bmax in the bulbectomized DBA/2j mice. Trazodone significantly decreased Bmax in FC and increased Kd in FC and LS. Imipramine decreased Bmax while increasing Kd in LS. The possible involvement of the serotonin receptor subtypes in the bulbectomy-induced behavioral deficits and in the restorative action of the antidepressants is discussed.

Some regional anatomical relationships of TRH to 5-HT in rat limbic forebrain

It is now a recognized principle that various neuropeptides are neuronally co-localized with biogenic amine or aminoacid neurotransmitters. In the rat CNS it has previously been shown that TRH is co-localized with 5-HT (and also with substance P) in cell bodies of the posterior raphe that project to the spinal cord. Although TRH cell bodies are known to be widely distributed throughout the forebrain there is no other known co-localization with 5-HT. In this study we further specify the forebrain there is no other known co-localization with 5-HT. In this study we further specify the anatomical relationship of TRH with 5-HT by use of surgical and neurotoxic lesioning with reference to limbic forebrain regions wherein TRH is greatly increased following seizures. In groups of rats, the fimbria-fornix was lesioned alone, or combined with a lesion of the dorsal perforant path or the ventral perforant path. There was a sham lesioned control group. Additional groups were lesioned with 5,7 dihydroxytryptamine, 100 micrograms i.v.t., 45 min. after i.p. desipramine, 25 mg/kg. All rats were sacrificed three weeks after lesions. Indoleamines were determined by HPLC in left anterior cortex, left pyriform/olfactory cortex, left dorsal hippocampus and left ventral hippocampus. TRH was determined by specific RIA in the corresponding right brain regions. The modal n was 7 rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Response suppression induced with selective 5-HT agonists can be differentially blocked with LY53857 in an animal model of depression

Studies from this laboratory have demonstrated that administration of the selective 5-HT2/1C antagonist LY53857 can block 5-HTP-induced response suppression. To further investigate the serotonergic mechanisms involved in this effect, we decided to test the capacity of LY53857 to block response suppression induced with two selective 5-HT agonists. After a 15 minute baseline period, rats trained to press a lever for milk reinforcement on a VI 1' schedule were given IP injections of 1.0 mg/kg DOI, or 1.0 mg/kg 8-OH-DPAT to induce response suppression. Subsequently, rats were injected with 1.0 mg/kg LY53857 1 hour prior to DOI- or 8-OH-DPAT-induced response suppression. Preinjections with LY53857 resulted in a 100% blockade of DOI-induced response suppression whereas the same dose did not block response suppression induced with 8-OH-DPAT. These results indicate that the 5-HTP-induced response suppression shows some pharmacological similarity to DOI-induced response suppression and may be mediated through 5-HT2 and/or 5-HT1C receptors.

A comparison of trazodone and fluoxetine: implications for a serotonergic mechanism of antidepressant action

Trazodone is an atypical antidepressant drug that is commonly referred to as a serotonin (5-hydroxytryptamine; 5-HT) uptake inhibitor. However, the most potent pharmacological effect of trazodone appears to be antagonist action at 5-HT2/1C receptors. This is in contrast to fluoxetine, for which inhibition of 5-HT uptake is the most potent pharmacological action. The effects of trazodone and fluoxetine on several antidepressant drug screens are mediated by antagonist action at 5-HT2 receptors and inhibition of 5-HT uptake, respectively. While fluoxetine is an effective agent for the treatment of major depression, obsessive-compulsive disorder (OCD) and panic disorder, trazodone does not appear to be effective in the treatment of OCD and panic disorder. In addition, trazodone and fluoxetine differ in humans with respect to their effects on sleep and weight. Taken together, the preclinical and clinical data suggest that trazodone acts as an antidepressant via antagonist action at 5-HT2/1C receptors, while fluoxetine likely acts as an antidepressant via inhibition of 5-HT uptake.

