Spongy degeneration in the central nervous system of domestic animals. Part III: Occurrence and pathogenesis hepatocerebral disease caused by hyperammonaemia.
Severe spongy degeneration of the central nervous system (CNS) was seen in 11 cattle, 19 sheep, 4 pigs and 1 goat, associated with a variety of hepatic diseases, particularly those caused by hepatotoxic pyrrolizidine alkaloids. It was also seen in a milder form in 2 of 8 horses examined, 1 dog of 5 dogs examined, and in 1 rabbit only of a large number of laboratory animals examined. This paper reports results of experiments which confirmed initially that the CNS disease cold be caused by pyrrolizidine alkaloid intoxication. This was done by poisoning lambs with lasiocarpine. As the disease was seen in hepatoses not caused by pyrrolizidine alkaloids, the hypothesis that CNS spongy degeneration in lambs could follow any hepatic disease irrespective of its cause, was tested by poisoning lambs with allyl formate, an hepatotoxin chemically unrelated to pyrrolizidine alkaloids. Three of 4 lambs poisoned by the allyl formate showed spongy degeneration in their brains. As the CNS spongy degeneration was an apparent form of hepatocerebral disease, an experiment was conducted to show that the neural disease in sheep was caused by hyperammonaemia. CNS spongy degeneration developed in the brains of all sheep infused intravenously with ammonium acetate, and advanced spongy changes developed in the sheep infused for more than 3 days. The cerebral changes were probably temporary, since sheep infused for 5 days and retained for 3 weeks showed marked regression of vacuolation. Hyperammonaemia caused by intravenous ammonium acetate infusion is a simple, rapid model of CNS spongy degeneration. The syndrome, CNS spongy degeneration caused by hepatic failure and hyperammonaemia, is probably one of the morphologic expressions of hepatocerebral disease in domestic animals and could be an analogue of similar congenital and hepatocerebral diseases in man.