We know that neurotransmitters transmit signals across the synapse and activate the receptors of the postsynaptic cell and include small-molecule and neuroactive peptides. All of the following are neurotransmitters except:

Choice A reason: Hyperventilation causes decreased CO2 levels (respiratory alkalosis) due to rapid breathing from pain, anxiety, or restlessness. This matches the patient’s symptoms and blood gas results, making it the correct cause.

Choice B reason: Nephrolithiasis causes pain but doesn’t typically lead to hyperventilation or low CO2. Respiratory alkalosis from hyperventilation better explains the findings, so this is incorrect for the cause.

Choice C reason: Acute fracture causes pain but not necessarily hyperventilation or low CO2. Anxiety-driven hyperventilation is more likely to cause respiratory alkalosis, so this is incorrect for the primary cause.

Choice D reason: Urinary tract infection may cause discomfort but not low CO2 or hyperventilation. Anxiety and pain causing hyperventilation align with the blood gas, so this is incorrect.

Choice A reason: Hallucinations are positive symptoms of schizophrenia, involving sensory experiences not based in reality, like hearing voices. Negative symptoms involve deficits, such as reduced emotional expression or social engagement. Since hallucinations add to experience, they are not negative, making this incorrect for negative symptoms.

Choice B reason: Apathy, a lack of motivation or interest, is a negative symptom of schizophrenia, reflecting diminished emotional and behavioral responses. It aligns with deficits in normal functioning, a hallmark of negative symptoms, making it a correct choice for this category of schizophrenia manifestations.

Choice C reason: Absence of normal social and interpersonal behaviors, such as social withdrawal, is a negative symptom, indicating reduced engagement and interaction. This deficit in typical social functioning is characteristic of negative symptoms in schizophrenia, making it a correct selection for this question.

Choice D reason: Sensory overload from impaired sensory filtering is not a standard negative symptom; it’s more related to cognitive or positive symptoms like hallucinations. Negative symptoms involve reduced behaviors, like apathy, so this is incorrect for the negative symptom category in schizophrenia.

Choice E reason: Anhedonia, the inability to experience pleasure, is a negative symptom, reflecting a deficit in emotional response. It is a core feature of reduced functioning in schizophrenia, aligning with negative symptom criteria, making it a correct choice for this question.

Choice F reason: Incomprehensible speech, such as disorganized speech, is a positive symptom, adding disordered communication to the patient’s experience. Negative symptoms involve reduced behaviors, like social withdrawal, so this is incorrect for the negative symptom category in schizophrenia.

Choice G reason: Delusions, false beliefs, are positive symptoms, adding to the patient’s mental experience. Negative symptoms involve deficits, such as lack of motivation, not added beliefs. This makes delusions incorrect for the negative symptom category in schizophrenia manifestations.