Anticholinergic drug abuse: a common problem?

Is SARS-CoV-2 a Risk Factor of Bipolar Disorder?-A Narrative Review

For 2.5 years we have been facing the coronavirus disease (COVID-19) and its health, social and economic effects. One of its known consequences is the development of neuropsychiatric diseases such as anxiety and depression. However, reports of manic episodes related to COVID-19 have emerged. Mania is an integral part of the debilitating illness-bipolar disorder (BD). Due to its devastating effects, it is therefore important to establish whether SARS-CoV-2 infection is a causative agent of this severe mental disorder. In this narrative review, we discuss the similarities between the disorders caused by SARS-CoV-2 and those found in patients with BD, and we also try to answer the question of whether SARS-CoV-2 infection may be a risk factor for the development of this affective disorder. Our observation shows that disorders in COVID-19 showing the greatest similarity to those in BD are cytokine disorders, tryptophan metabolism, sleep disorders and structural changes in the central nervous system (CNS). These changes, especially intensified in severe infections, may be a trigger for the development of BD in particularly vulnerable people, e.g., with family history, or cause an acute episode in patients with a pre-existing BD.

Misuse of Anticholinergic Medications: A Systematic Review

(1) Background: Over the last decade, misuse and diversion of medications has appeared to be increasingly concerning phenomena, including a range of different molecules. As current knowledge on the abuse of centrally acting anticholinergics is limited, the aim of the present study is to review the relevant published data, focusing on the following molecules: benztropine, biperiden, scopolamine, orphenadrine, and benzhexol/trihexyphenidyl (THP). (2) Methods: A systematic literature review was carried out using Pubmed, Scopus, and Web of Science databases following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Research methods were registered on PROSPERO (CRD42021257293). (3) Results: A total of 48 articles, including case reports, surveys, and retrospective case series analyses, were included. Most articles focused on benzhexol/THP (n = 25), and benztropine (n = 4). The routes of administration were mostly oral, and macrodoses together concomitant illicit drugs, e.g., cocaine, have been recorded. Toxidromes included both physical (e.g., tachycardia, tachypnoea, dilatated pupils, dry skin, urinary retention, ataxia, etc.) and psychiatric symptoms (e.g., anxiety, agitation, delirium, etc.). Fatal outcomes were very rare but reported. (4) Conclusion: Results from the present study show that anticholinergic misusing issues are both widespread worldwide and popular. Considering the potential adverse effects associated, healthcare professionals should be vigilant and monitor eventual misusing issues.

Amitriptyline Dependence and Its Associations: A Case Report and Literature Review

Amitriptyline, the second antidepressant invented next to imipramine, is indicated in many psychiatric conditions as well as for some organic disorders. The drug acts by increasing the availability of monoamines in the central nervous system postsynaptic clefts. Amitriptyline has long been suspected for abusive potential based on a few case reports, and the reports add evidence in favor of the hypothesis. This case report brings such material to the arena of evidence and discusses the probable mechanisms by which patients turn to abusing and be addicted to the drug. The article also argues matters associated with drug dispensing that might raise the risk of misuse of the drug, especially in countries where strict legislation for accessibility of prescribed drugs is not in practice.

The pattern of substance use disorder in the United Arab Emirates in 2015: results of a National Rehabilitation Centre cohort study

Background

Substance use disorder (SUD) is a global problem with no boundaries, which also afflicts individuals from countries of the Arabian Peninsula. Data from this region is limited. In an effort to develop targeted prevention and intervention initiatives in the United Arab Emirates (UAE), it was necessary to identify the nature of substance use by describing the characteristics of those using different substances. Consequently, this study in the UAE was conceived to describe the pattern of SUD in a first-ever cohort that was systematically recruited from the country’s National Rehabilitation Centre (NRC) in Abu Dhabi.

Methods

Two hundred and fifty male patients were recruited from the NRC. Information on substance use was collected using a questionnaire that was completed at an interview with patients who consented to participate. The questionnaire was based on information that the study was designed to capture. It was reviewed by members of institutional ethics committees and approved prior to use. Two hundred and fifty male subjects from the Emirates Family Registry (EFR) were used as a comparison group.

