Differences between anhedonic and normally hedonic depressive states

Severe anhedonia among adolescents with bipolar disorder is common and associated with increased psychiatric symptom burden

BACKGROUND

Anhedonia, a deficit in the ability to experience pleasure, is a cardinal symptom of major depressive episodes. In contrast to adolescent major depressive disorder, there is limited research examining anhedonia in the context of depression among adolescents with bipolar disorder (BD). We therefore examined clinical characteristics of anhedonia in a large sample of adolescents with BD.

METHODS

Participants were 197 adolescents, aged 13-20 years old, with BD type I, II or not otherwise specified. Diagnoses were determined using a semi-structured interview. Anhedonia severity was rated from one to six on the Depression Rating Scale (DRS). Adolescents were divided into "severe" and "non-severe" anhedonia groups based on the DRS item scoring. The association of anhedonia with clinical and demographic variables was evaluated in univariate analyses followed by logistic regression analyses for variables with p ≤ 0.1.

RESULTS

Threshold anhedonia was evident among 90.9% during their most severe depressive episode. Significant factors associated with severe most severe lifetime anhedonia ("lifetime anhedonia") included: female sex, lifetime history of self-injurious behavior, physical abuse, affective lability, higher lifetime depression severity, comorbid anxiety disorders, family history of ADHD, and second-generation antipsychotic use. In regression analyses, severe lifetime anhedonia was independently associated with female sex, comorbid anxiety disorders, most severe lifetime mania severity, and lifetime second-generation antipsychotic use.

CONCLUSION

The vast majority of adolescents with BD experience anhedonia. More severe anhedonia is associated with indicators of greater illness severity. Future research is warranted to evaluate the neurobiological underpinnings of anhedonia among adolescents with BD.

Measures of anhedonia and hedonic responses to sucrose in depressive and schizophrenic patients in comparison with healthy subjects

Anhedonia may be considered as a transnosological feature of depression and schizophrenia. The aim of the present study was to assess hedonic responses to sucrose solutions and sweet taste perception threshold in patients with major depression and in schizophrenic patients in comparison with healthy subjects (matched for age and gender with depressive patients), and to compare these responses to evaluations by the Physical and Social Anhedonia scale of Chapman and the Pleasure Scale of Fawcett, generally used to quantify anhedonia. Hedonic responses to sucrose solutions were similar in patients with major depression (n = 20), schizophrenia (n = 20), and healthy controls (n = 20). Sweet taste perception threshold was significantly higher in depressive patients than in controls. Hedonic response to sucrose was inversely correlated with physical Anhedonia Scores and sweet taste perception threshold with Pleasure Scale scores. Measures of hedonia/anhedonia were not related with the intensity of depression or anxiety as measured by the Montgomery-Asberg Depression Rating Scale (MADRS) and Hamilton Anxiety Scale, respectively. In 11 depressed patients hospitalised for 17 to 33 days, neither hedonic ratings to sucrose solutions, sweet taste perception threshold, Physical, Social Anhedonia scores nor Pleasure Scale scores were modified in spite of substantial decrease in MADRS or Hamilton Anxiety scores. Hedonic responses to sucrose solutions and sweet taste perception threshold may be used as complementary evaluation to quantify anhedonia.

A Model of Chronic Temporal Lobe Epilepsy Presenting Constantly Rhythmic and Robust Spontaneous Seizures, Co-morbidities and Hippocampal Neuropathology