Differential effect of 5-hydroxytryptophan on approach and avoidance behavior in rats

The current hypersensitive postsynaptic serotonin receptor theory of depression developed and expanded by Aprison and Hingtgen was based on an animal model of behavior in which food-reinforced approach behavior was suppressed following 5-hydroxytryptophan (5-HTP) administration. In this paper, data are presented to show that when the same animal is taught to emit, alternatingly, approach and avoidance behavior, and the serotonin precursor, 5-HTP, is administered, only the approach behavior is affected. Adult, male Wistar rats were trained on Sidman avoidance (RS20:SS10) and food-reinforced approach (VI 1) schedules. During the first part of this study, rats received separately 50-min sessions for approach and avoidance responding. For the second part, both schedules were given in the same experimental chamber. In the third part, 10-min alternating approach and avoidance components were combined in the same 50-min sessions. Significant behavioral suppression of approach responding was observed following administration of L-5-HTP (50 mg/kg IP), as well as after D,L-5-HTP (25 and 50 mg/kg IP) in a dose-dependent relationship, whereas no significant effect was seen for Sidman avoidance responding during this type of session. These results support the role of serotonin in food-reinforced approach behavior and suggest that suppression of Sidman avoidance behavior may be mediated by other neurotransmitter systems.

Fluoxetine, a selective inhibitor of serotonin uptake

In summary, fluoxetine is a highly selective serotonin uptake inhibitor in vitro and in vivo. The conformation of fluoxetine, which resembles that of sertraline and other serotonin uptake inhibitors, appears to be a key feature that enables its high affinity and selective interaction with the serotonin transporter. The para-trifluoromethyl substituent, however, is also a pivotal structural element. The molecular pharmacology of fluoxetine has been well-defined, and its in vivo pharmacological effects appear to be mediated almost exclusively by serotonin uptake inhibition. Its selectivity for the serotonin transporter, lack of affinity for neurotransmitter receptors, and retention of selectivity following metabolism to norfluoxetine make fluoxetine a useful tool to explore pharmacologically induced increases in serotonin neurotransmission. Fluoxetine has found a variety of therapeutic application. Its use in treating depression has been most extensively studied, but controlled clinical studies also suggest the drug may have a role in treating obesity and bulimia. Moreover, a variety of other psychiatric disorders may be treatable with this drug. Regardless of the outcome of these clinical trials, it is apparent that fluoxetine has found a useful niche in therapy, and can be used as a probe to determine the role of serotonin in modulating human pathophysiologies.

Chronic antidepressant and clonidine treatment effects on conflict behavior in the rat

The present studies examined the effects of chronic treatment with several antidepressants and clonidine on conflict behavior. In daily ten-minute sessions, water-deprived rats were trained to drink from a tube which was occasionally electrified (0.25 or 0.5 mA). Electrification was signalled by a tone. Chronic desipramine (5 mg/kg, IP, b.i.d.) or clonidine (40 micrograms/kg, b.i.d.) treatment resulted in time-dependent anticonflict effects, with a latency to onset of approximately 3-4 weeks. In contrast, chronic buproprion (up to 10 mg/kg, IP, b.i.d.), mianserin (up to 10 mg/kg, IP, b.i.d.) or trazodone (up to 40 mg/kg, IP, b.i.d.) treatment resulted in at best only a weak anticonflict effect. The efficacy of these antidepressants and clonidine to increase punished responding when administered chronically correlates well with their efficacy as antipanic agents in man.

