Disinhibition in cat motor cortex by ammonia.

Area of Science:

• Neuroscience
• Neurophysiology
• Motor Cortex Research

Background:

• Postsynaptic inhibition is crucial for regulating neuronal activity in the motor cortex.
• Understanding the effects of substances like ammonia on neuronal inhibition is vital for comprehending neurological function and dysfunction.

Purpose of the Study:

• To investigate the impact of systemically administered ammonium salts on postsynaptic inhibition in cat motor cortex pyramidal tract cells.
• To elucidate the specific mechanisms by which ammonia affects inhibitory postsynaptic potentials (IPSPs) and neuronal excitability.

Main Methods:

• Utilized extracellular and intracellular recordings in anesthetized cats.
• Administered ammonium salts intravenously to assess effects on antidromic action potentials and membrane potentials of pyramidal tract cells.

Main Results:

• Intravenous ammonia administration abolished both pyramidally and thalamically mediated inhibition of antidromic action potentials.
• Intracellular recordings showed the disappearance of hyperpolarizing IPSPs and the appearance of EPSPs.
• Neuronal resistance changes indicated intact inhibitory pathways, but the reversal potential for IPSPs (E(IPSP)) shifted to the resting membrane potential level.

Conclusions:

• Ammonia effectively disinhibits pyramidal tract cells by altering the E(IPSP), leading to impaired action potential generation and synaptic transmission.
• The findings suggest that ammonia significantly disrupts cortical functions that depend on intact postsynaptic inhibition, potentially leading to excitotoxicity or altered motor control.