Many animal prototypes illustrating the various attributes of human temporal lobe epilepsy (TLE) are available. These models have been invaluable for comprehending multiple epileptogenic processes, modifications in electrophysiological properties, neuronal hyperexcitability, neurodegeneration, neural plasticity, and chronic neuroinflammation in TLE. Some models have also uncovered the efficacy of new antiepileptic drugs or biologics for alleviating epileptogenesis, cognitive impairments, or spontaneous recurrent seizures (SRS). Nonetheless, the suitability of these models for testing candidate therapeutics in conditions such as chronic TLE is debatable because of a lower frequency of SRS and an inconsistent pattern of SRS activity over days, weeks or months. An ideal prototype of chronic TLE for investigating novel therapeutics would need to display a large number of SRS with a dependable frequency and severity and related co-morbidities. This study presents a new kainic acid (KA) model of chronic TLE generated through induction of status epilepticus (SE) in 6-8 weeks old male F344 rats. A rigorous characterization in the chronic epilepsy period validated that the animal prototype mimicked the most salient features of robust chronic TLE. Animals displayed a constant frequency and intensity of SRS across weeks and months in the 5th and 6th month after SE, as well as cognitive and mood impairments. Moreover, SRS frequency displayed a rhythmic pattern with 24-hour periodicity and a consistently higher number of SRS in the daylight period. Besides, the model showed many neuropathological features of chronic TLE, which include a partial loss of inhibitory interneurons, reduced neurogenesis with persistent aberrant migration of newly born neurons, chronic neuroinflammation typified by hypertrophied astrocytes and rod-shaped microglia, and a significant aberrant mossy fiber sprouting in the hippocampus. This consistent chronic seizure model is ideal for investigating the efficacy of various antiepileptic drugs and biologics as well as understanding multiple pathophysiological mechanisms underlying chronic epilepsy.

Cortico-Striatal-Thalamic Loop Circuits of the Orbitofrontal Cortex: Promising Therapeutic Targets in Psychiatric Illness

Corticostriatal circuits through the orbitofrontal cortex (OFC) play key roles in complex human behaviors such as evaluation, affect regulation and reward-based decision-making. Importantly, the medial and lateral OFC (mOFC and lOFC) circuits have functionally and anatomically distinct connectivity profiles which differentially contribute to the various aspects of goal-directed behavior. OFC corticostriatal circuits have been consistently implicated across a wide range of psychiatric disorders, including major depressive disorder (MDD), obsessive compulsive disorder (OCD), and substance use disorders (SUDs). Furthermore, psychiatric disorders related to OFC corticostriatal dysfunction can be addressed via conventional and novel neurostimulatory techniques, including deep brain stimulation (DBS), electroconvulsive therapy (ECT), repetitive transcranial magnetic stimulation (rTMS), and transcranial direct current stimulation (tDCS). Such techniques elicit changes in OFC corticostriatal activity, resulting in changes in clinical symptomatology. Here we review the available literature regarding how disturbances in mOFC and lOFC corticostriatal functioning may lead to psychiatric symptomatology in the aforementioned disorders, and how psychiatric treatments may exert their therapeutic effect by rectifying abnormal OFC corticostriatal activity. First, we review the role of OFC corticostriatal circuits in reward-guided learning, decision-making, affect regulation and reappraisal. Second, we discuss the role of OFC corticostriatal circuit dysfunction across a wide range of psychiatric disorders. Third, we review available evidence that the therapeutic mechanisms of various neuromodulation techniques may directly involve rectifying abnormal activity in mOFC and lOFC corticostriatal circuits. Finally, we examine the potential of future applications of therapeutic brain stimulation targeted at OFC circuitry; specifically, the role of OFC brain stimulation in the growing field of individually-tailored therapies and personalized medicine in psychiatry.

Reward Processing, Neuroeconomics, and Psychopathology

Abnormal reward processing is a prominent transdiagnostic feature of psychopathology. The present review provides a framework for considering the different aspects of reward processing and their assessment, and highlights recent insights from the field of neuroeconomics that may aid in understanding these processes. Although altered reward processing in psychopathology has often been treated as a general hypo- or hyperresponsivity to reward, increasing data indicate that a comprehensive understanding of reward dysfunction requires characterization within more specific reward-processing domains, including subjective valuation, discounting, hedonics, reward anticipation and facilitation, and reinforcement learning. As such, more nuanced models of the nature of these abnormalities are needed. We describe several processing abnormalities capable of producing the types of selective alterations in reward-related behavior observed in different forms of psychopathology, including (mal)adaptive scaling and anchoring, dysfunctional weighting of reward and cost variables, competition between valuation systems, and reward prediction error signaling.

