Venlafaxine's therapeutic reference range in the treatment of depression revised: a systematic review and meta-analysis

INTRODUCTION

The selective serotonin and norepinephrine reuptake inhibitor venlafaxine is among the most prescribed antidepressant drugs worldwide and, according to guidelines, its dose titration should be guided by drug-level monitoring of its active moiety (AM) which consists of venlafaxine (VEN) plus active metabolite O-desmethylvenlafaxine (ODV). This indication of therapeutic drug monitoring (TDM), however, assumes a clear concentration/effect relationship for a drug, which for VEN has not been systematically explored yet.

OBJECTIVES

We performed a systematic review and meta-analysis to investigate the relationship between blood levels, efficacy, and adverse reactions in order to suggest an optimal target concentration range for VEN oral formulations for the treatment of depression.

METHODS

Four databases (MEDLINE (PubMed), PsycINFO, Web of Science Core Collection, and Cochrane Library) were systematically searched in March 2022 for relevant articles according to a previously published protocol. Reviewers independently screened references and performed data extraction and critical appraisal.

RESULTS

High-quality randomized controlled trials investigating concentration/efficacy relationships and studies using a placebo lead-in phase were not found. Sixty-eight articles, consisting mostly of naturalistic TDM studies or small noncontrolled studies, met the eligibility criteria. Of them, five cohort studies reported a positive correlation between blood levels and antidepressant effects after VEN treatment. Our meta-analyses showed (i) higher AM and (ii) higher ODV concentrations in patients responding to VEN treatment when compared to non-responders (n = 360, k = 5). AM concentration-dependent occurrence of tremor was reported in one study. We found a linear relationship between daily dose and AM concentration within guideline recommended doses (75-225 mg/day). The population-based concentration ranges (25-75% interquartile) among 11 studies (n = 3200) using flexible dosing were (i) 225-450 ng/ml for the AM and (ii) 144-302 ng/ml for ODV. One PET study reported an occupancy of 80% serotonin transporters for ODV serum levels above 85 ng/ml. Based on our findings, we propose a therapeutic reference range for AM of 140-600 ng/ml.

CONCLUSION

VEN TDM within a range of 140 to 600 ng/ml (AM) will increase the probability of response in nonresponders. A titration within the proposed reference range is recommended in case of non-response at lower drug concentrations as a consequence of VEN's dual mechanism of action via combined serotonin and norepinephrine reuptake inhibition. Drug titration towards higher concentrations will, however, increase the risk for ADRs, in particular with supratherapeutic drug concentrations.

P01-50-Kratom and alcohol dependence: Clinical symptoms, withdrawal treatment and pharmacological mechanisms- A case report

Aim

1.

1.

Results

GCMS-urine screening on day 1: mitragynine, paynantheine, on day 3: monochlorbenzodiazepine, doxepine. The patient benefits regarding sleep quality and quantity (PSQI day 6 (12), day 20 (6) and mental symptoms (MADRS on day 6 (18) and on day 20 (5). The OWS Score shifts from 17 (day 1) to 2 (day 14). The blood pressure and heart rate decrease from 150/90 and 100/bpm (day 2) to 100/70 and 64/bpm (day 14). The GCMS analysis of kratom showed five indolalcaloids: mitragynine, 7-hydroxymitragynine, paynantheine, speciogynine, speciofoline, and unspecific plant contents. The 3H-DAMGO-radioligand-bindungsassay of kratom-powder showed 350-fold less affinity to μ-opiatereceptor than morphine.

Conclusion

The patient's selfmedication with kratom prevented alcohol withdrawal symptoms most probably by action on μ-opioidreceptors. 15 g of kratom seems to be equivalent to 45 mg of morphine. Withdrawl treatment with doxepine (and diazepam) clearly prevented withdrawal symptoms of dependence of kratom and alcohol.