Results

In the cohort studied, SUD correlated with smoking and marital status. Poly-substance users formed the majority of the cohort (84.4 %) with various combinations of substances identified across different age groups. Opioid and alcohol were the most common substances used. The use of pharmaceutical opioids, primarily Tramadol (67.2 % of opioid users), was higher among the youngest age group studied (<30 years old), while older opioid users (≥30 years old) commonly used illicit opioids (Heroin). The use of prescribed medication for non-medical use also included Pregabalin (mean of 8.3 capsules ± 0.5 per day), Procyclidin (6.1 tablets + 0.6 per day) and Carisoprodol (4.2 tablets ± 0.4 per day) and was again highest in the age group below 30 years.

Conclusion

This 2015 study highlights the importance of examining the pattern of poly-substance use in a population in order to develop targeted prevention programs to arrest the prevailing trends. It has drawn attention to the rise in use of prescription medication in the UAE, in particular among younger patients (<30 years), and continuing use of illicit opioid amongst males above 30 years. Specific prevention and intervention strategies, targeting differences between these distinct demographic profiles will capture a large subset of sufferers.

Benefits and limits of anticholinergic use in schizophrenia: focusing on its effect on cognitive function

All currently available antipsychotic drugs are the dopamine D2 receptor antagonists and are capable of producing extrapyramidal side-effects (EPS). Anticholinergic drugs are primarily used to treat EPS or prevent EPS induced by antipsychotics in the treatment of psychosis and schizophrenia. However, they can cause a variety of distressing peripheral side-effects (e.g. dry mouth, urinary disturbances, and constipation) and central adverse effects (e.g. cognitive impairment, worsening of tardive dyskinesia, and delirium). Disturbances in cognitive abilities are cardinal features of schizophrenia from its earliest phases and account for much of the functional disability associated with the illness. It is likely that long-term concomitant administration of anticholinergics exacerbates the underlying cognitive impairment in patients with schizophrenia and subsequently affects patients' quality of life. Thus, current treatment guidelines for schizophrenia generally do not recommend the prophylactic and long-term use of anticholinergics. However, the high use of long-term anticholinergic drugs with antipsychotics has been identified as an important issue in the treatment of schizophrenia in several countries. To assess the benefits and limits of anticholinergic use in psychosis and schizophrenia, this article will provide a brief review of the pharmacology and clinical profiles of anticholinergic drugs and will focus on their effects on cognitive function in schizophrenia, particularly during the course of the early phase of the illness. In addition, we will address the effects of discontinuation of anticholinergics on cognitive function in patients with schizophrenia and provide a strategy for adjunctive anticholinergic use in patients treated with long-acting injectable antipsychotics.

The role of antihistaminic effects in the misuse of quetiapine: a case report and review of the literature

Recent case reports and case series suggest that the atypical antipsychotic quetiapine has the potential for misuse. This includes drug-seeking behaviors motivated by quetiapine as well as inappropriate (intranasal or intravenous) administration. We present an additional case of quetiapine misuse and review other published cases. In general, quetiapine misuse is associated with prior CNS depressant use and is more common in forensic settings. The mechanism of reinforcement for this misuse is unknown, but we hypothesize that it is related to quetiapine's pharmacological profile as an antihistamine with a relative low affinity for dopamine receptors. The risks to individuals and society of exaggerating/simulating symptoms to obtain high-dose quetiapine in the absence of a clinical indication are discussed. This includes the unwelcome possibility of restricting access to this effective medication.

Amitriptyline Abuse and Misuse

Deaths related to amitriptyline toxicity are relatively common and are typically related to suicidal overdose. A less well-recognized situation of amitriptyline intoxication occurs when the drug is abused for its euphorigenic effects. An amitriptyline-related death due to a mixed drug intoxication is presented. Death investigation revealed that the death was accidental rather than suicidal. The case serves to remind forensic investigators that not all amitriptyline overdose deaths represent suicides. A segment of the population is known to abuse amitriptyline.