Anhedonia, but not irritability, is associated with illness severity outcomes in adolescent major depression

OBJECTIVES

Unlike adult major depressive disorder (MDD) which requires anhedonia or depressed mood for diagnosis, adolescent MDD can be sufficiently diagnosed with irritability in the absence of the former symptoms. In addition, the current Diagnostic and Statistical Manual of Mental Disorders (DSM) schema does not account for the interindividual variability of symptom severity among depressed adolescents. This practice has contributed to the high heterogeneity and diagnostic complexity of adolescent MDD. Here, we sought to examine relationships between two core symptoms of adolescent MDD - irritability and anhedonia, assessed both quantitatively and categorically - and other clinical correlates among depressed adolescents.

METHODS

Ninety adolescents with MDD (51 females), ages 12-20, were enrolled. Anhedonia and irritability scores were quantified by summing related items on the Children's Depression Rating Scale-Revised and the Beck Depression Inventory. Extremes of score distribution were defined as high or low irritability/anhedonia subgroups. A significance level of p=0.01 was set to adjust for the five comparisons.

RESULTS

Despite all subjects exhibiting moderate to severe MDD, both irritability and anhedonia scores manifested a full and normally distributed severity range including the lowest values possible. However, only anhedonia severity was associated with more severe clinical outcomes, including greater overall illness severity (p<0.001), suicidality scores (p<0.001), episode duration (p=0.006), and number of MDD episodes (p=0.01). Similarly, only the high-anhedonia subgroup manifested more severe outcomes; specifically, greater illness severity (p<0.0001), number of MDD episodes (p=0.01), episode duration (p=0.01), and suicidality scores (p=0.0001).

CONCLUSIONS

Our findings suggest the significance of anhedonia as a hallmark of adolescent MDD and the need to incorporate dimensional analyses. These data are preliminary, and future prospective studies are needed to better characterize the syndrome of adolescent MDD.

A comparative study of anhedonia components between major depression and schizophrenia in Chinese populations

BACKGROUND

Anhedonia is a prominent symptom of major depressive disorder (MDD) and schizophrenia. At present, it is believed that hedonic processing rather consists of the anticipatory and consummatory phase. The aim of this research is to explore the different anhedonia components in MDD and schizophrenia in Chinese populations.

METHODS

A Chinese version of the Temporal Experience of Pleasure Scale (TEPS) was used to evaluate 176 MDD patients, 346 schizophrenia patients, and 268 healthy controls. Additionally, the 17-item Hamilton Depression Rating Scale (HAMD-17) was used for MDD patients, while the Positive and Negative Syndrome Scale (PANSS) was applied for schizophrenia.

RESULTS

The scores of consummatory (TEPS-CON) and anticipatory pleasure (TEPS-ANT) in MDD and schizophrenia were both significantly lower than healthy controls (both P < 0.001). TEPS-CON and TEPS-ANT were negatively correlated with the score of HAMD-17, the duration of illness and admission times in MDD (P < 0.05 or 0.01). TEPS-CON was negatively related to PANSS total scores and negative symptoms (P < 0.05 or 0.01), but no significant correlation was found with duration of illness and admission times in schizophrenia (P > 0.05). There was no significant correlation between TEPS-ANT and any clinical variables (P > 0.05).

CONCLUSIONS

The consummatory and anticipatory pleasures were both impaired in MDD and schizophrenia. Consummatory and anticipatory anhedonia can be considered as a "state" in MDD, but as a "trait" in schizophrenia.

The Role of Depression in the Uptake and Maintenance of Cigarette Smoking

Cigarette smoking and depression both account for significant morbidity, mortality, and economic burden. The prevalence of both smoking and depression increase across mid-to-late adolescence and show high rates of comorbidity. While little is known about why smoking is disproportionately higher among depressed adolescents than adolescents without depression, emerging research has begun to offer some initial insights. The high rates of comorbidity between depression and smoking emphasize the importance of identifying intervention targets to inform smoking prevention efforts for this high-risk group. Interventions during adolescence may lessen the prevalence of depression-prone adult smokers. Depression is over-represented among adult smokers and contributes to lower smoking cessation rates. Negative mood management and pharmacotherapy have been the central focus of smoking cessation interventions for depression-prone populations to date. Converging lines of research highlight novel smoking cessation targets such as the maintenance of positive mood and reward regulation. Smoking cessation research in depression-prone smokers is critical to identify efficacious treatments that will ultimately decrease the excess smoking burden for this population.