Gene expression signature in brain regions exposed to long-term psychosocial stress following acute challenge with cannabinoid drugs

Repeated exposure to life stressors can overwhelm the body's capacity to restore homeostasis and result in severe negative consequences. Cannabinoid CB₁ receptors are highly expressed in the Central Nervous System (CNS) and regulate both glucocorticoid signalling and neurotransmitter release. In rodents, WIN55212.2 is a full agonist at the cannabinoid receptor type-1, while Rimonabant is a potent and selective cannabinoid inverse agonist at this receptor. This study aims to investigate the effect of long-term psychosocial stress following acute challenge with cannabinoid drugs on gene expression in distinct brain regions; this is done by employing digital multiplexed gene expression analysis. We found that repeated stress increased cortical mRNA levels of dopamine receptor D2, while the expression of neuregulin-1 decreased in both the prefrontal cortex and cerebellum. Further, we found that the acute injection of the agonist WIN55212.2 reduced striatal levels of dopamine receptor D2, while the use of inverse agonist Rimonabant acted in the opposite direction. The analysis of the interaction between the drugs and repeated stress revealed that defeat mice treated with WIN55212.2 showed lower expression of a set of myelin-related genes, as did the expression of SRY-box 10 and dopamine receptors-D1 and -D2 in the prefrontal cortex when compared to vehicle. In addition, in the hippocampus of stressed mice treated with WIN55212.2, we found an elevated expression of oligodendrocyte transcription factor-1, -2 and zinc finger protein 488 when compared to vehicle. In comparison to vehicle, an increase in 2',3'-Cyclic nucleotide 3'-phosphodiesterase and oligodendrocyte transcription factor-1 occurred in the cerebellum of stressed animals treated with the agonist. Moreover, treatment with Rimonabant under the influence of stress induced an overexpression of a set of myelin-related genes in the prefrontal cortex when compared to WIN-treated animals. In conclusion, repeated stress interfered with the dopaminergic system in the prefrontal cortex. We demonstrated that the expression of dopamine receptor D2 in the striatum was mediated by the CB₁ receptor. Stressed mice exposed to either WIN55212.2 or Rimonabant displayed pronounced deficits in CNS myelination. In addition, the pharmacological blockage of CB₁ receptor in stressed mice deregulated the expression of dopamine receptors and might lead to dysfunctions in dopamine metabolism.

Grey matter structural differences in alcohol-dependent individuals with and without comorbid depression/anxiety-an MRI study

Although depression and anxiety disorders are common comorbid conditions in alcohol dependence, few structural brain imaging studies have compared alcohol-dependent subjects with and without such comorbidity. In the current study, brain scans of 35 alcohol-dependent with and 40 individuals without diagnosis of a comorbid ICD-10 depressive or anxiety disorder receiving detoxification inpatient treatment were evaluated. Thickness and volumes of automatically segmented neuroanatomical structures were measured in FreeSurfer. Furthermore, associations of brain structure with biological markers and clinical severity markers of alcohol dependence were assessed. Despite comparable addiction severity, the non-comorbid group had evidence of higher cytotoxic effects of alcohol use on hepatic and haematological markers, and showed significantly smaller volumes of total cerebral, and cerebellar grey matter. Similarly, they showed unexpected smaller hippocampal and nucleus accumbens volumes, and thinner frontal, temporal and occipital cortices. Smaller brain volumes correlated with increased markers of hepatic and haematological dysfunction, and with longer duration of alcohol dependence in the non-comorbid group. Evidence of higher biomarkers of alcohol use may be indicative of more severe alcohol dependence or higher vulnerability to ethanol toxicity in this group. Furthermore, psychopathology-related drug treatment, which occurred in 53% of the comorbid group over the recent years, or tissue inflammation may have a moderate effect on the grade of cerebral atrophy in alcohol-dependent patients. Longitudinal studies are needed to investigate this issue more fully.