Antidepressant-like effects of trazodone on a behavioral screen are mediated by trazodone, not the metabolite m-chlorophenylpiperazine

Trazodone is an atypical antidepressant drug (i.e. blocks neither monoamine uptake nor monoamine oxidase) which tests as an antidepressant drug on the differential-reinforcement-of-low-rate 72-s (DRL 72-s) schedule of reinforcement by increasing the reinforcement rate and decreasing the response rate. m-Chlorophenylpiperazine (m-CPP) is a 5-HT1B and 5-HT1C agonist, weak 5-HT2 antagonist, and trazodone metabolite. It has been suggested that formation of m-CPP is responsible for the antidepressant action of trazodone. Administration of m-CPP (1-10 mg/kg i.p.) 60, 30 or 10 min before the behavioral session did not mimic the reinforcement rate-increasing effects of trazodone (10-20 mg/kg i.p.) on rats performing under the DRL 72-s schedule of water reinforcement. Pretreatment with proadifen (50 mg/kg i.p.), an inhibitor of trazodone metabolism, caused a greater than 30-fold leftward shift in the dose-response curve for both the reinforcement rate and the response rate. These results suggest that the parent compound and not the trazodone metabolite m-CPP, mediates the antidepressant-like effects of trazodone on DRL 72-s behavior.

Depression and antidepressant therapy: receptor dynamics

1. The classical norepinephrine (NE) and serotonin (5-HT) theories of depression have been abandoned in light of recent chronic antidepressant drug studies. 2. The new NE and 5-HT theories of depression focus on the dynamics of receptor subtypes in depression and chronic antidepressant treatments. 3. Recent studies in molecular genetics suggest a reclassification of monoamine receptors based on receptor structural homologies in DNA and amino acid sequences rather than receptor affinity for ligands. 4. Electrophysiologic studies in rats suggest that 5-HT1 receptor function is facilitated by chronic antidepressant treatment. 5. Preclinical studies employing a range of 5-HT1 mediated behavioral models also suggest that chronic antidepressant treatment facilitates transmission at central 5-HT1 receptors. 6. Patient studies, employing a 5-HT1 mediated neuroendocrine model, suggest that depression is associated with decreased transmission at CNS 5-HT1 receptors; and that chronic antidepressant treatment facilitates 5-HT1 receptor responsiveness in depressed patients. 7. New 5-HT1 selective agonists have been developed and found to be clinically effective antidepressants. 8. The above clinical and preclinical data suggest that some forms of depression are related to a decreased responsiveness of 5-HT1 receptors which is reversed by chronic antidepressant treatment. 9. Beta adrenergic and NE-stimulated cyclic AMP studies suggest that chronic antidepressant treatment decreases the responsiveness of central beta-adrenergic receptors, particularly beta-1 receptors. 10. A novel approach to antidepressant drug development focuses on identifying centrally active beta-1 agonists, which like clinically proven antidepressants, decrease beta-1 receptor responsiveness with chronic treatment. 11. 5-HT2 receptor binding studies and initial studies of 5-HT2 receptor coupled PI turnover suggest that chronic antidepressant treatment decreases 5-HT2 receptor number and function. 12. The development of new atypical antidepressants with 5-HT2 receptor related mechanisms of action suggest that 5-HT2 receptors may be associated with certain types of depression and their clinical treatment.

Disruption of FR-40 by 5-HT agonists. I. Effects of chronic imipramine or trazodone

Doses of LSD, quipazine, 8-OHDPAT and TFMPP were established that prominently disrupted FR-40 operant response pattern in two groups of rats. Subsequently, one group received daily intraperitoneal (IP) injections of imipramine, 2.5 mg/kg, for 4 weeks, then 10 mg/kg for 2 additional weeks. The second group received 5 mg/kg/day, IP, of trazodone for the first 4 weeks, then 20 mg/kg/day for the next two weeks. For these periods and the 3 weeks after discontinuing the chronic drug treatments (washout), test doses of the 4 agonists were evaluated twice weekly in random order for their effects to decrease FR-40 reinforcements and increase pauses. No consistent, systematic changes in sensitivity to the agonist effects on FR-40 behavior were observed during chronic drug treatments, although significant effects were at times observed. However, during the washout period in the imipramine group, both LSD and 8-OHDPAT effects on reinforcements were reversed to baseline levels. The effect of 5-OHDPAT on pauses during washout in this group was also attenuated. During washout in the trazodone group, the 8-OHDPAT-induced pausing and loss of reinforcements was reduced so as to be not significantly different from baseline values. Previous studies have demonstrated antagonism of LSD- and quipazine-induced disruption of FR-40 by pretreating with the 5-HT2-selective antagonist pirenperone (28). Since chronic antidepressants down-regulate brain 5-HT2 binding sites, the effects of LSD and quipazine were expected to be attenuated, which was not the case.(ABSTRACT TRUNCATED AT 250 WORDS)