Development of a screening method for the most commonly abused anticholinergic drugs in Jordan; trihexyphenidyl, procyclidine and biperiden

A sensitive and rapid method for the simultaneous determination of three commonly abused anticholinergic drugs in Jordan; trihexyphenidyl, procyclidine, and biperiden in plasma and urine has been developed using solid phase extraction and GC-MS. Linearity was established from therapeutic to fatal concentrations of the three drugs; 5-300 ng/ml in plasma, with correlation coefficient r(2) > or = 0.9978 and 10-800 ng/ml in urine r(2) > or = 0.9993. Recoveries were in the range of 86-92% and intra-day and inter-day relative standard deviations (n = 6) were in the range of 6.6-10.3% for the three drugs at three different concentrations in plasma and urine. The base peak m/z 98 for trihexyphenidyl, m/z 84 for procyclidine, and m/z 98 and 218 for biperiden, and m/z 339 for papaverine (internal standard) were monitored at selective ion monitoring; their retention times were 8.10, 8.67 and 8.92 min, respectively, and 14.79 min for the internal standard with analysis time of 16.75 min. The limit of detection of 0.5 ng/ml was attained for trihexyphenidyl and procyclidine, while for biperiden 2.0 and 1.0 ng/ml in spiked plasma and urine, respectively. This method has been applied to forensic and authentic samples taken from abuser and patients using these drugs. The method will offer the clinicians and the legal authority the right diagnosis regarding the anticholinergic involved in any case of abuse with less than 1 h per sample (plasma or urine) from the time of receiving.

Détournement d’usage du trihexyphénidyle (Artane®, Parkinane®) : tendances récentes

Recent observations suggest the existence of trihexyphenidyl abuse linked to its hallucinogenic and euphoric effects. In order to determine the importance of this practice and the characteristics of those involved, a study based on data from the Provence-Alpes-Côte-d'Azur and the Corsica health reimbursement system was carried out. Individuals from these regions affiliated to the French health reimbursement system who had a prescription for trihexyphenidyl (Artane, Parkinane) reimbursed between January 1, 2001, and February 15, 2001, were selected. The delivery of prescriptions was monitored over a 9-month period. In total, 3028 subjects were selected. A subgroup comprising 2.1% of subjects with deviant behaviour was identified by factorial analysis and compared with the subgroup without deviant behaviour. The subjects with deviant behaviour were young and mostly male. The dosage of trihexyphenidyl was higher in these subjects (28 mg/day versus 7 mg/day) and a greater proportion used benzodiazepine and high-dose buprenorphine compared with those without deviant behaviour. The number of prescriptions delivered was higher (23.0 versus 7.7) as well the number of different physicians (4.9 versus 1.5) and pharmacies (5.0 versus 1.3) for those subjects with deviant behaviour. This study confirms the abuse and dependence potential associated with trihexyphenidyl use and the need to increase the supervision of this drug.

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

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

Investigating the presence of a common drug of abuse (benzhexol) in hair; the Jordanian experience

The analysis of hair is now accepted as a recognised alternative method for the determination of drug misuse. It has several advantages over the biological fluids; blood and urine, including collection of information regarding long-term drug use and determination of compliance with treatment programmes. In Jordan, the abuse of Artane (benzhexol hydrochloride) has been recognised as the most commonly abused drug among Jordanian youths. Hair samples were collected from nine patients (Male 25-55 years, M=39.11, SD=10.53, CV=26.93%). Samples were analysed for the presence of benzhexol and the toxicological analysis revealed the presence of benzhexol in all samples and its concentration ranged from 0.104 to 7.81 ng/mg hair. Solid phase extraction and GC-MS on selective ion storage (SIS) were used for extraction and detection of the drug with papaverine as external standard. The mass detector was operated at selective ion storage (SIS) to monitor the m/z of 98 and 218 for benzhexol and m/z 339 and 324 for the papaverine. The retention times of benzhexol and papaverine were 6.77 and 12.48 min, respectively. The method was linear in the range of 0.5 to 40 ng/mg hair, with a mean coefficient of determination (R2=0.9982). The limit of detection was 0.04 ng/mg. The intra- and inter-day variations were 3.85% and 3.35%. Recovery was found to be above 90%.

Potencial de abuso de drogas dopaminérgicas

Os autores fazem uma revisão do potencial de abuso de substâncias que atuam no sistema dopaminérgico, analisando possíveis etiologias e alertando para a necessidade da prescrição cautelosa dessas substâncias, sobretudo em pacientes com antecedente de abuso de outras substâncias psicoativas.