Chronic exposure to cannabinoids during adolescence causes long-lasting behavioral deficits in adult mice

Regular use of marijuana during adolescence enhances the risk of long-lasting neurobiological changes in adulthood. The present study was aimed at assessing the effect of long-term administration of the synthetic cannabinoid WIN55212.2 during adolescence in young adult mice. Adolescent mice aged 5 weeks were subjected daily to the pharmacological action of WIN55212.2 for 3 weeks and were then left undisturbed in their home cage for a 5-week period and finally evaluated by behavioral testing. Mice that received the drug during adolescence showed memory impairment in the Morris water maze, as well as a dose-dependent memory impairment in fear conditioning. In addition, the administration of 3 mg/kg WIN55212.2 in adolescence increased adult hippocampal AEA levels and promoted DNA hypermethylation at the intragenic region of the intracellular signaling modulator Rgs7, which was accompanied by a lower rate of mRNA transcription of this gene, suggesting a potential causal relation. Although the concrete mechanisms underlying the behavioral observations remain to be elucidated, we demonstrate that long-term administration of 3 mg/kg of WIN during adolescence leads to increased endocannabinoid levels and altered Rgs7 expression in adulthood and establish a potential link to epigenetic changes.

Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology: Update 2017

Therapeutic drug monitoring (TDM) is the quantification and interpretation of drug concentrations in blood to optimize pharmacotherapy. It considers the interindividual variability of pharmacokinetics and thus enables personalized pharmacotherapy. In psychiatry and neurology, patient populations that may particularly benefit from TDM are children and adolescents, pregnant women, elderly patients, individuals with intellectual disabilities, patients with substance abuse disorders, forensic psychiatric patients or patients with known or suspected pharmacokinetic abnormalities. Non-response at therapeutic doses, uncertain drug adherence, suboptimal tolerability, or pharmacokinetic drug-drug interactions are typical indications for TDM. However, the potential benefits of TDM to optimize pharmacotherapy can only be obtained if the method is adequately integrated in the clinical treatment process. To supply treating physicians and laboratories with valid information on TDM, the TDM task force of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) issued their first guidelines for TDM in psychiatry in 2004. After an update in 2011, it was time for the next update. Following the new guidelines holds the potential to improve neuropsychopharmacotherapy, accelerate the recovery of many patients, and reduce health care costs.

[On the legalization debate of non-medical cannabis consumption : Position paper of the German Association for Psychiatry, Psychotherapy and Psychosomatics]

Calls are increasing for the legalization of cannabis. Some legal experts, various politicians, political parties and associations are demanding a change in drug policy. The legalization debate is lively and receiving wide coverage in the media. The German Association for Psychiatry, Psychotherapy and Psychosomatics (DGPPN) comments on the most important questions from a medical scientific perspective: can cannabis consumption trigger mental illnesses, what consequences would legalization have for the healthcare system and where is more research needed?

AGNP Consensus Guidelines for Therapeutic Drug Monitoring in Psychiatry: Update 2011

