Which of these is a sign of decreased activity in the parasympathetic nervous system due to heroin use?

The choice of slowed breathing is indeed associated with decreased activity in the parasympathetic nervous system due to the use of heroin. Heroin, an opioid, primarily affects the central nervous system by acting on specific receptors, which leads to various physiological responses. One of the key impacts of heroin is respiratory depression. This means that it slows down the breathing rate, which is a direct result of its depressant effects on the brain.

In contrast, increased appetite, heightened senses, and increased energy are not associated with the effects of heroin or decreased parasympathetic activity. Increased appetite may be seen in certain contexts, but the overall profile of heroin use typically leads to suppressed appetite. Heightened senses contradict the sedative nature of opioids, which dampen sensory perception rather than enhance it. Increased energy is also inconsistent, as heroin tends to produce relaxation and sedation, further supporting why slowed breathing is the characteristic sign of decreased parasympathetic nervous system activity in this context.