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The Journal of Neurophysiology Vol. 82 No. 3 September 1999, pp. 1198-1208
Copyright ©1999 by the American Physiological Society
1Department of Physiology,
Yoshida, Kaoru,
Yoshiki Iwamoto,
Sohei Chimoto, and
Hiroshi Shimazu.
Saccade-Related Inhibitory Input to Pontine Omnipause
Neurons: An Intracellular Study in Alert Cats. J. Neurophysiol. 82: 1198-1208, 1999. Omnipause neurons (OPNs)
are midline pontine neurons that are thought to control a number of
oculomotor behaviors, especially saccades. Intracellular recordings
were made from OPNs in alert cats to elucidate saccade-associated
postsynaptic events in OPNs and thereby determine what patterns of
afferent discharge impinge on OPNs to cause their saccadic inhibition.
The membrane potential of impaled OPNs exhibited steep
hyperpolarization before each saccade that lasted for the whole period
of the saccade. The hyperpolarization was reversed to depolarization by
intracellular injection of Cl
ions, indicating it
consisted of temporal summation of inhibitory postsynaptic potentials
(IPSPs). The duration of the saccade-related hyperpolarization was
almost equal to the duration of the concurrent saccades. The time
course of the hyperpolarization was similar to that of the radial eye
velocity except for the initial phase. During the falling phase of eye
velocity, the correlation between the instantaneous amplitude of
hyperpolarization and the instantaneous eye velocity was highly
significant. The amplitude of hyperpolarization at the eye velocity
peak was correlated significantly with the peak eye velocity. The time
integral of the hyperpolarization was correlated with the radial
amplitude of saccades. The initial phase disparity between the
hyperpolarization and eye velocity was due to the relative constancy of
peak time (~20 ms) of the initial steep hyperpolarization regardless
of the later potential profile that covaried with the eye velocity. The
initial steep hyperpolarization led the beginning of saccades by
15.9 ± 3.8 (SD) ms, which is longer than the lead time for
medium-lead burst neurons. These results demonstrate that the pause of
activity in OPNs is caused by IPSPs initiated by an abrupt, intense
input and maintained, for the whole duration of the saccade, by
afferents conveying eye velocity signals. We suggest that the initial
sudden inhibition originates from central structures such as the
superior colliculus and frontal eye fields and that the eye
velocity-related inhibition originates from the burst generator in the
brain stem.
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