Therapeutic drug monitoring (TDM), i. e., the quantification of serum or plasma concentrations of medications for dose optimization, has proven a valuable tool for the patient-matched psychopharmacotherapy. Uncertain drug adherence, suboptimal tolerability, non-response at therapeutic doses, or pharmacokinetic drug-drug interactions are typical situations when measurement of medication concentrations is helpful. Patient populations that may predominantly benefit from TDM in psychiatry are children, pregnant women, elderly patients, individuals with intelligence disabilities, forensic patients, patients with known or suspected genetically determined pharmacokinetic abnormalities or individuals with pharmacokinetically relevant comorbidities. However, the potential benefits of TDM for optimization of pharmacotherapy can only be obtained if the method is adequately integrated into the clinical treatment process. To promote an appropriate use of TDM, the TDM expert group of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) issued guidelines for TDM in psychiatry in 2004. Since then, knowledge has advanced significantly, and new psychopharmacologic agents have been introduced that are also candidates for TDM. Therefore the TDM consensus guidelines were updated and extended to 128 neuropsychiatric drugs. 4 levels of recommendation for using TDM were defined ranging from "strongly recommended" to "potentially useful". Evidence-based "therapeutic reference ranges" and "dose related reference ranges" were elaborated after an extensive literature search and a structured internal review process. A "laboratory alert level" was introduced, i. e., a plasma level at or above which the laboratory should immediately inform the treating physician. Supportive information such as cytochrome P450 substrate- and inhibitor properties of medications, normal ranges of ratios of concentrations of drug metabolite to parent drug and recommendations for the interpretative services are given. Recommendations when to combine TDM with pharmacogenetic tests are also provided. Following the guidelines will help to improve the outcomes of psychopharmacotherapy of many patients especially in case of pharmacokinetic problems. Thereby, one should never forget that TDM is an interdisciplinary task that sometimes requires the respectful discussion of apparently discrepant data so that, ultimately, the patient can profit from such a joint effort.

AGNP consensus guidelines for therapeutic drug monitoring in psychiatry: update 2011

Therapeutic drug monitoring (TDM), i. e., the quantification of serum or plasma concentrations of medications for dose optimization, has proven a valuable tool for the patient-matched psychopharmacotherapy. Uncertain drug adherence, suboptimal tolerability, non-response at therapeutic doses, or pharmacokinetic drug-drug interactions are typical situations when measurement of medication concentrations is helpful. Patient populations that may predominantly benefit from TDM in psychiatry are children, pregnant women, elderly patients, individuals with intelligence disabilities, forensic patients, patients with known or suspected genetically determined pharmacokinetic abnormalities or individuals with pharmacokinetically relevant comorbidities. However, the potential benefits of TDM for optimization of pharmacotherapy can only be obtained if the method is adequately integrated into the clinical treatment process. To promote an appropriate use of TDM, the TDM expert group of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) issued guidelines for TDM in psychiatry in 2004. Since then, knowledge has advanced significantly, and new psychopharmacologic agents have been introduced that are also candidates for TDM. Therefore the TDM consensus guidelines were updated and extended to 128 neuropsychiatric drugs. 4 levels of recommendation for using TDM were defined ranging from “strongly recommended” to “potentially useful”. Evidence-based “therapeutic reference ranges” and “dose related reference ranges” were elaborated after an extensive literature search and a structured internal review process. A “laboratory alert level” was introduced, i. e., a plasma level at or above which the laboratory should immediately inform the treating physician. Supportive information such as cytochrome P450 substrate and inhibitor properties of medications, normal ranges of ratios of concentrations of drug metabolite to parent drug and recommendations for the interpretative services are given. Recommendations when to combine TDM with pharmacogenetic tests are also provided. Following the guidelines will help to improve the outcomes of psychopharmacotherapy of many patients especially in case of pharmacokinetic problems. Thereby, one should never forget that TDM is an interdisciplinary task that sometimes requires the respectful discussion of apparently discrepant data so that, ultimately, the patient can profit from such a joint eff ort.

Therapeutic drug monitoring of drugs for treatment of substance-related disorders

Introduction

The effect of pharmacotherapy of substance-related disorders is moderate at best.

Objectives

Therapeutic drug monitoring (TDM) could be an instrument to improve the outcomes. TDM is for most of these drugs not established yet.

Aims

The authors built a literature based rating scale to evaluate the necessity of TDM for these pharmacological agents.

Methods

A literature research was performed for TDM related properties of acamprosate, bupropion, buprenorphine, clomethiazole, disulfiram, methadone, naltrexone, and varenicline. A rating scale was established for evaluation. It included 28 items related to five categories (efficacy, toxicity, pharmacokinetics, patient characteristics and cost effectiveness). For comparison, three reference substances with established TDM were similarly assessed: clozapine, lithium and nortriptyline.