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

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

Effects of antimuscarinic antiparkinsonian drugs on brightness discrimination performance in rats

Biperiden (BPR) and trihexyphenidyl (THP), the current antimuscarinic drugs of choice in the management of parkinsonism, have been shown to exert anticonvulsant effects induced by poisoning by the organophosphorus compound soman. The present study was undertaken to evaluate the effects of these drugs on performance of a simple light-intensity discrimination task in rats under a tandem schedule of fixed-ratio (FR) reward/ differential-reinforcement-of-low-rate (DRL) nonreward contingencies, for water reinforcement in 2-h experimental sessions. Both BPR (0.125-2.0 mg/kg, SC) and THP (0.25-8.0 mg/kg, SC) in general decreased overall reinforcement rates in a similar dose dependent and parallel manner, concurrent with increased overall nonreinforced responses in an inverted U-shaped dose-response relationship. Lower doses of BPR (0.125-0.5 mg/kg) and and THP (0.25-2.0 mg/kg) produced a moderate reduction in reinforcement (> or = 50% of baseline controls), which was correlated well with increases in nonreinforced responses emitted, whereas, higher doses of BPR (> 0.5 mg/kg) and TPH (> or = 2.0 mg/kg) markedly decreased reinforcements, which mainly resulted from the pausing of responding in the presence of stereotyped behavior. The behavioral disruption induced by BPR was much more rapid than that induced by THP. The ED50 values (0.6 mg/kg vs. 1.3 mg/kg, respectively) and parallel dose-effect curves suggest that these drugs have similar efficacy, and that BPR is about twice as potent as THP, a ranking that corresponds with their binding affinity at M-1 muscarinic acetylcholine receptors in rat cerebral cortex. Based on the similarity between the anticonvulsant doses of these drugs and the maximal doses that in this study did not disrupt operant responses (0.125 mg/kg vs. 0.25 mg/kg, respectively), it is suggested that both drugs may be useful in protection against seizures produced by the cholinesterase inhibitor soman. Overall, these results suggest that this multiple schedule operant contingency may have promise as a behavioral model to identify the therapeutic or toxic potentials of centrally acting antimuscarinic antiparkinsonian drugs based on their congnitive side effects.

Long-term depot antipsychotics. A risk-benefit assessment

The main advantage of depot antipsychotic medication is that it overcomes the problem of covert noncompliance. Patients receiving depot treatment who refuse their injection or fail to receive it for any other reason can be immediately identified and appropriate action taken. In the context of a carefully monitored management programme, depot treatment can have a major impact on compliance and, consequently, the risk of relapse and hospitalisation can be reduced. Another major advantage is that the considerable individual variation in bioavailability and metabolism with oral antipsychotic drugs is markedly reduced with depot treatment. A better correlation between the dose administered and the concentration of medication found in blood or plasma is achieved with depot treatment, and thus, the clinician has greater control over the amount of drug being delivered to the site of activity. A further benefit of depot treatment is the achievement of stable plasma concentrations over long periods, allowing injections to be given every few weeks. However, this also represents a potential disadvantage in that there is a lack of flexibility of administration. Should adverse effects develop, the drug cannot be rapidly withdrawn. Furthermore, adjustment to the optimal dose becomes a long term strategy. The controlled studies of low dose maintenance therapy with depot treatment suggest that it can take months or years for the consequences of dose reduction, in terms of increased risk of relapse, to become manifest. When weighing up the risks and benefits of long term antipsychotic treatment for the individual patient with schizophrenia, the clinician must take into account the nature, severity and frequency of past relapses, and the degree of distress and disability related to any adverse effects. However, the clinical decision to prescribe either a depot or an oral antipsychotic for maintenance treatment will probably rest largely on an assessment of the risk of poor compliance in the particular patient. There is no convincing evidence that the range, nature or severity of adverse effects reported with depot treatment is significantly different from that seen with oral treatment, and depot treatment has been shown to be as good or better than oral medication in preventing or postponing relapse. Furthermore, when adjusting the dose or frequency of depot injection, to improve control of psychotic symptoms or reduce adverse effects, the clinician can be confident that the dose prescribed is the dose being received by the patient.

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

OBJECTIVE

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

DESIGN

A between subjects design was employed.

SUBJECTS

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

MEASUREMENTS

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

RESULTS

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

CONCLUSIONS

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

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

Theorists have extrapolated the cholinergic supersensitivity theory of affective disorder from a convincing and broad spectrum of clinical observation and research. This hypothesis is tested using a neuroendocrine probe approach with the challenge drug pyridostigmine, an indirect cholinergic agent thought to release growth hormone (GH) by decreasing inhibitory somatostatin tone. The consequent increments in plasma GH were considered to reflect central acetylcholine responsivity. Fifty-four volunteers were tested: 27 DSM-III-R major depressives (18 women and 9 men) and 27 age- and sex-matched healthy controls. Subjects were cannulated at 9.00 h following an overnight fast and two baseline samples were taken at 15 min intervals. Pyridostigmine 120 mg was administered orally and thereafter samples were taken at the time points +60, +90, +120 and +180 min. GH responses were significantly greater in depressives than controls and this effect was more marked for men than women. These results support the proposal that muscarinic upregulation and/or supersensitivity is associated with depression.

