Responses of flexor alpha-motoneurones in cats anaesthetised with chloralose.

Abstract

1. Ninety flexor α-motoneurones mainly belonging to the PBST nucleus were examined in 27 cats anaesthetised with 50 mg/kg chloralose. 2. A fairly uniform intracellular response pattern was recorded on stimulation of ipsilateral cutaneous and muscle afferent fibres. There was an early EPSP corresponding to the flexor reflex; a second EPSP (usually with spikes superimposed) was designated a “chloralose EPSP” as it was associated with the chloralose jerk discharge recorded from the peripheral nerve; finally a prolonged hyperpolarisation, frequently associated with a reduction in synaptic activity. 3. The “chloralose EPSP” was more susceptible to increases in stimulus frequency and small doses of barbiturate than the flexor reflex EPSP. 4. The prolonged hyperpolarisation was unaltered by increased intracellular chloride ion concentration, and was therefore unlikely to be an IPSP generated at the motoneurone soma. 5. On spinal cord section, the flexor reflex EPSP and a late and prolonged hyperpolarisation were still recorded. However, the “chloralose EPSP” and the chloralose jerk discharge recorded from the peripheral nerve were abolished.