Schizophrenia

Observations of overactivity in the mesolimbic pathway originating from the ventral tegmental area (VTA) signaling to limbic structures.
This overactivity is believed to drive the positive symptoms associated with schizophrenia, such as hallucinations and delusions.
Evidence shows that drugs that block dopamine signaling are effective in reducing positive symptoms.

Research involving individuals with schizophrenia and control subjects demonstrated that those with schizophrenia release higher levels of dopamine in response to the same dosage of amphetamine.
Amphetamine administration leads to increased dopamine release, suggesting sensitization of dopamine signaling in individuals with schizophrenia.
A correlation exists between dopamine release levels and severity of positive symptoms: increased dopamine release corresponds to worsening positive symptoms.

Treatments primarily focus on alleviating positive symptoms (hallucinations, delusions) to improve daily functioning.
Types of Antipsychotics:
- Typical Antipsychotics (First Generation):
- Includes well-known drugs like Thorazine and Haldol.
- Primarily act as D2 dopamine receptor antagonists, blocking dopamine receptors to reduce symptoms.
- Discovered in the 1950s and effective for positive symptoms, but they can disrupt motor behavior.
- Side effects, such as tardive dyskinesia, may occur due to antagonism in dopamine pathways responsible for motor control.
- Atypical Antipsychotics (Second Generation):
- Newer medications that also target D2 receptors but have a broader mechanism, affecting other neurotransmitter systems like serotonin and acetylcholine, attempting to treat both positive and some negative symptoms.
- While less potent in blocking D2 receptors compared to typical antipsychotics, they have shown efficacy with potentially lower side effects.

Motor Effects:
- Dyskinesia: Abnormal involuntary movements typically presenting as tics in the face and head.
- Tardive Dyskinesia: Involuntary movements that may persist even after cessation of antipsychotic medication.
Research has indicated that while traditional views limited tardive dyskinesia to typical antipsychotics, it can also occur with atypical antipsychotics.

The role of glutamate, a major excitatory neurotransmitter, is significant in schizophrenia.
Evidence suggests reduced glutamate signaling may contribute to negative and cognitive symptoms (e.g., memory and attention deficits).
Hypofrontality:
- Refers to decreased activity levels in the prefrontal cortex in individuals with schizophrenia compared to controls, further linking glutamatergic dysfunction to cognitive and negative symptoms.

The imbalance of neurotransmitter systems (e.g., excessive dopamine, insufficient glutamate) contributes to the complexity of schizophrenia.
Polypharmacy Strategies:
- Treating schizophrenia requires an understanding of both dopamine and glutamatergic systems, leading to a combination of atypical antipsychotics affecting multiple neurotransmitter systems.

Transition to discussion of depressive disorders (major depressive disorder - MDD), covering their prevalence, etiology, and anatomical correlates.
Prevalence of MDD reported at approximately 1 in 10 individuals in the U.S., with identifiable spikes during adolescence and later adulthood.
Gender differences show females at higher risk for MDD, and symptoms may vary significantly between sexes.

Brain imaging studies reveal hyperactivity in the amygdala and prefrontal cortex for individuals with major depression.
- The prefrontal cortex's overactivity relates to rumination patterns, while amygdala hyperactivity indicates heightened threat responsiveness.
Effective treatments (e.g., SSRIs, CBT) typically result in reduced activity in the prefrontal cortex but may not fully normalize amygdala hyperactivity.

Monoamine Hypothesis: Argues that low levels of monoamine neurotransmitters (serotonin, norepinephrine, dopamine) increase susceptibility to depression.
Genetic predisposition is indicated by twin studies showing high concordance rates, particularly in identical twins (60% for MDD).

First-line treatments include SSRIs, which selectively inhibit serotonin reuptake; successful antidepressant treatment may take several weeks.
- Other Drug Classes:
- Tricyclic antidepressants, monoamine oxidase inhibitors (MAOIs), selective norepinephrine reuptake inhibitors (SNRIs) targeting various monoamine pathways.
Cognitive Behavioral Therapy has shown similar effectiveness to pharmacological treatments, and combined therapy can yield additive benefits.

Electroconvulsive Therapy (ECT):
- Effective for treatment-resistant depression; induces controlled seizures that may provide rapid symptom relief, particularly in acute instances of suicidal ideation.
Transcranial Magnetic Stimulation (TMS):
- A non-invasive method that uses magnetic fields to stimulate nerve cells, yet does not encapsulate all treatment categories.
Ketamine:
- NMDA receptor antagonist that addresses depressive symptoms swiftly, usually through a nasal spray. Can significantly reduce symptoms shortly after administration but requires careful monitoring.

Transition from depressive to bipolar disorder, characterized by mood episodes ranging from depression to mania (high energy, impulsive behavior).
Epidemiological Link with Schizophrenia: High genetic relatedness evident from twin studies, indicating similar familial patterns.

Common Treatments:
- Lithium: Mood stabilizer effective in preventing manic episodes but requires monitoring for side effects.
- Valproate: Anticonvulsant used for seizure control that also mitigates bipolar symptoms, lower side effects, and less required monitoring than lithium.
Antidepressants may be used cautiously, often in conjunction with other treatments due to risks of exacerbating manic episodes.