Disruption of FR-40 by 5-HT agonists. II. Effects of chronic phenelzine or isocarboxazid

Effects of chronic treatment with the monoamine oxidase inhibitors phenelzine and isocarboxazid on disruption of FR-40 operant responses by 5-HT agonists have been studied. Three groups of rats that were trained in the FR-40 operant schedule showed marked disruption by 0.1 mg/kg IP lysergic acid diethylamide (LSD), 2 mg/kg IP quipazine (Q), 0.05 mg/kg SC 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT), and 1 mg/kg SC (m-trifluoromethyl-phenyl)piperazine (TFMPP), administered twice weekly in random order. Subsequently, one group received daily IP injection of phenelzine (5 and 10 mg/kg), the second group received 5 mg/kg IP of isocarboxazid, and the third group received vehicle (0.5% methyl cellulose) for 24 days (Period 1 and Period 2). For these periods and 12 days after discontinuing the MAOI treatments (Washout Period), test doses of 5-HT agonists were evaluated for their effects to decrease reinforcements (R) and increase pauses (P). No change in sensitivity to the LSD, Q and TFMPP effects on FR-40 behavior was observed in the vehicle-treated group. However, an attenuated effect of 8-OHDPAT was found in this group. In phenelzine- and isocarboxazid-treated rats the disruption of FR-40 responses by LSD and 8-OHDPAT were significantly reduced during Period 1, Period 2 and Washout Period. A significantly less effect on disruption in FR-40 responses by quipazine and TFMPP during Period 2 and the Washout Period was also seen. Since MAO inhibitors appear to down-regulate both 5-HT1 and 5-HT2 binding sites in brain, the attenuated effects of the 5-HT agonists were anticipated.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of repeated trazodone administrations on serotonergic neurotransmission: biochemical studies

1. Repeated administrations of trazodone as well as imipramine or mianserin (10 mg/kg i.p. twice daily for 3 weeks) attenuated the norepinephrine (NE) stimulation of adenylate cyclase studied in brain minces. Therefore trazodone shares with "tricyclic" (imipramine) and "atypic" (mianserin) antidepressants the capability to modulate the beta-adrenergic function. 2. Daily treatments with imipramine or trazodone enhanced the Vmax of neural uptake of serotonin (5HT) in minces prepared from rat frontal cortex; in contrast mianserin failed to modify the [3H]-5HT uptake. 3. Repeated administrations of imipramine but not of trazodone or mianserin reduced the maximum number of [3H]-imipramine recognition sites which are located on serotonergic axon terminals. 4. Differently, only repeated administration of trazodone decreased Bmax values of [3H]-mianserin binding sites which are located on membranes innervated by serotonergic neurons. Moreover trazodone did not change the number or affinity of 5HT2 receptors either after single or repeated administrations; in contrast even a single administration with mianserin or repeated administrations with imipramine down-regulated [3H]-ketanserin specific binding in membranes prepared from the frontal cortex. 5. Our observations therefore suggest that trazodone, imipramine or mianserin exerts similar effects on the adenylate cyclase system, by acting on a interneuronal loop which links serotonergic and noradrenergic transmission function. However, its exact mechanism of action, in part resembling both tricyclic and atypic depressants, requires further examination.