Muscarinic receptor subclassification and G-proteins: significance for lithium action in affective disorders and for the treatment of the extrapyramidal side effects of neuroleptics

The classification of muscarinic receptors into M1 and M2 subtypes and the involvement of guanine nucleotide binding proteins (G-proteins) as major mediators of receptor information transduction in the cholinergic and other neurotransmitter systems have prompted us to undertake studies both at receptor and postreceptor levels that may shed light on the importance of these new findings to the pharmacotherapy of manic-depressive illness and of extrapyramidal syndromes. We searched for patterns of muscarinic selectivity among the commonly used anticholinergics (biperiden, procyclidine, trihexyphenidyl, benztropine, and methixen) through radioligand receptor studies in various rat tissues. The drugs showed a range of selectivity, from the totally nonselective methixen to the highly M1-selective biperiden. Sinus arrhythmia measurements were undertaken in psychiatric patients treated with different antiparkinsonian anticholinergics. The extent of sinus arrhythmia suppression was inversely correlated with the degree of M1 selectivity of the drugs used, advocating the use of M1-selective antiparkinsonian anticholinergics like biperiden in the treatment of extrapyramidal side effects. The implications of muscarinic receptor subclassification were further extended to include postreceptor phenomena. We have directly studied G-protein function by measuring cholinergic agonist-induced increases in guanosine triphosphate (GTP) binding to these proteins. This cholinergic agonistic effect was shown to be exerted by G-proteins other than Gs (the adenylate cyclase stimulatory G-protein), i.e., Gi (the adenylate cyclase inhibitory G-protein) or Gp [the G-protein activating phosphatidylinositol (PI) turnover], as ribosylation by pertussis toxin abolished this cholinergic effect, whereas it was unaffected by cholera toxin. Pertussis toxin-blockable, carbamylcholine-induced increases in GTP binding capacity were found to be mediated through M1 muscarinic receptors, as M1-selective antagonists were 100-fold more effective than M2 selective antagonists in blocking carbamylcholine effects. Moreover, carbamylcholine effect was exclusively detected in tissues predominantly populated by M1 receptors. Our results thus suggest that carbamylcholine-induced increases in GTP binding are exerted through M1 receptors interacting with Gp. At therapeutically efficacious concentrations, lithium completely blocked carbamylcholine-induced increases in GTP binding capacity in both in vitro and in vivo experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

Prescribing for the long-term mentally ill. A study of treatment practices

A survey of the drug treatment of long-term mentally ill users of a district psychiatric service is described. The appropriateness of prescriptions was assessed against standard criteria after a detailed clinical review of each patient. Overprescribing, particularly of sedative/hypnotic and of anticholinergic and antipsychotic drugs, was common. Junior psychiatrists and general practitioners are in need of improved training in the management of chronic psychiatric illness: a review of treatment practices might be an appropriate medium for this training.

Cyproheptadine dependence associated with an atypical somatoform disorder

A case is described of cyproheptadine dependence in a woman with a persistent belief that she was too thin, and diagnosed with an atypical somatoform disorder. The cyproheptadine was initially prescribed to promote weight gain but its continued use seemed related to other psychological and/or pharmacological effects. Cognitive impairment was present, possibly as a result of the longstanding cyproheptadine abuse. There have been no previous reports of cyproheptadine dependence or of CNS toxicity from its long-term use.

Simple and rapid GLC method for the determination of orphenadrine in human plasma

A rapid and specific method has been developed for the determination of orphenadrine concentration in plasma. It involves a one-step sample preparation using n-hexane/isopropyl alcohol (98:2) extraction, and analysis by gas chromatography on a wide bore capillary column using nitrogen/phosphorus detection. This procedure considerably simplifies previously reported assays and is specific and sensitive enough for the determination of orphenadrine in plasma of patients on chronic therapy.

