Residual vestibular function after vestibular schwannoma surgery.

OBJECTIVES: This study aimed to assess vestibular function in 39 patients who underwent neurectomy for vestibular schwannoma. METHOD: Semicircular canal reactivity was measured by video head-impulse test using high-frequency passive head acceleration. Response gain was calculated as a ratio between the areas under the eye-velocity curve and the head-velocity curve. STATISTICAL ANALYSIS: Student t-test was used for to compare quantitative variables. ANOVA was used to test inter-group differences in categoric variables. RESULTS: In all cases, surgery-side gain on head impulse test was low, with increased gain asymmetry. A subgroup of 7 patients (18%) showed relatively high gain in vestibulo-ocular reflex on the surgery side. Caloric reaction was absent in all cases. These findings indicate that residual vestibular function can be conserved following vestibular schwannoma extirpation. CONCLUSION: Cases with moderate vestibulo-ocular reflex gain were a subgroup with partial conservation of vestibular nerve fibers. Whether this is a predictor of better functional prognosis remains to be elucidated. Higher gain correlated with less extensive surgery and sparing of the inferior vestibular nerve. Low gain correlated with complete vestibular neurectomy. This information may guide rehabilitation strategy following surgery.

Hydration-induced changes of structure and vibrational frequencies of methylphosphocholine studied as a model of biomembrane lipids.

The chemical characteristics of the polar parts of phospholipids as the main components of biological membranes were investigated by using infrared (IR) spectroscopy and theoretical calculations with water as a probe molecule. The logical key molecule used in this study is methylphosphocholine (MePC) as it is not only a representative model for a polar lipid headgroup but itself has biological significance. Isolated MePC forms a compact (folded) structure which is essentially stabilized by two intramolecular C-H...O type hydrogen bonds. At lower hydration, considerable wavenumber shifts were revealed by IR spectroscopy: the frequencies of the (O-P-O)- stretches were strongly redshifted, whereas methyl and methylene C-H and O-P-O stretches shifted surprisingly to blue. The origin of both red- and blueshifts was rationalized, on the basis of molecular-dynamics and quantum-chemistry calculations. In more detail, the hydration-induced blueshifts of C-H stretches could be shown to arise from several origins: disruption of the intramolecular C-H...O hydrogen bonds, formation of intermolecular C-H...O(water) H-bonds. The stepwise disruption of the intramolecular hydrogen bonds appeared to be the main feature that causes partial unfolding of the compact structure. However, the transition from a folded to extended MePC structure was completed only at high hydration. One might hypothesize that the mechanism of hydration-driven conformational changes as described here for MePC could be transferred to other zwitterions with relevant internal C-H...O hydrogen bonds.

Lipid hydration: headgroup CH moieties are involved in water binding.

To explore the interaction potential of phospholipids, we have studied the hydration of diacyl phosphatidylcholine (PC) and methylphosphocholine (MePC), a pertinent model compound, by ir spectroscopy. Related ab initio Hartree-Fock calculations were performed for MePC. Water is considered ideal as a relevant probe molecule. Spectroscopic data for MePC reveal a strong influence of bound hydration water not only on the phosphate groups but also onto the putatively apolar CH(n) groups. The same could be demonstrated for deuterated dimyristoyl PC taken as a "complete" lipid molecule: both headgroup methyl and methylene moieties are gradually, but remarkably affected by hydration, as evidenced by strong wavenumber upshifts of C-H stretching vibration bands. These findings may originate in directed interactions of the CH(n) groups with bound water molecules, but hydration-driven conformational changes of PC headgroups could also occur. The results of the ab initio calculations rationalize the first explanation by predicting a substantial contribution of specific C-H...OH(2) interactions, mainly characterized by a dramatic loss of electron density of the sigma* antibonding molecular orbitals of C-H bonds. Hence, the propensity of the lipid headgroup methyl and methylene groups to act as donor sites in hydrogen bonding must no longer be ignored when considering the interaction potential of PCs.