Effects of trazodone treatment on serotonergic function in depressed patients

Changes in serotonergic (5HT) neurotransmission may mediate the therapeutic actions of some antidepressant drugs. In the present study, the 5HT precursor L-tryptophan (L-TRP) was administered intravenously to nine depressed patients before and during treatment with the triazolopyridine antidepressant trazodone (TRZ). Neuroendocrine, subjective mood, and cardiovascular responses to L-TRP were assessed. Unlike tricyclic antidepressants and monoamine oxidase inhibitors, TRZ did not enhance the prolactin response to L-TRP and had little effect on other measures. Since other studies indicate that the TRP-induced increase of prolactin in humans may reflect 5HT function, the present study suggests that TRZ treatment does not enhance net 5HT function in depressed patients.

Response suppression in rats after bilateral microinjection of 5-hydroxytryptophan in lateral hypothalamus

Studies using the 5-hydroxytryptophan (5-HTP) animal model of depression have led to the development of the hypersensitive postsynaptic serotonin receptor theory of depression. To demonstrate more clearly that the 5-HTP-induced suppression is a centrally mediated phenomenon, rats were implanted with bilateral cannulae in the lateral hypothalamus and received microinjections of D,L-5-HTP (100-500 ng) 15 min after the start of a VI operant session (milk reinforcement). Significant decreases in responding were observed that were comparable to those obtained after a systemic injection of 50 mg/kg D,L-5-HTP. Rats receiving a microinjection of 5-HTP in the posterior hypothalamus did not exhibit a behavioral effect. Rats working on shock-avoidance schedules did not demonstrate response suppression following microinjection of 5-HTP into the lateral hypothalamus, which is the same result as that following systemic 5-HTP administration. These data support the important role previously assigned to central 5-HT mechanisms in the 5-HTP animal model of depression.

Effects of trazodone on the sleep of depressed subjects--a polygraphic study

The effects of 400-600 mg trazodone on the sleep patterns of ten depressed in-patients treated for 5 weeks were studied during the initial (days 1-3) and terminal (days 26-28) treatment periods. The sleep parameters were compared to those obtained from three sleep recordings performed just prior to the initiation of the treatment and after 2 adaptation nights at the end of a 2-week drug-free period. At the same time, the clinical evolution of patients was evaluated weekly using MADRS and Hamilton-Anxiety scales for anxiety-depression symptomatology and Spiegel and Norris sleep scales. Weekly blood samples were collected to measure plasma levels of trazodone and, at the end of the study, the elimination half-life at steady state was calculated by repeated measurements of plasma levels. Clinical improvement, as assessed by a reduction of more than 60% in MADRS scale scores, was accompanied by evidence of the definitely beneficial effects of trazodone on the disturbed sleep of these depressed patients. From the beginning of treatment, there was a hypnotic-like effect (increase in total duration of sleep and stage II, decrease in sleep latency and intrasleep awakenings). In addition, records at the end of the study showed an increase in delta sleep and an increase in REM latency, an effect classically associated with an antidepressant action. These particularly valuable effects of trazodone on sleep would suggest that this drug should especially be given in cases of depression with major insomnia.

Selective enhancement of shock avoidance responding elicited by GABA blockade in the posterior hypothalamus of rats

Recent studies have shown that blockade of gamma-aminobutyric acid (GABA) in the posterior hypothalamus in anesthetized rats elicits cardio-respiratory stimulation similar to that seen in emotional defense reactions and, in conscious rats, locomotor arousal suggesting a flight response. The present study was conducted in order to test the hypothesis that the behavioral effects elicited by GABA blockade in the posterior hypothalamus were the results of disinhibiting a mechanism whose activation selectively enhances reactivity to aversive stimuli. Male rats were trained on a Sidman shock avoidance schedule (RS20:SS10) as well as a food-reinforced approach schedule (VI 1). Under anesthesia, guide cannulae were stereotaxically implanted bilaterally in the posterior hypothalamus at sites where microinjection of the GABA antagonist, bicuculline methiodide (BMI) 25 ng, increased heart rate. After recovery, rats were tested in both the avoidance and VI 1 schedules after hypothalamic microinjection of saline, BMI 25 ng, and the GABA agonist, muscimol 25 ng. Microinjection of BMI significantly increased the avoidance responses but had no effect on the approach responses. Muscimol decreased both the avoidance and approach responses. When microinjected into the lateral hypothalamic area, BMI had no effect on the response rates in either schedule while muscimol decreased the approach responding only. Therefore, GABA blockade at the discrete area of the posterior hypothalamic nucleus appears to elicit a selective enhancement of avoidance responses. These results suggest that an endogenous GABAergic system in the posterior hypothalamus may tonically inhibit a constellation of autonomic, locomotor and motivational responses that are necessary for some types of defense reaction.

