Intrathecal glutamate promotes glycinergic neuronal activity and inhibits the micturition reflex in urethane-anesthetized rats.
OBJECTIVE
In order to clarify the role of glutamate in the micturition reflex and in glutamatergic and glycinergic neuronal activity, we examined the effects of intrathecal (IT) injection of glutamate or MK-801 (an N-methyl-D-aspartate receptor antagonist) on bladder activity and on the glutamate and glycine levels in the lumbosacral cord of female rats with or without acute lower thoracic spinal cord injury (SCI).


METHODS
Under urethane anesthesia, isovolumetric cystometry was performed in rats with or without SCI before and after IT injection of glutamate or MK-801 at the lumbosacral cord level. The glutamate and glycine levels of the whole lumbosacral cord were measured after IT injection of glutamate or MK-801 in both groups.


RESULTS
In intact rats, IT glutamate (100 microg) prolonged the interval between bladder contractions and decreased the amplitude of contractions. IT MK-801 (3-100 microg) also prolonged the interval between bladder contractions and decreased the amplitude in intact rats. In SCI rats, cystometry demonstrated the disappearance of bladder contractions, and the glycine level in the lumbosacral cord was elevated. In intact rats, IT glutamate (0.3-100 microg) increased the glycine level in the lumbosacral cord. On the other hand, IT MK-801 (3-100 microg) decreased both glutamate and glycine levels in intact and SCI rats.


CONCLUSIONS
These results suggest that glutamatergic neurons have stimulatory projections to both glutamatergic and glycinergic neurons in the lumbosacral cord, and that glutamatergic neurons inhibit the micturition reflex by stimulating glycinergic neurons.
Ashitomi
Katsuhiro
K
Department of Urology, Faculty of Medicine, University of the Ryukyus, Okinawa, Japan.
Sugaya
Kimio
K
Miyazato
Minoru
M
Nishijima
Saori
S
Ogawa
Yoshihide
Y
D000818:Animals; D016291:Dizocilpine Maleate / Q000008:administration & dosage; D018691:Excitatory Amino Acid Antagonists / Q000008:administration & dosage; D005260:Female; D018698:Glutamic Acid / Q000008:administration & dosage* / Q000493:pharmacokinetics; D005998:Glycine / Q000378:metabolism*; D007278:Injections, Spinal; D008160:Lumbosacral Plexus; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000187:drug effects*; D013127:Spinal Nerves / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D001743:Urinary Bladder / Q000294:innervation* / Q000503:physiopathology; D014563:Urodynamics / Q000187:drug effects*
D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D005998:Glycine