The neural correlates of emotional face-processing in adolescent depression: a dimensional approach focusing on anhedonia and illness severity

Deficits in emotion processing, a known clinical feature of major depressive disorder (MDD), have been widely investigated using emotional face paradigms and neuroimaging. However, most studies have not accounted for the high inter-subject variability of symptom severity. Similarly, only sparse research has focused on MDD in adolescence, early in the course of the illness. Here we sought to investigate neural responses to emotional faces using both categorical and dimensional analyses with a focus on anhedonia, a core symptom of MDD associated with poor outcomes. Nineteen medication-free depressed adolescents and 18 healthy controls (HC) were scanned during presentation of happy, sad, fearful, and neutral faces. ANCOVAs and regressions assessed group differences and relationships with illness and anhedonia severity, respectively. Findings included a group by valence interaction with depressed adolescents exhibiting decreased activity in the superior temporal gyrus (STG), putamen and premotor cortex. Post-hoc analyses confirmed decreased STG activity in MDD adolescents. Dimensional analyses revealed associations between illness severity and altered responses to negative faces in prefrontal, cingulate, striatal, and limbic regions. However, anhedonia severity was uniquely correlated with responses to happy faces in the prefrontal, cingulate, and insular regions. Our work highlights the need for studying specific symptoms dimensionally in psychiatric research.

Dimensions in major depressive disorder and their relevance for treatment outcome

BACKGROUND

Major depressive disorder (MDD) is a heterogeneous disease. More homogeneous psycho(patho)logical dimensions would facilitate MDD research as well as clinical practice. The first aim of this study was to find potential dimensions within a broad psychopathological assessment in depressed patients. Second, we aimed at examining how these dimensions predicted course in MDD.

METHODS

Ten psychopathological variables were assessed in 75 MDD inpatients. Factor and regression analyses assessed putative relations between psychopathological factors and depression severity and outcome after 8 weeks of treatment.

RESULTS

A 3-factor model (eigenvalue: 54.4%) was found, representing a psychomotor change, anhedonia and negative affect factor. Anhedonia and negative affect predicted depression severity (R(2)=0.37, F=20.86, p<0.0001). Anhedonia predicted non-response (OR 6.00, CI 1.46-24.59) and both negative affect (OR 5.69, CI 1.19-27.20) and anhedonia predicted non-remission (OR 9.28, CI 1.85-46.51).

LIMITATIONS

The sample size of the study was relatively modest, limiting the number of variables included in the analysis.

CONCLUSIONS

Results confirm that psychomotor change, anhedonia and negative affect are key MDD dimensions, two of which are related to treatment outcome.

Where is the pleasure in that? Low hedonic capacity predicts smoking onset and escalation

INTRODUCTION

Hedonic capacity is a dispositional ability to experience pleasure in response to stimuli that are typically rewarding. The ability to derive pleasure from natural reinforcers has been relatively overlooked as a risk factor for adolescent smoking. The present study sought to provide initial evidence for a relationship between hedonic capacity and adolescent smoking onset and escalation.

METHODS

The sample was composed of 1,106 adolescents participating in a prospective longitudinal survey study of adolescent health behaviors. Variables were measured via self-report every 6 months for 4 waves of data spanning 18 months. We hypothesized that adolescents with lower hedonic capacity may be less responsive to natural reinforcers and therefore be prone to take up and rely on smoking as a reinforcer.

RESULTS

A two-part latent growth curve model indicated that adolescents low in hedonic capacity were over two and a half times more likely to have smoked a cigarette in the past month at age 15.5 years (odds ratio = 2.64, 95% CI = 1.08-6.45) and to show a 90% increase (β = 0.9, z = 2.28, p = .02) in the rate of smoking escalation every 6 months across the following 18 months compared with adolescents with high hedonic capacity.

