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The Journal of Neurophysiology Vol. 84 No. 4 October 2000, pp. 1942-1948
Copyright ©2000 by the American Physiological Society
Neurobiology Research, Veterans Administration Medical Center, Sepulveda 91343; and Department of Psychiatry, School of Medicine, University of California, Los Angeles, California 90024
Hajnik, T.,
Y. Y. Lai, and
J. M. Siegel.
Atonia-Related Regions in the Rodent Pons and Medulla. J. Neurophysiol. 84: 1942-1948, 2000. Electrical stimulation of circumscribed areas of the pontine and
medullary reticular formation inhibits muscle tone in cats. In this
report, we present an analysis of the anatomical distribution of
atonia-inducing stimulation sites in the brain stem of the rat. Muscle
atonia could be elicited by electrical stimulation of the nuclei
reticularis pontis oralis and caudalis in the pons as well as the
nuclei gigantocellularis, gigantocellularis alpha, gigantocellularis
ventralis, and paragigantocellularis dorsalis in the medulla of
decerebrate rats. This inhibitory effect on muscle tone was a function
of the intensity and frequency of the electrical stimulation. Average
latencies of muscle-tone suppressions elicited by electrical
stimulation of the pontine reticular formation were 11.02 ± 2.54 and 20.49 ± 3.39 (SD) ms in the neck and in the hindlimb
muscles, respectively. Following medullary stimulation, these latencies
were 11.29 ± 2.44 ms in the neck and 18.87 ± 2.64 ms in the
hindlimb muscles. Microinjection of
N-methyl-D-aspartate (NMDA, 7 mM/0.1 µl)
agonists into the pontine and medullary inhibitory sites produced
muscle-tone facilitation, whereas quisqualate (10 mM/0.1 µl)
injection induced an inhibition of muscle tone. NMDA-induced muscle
tone change had a latency of 31.8 ± 35.3 s from the pons and
10.5 ± 0.7 s from the medulla and a duration of 146.7 ± 95.2 s from the pons and 55.5 ± 40.4 s from the
medulla. The latency of quisqualate (QU)-induced reduction of neck
muscle tone was 30.1 ± 37.9 s after pontine and 39.5 ± 21.8 s after medullary injection. The duration of muscle-tone
suppression induced by QU injection into the pons and medulla was
111.5 ± 119.2 and 169.2 ± 145.3 s. Smaller rats (8 wk old)
had a higher percentage of sites producing muscle-tone inhibition than
larger rats (16 wk old), indicating an age-related change in the
function of brain stem inhibitory systems. The anatomical distribution
of atonia-related sites in the rat has both similarities and
differences with the distribution found in the cat, which can be
explained by the distinct anatomical organization of the brain stem in
these two species.
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