Disinhibition in cat motor cortex by ammonia.

The effect of intravenously administered ammonium salts on postsynaptic inhibition of pyramidal tract cells was investigated in cat motor cortex. Extracellular recordings revealed that pyramidally or thalamically mediated inhibition of antidromic action potentials is abolished by ammonia. Intracellular recordings demonstrated that hyperpolarizing IPSPs vanished and EPSPs appeared while the inhibitory stimuli still triggered a decrease of neuronal resistance and the resting membrane potential was unchanged. It is concluded that ammonia disinhibited action-potential generation and EPSPs by shifting E(IPSP) to the level of the resting membrane potential. With disinhibition and facilitation replacing inhibitation of action potentials, ammonia clearly disturbs those cortical functions involving postsynaptic inhibition.