Serotonergic involvement in the backward tumbling response of the parlor tumbler pigeon

The parlor tumbler is a breed of domestic pigeon which displays a hereditary movement disorder resulting in backward somersaulting upon attempting to fly. A neurochemical abnormality has been suggested to underlie this behavior. The effect on tumbling of several drugs with serotonergic actions was studied. Increasing available serotonin with 5-hydroxytryptamine (50 mg/kg) plus fluoxetine (10 mg/kg) as well as using amitriptyline (10-20 mg/kg) significantly suppressed tumbling without sedation. This suggests that serotonin mechanisms may be involved in the tumbling response.

Action of chronically administered antidepressants on the serotonergic postsynapse in a model of depression

A theory of excessive transmission of serotonin (5-HT) in depression has been previously proposed. The purpose of the present study was to test this theory further by using the model of depression in rats induced by L-5-hydroxytryptophan (5-HTP), the precursor of 5-HT. The drug effects on 5-HTP (25 mg/kg) induced behavioral depression were tested by chronic administration using methysergide which is a postsynaptic blocker of 5-HT, or by comparable clinical doses of antidepressant drugs. Methysergide (2 mg/kg) blocked 5-HTP induced depression on days 8 and 22 after initiation of medication by 70% and 83%, respectively. Among antidepressants, mianserin (2 mg/kg) was the first to produce an effect, displaying a 38% effect as early as 1 day after the start of medication and having blocking effects of 52% and 72% on days 8 and 22. Desipramine (5 mg/kg), doxepine (5 mg/kg), imipramine (5 mg/kg) and trazodone (10 mg/kg) showed no significant effect on days 1 and 8, and on day 22, 64, 36, 33 and 32% blocking, respectively. Amitriptyline had an initial effect of 41% at a dose of 10 mg/kg. Clomipramine (5 mg/kg), zimelidine (6 mg/kg) and chlorpromazine (2.5 mg/kg), which is a neuroleptic, showed no effect. Considering these results in light of recent data reported on the 5-HT synapse, it was suggested that 5-HTP induced depression may be induced by excessive transmission of 5-HT and that some antidepressant drugs may produce their effect by blocking this postsynaptic transmission. Based on these results, the mechanisms of human depression were discussed.

Effects of trazodone treatment on alpha-2 adrenoceptor function in depressed patients

Tricyclic antidepressant drugs reduce the sensitivity of alpha 2 adrenoceptors during long-term treatment. In the present study, the alpha 2 adrenergic agonist clonidine was administered to 11 depressed patients before and during treatment with the triazolopyridine antidepressant trazodone (TRZ). Clonidine's ability to decrease blood pressure (BP) and plasma levels of the norepinephrine metabolite 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), and to increase sedation and plasma growth hormone (GH), were measured. TRZ had little effect on these indices of pre- and postsynaptic alpha 2 receptor function, suggesting that the antidepressant properties of TRZ are not related to changes in alpha 2 adrenoceptor sensitivity.

