Journal of Neuroscience, Vol 14, 6153-6159, Copyright © 1994 by Society for Neuroscience
Reduction of perineal evoked excitatory postsynaptic potentials in cat lumbar and sacral motoneurons during micturition
B Fedirchuk, JW Downie and SJ Shefchyk
Department of Physiology, University of Manitoba, Winnipeg, Canada.
These experiments were undertaken to examine whether both premotoneuronal
mechanisms and direct actions on motoneurons could contribute to
suppression of excitatory perineal reflex pathways during micturition.
Intracellular recordings were obtained from motoneurons innervating the
external urethral sphincter (EUS), external anal sphincter (EAS), and
selected hindlimb muscles in decerebrate male cats. The peak amplitudes of
EPSPs evoked by electrical stimulation of peripheral cutaneous afferents
were measured during micturition. In the EUS, EAS, and hindlimb motoneurons
examined, EPSPs produced by stimulation of perineal afferents (superficial
perineal or sensory pudendal nerves) were reduced in amplitude during
micturition. The sample of PSPs evoked by stimulation of hindlimb cutaneous
nerves recorded in hindlimb motoneurons revealed that these PSPs could also
be reduced. In contrast, no changes were seen in monosynaptic EPSPs evoked
by muscle afferent stimulation. The present study demonstrates that during
micturition there is a strong suppression of perineal reflexes to both
sphincter and hindlimb motoneurons. Since reduced EUS activity is required
for efficient micturition, suppression of the strong excitatory perineal
input to EUS motoneurons likely contributes to decreased EUS activity
during the bladder contraction. It appears that the micturition circuitry
utilizes both premotoneuronal mechanisms and direct motoneuronal inhibition
to achieve this reflex suppression. The function of the micturition-related
reduction of perineal reflexes to hindlimb or EAS motoneurons is not known
at this time and further investigations are required to elucidate the
interaction between micturition circuitry and hindlimb cutaneous pathways.
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