Abstract

The purpose of this study was to investigate involvement of xcitatory neurotransmitter for activation of rat vestibular nuclei following acute hemorrhagic hypotension. A single systemic injection of either K801 or CNQX resulted in a significant reduction in the number of pERK1/2-LI neurons activated by acute hypotension in the medial (MVN) and inferior vestibular nuclei, which was confirmed by Western blot analysis for pERK1/2 protein from the MVN. The MVN show a significant decrease in the number of cFos-LI neuron by pretreatment of MK801 as well as CNQX compared with that of saline group. A single injection of either MK801 or CNQX reversed hemorrhage-induced expression of mkp-1 mRNA in MVN wherein MK801 was likely more potent than CNQX. Furthermore, hemorrhagic hypotension induced phosphorylated forms of AMPA receptor in the MVN of rats with intact vestibular end organs but not in that of bilaterally labyrinthectomized rats. Microdialysis study also showed that hemorrhagic hypotension significantly increased the concentration of glutamate in the vestibular nuclei. These results suggest that glutamate receptors take part in transmission of excitatory afferent activity from the peripheral vestibular receptor to the central vestibular nuclear neurons following acute hemorrhagic hypotension (This study was supported by a grant of Vestibulocochlear Research Center from the Ministry of Science and Engineering).