Animal models of depression: parallels and correlates to severe depression in humans

Drugs with antidepressant properties in patients with severe depression also have various behavioral and neurochemical effects in animals. This has given rise to numerous animal models that have been suggested to be valid for research into the neurobiology of depression and the neurochemical mechanisms of the antidepressant drugs. However, considerable evidence from many avenues of research indicates that severe depression is a biochemical disorder that develops in those individuals with some predisposing neurochemical vulnerability. Although the predisposing biochemical abnormality has not been identified, it may be related to the neurochemical mechanisms that regulate impulse traffic in various neural systems and maintain the homeostatic balance of neural activity within the brain. Therefore, the appropriate animal model for severe depression should have some disruption of neural functioning that is returned to normal by the chronic administration of antidepressant drugs. Of the numerous animal models of depression that have been presented in the literature, only the rat with olfactory bulb lesions meets this requirement. The behavioral and endocrine abnormalities induced by the olfactory bulb lesions are reversed by chronic (but not acute) treatment with antidepressants of various classes. Of the existing animal models of severe depression, the olfactory bulbectomy model holds the most promise for elucidating the neurobiology of depression and the neurochemistry of antidepressant drugs.

Prolongation of thiopentone-induced sleep by trazodone and its metabolite, m-chlorophenylpiperazine

Trazodone and its metabolite, m-chlorophenylpiperazine (CPP) prolonged significantly thiopentone-induced sleep in mice. Neither trazodone, nor CPP changed the cerebral concentrations of thiopentone. As cyproheptadine by itself did not affect thiopentone sleep and did not antagonize the effect of CPP, the effect of trazodone and CPP seems to be independent of their respective 5-HT-antagonistic and 5-HT-agonistic properties.

The role of trazodone metabolism in its inhibitory action on avoidance response

To assess the role of trazodone metabolism in its depressant action on conditioned avoidance response we investigated whether in the mouse brain 3-chlorophenylpiperazine (CPP) is formed from trazodone, whether trazodone metabolism is affected by a drug metabolism inhibitor, proadifen, and how trazodone, CPP and their combinations act on avoidance responses in proadifen-pretreated mice. It was found that CPP is formed from trazodone in mice, that proadifen inhibits trazodone metabolism, and that the moderate and transient inhibitory effect of trazodone on avoidance responses is dramatically potentiated and prolonged in proadifen-pretreated mice. This effect, and inhibition of unconditioned escape response observed in mice receiving lower doses of trazodone after proadifen pretreatment, were counteracted by CPP. The results indicate that the inhibitory action of trazodone on avoidance response is caused by the parent compound, and that it is brief and moderate because of the rapid metabolism of the drug with formation of CPP which counteracts the depressant effect of the parent compound.

Blockade of a 5-hydroxytryptophan-induced animal model of depression with a potent and selective 5-HT2 receptor antagonist (LY53857)

To test the hypothesis that a new potent and selective 5-HT2 receptor antagonist would be an excellent blocker of D,L-5-hydroxytryptophan (5-HTP)-induced response suppression in an animal model of depression, we administered LY53857 60 min prior to 5-HTP injections into rats working on an operant schedule for milk reinforcement. As predicted, LY53857 pretreatment significantly blocked 5-HTP depression (90%) in doses as low as 0.1 mg/kg ip. When the dose of LY58357 was further reduced to 0.025 mg/kg, blockade of 5-HTP-induced depression was still greater than 30%. In doses as high as 5.0 mg/kg, LY53857 alone had no effect on the baseline performance of rats working a VI 1 schedule. Pretreatment with desipramine (2.5 mg/kg), an antidepressant characterized as having major noradrenergic effects, did not significantly block the 5-HTP-induced depression. These data suggest that the 5-HTP-induced depression is mediated by serotonergic mechanisms involving 5-HT2 receptors, as LY53857 is a selective antagonist of these receptors. These data also support the suggestion, based on other published data from this laboratory, that some antidepressants are antagonizing 5-HT2 receptors in our animal model of depression and may also act in a similar manner in depressed patients. Thus, this new drug could be of interest as a possible antidepressant agent of the general type that was proposed earlier by Aprison and Hingtgen (1981).