CONCLUSIONS

This study provides the first evidence implicating hedonic capacity as a risk factor for adolescent smoking initiation and progression. Adolescents low in hedonic capacity may be an important population to target for smoking prevention and smoking cessation efforts possibly through behavioral skills to enhance pleasure derived through natural reinforcers.

Effects of anhedonia on days to relapse among smokers with a history of depression: a brief report

INTRODUCTION

Despite the strong co-occurrence between lifetime prevalence of depression and smoking, a history of major depressive disorder (MDD history) does not reliably predict smoking cessation outcomes. However, depression is a heterogeneous syndrome comprising several dimensions (e.g., anhedonia, vegetative symptoms, negative affect), and each symptom expression may differentially influence cessation failure. Measuring proximal depressive dimensions may provide a more reliable way of identifying MDD history smokers most at risk for smoking relapse. Anhedonia, in particular, is a core feature of depression that may increase risk for smoking relapse among MDD history smokers. The primary goal of the present study was to investigate the relation between anhedonia and relapse latency among MDD history smokers following a brief smoking cessation workshop.

METHODS

Participants (N = 45, 48.9% female), who were euthymic regular smokers with a history of MDD, were randomized to 1 of 3 treatment groups that all involved participation in a daylong group workshop. Workshops were followed by 48 hr of bioverified abstinence and weekly follow-up visits for 1 month.

RESULTS

Cox proportional hazard modeling was used to evaluate the effect of anhedonia on relapse latency 30 days following quitting smoking. Results showed that higher levels of anhedonia predicted reduced relapse latencies, both with and without prequit depressive symptom severity included in the model.

DISCUSSION

Results suggest that anhedonia may constitute a proximal risk factor identifying depressive history smokers more likely to relapse to smoking.

Reconsidering anhedonia in depression: lessons from translational neuroscience

Anhedonia is a core symptom of major depressive disorder (MDD), the neurobiological mechanisms of which remain poorly understood. Despite decades of speculation regarding the role of dopamine (DA) in anhedonic symptoms, empirical evidence has remained elusive, with frequent reports of contradictory findings. In the present review, we argue that this has resulted from an underspecified definition of anhedonia, which has failed to dissociate between consummatory and motivational aspects of reward behavior. Given substantial preclinical evidence that DA is involved primarily in motivational aspects of reward, we suggest that a refined definition of anhedonia that distinguishes between deficits in pleasure and motivation is essential for the purposes of identifying its neurobiological substrates. Moreover, bridging the gap between preclinical and clinical models of anhedonia may require moving away from the conceptualization of anhedonia as a steady-state, mood-like phenomena. Consequently, we introduce the term "decisional anhedonia" to address the influence of anhedonia on reward decision-making. These proposed modifications to the theoretical definition of anhedonia have implications for research, assessment and treatment of MDD.

Anhedonia in schizophrenia and major depression: state or trait?

BACKGROUND

In schizophrenia and major depressive disorder, anhedonia (a loss of capacity to feel pleasure) had differently been considered as a premorbid personological trait or as a main symptom of their clinical picture. The aims of this study were to examine the pathological features of anhedonia in schizophrenic and depressed patients, and to investigate its clinical relations with general psychopathology (negative, positive, and depressive dimensions).

METHODS

A total of 145 patients (80 schizophrenics and 65 depressed subjects) were assessed using the Physical Anhedonia Scale and the Social Anhedonia Scale (PAS and SAS, respectively), the Scales for the Assessment of Positive and Negative Symptoms (SAPS and SANS, respectively), the Calgary Depression Scale for Schizophrenics (CDSS), and the Hamilton Depression Rating Scale (HDRS). The statistical analysis was performed in two steps. First, the schizophrenic and depressed samples were dichotomised into 'anhedonic' and 'normal hedonic' subgroups (according to the 'double (PAS/SAS) cut-off') and were compared on the general psychopathology scores using the Mann-Whitney Z test. Subsequently, for the total schizophrenic and depressed samples, Spearman correlations were calculated to examine the relation between anhedonia ratings and the other psychopathological parameters.