Results

The three reference substances, lithium, clozapine and nortriptyline, achieved scores of 15, 18, and 14 points, respectively. Rating of methadone (19 points), bupropion (14 points), buprenorphine (14 points), disulfiram (13) and naltrexone (12 points in the indication opioid-dependency and 10 points in the indication alcohol dependency) achieved more than 30% of the reachable points, whereas acamprosate (9 points), clomethiazole (9 points), and varenicline (5 points) had fewer points especially in the main characteristics in favor of TDM.

Conclusions

These results suggest this rating scale is sensitive to detect the appropriateness of TDM for drug treatment. Literature based rating and clinical experience give evidence that TDM has the potential to optimize the pharmacotherapy of substance related-disorders with different rank orders of the single substances.

Principles of Analgesic Effects of Opioids and Dependence of Opioids (F.E. Tramadol)

German epidemiological data (Poser and Havemann-Reinecke 2002) showed 12% of all addicted treated patients in Lower Saxony being dependent from prescribed opioid analgesics.

Here we report new clinical data of 150 patients being treated because of dependence on the opioid analgesic tramadol. The documents of these patients were evaluated to social-, family-, pain- and addiction development - data, psychiatric and somatic diseases; suicidality, source of tramadol (prescription: "legal", black market: "illegal" ), withdrawl symptoms, therapy.

Results:

Of 140 patients (P) 123 P (88%) were "legally" dependent on tramadol (51% f, 49 m), 17 P (12.%) "illegally" dependent (54% f, 47% m). The ages of "legally" dependent P were: 20-30J: 7%; 30-40J: 16% ; 40-50J: 24%; 50-60J: 21%; 60-70J: 19%; 70-80J: 14%. In the group of "legally dependent" patients 20% were medical staff (16% nurses, 4% medical doctors), and 16% had academic professions; 19% reported an addiction disease of the parents (mostly of alcohol), 16% another psychiatric disease of the parents. 75% of the "legally" dependent patients suffered from depression, 40 % had performed suicidal trial(s), 53% have had a somatic disease before the intake of tramadol, 17% after the treatment of tramadol dependence. 69% suffered from pain before intake of tramadol (22% disc/ back, 15% megrim/ head, 5% tooth, maxillary sinus, 6% pancreas, 4% legs, 2 % abdomen, bile), 22% had no experience of pain before first intake of tramadol. 76% of the pain-patients were also ill with depression. Seizures were documented in 23% of all patients with tramadol dependence/withdrawal as cause.

Conclusion:

Pain, depression and pain, somatic diseases, previous addiction diseases, psychiatric family history, being a member of medical staff increase the risk to develop dependence to prescribed tramadol. Tramadol dependent patients show a high rate of suicidal trials and of seizures. Different therapies are under evaluation. Data will be discussed with respect to pathophysiological principles of analgesic and addiction effects of opioids.

Value and actuality of the prescription information for therapeutic drug monitoring of psychopharmaceuticals: a comparison with the medico-scientific evidence

Therapeutic drug monitoring (TDM) of psychopharmaceuticals, i.e., the assay of plasma concentrations, is a practical therapeutic application of pharmacokinetic principles in psychiatry. The prescription information (summary of product characteristics, SPC) is provided by pharmaceutical companies according to the requirements of regulatory authorities. The present study investigated the degree of agreement of German SPCs for 48 psychopharmaceuticals with the existing medico-scientific evidence in the area of TDM. For this aim, an empirical summary score of SPC content related to TDM (SPCC (TDM)) was calculated and compared with the level of recommendation of TDM (LOR) of the AGNP-TDM expert group consensus guidelines. Considerable disagreement was found between the information on TDM in SPCs and existing medico-scientific evidence, e.g., in the case of antidepressant and antipsychotic drugs. Even for well studied compounds, such as amitriptyline and clozapine, insufficient information on TDM is included in German SPCs. Small differences existed in the TDM-related information in SPCs of generic drugs with, however, much variance between Germany, Austria and Switzerland. Generally, it must be concluded that deficits exist in the preparation of German SPCs for psychopharmaceutical drugs with respect to empirical pharmacokinetic data, i.e., TDM-relevant information. It is recommended that SPCs of psychopharmaceuticals should be improved in terms of TDM-related information and that target plasma concentrations be adjusted according to the guidelines of the AGNP-TDM expert group. A higher level of good pharmacokinetic practice may be thus achieved.

