The Brain's Reward Pathway

• Scientist believe that heroin impacts the brain like other drugs of abuse, through the so-called reward pathway, a linked set of areas deep in the brain.
• The reward pathway is a neural network in the middle of the brain that prompts good feelings in response to certain behaviors, such as quenching thirst, relieving hunger, or having sex, thereby reinforcing these important evolutionary drives.

The Effect of Heroin on the Brain's Reward Pathway

• Heroin converges on this brain region, masquerading as natural chemicals - including dopamine, a neurotransmitter involved in the experience of pleasure - in those reward circuits.
• Heroin resembles the bits of protein in the brain and central nervous system that plug into internal receptors, the biochemical triggers that help regulate pain, pleasure, and emotion, and which otherwise produce effects identical to narcotics.
• Opiate-drug molecules can be thought of as perfectly shaped keys to the system of internal locks that activate the endorphin system.
• When heroin enters the brain's reward pathway it binds to opiate receptors causing the amount of dopamine in the synaptic clefts in the reward pathway to increase dramatically.

Heroin's Effect on the Limbic System

• The highest density of opioid receptors is found in the limbic system. Increased euphoria, relaxation, fearlessness and tolerance to pain is the result of heroin's effect on the limbic system, which controls emotions.
• Prolonged heroin use may cause the brain to adapt, so that it depends on the presence of the drug just to function normally. When a person abruptly stops using the drug the opposite of pleasure is experienced - anxiety, irritability, low mood, as well as physical symptoms of withdrawal.

Heroin's Effect on the Respiratory and Central Nervous Systems

• Opioids briefly stimulate the higher centers of the brain before depressing activity of the central nervous system, including such reflexes as coughing, breathing and heart rate. Extreme respiratory depression can result in death.
• Opiates can act as an analgesic by blocking pain messages transmitted by the spinal cord from the body.