RESULTS

In the schizophrenic sample, anhedonia reached high significant levels only in 45% of patients (n = 36). This 'anhedonic' subgroup was distinguished by high scores in the disorganisation and negative dimensions. Positive correlations of anhedonia with disorganised and negative symptoms were also been detected. In the depressed sample, anhedonia reached high significant levels in only 36.9% of subjects (n = 24). This 'anhedonic' subgroup as distinguished by high scores in the depression severity and negative dimensions. Positive correlations of anhedonia with depressive and negative symptoms were also been detected.

CONCLUSION

In the schizophrenic sample, anhedonia seems to be a specific subjective psychopathological experience of the negative and disorganised forms of schizophrenia. In the depressed sample, anhedonia seems to be a specific subjective psychopathological experience of those major depressive disorder forms with a marked clinical depression severity.

Emotional reactivity across individuals with varying trauma and substance dependence histories

BACKGROUND: Research has reported a high rate of substance dependence in traumatized individuals who do not develop PTSD (TWP). While past studies have failed to consistently demonstrate that TWP individuals experience PTSD symptoms, findings have indicated that TWP and a history of substance dependence aside from nicotine dependence (SDH) are linked to affect disruption. AIMS: The present study explored positive and negative affective mechanisms across four groups with varying SDH and TWP including TWP + SDH, TWP only, SDH only, or no history. Researchers hypothesized that adults (n = 78) would be more emotionally reactive to an experimentally-induced negative mood compared to a neutral mood induction as the presence of co-existing TWP and SDH increased. METHOD: After a brief telephone screening, eligible participants completed baseline self-report questionnaires and experimentally-manipulated negative and neutral mood inductions. RESULTS: Most notably, results showed a significant TWP x SDH x Mood induction interaction (F (1, 63) = 4.154; Mse = 51.999; p = .046) for positive affect responses. Simple effects indicated that all participants except TWP + SDH individuals experienced a significant decrease in positive affect during the negative compared to the neutral mood condition. CONCLUSION: Findings may identify a protective mechanism for relapse among individuals with a history of both TWP and SDH.

Implications of the DSM's emphasis on sadness and anhedonia in major depressive disorder

At least five symptoms must occur for a DSM diagnosis of major depressive disorder (MDD), one of which must be sadness or anhedonia. The present study is the first known investigation of the implications of the presence or absence of these prioritized symptoms on symptom expression and clinical characteristics among 564 young adults with MDD. Differences in symptom expression and clinical characteristics occurred among MDD participants with sadness relative to those without sadness as well as among MDD participants with anhedonia relative to those without anhedonia. Differential symptom expression could have important implications for the etiology, prevention, and treatment of MDD.

Affective and adrenocorticotrophic responses to photoperiod in Wistar rats

The present study tested the hypothesis that seasonal intervals of exposure to modest changes in photoperiod, typical of those experienced by humans living in temperate latitudes (10-14 h light/day), engage changes in emotional behaviour of Wistar rats, a commonly-used animal model for investigations of affective physiology. Short day lengths (<or= 12 h light/day) induced behavioural despair in a forced-swim test, exploratory anxiety in an open field arena, and anhedonia in a two-bottle sucrose preference task, relative to longer day lengths. Plasma adrenocorticotrophic hormone was lower in short-day relative to long-day rats, but testosterone and corticosterone concentrations were comparable across treatments. In common with animals that engage reproductive responses to day length, reproductively nonresponsive mammals such as Wistar rats exhibit changes in affective state following small changes in day length. Wistar rats may provide an animal model for the study of seasonal mood regulation because the neuroendocrine, depressive, anxious and anhedonic responses of Wistar rats to short days bear similarities to those observed in some human populations. Standard laboratory husbandry practices (exposure to a 12 : 12 h light/dark cycle) may inadvertently deliver a chronic background depressive and anxiogenic stimulus.

