1. Cerebrospinal fluid (CSF) γ-aminobutyric acid (GABA) levels were measured in a dog model of spontaneous chronic portosystemic encephalopathy.

2. Dogs with congenital portacaval shunts (intra- or extra-hepatic) develop neurological features of abnormal psychomotor behaviour and depressed consciousness that are consistent with the symptoms of chronic portosystemic encephalopathy in humans. In the five dogs studied, plasma ammonia was elevated, as was CSF tryptophan, both usual biochemical abnormalities in portosystemic encephalopathy.

3. CSF levels of GABA in five dogs with portosystemic encephalopathy (100 ± 13 pmol/ml) were not significantly different from those in five control dogs (96 ± 14 pmol/ml). CSF levels of GABA were not altered after ammonia infusion.

4. If enhanced GABA-ergic neurotransmission, due to influx of gut-derived GABA into the brain, is responsible for the pathophysiology of chronic portosystemic encephalopathy in this model, it is not reflected by increased levels of GABA in CSF.

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