Unit analysis of mesencephalic reticular formation control of spinal cord neurons

Abstract

1. 1. The cervical cord of the locally anesthetized and immobilized cat was explored with a microelectrode for neurons whose rates of spontaneous or evoked discharges were influenced by brainstem reticular formation stimulation. 2. 2. Four patterns of response were found: (a) the discharge rate of the unit was not affected; (b) the unit was driven by high rates of electrical stimulation of the reticular formation (HFD); (c) the unit was driven by low rates of stimulation (LFD); (d) the unit was inhibited by high rates of stimulation (HFD). 3. 3. HFD and HFI of spinal cord neurons are probably associated with a long latency multi-synaptic tegmento-bulbo-spinal tract. Low frequency driving (LFD) is probably associated with a short latency rubro-spinal or corticospinal tract. 4. 4. HFD is extremely sensitive to barbiturate depression, HFI much less so (and is probably of a pre-synaptic type) and LFD is the least sensitive. 5. 5. Stimulation of the mesencephalic reticular formation produces a mixture of excitatory and inhibitory impulses feeding onto the interneurons and motoneurons of the spinal cord. The net result is usually, but not always, excitation of spinal cord neurons. 6. 6. It is proposed that the long latency multi-synaptic tegmento-bulbo-spinal system represent an “ and” circuit such that learned patterns of sensory stimuli can influence spinal reflexes.