Final answer:
A partial agonist has limited efficacy and can act as both an agonist and antagonist; Buprenorphine is an example, providing analgesic effects at lower doses and narcotic effects at higher doses. Agonists and antagonists modulate neural transmission by either mimicking or blocking the action of neurotransmitters, such as dopamine in Parkinson's disease or opiates in dependence treatments.
Step-by-step explanation:
A partial agonist is a type of drug that can act as an agonist or antagonist depending on the presence of other compounds, such as full agonists or the concentration of the natural ligand. Partial agonists have limited efficacy compared to full agonists, meaning they can activate receptors but only produce a submaximal response, even when all receptors are bound. An example of a partial agonist is buprenorphine, which acts on opioid receptors. Buprenorphine is an analgesic that can reduce pain without causing full opioid effects, and in higher doses, it exhibits narcotic properties with drowsiness and loss of consciousness.In cases like Parkinson's disease, dopamine agonists mimic the effects of dopamine by binding to dopamine receptors due to the low levels of neurotransmitter. On the other hand, naltrexone is an example of a narcotic antagonist that blocks the effect of opiates by binding to receptors without activating them, used in treatment programs for narcotic dependence. Antagonists essentially decrease neural transmission by blocking neurotransmitters, often through receptor site competition, which opposes the action of endogenous neurotransmitters.