Hyperhomocysteinemia as a new risk factor for brain shrinkage in patients with alcoholism

Chronic alcohol consumption can induce brain atrophy, whereby the exact mechanism of brain damage in alcoholics remains unknown. There is evidence that chronic alcoholism is associated with hyperhomocysteinemia. Homocysteine is an excitatory amino acid which markedly enhances the vulnerability of neuronal cells to excitotoxic and oxidative injury in vitro and in vivo. The present volumetric magnetic resonance imaging study included 52 chronic alcoholics and 30 non-drinking healthy controls. Patients were active drinkers and had an established diagnosis of alcohol dependence. We investigated the influence of different variables on the hippocampal volume of patients suffering from chronic alcoholism. We observed that pathological raised levels of plasma homocysteine showed the most significant correlation to hippocampal volume reduction (P<0.001, multiple regression analysis). Raised plasma levels of homocysteine are associated with hippocampal (brain) atrophy in alcoholism.

Lack of association between hippocampal volume reduction and first-onset alcohol withdrawal seizure. A volumetric MRI study

AIMS AND METHODS

Magnetic resonance imaging (MRI) of the hippocampus has been extensively studied in both neurological and psychiatric disorders. Furthermore, hippocampal volume reductions on MRI have been reported in patients with chronic alcoholism. The present volumetric MRI study was undertaken to determine whether an association exists between hippocampal volume reduction and first-onset alcohol withdrawal seizure. Until recently, no data as to whether hippocampal volume reductions in alcoholics might serve as a predictor of withdrawal seizures were available.

RESULTS

We found the average hippocampal volumes measured by high resolution MRI to be significantly reduced in 52 alcoholics compared with 30 healthy controls. Besides a decrease of hippocampal volume in patients with chronic alcoholism, we could not find any significant correlation between the occurrence of seizures during alcohol withdrawal and the amount of hippocampal volume reduction in these patients.

CONCLUSIONS

Thus, the alcoholism-related atrophy within the hippocampal formation in patients suffering from chronic alcoholism does not seem to be the source of convulsive activity in these patients. Neither does the amount of atrophy allow the occurrence of first-onset withdrawal seizures to be predicted.

Comorbid anxiety and affective disorder in alcohol-dependent patients seeking treatment: the first Multicentre Study in Germany

The goals of this study were to describe demographic variables, drinking history, and the 6-month prevalence of Axis I comorbidity among alcohol-dependent subjects in GERMANY: The variables: amount of alcohol consumption, age at onset of the first alcohol consumed, age at onset of daily alcohol consumption, age at onset of withdrawal symptoms and number of detoxifications were related to the different comorbid disorders and gender. In this study, 556 patients from 25 alcohol treatment centres were enrolled between 1 January 1999 and 30 April 1999. After a minimum of 10 days of sobriety patients who fulfilled ICD-10 and DSM-IV criteria of alcohol dependence were interviewed for data collection using the Mini-DIPS (German version of the Anxiety Disorders Interview Schedule) and a standardized psychosocial interview. The 6-month prevalence of comorbid Axis I disorders was 53.1%. Among the patients with comorbidity, affective and anxiety disorders were most frequent. Comorbid stress disorder was associated with an early start of drinking, an early beginning of withdrawal symptoms, highest number of detoxifications, and the highest amount of alcohol consumed. Female patients with anxiety disorder consumed more alcohol and started earlier than females without this comorbid disorder. The data do not answer the question of the pathogenesis of comorbid disorders and alcoholism, but indicate that stress disorders in alcoholic patients and anxiety disorders in female alcoholics influence the course and severity of alcoholism.

