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 (O℃) (n=8),and two control groups,one with irrigation of the ear canal with warm water(38℃)(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 canalinduced 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±90)% (n=8) of the basal dialysate level (2.61±0.92)μmol/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.