Abstract
1. Pontine and bulbar reticular formation (RF) and Deiters' nucleus were stimulated stereotaxically with brief electric stimuli (2-3msec.) and their effects. on the intracellular potential of lumbar alpha motoneurons as wall as on the size of monosynaptic reflex were studied in the cat. Secondary effects through. the gamma efferents-muscle spindle loop were eliminated.
2. Stimulation of pontine RF, especially its rostral part, produced a marked inhibition of extensor monosynaptic reflex at a latency of 15-20msec. and a slight facilitation of flexor monosynaptic reflex at a latency of about 10msec.
3. Stimulation of Deiters' nucleus was facilitatory to extensor monosynaptic reflex. The facilitation appeared in two separate phases, the one set up at a latency of less than 10msec. with relatively short and simple time course and the other at a latency of 15-20msec. with a longer duration.
4. The effect of stimulation of the bulbar RF varied extensively with a, slight change in the electrode position. The most prevalent effect was facilitatory to extensor monosynaptic reflex, which in some cases resembled that of Deiters' nucleus in its time course.
5. Generally speaking, changes by stimulation of intracellular potential of spinal motoneurons reflected the influences elicitable from the same site upon the size of monosynaptic reflex. Facilitatory or inhibitory influence upon the reflex size could mostly be accounted for by the potential change of the motoneuron membrane which was most likely due to EPSP's and IPSP's.
6. Single spinal motoneurons fired from different levels of depolarization, when the rate of rise of depolarizing PSP's was different according to the stimulated site in the brain stem.
7. The effect of repetitive stimulation of the RF on the membrane potential. of single spinal motoneurons could be illustrated in general as a summated. effect of single stimulation of the same site.
8. Tonic suprasegmental influences and their modification by reticular stimulation were visualized as maintained discharges of descending tract fibers and. spinal interneurons.
9. A hypothetical accout for the decerebrate rigidity was put forward based on the present findings.
