Research paperEffects of reversible shutdown of the monkey flocculus on the retention of adaptation of the horizontal vestibulo-ocular reflex
Section snippets
Abbreviations used in the figures
- DP
dorsal paraflocculus
- FL
flocculus
- FR
Fresnel lens
- Lat
lateral
- LP
lobulus petrosus of the paraflocculus
- PLF
postero-lateral fissure which demarcates flocculus and ventral paraflocculus
- TT
turntable
- VN
vestibular nuclei
- VO
vestibular organ
- VP
ventral paraflocculus
- VIII
nerve VIII
Experimental procedures
Three males (monkeys TO, IR and MA) and one female (monkey YU) Macaca fuscata (body weight 5–7 kg) were used. Under 40 mg/kg of sodium pentobarbital (Nembutal, Dainippon, Tokyo, Japan) plus 5 mg/kg of ketamine (Ketalar, Sankyo, Tokyo, Japan) anesthesia and sterile conditions, the monkeys were surgically fitted with four anchor bolts and a cylinder for head fixation, and two chambers for drug injection. Sclera-search coil was also implanted in the left eye. After a 1-week recovery period, the
Adaptation of the HVOR
Collectively, adaptation of the HVOR was investigated in 17 sessions for the four monkeys; six for monkey TO, six for monkey IR, four for monkey YU and one for monkey MA. For monkey TO, IR and YU, a lidocaine solution was injected in half of the sessions, and the same amount of Ringer’s solution was injected in the remaining half. For monkey MA, only a lidocaine solution was injected. The gains and phases of the HVOR before the adaptation were 0.91±0.01 and 6.9±1.2° (n=6) for monkey TO,
Discussion
The present study reveals that 2 h of sustained visual–vestibular interactions induced adaptive gain increase in monkeys, which lasted at least for 1 h when the monkey’s head was fixed in darkness. This adaptive effect in the HVOR gain disappeared immediately after the local injections of 8 μl of 5 or 10% lidocaine chloride into the flocculi. These effects of lidocaine on the HVOR gain continued for 1 h. On the contrary, injections of Ringer’s solution into the flocculi hardly affected the HVOR
Acknowledgements
The authors are very grateful to Dr. Masao Ito (RIKEN, BSI) for his encouragement and valuable suggestions throughout the course of experiment and preparation of the manuscript.
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