An experimental evaluation of the euphoric properties of antiparkinson drugs on psychotic patients

Seven psychotic inpatients (two women and five men) aged between 18 and 74 years, treated with neuroleptic and antiparkinson drugs, participated in a double-blind study with 1/3 DDD (Defined Daily Dose) of procyclidine, orphenadrine, or trihexyphenidyl hydrochloride against placebo. Euphoric effects were scored on a self-rating scale and extrapyramidal side-effects on the Simpson-Angus rating scale at drug administration and 1, 3 and 6 h thereafter. With regard to euphoric effect, there was a significant (P less than 0.02) difference between start and end point (0 and 6 h) for placebo but not for the active antiparkinson drugs. There was no significant difference in extrapyramidal side-effects. No preference of drug was found, and it was not possible to recognize the patient's own drug among the tested drugs. Side-effects from the antiparkinson drugs were also measured prior to the administration. Five patients did not return to their earlier antiparkinson drugs after the study.

Cholinergic mechanisms in affective disorders. Future directions for investigation

Advances in clinical and basic research methodology combined with clearly articulated concepts create new opportunities for researching the roles of cholinergic mechanisms in the pathophysiology of affective disorders. Areas for study include: roles of cholinergic mechanisms in mediating effects of stress and cholinergic mechanisms linking the pathophysiologies of affective and panic disorders, use of pharmacologic agents to produce cholinergic system supersensitivity in modeling biologic aspects of affective illness, use of multigenerational intrapedigree studies of cholinergic markers associated with affective disease, research into the neurobiology of lithium and ECT as they pertain to muscarinic cholinergic mechanisms, study of the interrelationship of sodium, calcium and lithium ion metabolism and their relationship to cholinergic-monoaminergic interaction, the development of brain imaging strategies and techniques, e.g., positron emission tomography (PET), to measure changes in cholinergic receptor density and affinity as a function of clinical state, identification and validation of a peripheral model of the central muscarinic receptor, study of the pharmacology of abusable substances and its relationship to mechanisms regulating mood, affect, psychomotor function and other variables related to the affective disorders, and development of in vitro and in vivo models useful in studying the physiology and biochemistry of the interaction of cholinergic and monoaminergic neurons. These models may allow us to bridge the traditional cholinergic and monoamine hypotheses of affective disorders.

Cholinergic mechanisms in depression

Evidence supporting a cholinergic hypothesis of depression is presented. First, cholinergic overdrive produces behavioral, neuroendocrine, and polysomnographic features of melancholia, and melancholics exhibit state-independent supersensitivity to cholinergic overdrive. Drugs inducing up-regulation and supersensitivity of cholinergic systems produce behavioral, polysomnographic, and neuroendocrine effects of melancholia when withdrawn. These observations also implicate cholinergic system supersensitivity as a factor in the pathophysiology of certain affective disorders. Cholinergic and monoaminergic mechanisms reciprocally regulate drive-reduction, and substances of abuse either activate monoaminergic networks or antagonize cholinergic systems. These points are consistent with the hypothesis that dynamic interaction between cholinergic and monoaminergic systems is involved in the regulation of mood and affect. Finally, antimuscarinic agents have antidepressant effects. Thus, the hypothesis that supersensitivity of cholinergic systems is involved in the pathophysiology of affective disorders is supported by several lines of evidence. This evidence is reviewed; directions for future research and promising methods of investigation are discussed.

Pathophysiology of "cholinoceptor supersensitivity" in affective disorders

Phenomenological and physiological variables demonstrate supersensitive changes to cholinergic challenge in affective disorder subjects. Theorists generally assume the primary defect is the postsynaptic muscarinic receptor. However, in addition to defectiveness or up-regulation of this receptor, the appearance of postsynaptic "cholinoceptor supersensitivity" can result from abnormal presynaptic mechanisms, membrane "pathology," derangement of intrasystolic mechanisms that amplify effects of receptor-agonist coupling, or aberrant cholinergic-monoaminergic interaction. This article discusses abnormalities of the postsynaptic receptor, regulation of postsynaptic receptor density, the presynaptic muscarinic receptor, and other mechanisms regulating the release of acetylcholine, membrane dynamics, and "cascade" mechanisms-specifically the phosphatidylinositol (PI) cycle, Ca2+ mobilization, and cyclic guanosine monophosphate (GMP) generation-as causes of cholinergic system "supersensitivity." It is suggested that an approach to the topic emphasizing site of abnormality will encourage greater clarity of thought in the study of the cholinergic component of the pathophysiology of affective illness.