Depression

Neurobiology of Depression

Introduction

  • Speaker: Abdallah Hayar

  • Affiliation: University of Arkansas for Medical Sciences, Department of Neurobiology & Developmental Sciences.

  • Presentation focus: Neurobiology of depression, statistical data, risk factors, types, treatment options, and animal models.

Epidemiology

  • Global Impact:
      - Approximately 350 million individuals are affected by depression worldwide.

  • US Prevalence:
      - Lifetime prevalence of 17%: About 1 in 6 people in the U.S. will experience depression during their lifetime.
      - Projected by the World Health Organization to become the second leading cause of global disease burden by 2020 (cited from Murray & Lopez, 1997).

  • Impact of Depression in the US:
      - Accounts for 8.3% of all years lived with disability (YLD).
      - Annual prevalence among US adults (2014): 6.7%.

  • Sex Differences:
      - Depression prevalence varies: 3-5% in males; 8-10% in females.
      - Factors for increased prevalence in females: declining estrogen levels, lack of social support.   - Suicide risk is greater for men, increasing with age; women face higher rates of suicide attempts but lower completion rates, which decline with age.
      - Women exhibit increased anxiety levels.

  • Response to Treatment:
      - Approximately 1/3 of patients respond to their first antidepressant.
      - An additional 1/3 may respond after 4 antidepressants, leaving 1/3 with treatment-resistant depression.

Depression Statistics

  • DALY Rates:
      - Age-standardized disability-adjusted life year (DALY) rates in 2004 indicate the US has the highest DALY rates due to unipolar depressive disorders.   - Lifetime prevalence ranges from 3% in Japan to 17% in the US.

Risk Factors for Depression

Biochemical Factors

  • Neurotransmitter Levels:
      - Low levels of key neurotransmitters (e.g., serotonin, norepinephrine, dopamine) may increase susceptibility to depression.

Genetic Factors

  • Twin Studies:
      - If one identical twin has depression, the other twin has a 70% chance of developing it, indicating a strong genetic component.

Sleep Disorders

  • While the causal relationship between sleep and depression is unclear, periods of poor sleep are often followed by episodes of low mood.

Serious Illness

  • Chronic conditions linked to increased rates of depression include:
      - Chronic pain, heart disease, diabetes, stroke, and neurodegenerative diseases.

Social Factors

  • Negative social experiences (e.g., childhood neglect/abuse, isolation) increase depression risk, as do major life events such as job loss or bereavement.

Substance Use

  • Impact of Drugs and Alcohol:
      - Use of drugs, alcohol, and certain medications (e.g., blood pressure medications, sedatives) can exacerbate depression.

Visual Representation

  • Vincent van Gogh’s painting - Sorrowing old man highlights themes of sorrow and depression.

Clinical Findings in Depression

Differential Symptoms

  • Mood Changes:
      - Excess: Unrelenting sadness.
      - Deficient: Emotional numbing.

  • Sleep Patterns:
      - Excess: Hypersomnia.
      - Deficient: Insomnia.

  • Cognitive Patterns:
      - Excess: Hyper-focus on negative themes (guilt, hopelessness, etc.).
      - Deficient: Emotional blunting, poor concentration.

  • Motor Symptoms:
      - Excess: Agitation.
      - Deficient: Fatigue, psychomotor slowing.

  • Appetite Changes:
      - Excess: Hyperphagia (weight gain).
      - Deficient: Loss of appetite (weight loss).

Diagnostic Criteria for Major Depression (DSM-IV-TR)

  • Diagnosis requires at least 5 of the following symptoms:
      - Decreased interest/pleasure, depressed mood, reduced energy, weight gain/loss, insomnia/hypersomnia, feelings of worthlessness, guilt, recurrent morbid thoughts, psychomotor changes, fatigue, poor concentration, self-harm ideation, and pessimistic views.

Types of Depression

  1. Major Depression:
       - Symptoms present most of the day, nearly every day for at least 2 weeks, affecting daily functions.