Increased perceived stress is associated with blunted hedonic capacity: potential implications for depression research

Preclinical studies suggest that stress exerts depressogenic effects by impairing hedonic capacity; in humans, however, the precise mechanisms linking stress and depression are largely unknown. As an initial step towards better understanding the association between stress and anhedonia, the present study tested, in two independent samples, whether individuals reporting elevated stress exhibit decreased hedonic capacity. The Perceived Stress Scale (PSS) measured the degree to which participants appraised their daily life as unpredictable, uncontrollable, and overwhelming. Hedonic capacity was objectively assessed using a signal-detection task based on a differential reinforcement schedule. Decreased reward responsiveness (i.e., the participants' propensity to modulate behavior as a function of reward) was used as an operational measure of hedonic capacity. In both Study 1 (n=88) and Study 2 (n=80), participants with high PSS scores displayed blunted reward responsiveness and reported elevated anhedonic symptoms. Additionally, PSS scores predicted reduced reward responsiveness even after controlling for general distress and anxiety symptoms. These findings are consistent with preclinical data highlighting links between stress and anhedonia, and offer promising insights into potential mechanisms linking stress to depression.

Endotoxin- or pro-inflammatory cytokine-induced sickness behavior as an animal model of depression: focus on anhedonia

In humans, exposure to endotoxins or pro-inflammatory cytokines induces a number of neuropsychological symptoms collectively referred to as 'flu-like syndrome'. The degree of overlap between flu-like syndrome and major depressive disorder is considerable and a close linkage between these has been predicted to arise due to hypersecretion of endogenous pro-inflammatory cytokines and activation of the hypothalamic pituitary adrenal axis. In animals, exposure to pro-inflammatory cytokines or endotoxins induces a 'sickness behavior' syndrome that is analogous to flu-like symptoms observed in human patients. The goal of the current paper is to review evidence implicating endotoxin- or cytokine-induced sickness behavior as an animal model of depression, with an emphasis on reduced consumption of highly palatable substances as a defining feature.

Toward an objective characterization of an anhedonic phenotype: a signal-detection approach

BACKGROUND

Difficulties in defining and characterizing phenotypes has hindered progress in psychiatric genetics and clinical neuroscience. Decreased approach-related behavior and anhedonia (lack of responsiveness to pleasure) are considered cardinal features of depression, but few studies have used laboratory-based measures to objectively characterize these constructs.

METHODS

To assess hedonic capacity in relation to depressive, particularly anhedonic, symptoms, 62 participants completed a signal-detection task based on a differential reinforcement schedule. Anhedonia was operationalized as decreased reward responsiveness.

RESULTS

Unequal frequency of reward between two correct responses produced a response bias (i.e., a systematic preference to identify the stimulus paired with the more frequent reward). Subjects with elevated depressive symptoms (Beck Depression Inventory scores >/= 16) failed to show a response bias. Impaired reward responsiveness predicted higher anhedonic symptoms 1 month later, after controlling for general negative affectivity.

CONCLUSIONS

Impaired tendency to modulate behavior as a function of prior reinforcement might underline diminished hedonic capacity in depression. When applied to a clinical population, objective assessments of participants' propensity to modulate behavior as a function of reward might provide a powerful tool for improving the phenotypic definition of depression and thus offer a reliable behavioral screening approach for neuroscience studies of depression.

The anhedonias: Clinical and neurobiological aspects

During the last 30 years there has been renewed clinical interest in the state of 'lack of pleasure' (anhedonia) seen in conditions such as schizophrenia and depression. In spite of some important work, confusion still remains about the term, behaviours and explanatory concepts pertaining to anhedonia. This paper reviews the clinical and basic scientific studies that throw light on this interesting clinical phenomenon and then presents a new model of anhedonia which can be tested empirically and should facilitate research in this field.

