Biological Bases of Psychological Disorders (7A)
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MCAT Psychological and Social Foundations › Biological Bases of Psychological Disorders (7A)
The dopamine hypothesis of schizophrenia primarily attributes which class of symptoms to hyperactivity in mesolimbic dopamine pathways?
Positive symptoms
Negative symptoms
Cognitive symptoms
Affective symptoms
Explanation
The dopamine hypothesis posits that positive symptoms of schizophrenia (e.g., hallucinations, delusions, disorganized thought) are caused by excessive dopaminergic activity in the mesolimbic pathway. In contrast, negative symptoms (e.g., avolition, anhedonia) are thought to be associated with dopamine hypoactivity in the mesocortical pathway.
A researcher proposes that the therapeutic lag of several weeks for selective serotonin reuptake inhibitors (SSRIs) is due to downstream neuroadaptive changes, such as receptor downregulation and increased neurogenesis, rather than an immediate increase in synaptic serotonin. This proposal most directly challenges the assumption that:
the hypothalamic-pituitary-adrenal (HPA) axis is not involved in the etiology of depression.
depression is caused by a simple deficit in monoamine neurotransmitters.
dopamine and norepinephrine are less important than serotonin in depression.
increased synaptic serotonin levels are the direct and sufficient cause of mood improvement.
Explanation
The therapeutic lag suggests that simply increasing synaptic serotonin is not enough to alleviate depressive symptoms. If it were, SSRIs would work almost immediately. The delay implies that the brain must undergo slower, adaptive changes (like altering receptor density or growing new neurons) in response to the sustained increase in serotonin, and it is these long-term changes that are ultimately responsible for the therapeutic effect. This challenges the idea that the increased serotonin level itself is the direct mechanism of action.
A patient with Parkinson's disease is treated with L-DOPA, a precursor to dopamine. While this alleviates motor symptoms, the patient begins to experience hallucinations and paranoia. This side effect is best explained by:
overstimulation of dopaminergic pathways in the mesolimbic system.
insufficient conversion of L-DOPA to dopamine in the nigrostriatal pathway.
degeneration of serotonergic neurons as a result of treatment.
an antagonistic effect of L-DOPA on acetylcholine receptors.
Explanation
L-DOPA increases dopamine levels throughout the brain. While this is intended to compensate for the dopamine deficiency in the nigrostriatal pathway (improving motor function), it can cause dopamine hyperactivity in other pathways. Overstimulation of the mesolimbic pathway is associated with the positive symptoms of psychosis, such as hallucinations and paranoia, which is what the patient is experiencing.
A physician is treating a patient with bipolar I disorder. Which of the following biological considerations most justifies the use of a mood stabilizer like lithium over an antidepressant alone for long-term management?
Antidepressants are uniformly ineffective at treating the depressive episodes of bipolar disorder.
Lithium directly increases the synthesis of serotonin and norepinephrine.
Antidepressant monotherapy can precipitate manic or hypomanic episodes.
Bipolar disorder is primarily a disorder of dopamine, which antidepressants do not affect.
Explanation
A primary danger in treating bipolar disorder is that antidepressant medications, when used without a mood stabilizer, can induce a switch from a depressive state into a manic or hypomanic episode. Mood stabilizers like lithium are used to prevent these mood swings in both directions (depressive and manic), providing stability that antidepressants alone cannot and may actively disrupt.
Neuroimaging studies of individuals with obsessive-compulsive disorder (OCD) have most consistently implicated hyperactivity in which of the following neural circuits?
The mesolimbic dopaminergic pathway
The hypothalamic-pituitary-adrenal (HPA) axis
The cortico-striato-thalamo-cortical (CSTC) loop
The default mode network (DMN)
Explanation
The cortico-striato-thalamo-cortical (CSTC) loop is the neural circuit most strongly and consistently associated with the pathophysiology of OCD. This circuit, which includes the orbitofrontal cortex, the striatum (specifically the caudate nucleus), and the thalamus, is thought to be involved in error detection and habit formation. Hyperactivity in this loop is believed to underlie the intrusive thoughts (obsessions) and repetitive behaviors (compulsions) characteristic of OCD.
