F. Baldissera et al., SHORT-LATENCY EXCITATION OF HINDLIMB MOTONEURONS INDUCED BY ELECTRICAL-STIMULATION OF THE PONTOMESENCEPHALIC TEGMENTUM IN THE RAT, Neuroscience letters, 169(1-2), 1994, pp. 13-16
The monosynaptic reflex response evoked by stimulating the dorsal root
L6 was greatly facilitated when a low intensity conditioning stimulus
was applied to the pontomesencephalic tegmentum (PT) 1-2 ms in advanc
e. When increasing the stimulus strength or the number of stimuli, mot
or discharges were recorded in the ventral roots and in nerves innerva
ting hindlimb muscles. The lowest threshold site for reflex facilitati
on was found in a region just ventral to the superior colliculus. A de
scending volley was recorded from the medulla midline, in the region o
f the medial longitudinal fascicle (MLF) and from the spinal cord surf
ace at thoracic and lumbar level. The latency of the descending volley
and of the motor responses indicates that excitation of hindlimb moto
neurons was due to activation of a disynaptic pathway having a relay i
n the lower brainstem. All spinal and peripheral responses evoked by P
T stimulation disappeared when a small electrolytic lesion was placed
in the MLF 1-2 mm rostral to the obex. The results show that in the ra
t the PT region may exert a powerful facilitatory action on hindlimb m
otoneurons.