Suicide: a four-pathway clinical-biochemical model

This chapter, based on a review of recent research as well as data presented in this report, proposes four hypothetical pathways leading to suicide in clinical depression: (1) an acute pathway involving severe anxiety/agitation associated with high brain corticotrophin-releasing factor (CRF or CRH) levels, (2) trait baseline and reactivity hopelessness, (3) severe anhedonia, and (4) trait impulsiveness associated with low brain serotonin turnover and low total cholesterol as a possible peripheral correlate. Clinical research showing evidence for acute versus chronic high-risk suicide factors and other studies linking severe anxiety/agitation to high CRF levels will be presented as associated with acute suicidal risk, which is potentially reversible with recognition and treatment. Evidence for anhedonia severity as a risk factor and trait, as well as evidence that baseline hopelessness and sensitivity are traits related to chronic suicide risk, will be presented. Finally, evidence relating low serum cholesterol to suicide in depressed inpatients will be presented in the context of literature suggesting a relationship between low serum cholesterol and violent death and suicide in population studies. Data suggesting a relationship between low serum cholesterol and decreased CSF 5-HIAA, suggesting reduced serotonin turnover, will be presented, in light of prior studies relating low CSF 5-HIAA and violent suicide. These data taken together suggest four pathways to suicide that are worth investigating in order to better understand the mechanisms leading to this behavior. Future possibilities and applications of these findings are discussed.

Vulnerability to depression: a model centered on anhedonia

The aim of the present study is to present a model of depressive vulnerability centered on anhedonia. After a review of the literature, we suggest a specific symptomatic profile associating anhedonia, introversion, low sensation-seeking, autonomy, dysfunctional attitudes, high displeasure capacity, obsessive-compulsive features, passitivity and pessimism. This symptomatic profile could constitute a mild chronic mood disorder which, following stress, might decompensate into unipolar endogenomorphic depression. Several methods of research are suggested to test the validity of our model.

Physical anhedonia in major depressive disorder

Physical anhedonia, evaluated by the score on the physical anhedonia scale (PAS) of Chapman et al. [J. Abnorm. Psychol. 4 374-382 (1976)] was studied in 61 patients, who met RDC criteria for major depressive disorder and in 61 normal subjects. The depressed patients scored significantly higher than the normal group and presented a continuous distribution. Physical anhedonia of depressed patients seems related to the severity of the depression and does not appear to identify a qualitatively distinct subgroup.

Desmethylimipramine promotes recovery of self-stimulation from the prefrontal cortex following footshock

Intracranial self-stimulation (ICSS) was assessed from the prefrontal cortex in CD-1 mice immediately (0 h), 24 h and 168 h following exposure to uncontrollable footshock. Marked reductions in ICSS rates were observed in all mice immediately following the stressor. Although the ICSS alterations were transient in some animals, ICSS rates were reduced in the majority of animals 24-h and 168-h poststressor. Mice of either the shock or no shock treatment groups were administered either saline or desmethylimipramine (DMI, 5 mg/kg x 2) for 20 consecutive days. Chronic DMI ameliorated the stressor-induced ICSS deficits from the prefrontal cortex. Potential explanations for the stressor-provoked variations in ICSS and the effects of DMI are discussed.

Hedonic capacity in schizophrenics and their twins

Audio-taped interviews recorded in the Gottesman-Shields schizophrenic twin series (17 pairs of identical twins, 14 pairs of fraternal same-sex twins, and 12 unpaired twins) were rated for level of hedonic capacity. Schizophrenics who were not hospitalized at the time of their interview were rated significantly lower (more impaired) on hedonic capacity than their normal co-twins. A significant negative correlation was also found between hedonic capacity and severity of illness. Hedonic capacity was found to be genetically influenced, although it appeared to be less heritable than the global diagnosis of schizophrenia. These results are consistent with Meehl's suggestion that reduced hedonic capacity is a heritable personality trait which potentiates the development of schizophrenia among those who are genetically predisposed to the disorder. The results suggest that anhedonia is not a phenotypic vulnerability marker for schizophrenia.

Pharmacologic perturbation strategies in the study of the neurobiology of depression

1. Psychological, behavioral, physiological, biochemical, and receptor binding measurements are useful as dependent variables when studying the biology of depression and mania. 2. Pharmacological perturbations of cholinergic mechanisms can produce changes mimicking aspects of the neurobiology of affective disorders. 3. These changes can be quantitated by measuring their impact on variables in each of these classes. 4. Pharmacological methods for inducing these changes in cholinergic systems and their application to clinical and basic research in the field of affective disorders are highlighted.

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.