Which of the following was most likely one of the postreceptor mechanisms triggered by methadone?

Correct Answer: D

Rationale: The correct answer is D because methadone stimulates adenylyl cyclase activity as a postreceptor mechanism. Methadone is an opioid receptor agonist that activates G-protein coupled receptors, leading to the activation of adenylyl cyclase and subsequent increase in cAMP levels. This increased cAMP signaling pathway results in various downstream effects, including modulation of neurotransmitter release and neuronal excitability. A: Inhibition of the synthesis of inositol triphosphate/diacylglycerol (IP3/DAG) is not a postreceptor mechanism triggered by methadone. B: Blockade of Ca2+ channels on presynaptic nerve terminals is not a postreceptor mechanism triggered by methadone. C: Opening of Na+ channels on neuronal cell membrane is not a postreceptor mechanism triggered by methadone. In summary, methadone's stimulation of adenylyl cyclase activity is the correct choice as it align

Correct Answer: B

Rationale: The correct answer is B: Increased heart rate. When smoking, nicotine enters the bloodstream and stimulates the release of adrenaline, leading to increased heart rate. Hypertension (choice A) may occur over time with consistent smoking. Depressive mood (choice C) is more commonly associated with withdrawal symptoms rather than immediate effects. Hyperalgesia (choice D), increased sensitivity to pain, is not a typical immediate effect of smoking.

Correct Answer: D

Rationale: The correct answer is D: Heroin. Heroin withdrawal can lead to seizures due to the sudden decrease in brain activity when the drug is removed. This causes an imbalance in neurotransmitters, increasing the risk of seizures. LSD (A) and cannabis (B) are not associated with seizure risk during withdrawal. Alprazolam (C) withdrawal can cause seizures but is less common compared to heroin withdrawal.

Correct Answer: C

Rationale: The correct answer is C: Phencyclidine. PCP is a dissociative anesthetic that can cause hallucinations, agitation, and violent behavior. The patient's signs and symptoms align with the effects of PCP use. Cocaine (A) typically causes increased energy and alertness, heroin (B) causes sedation and respiratory depression, and LSD (D) causes hallucinations and altered perceptions, but these do not match the patient's presentation.

Correct Answer: B

Rationale: The correct answer is B: Serotonin. Given the drug's effects, which are likely related to mood regulation and emotional stability, serotonin is the most likely neurotransmitter involved. Serotonin plays a key role in mood, anxiety, and depression. Acetylcholine (A) is more related to muscle movement and memory. Norepinephrine (C) is associated with the fight-or-flight response. GABA (D) is an inhibitory neurotransmitter, primarily involved in reducing neuronal excitability and promoting relaxation, not mood regulation.