While both major depressive disorder (MDD) and post-traumatic stress disorder (PTSD) can involve dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, a key distinction often observed in their neuroendocrine profiles is that:
PTSD is often associated with enhanced negative feedback sensitivity of the HPA axis, leading to lower basal cortisol, whereas MDD is often linked to impaired negative feedback and hypercortisolism.
cortisol levels are elevated in the morning for PTSD patients but in the evening for MDD patients.
MDD is associated with hypocortisolism, while PTSD is associated with hypercortisolism.
the HPA axis is hyperactive in MDD but completely hypoactive in PTSD.
Explanation
This question addresses a nuance in HPA axis dysregulation. While both disorders involve HPA axis changes, a classic finding in a significant subset of individuals with PTSD is enhanced glucocorticoid receptor sensitivity. This leads to a more robust negative feedback signal, which can result in lower baseline levels of circulating cortisol. In contrast, classic melancholic depression is frequently associated with glucocorticoid receptor resistance, impaired negative feedback, and chronically elevated cortisol levels (hypercortisolism).
A person has a specific allele of the serotonin transporter gene (SLC6A4) that confers a higher risk for depression. However, they only develop depression after experiencing a significant life stressor, such as the loss of a job. This scenario is a classic example of:
a purely genetic etiology.
the diathesis-stress model.
the dopamine hypothesis.
a somatoform disorder.
Explanation
The diathesis-stress model posits that psychopathology is the result of an interaction between a pre-existing vulnerability (the diathesis) and a precipitating event or condition (the stress). In this case, the genetic allele is the diathesis, and the job loss is the stressor. The disorder manifests only when both factors are present.
Based on the mechanism described, a patient taking RX-500 might be at an increased risk for which of the following side effects, especially at the beginning of treatment?
Bradycardia and sedation
Weight gain and metabolic syndrome
Increased blood pressure and insomnia
Extrapyramidal motor symptoms
Explanation
The passage states that RX-500 blocks norepinephrine (NE) reuptake. Increasing the amount of NE in the synapse enhances noradrenergic signaling, which is associated with activation of the sympathetic nervous system. This can lead to side effects such as increased heart rate (tachycardia), increased blood pressure (hypertension), and a state of hyperarousal that can manifest as anxiety or insomnia. Bradycardia (slow heart rate) and sedation are the opposite effects.
The drug's action as a 5-HT₁ₐ partial agonist is mechanistically similar to which existing class of anxiolytic medication?
Benzodiazepines
Typical antipsychotics
Barbiturates
Buspirone
Explanation
Buspirone (brand name BuSpar) is an anxiolytic medication whose primary mechanism of action is as a partial agonist at the serotonin 5-HT₁ₐ receptor. This action is distinct from benzodiazepines and barbiturates, which act on the GABA system, and typical antipsychotics, which are primarily dopamine D₂ receptor antagonists.
Research into the neurobiology of borderline personality disorder (BPD) frequently highlights dysregulation in circuits connecting the prefrontal cortex and the amygdala. This finding is most consistent with which core feature of the disorder?
Emotional dysregulation and impulsivity
Transient, stress-related paranoid ideation
Frantic efforts to avoid abandonment
Identity disturbance and feelings of emptiness
Explanation
The amygdala is a key brain structure for generating emotional responses, particularly negative emotions like fear and anger. The prefrontal cortex exerts top-down control, regulating these emotional responses and inhibiting impulsive behaviors. A dysregulated connection between a hyperactive amygdala and an underactive prefrontal cortex is believed to underlie the intense, rapidly shifting moods (emotional dysregulation) and poor impulse control that are hallmarks of BPD.