A 29-year-old woman comes to the office for treatment of anxiety that has worsened over the past year. She finds herself worrying all the time and fears that she may not complete her graduate studies in time to meet requirements for her degree. The patient is also worried about her son's health and anxiously obsesses about him all the time. She says, "My anxiety just comes out of the blue; one way or another, I'm anxious all the time." The patient has no history of medical problems. Physical examination is unremarkable; complete blood count, chemistry panel, and TSH and B₁₂ levels are normal. An anxiety disorder is diagnosed and fluoxetine is prescribed. The patient's anxiety begins to improve over the next 4-6 weeks. The physician explains that the medication inhibits the reuptake of a neurotransmitter released by a specific set of neurons. These neurons are most likely part of which of the following structures?

Question

Quizplus · Accepted Answer

In the central nervous system (CNS), serotonergic (serotonin-releasing) neurons are primarily found in the raphe nuclei of the brainstem. The raphe nuclei are located in the midbrain, pons, and medulla, and axons from these cell bodies project widely throughout the CNS to synapse on structures such as the cerebral cortex, thalamus, hypothalamus, cerebellum, hippocampus, and spinal cord. These neurons play a role in the sleep-wake cycle, anxiety, mood, psychosis, sexuality, eating behavior, and impulsivity. Medications that target serotonin neurons are widely used in psychiatric disorders. Serotonergic antidepressants are the primary pharmacotherapy for most depressive and anxiety disorders. Antidepressants such as selective serotonin reuptake inhibitors (SSRIs [eg, fluoxetine]), serotonin-norepinephrine reuptake inhibitors, and tricyclic antidepressants work by prolonging the amount of time that serotonin spends in the synaptic clefts of these neurons before being taken up by presynaptic neurons. (Choice A) The caudate nucleus and putamen form the striatum, which functions in motor activities. In Huntington disease, there is loss of cholinergic and GABA-releasing neurons in the striatum. (Choice B) The locus ceruleus houses norepinephrine-secreting neurons that participate in activation of the "fight or flight" response to physical and emotional stressors. It is located in the dorsal pons. These neurons are implicated in some anxiety symptoms, but they are not serotonergic and not affected by SSRIs. (Choice C) The nucleus basalis of Meynert houses the cell bodies of cholinergic neurons. In Alzheimer disease, these neurons secrete decreased amounts of acetylcholine. (Choice E) The red nucleus is located in the anterior midbrain. Its neurons participate in motor coordination of the upper extremities. (Choice F) The substantia nigra contains dopaminergic neurons. In Parkinson disease, these neurons are depleted. Educational objective: Serotonin-releasing neurons in the central nervous system (CNS) are located in the raphe nuclei. These neurons disseminate widely to synapse on numerous structures in the CNS. Antidepressants such as selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, and tricyclic antidepressants inhibit serotonin reuptake at these synapses. __________ References: Stress-related serotonergic systems: implications of symptomatology of anxiety and affectivedisorders. (http://www.ncbi.nlm.nih.gov/pubmed/22484834)

A 29-Year-Old Woman Comes to the Office for Treatment of Anxiety