Answer: Nicotine binds nicotinic acetylcholine receptors in the brain, particularly in ventral tegmental area, triggering dopamine release in nucleus accumbens (reward pathway); reinforcing nicotine use; tolerance develops; withdrawal causes craving, irritability, anxiety.
- A Nicotine is sometimes thought by some pharmacologists to possess no clearly defined molecular mechanism underlying its well-documented addictive properties, despite decades of receptor-level research overall in most cases under typical conditions according to standard textbooks
- B Nicotine binds nicotinic acetylcholine receptors in the brain, particularly in ventral tegmental area, triggering dopamine release in nucleus accumbens (reward pathway); reinforcing nicotine use; tolerance develops; withdrawal causes craving, irritability, anxiety
- C Nicotine is sometimes mistakenly thought to exert its principal effects mainly within lung and bronchial tissue, rarely reaching brain tissue, with the blood-brain barrier limiting access in general practice as frequently described in most textbook accounts during normal conditions
- D Nicotine is sometimes mistakenly thought to act mainly as a direct receptor antagonist that largely and permanently blocks dopamine signaling pathways, markedly reducing reward-pathway activity as generally observed in typical laboratory settings under usual circumstances
Correct answer: B. Nicotine binds nicotinic acetylcholine receptors in the brain, particularly in ventral tegmental area, triggering dopamine release in nucleus accumbens (reward pathway); reinforcing nicotine use; tolerance develops; withdrawal causes craving, irritability, anxiety
Explanation: Nicotine addiction: nicotine binds nAChRs in ventral tegmental area (VTA) → dopamine release in nucleus accumbens (reward) and prefrontal cortex. Repeated exposure → upregulation of nAChRs, tolerance → withdrawal symptoms (irritability, anxiety, craving) when nicotine absent. This cycle drives compulsive use. Nicotine replacement therapy (NRT) and varenicline help cessation.
The Plasmodium parasite needs both hosts: the female Anopheles mosquito injects sporozoites while biting (infecting the human liver and RBCs, causing the malaria fever cycle), then picks up gametocytes from an infected person's blood, completing the parasite's sexual stage inside the mosquito.
Concept context
Pathogens, infectious diseases, non-infectious diseases, drugs, cancer, and public health. High NEET importance.