Change of extracellular ascorbic acid in the brain cortex following ice water vestibular stimulation: an on-line electrochemical detection coupled with in vivo microdialysis sampling.
BACKGROUND
Ascorbic acid (AA) represents one of the most important enzyme co-factors, antioxidants and neuromodulators and plays an important role in the cerebral system. Increasing evidence has suggested that AA could treat certain kinds of vertigo diseases such as Meniere's disease. To elucidate the neurochemical functions associated with AA in vertigo, the change of extracellular AA in the brain cortex following caloric vestibular stimulation (CVS) was evaluated.


METHODS
An on-line electrochemical detection was coupled with in vivo microdialysis to continuously monitor the change of extracellular AA in the primary somatosensory (SI) area of guinea pigs following a caloric vestibular stimulation. Sixteen guinea pigs were divided into three groups, i.e., experimental group with irrigation of the ear canal with ice water (0 degrees C) (n = 8), and two control groups, one with irrigation of the ear canal with warm water (38 degrees C) (n = 4) and the other with irrigation of the auricle with ice water (n = 4).


RESULTS
In the experimental group, the ice water irrigation of the left external ear canal induced a horizontal nystagmus towards the right side lasting about 45 seconds. No nystagmus was induced by warm water irrigation of the external ear canal or by ice water irrigation of the auricle. The extracellular AA concentration significantly increased following the ice water vestibular stimulation, reaching a maximum of (130 +/- 20)% (n = 8) of the basal dialysate level (2.61 +/- 0.92) micromol/L (n = 8), lasting at least for an hour. AA level did not change distinctly after the irrigation of the left external ear canal with warm water or the irrigation of the auricle with ice water.


CONCLUSIONS
The concentration of extracellular AA in the brain cortex of the SI area increased following the ice water vestibular stimulation. This demonstration may be useful for the investigation of the neurochemical processes associated with AA in the process of vertigo.
Zhang
Na
N
Department of Otorhinolaryngology, Peking University Third Hospital, Beijing 100083, China.
Liu
Jun-xiu
JX
Ma
Fu-rong
FR
Yu
Li-sheng
LS
Lin
Yu-qing
YQ
Liu
Kun
K
Mao
Lan-qun
LQ
D000818:Animals; D001205:Ascorbic Acid / Q000032:analysis*; D002540:Cerebral Cortex / Q000378:metabolism*; D004563:Electrochemistry / Q000379:methods; D005110:Extracellular Space / Q000378:metabolism; D006168:Guinea Pigs; D007053:Ice; D008297:Male; D017551:Microdialysis / Q000379:methods; D010812:Physical Stimulation / Q000379:methods; D014722:Vestibule, Labyrinth / Q000503:physiopathology*
D007053:Ice; D001205:Ascorbic Acid