Final answer:
In hepatic encephalopathy, the neurotoxin is ammonia, which accumulates in the blood due to liver dysfunction and leads to neurotoxic effects on the CNS.
Step-by-step explanation:
The neurotoxin seen in hepatic encephalopathy is ammonia. Hepatic encephalopathy is a reversible neuropsychiatric abnormality that occurs in the setting of liver failure, which can be either chronic, as with cirrhosis, or acute. The liver normally metabolizes ammonia into urea for excretion, but with impaired liver function, ammonia accumulates in the blood and can cross the blood-brain barrier, leading to neurotoxic effects. High levels of ammonia in the blood are particularly toxic to the central nervous system (CNS), with symptoms that can range from mild cognitive impairment to coma and death. Prompt removal of ammonia is crucial, and in cases where liver function cannot be restored, treatments such as shunting may be necessary to lower the ammonia levels.