  2. Persistent Depressive Disorder (Dysthymia):
       - Symptoms last for at least 2 years.

  3. Perinatal Depression:
       - Major depression during pregnancy or postpartum.

  4. Seasonal Affective Disorder (SAD):
       - Symptoms typically arise in late fall and resolve in spring/summer.

  5. Psychotic Depression:
       - Involves psychosis (e.g., hallucinations).

  6. Bipolar Disorder:
       - Characterized by alternating episodes of depression and mania.

Co-Morbid Psychiatric Disorders

  • Lifetime Prevalence Rates:
      - 48% of PTSD patients also have major depression.
      - 34-70% of social phobia patients have depression.
      - 50-60% of panic disorder patients have major depression.
      - 67% of OCD patients develop major depression.
      - 8-39% of GAD patients have major depression (Kessler et al., Arch Gen Psychiatry, 1995).

Animal Models of Depression

Insights from Chronic Stress Protocols

  • Initial protocols induced stress via electric shocks, cold water immersion, and food deprivation, leading to increased plasma corticosteroids.

  • Suggests that chronic stress could lead to anhedonia, indicated by reduced interest.

Learned Helplessness Model

  • After exposure to uncontrollable stressors, animals displayed helplessness, failing to escape even when an escape was possible.

  • Behavioral symptoms include: reduced weight, increased motor activity, cognitive deficits.

Other Models

  1. Maternal Deprivation:
       - Mimics early life neglect.

  2. Olfactory Bulbectomy:
       - Results in changes mimicking human depressive symptoms.

  3. Sleep Deprivation:
       - Alters stress-related pathways.

Predictive Models of Antidepressant Activity

Forced Swimming Test (FST)

  • High reproducibility; assesses new antidepressant drug efficacy.

  • Antidepressants reduce immobility time by affecting swimming and climbing behaviors related to serotonergic and noradrenergic systems.

Tail Suspension Test (TST)

  • Widely used to assess antidepressant activity in mice.

  • Immobility time interpreted as depressive-like behavior; antidepressants promote escape behavior.

Validity Criteria for Animal Models

  • Models must show:
      1. Face Validity: Behavioral symptoms resemble human depression symptoms.   2. Construct Validity: Pathophysiological changes evident in humans (e.g. changes in HPA axis).   3. Predictive Validity: Effective treatments should reverse behavioral changes.

Neurobiological Mechanisms

Monoaminergic Hypothesis of Depression

  • Proposes depression is caused by a deficit in monoamines, especially serotonin (5-HT).

  • Controversies exist regarding feedback mechanisms in serotonergic transmission in the brain.

Dorsal Raphe Neurons

  • Electrophysiological Properties:
      - Neurons are quiescent in slices but exhibit 2 Hz firing with norepinephrine application.
      - They are hyperpolarized by 5-HT1A agonists; show tonic inhibition when exposed to 5-HT under certain conditions.

Heart Rate Variability in Depression

Connection Between HRV and Mood

  • Decreased HRV correlates with mood disorders, particularly depression and anxiety.

  • Antidepressants often fail to restore HRV despite alleviating mood symptoms.

Physical Health Indicators

  • Healthy HRV is associated with better mental and physical health outcomes; lower HRV signals potential pathology.

Treatment Options

Pharmacological Interventions

  • Tricyclic Antidepressants (TCAs):
      - Effective but can cause sedation, and are dangerous in overdose.

  • Monoamine Oxidase Inhibitors (MAOIs):
      - Require dietary restrictions; risk of rare fatalities.

  • Selective Serotonin Reuptake Inhibitors (SSRIs):
      - Preferred for their effectiveness and lower sedation; include drugs like fluoxetine.

  • Dual Norepinephrine and Serotonin Reuptake Inhibitors:
      - Similar effects as SSRIs but also target norepinephrine pathways; caution with hypertensive patients.

Non-Pharmacological Interventions

  • Cognitive Behavioral Therapy (CBT):
      - Effective in treating depression.

  • Electroconvulsive Therapy (ECT):
      - Used for severe cases; induces quick response in treatment-resistant depression.

  • Deep Brain Stimulation (DBS):
      - Invasive, targeting overactive brain regions in depression.

  • Physical Exercise:
      - Recognized as an adjunct treatment; increases circulation and neurotransmitter levels.

Closing Perspectives

  • Importance of recognizing depression's complexity, incorporating biological, psychological, and social factors into effective treatment strategies.

  • Impact of depression extends beyond individual health, emphasizing the necessity for holistic approaches.