Injection of apomorphine--a test to predict individual different dopaminergic sensitivity?

Male rats, treated with apomorphine (APO: 2mg/kg s.c.) in an Animex-Motility-Meter, showed individually different motility patterns, each expressed by oral stereotyped behaviour and enhanced locomotor activation reproducible in a second test 4 days later. One group of the rats showed stereotyped sniffing with an increased locomotor activation, S(L,G)-rats, being predominantly "mesolimbic active" rats. The other groups could be classified as mainly licking or gnawing rats, L(S,G)-rats or G(L,S)-rats, with less increase of locomotor activation, resembling predominantly "nigrostriatal active" rats. The G(L,S)-rats seemed to be mostly "nigrostriatal active". In this study the different types of rats were treated with neuroleptic drugs in presence of APO. Haloperidol (HAL; 0.2 and 0.4 mg/kg i.p.) had a clear dose dependent antagonizing effect on APO-induced stereotypies and locomotor activity: a pronounced effect on the L(S,G)- and G(L,S)-rats and less on S(L,G)-rats. In contrast, clozapine (CLO; 10 and 15 mg/kg i.p.) did not antagonize the stereotyped behaviour in the rats tested but showed a characteristic shift in the S(L,G)- and G(L,S)-rats: the predominant stereotypy of these rats, quantified by scoring, changed to licking. In the L(S,G)-rats the predominant licking stereotypy was not changed and the locomotor activity, which was completely antagonized in the S(L,G)- and G(L,S)-rats at both CLO-doses, was affected by 15 mg/kg, only. Furthermore, after the combined treatment with APO and HAL or APO and CLO these rat-types also differed in their amount of ACTH and corticosterone release. DA-1/DA2 and/or DA-1/DA3 receptor mechanisms may be involved in these individually different motility patterns and endocrine reactions. In summary, pretesting of rats with APO and measuring the motility and endocrine parameters may give us information on a preexisting different sensitivity of individuals to react to DAergic stimulation.

Morphine-induced hyperactivity in rats--a rebound effect?

The behavioural nature of the delayed hyperactivity induced by systemic administration of morphine was studied in rats. Different components of motility induced by morphine with or without naloxone or haloperidol at different times were analyzed by observation and quantified by an Opto-Varimex-3 Activity Meter. By this automatic recording system motility was discriminated into horizontal and two different vertical components and the total distance run by each of the rats was quantified by a computer program. Simultaneously the running pattern was recorded by a XY-plotter. By means of these recordings, three subsequent phases of behaviour could be recorded after morphine (15 mg/kg i.p.): 1. a depressed phase (akinesia) lasting 1.5-2 h, followed, 2. by an intermediate phase for 1-1.5 h, still dominated by akinesia but interrupted by sudden bursts of hyperactivity. Finally, 3. a hyperactivity phase lasted for 1.5-2 h, characterized by an equal enhancement of locomotor activity and stereotypy. After 30 mg/kg of morphine the hyperactivity was predominantly characterized by locomotor activity and stereotypy and rearing were less prominent than after the smaller dose. Naloxone (2 mg/kg i.p.) given at the beginning of the hyperactivity phase significantly antagonized rearing but not other motility parameters. However, coadministration of naloxone (2 mg/kg i.p.) simultaneously with morphine (15 mg/kg) clearly antagonized akinesia and completely prevented the development of the delayed hyperactivity. Haloperidol (0.2 mg/kg i.p.) at the beginning of the hyperactivity phase clearly antagonized all of the motility parameters seen during this phase.(ABSTRACT TRUNCATED AT 250 WORDS)