Hypertonic activation of the renal betaine/GABA transporter is microtubule dependent.

BACKGROUND: Epithelial cells in the renal inner medulla accumulate osmolytes such as betaine to maintain normal cell volume during prolonged extracellular hypertonic stress. Betaine accumulation is the result of activation of transcription of the BGT1 transporter gene followed by increased betaine transport. METHODS: We studied the possible role of microtubules in this adaptive mechanism using renal cells in culture. RESULTS.: In cultured renal cell lines [Madin-Darby canine kidney (MDCK) and mouse inner medullary collecting duct (mIMCD-3)], up-regulation of BGT1 activity was maximal after 24 to 30 hours in growth medium made hypertonic (510 mOsm/kg) by the addition of sucrose or NaCl. Up-regulation was reversed within 24 to 36 hours after returning cells to isotonic medium. Both cycloheximide (20 micromol/L) and nocodazole (20 micromol/L) blocked the hypertonic up-regulation of BGT1. Nocodazole was partially effective even when added 16 to 20 hours after the switch to hypertonic medium. Recovery from nocodazole action was rapid, and there was full activation of BGT1 transport within three to six hours after nocodazole removal, suggesting rapid trafficking to the cell surface once microtubules repolymerized. Hypertonic activation of BGT1 transport was detected in an isolated membrane fraction and was blocked by cycloheximide but not by nocodazole. Confocal microscopy confirmed the increased abundance of BGT1 proteins in the plasma membrane of hypertonic cells and showed that BGT1 remained intracellular during nocodazole treatment. CONCLUSIONS: Hypertonic activation of BGT1 in renal cells requires de novo protein synthesis and microtubule-dependent trafficking of additional transporters to the cell surface. The apparent resistance of membrane BGT1 to nocodazole blockade is likely due to the presence in the membrane fraction of an increased intracellular pool of active BGT1 transporters.

The central role of the prefrontal cortex in directing attention to novel events.

The physiological basis for the striking decrease of attention to novel events following frontal lobe injury is poorly understood. In this study, event-related potentials (ERPs) were recorded from patients with frontal lobe damage and matched subjects, who controlled the duration of viewing of background, novel and target stimuli. Frontal lobe patients did not differ from normal controls in terms of age, education, estimated IQ or mood. However, they were judged to be more apathetic as measured by self-report and informants' ratings. Patients with frontal lobe damage exhibited markedly reduced amplitude of the novelty P3 response and the duration of viewing of novel stimuli. In contrast, injury to the frontal lobes had a limited impact on P3 amplitude and behavioural responses (viewing duration and reaction time) to target stimuli. A strong correlation was found between measures of apathy and both attenuated P3 amplitude and viewing duration in response to novel but not target stimuli. Differences in amplitude of the novelty P3 response explained a large portion of the variance associated with duration of viewing of novel stimuli. After controlling for the influence of P3 amplitude, there was no association between frontal lobe injury and reduced viewing of novel stimuli. The results of this study suggest that frontal lobe damage leads to diminished visual attention to novel events through its disruption of neural processes underlying the novelty P3 response. These processes appear to regulate the allocation of attentional resources and early exploratory behaviours, and are not limited to immediate orienting responses. Damage to the frontal lobes may prevent the generation of a signal which indicates that a novel event in the environment requires additional attention due to its potential behavioural significance. The disruption of these processes is likely to contribute to the apathy observed in patients after injury to the frontal lobes.

Disruption of attention to novel events after frontal lobe injury in humans.

OBJECTIVE: To investigate whether frontal lobe damage in humans disrupts the natural tendency to preferentially attend to novel visual events in the environment. METHODS: Nine patients with chronic infarctions in the dorsolateral prefrontal cortex (DLPFC) and 23 matched normal controls participated in a study in which subjects viewed repetitive background stimuli, infrequent target stimuli, and novel visual stimuli (for example, fragmented or "impossible" objects). Subjects controlled viewing duration by a button press that led to the onset of the next stimulus. They also responded to targets by pressing a foot pedal. The amount of time spent looking at the different kinds of stimuli, and the target detection accuracy and speed served as dependent variables. RESULTS: Overall, normal controls spent significantly more time than frontal lobe patients looking at novel stimuli. Analysis of responses across blocks showed that initially frontal lobe patients behaved like normal controls by directing more attention to novel than background stimuli. However, they quickly began to distribute their viewing time evenly between novel and background stimuli, a pattern that was strikingly different from normal controls. By contrast, there were no differences between frontal lobe patients and normal controls for viewing duration devoted to background and target stimuli, target detection accuracy, or reaction time to targets. Frontal lobe patients did not differ from normal controls in terms of age, education, estimated IQ, or mood, but were more apathetic as measured by self report and informants' judgments. Attenuated responses to novel stimuli significantly correlated with degree of apathy. CONCLUSIONS: This study demonstrates that DLPFC injury selectively impairs the natural tendency to seek stimulation from novel and unusual stimuli. These data provide the first quantitative behavioural demonstration that the human frontal lobes play a critical part in directing and sustaining attention to novel events. The impairment of novelty seeking behaviour may contribute to the characteristic apathy found in patients with frontal lobe injury.

Excision of cortical dysplasia in the language area with use of a surgical navigator: a case report.

PURPOSE: We have developed an intraoperative optical tracking-based navigational system that allows localization in the operative space. Using three-dimensional reconstruction, this system has provided precise spatial information for intraoperative cortical mapping in patients with intractable epilepsy in whom the lesion lies close to eloquent cortex. METHODS: A 23-year-old man with intractable complex partial seizures (CPS) presented to our institution. Proton-density magnetic resonance imaging (MRI) showed a 3-cm lesion which lay 2 cm beneath the left frontal operculum. A three-dimensional model of the patient was reconstructed using MR modalities. Intraoperatively, subdural grid and strips were placed over the lesion and their electrodes were registered to the three-dimensional model, which was displayed on a monitor. The navigational system was used to localize each electrode on the three-dimensional model. By the second operation, the sites of seizure activity were established and recorded on the three-dimensional model. A bipolar stimulator was also used to determine the speech area. RESULTS: The lesion, which proved to be cortical dysplasia, was removed completely and the cortical speech area was avoided. During the postoperative period, the patient had no neurological symptoms and no seizure activity. CONCLUSIONS: The localization of a lesion and its correlation with epileptogenic foci is important in optimizing treatment in patients with cortical dysplasia. Our navigational system provided accurate localization of the lesion and correlation with the epileptogenic focus and related eloquent cortex. We believe that the safe removal of the lesion was facilitated by this system.

Three-dimensional image reconstruction for low-grade glioma surgery.

Three-dimensional image reconstruction for preoperative surgical planning and intraoperative navigation for the resection of low-grade gliomas was performed in 20 patients. Thirteen of these surgeries were performed while the patient received a local anesthetic to allow for cortical mapping. Ninety percent of the patients were functionally intact postoperatively. The authors propose that the combination of the three-dimensional image reconstruction and surgical navigation, in conjunction with intraoperative cortical mapping, provides an additional means for surgeons to improve the safety and precision of the procedures.

Three-dimensional reconstruction and surgical navigation in pediatric epilepsy surgery.

We have used MRI-based three-dimensional (3D) reconstruction and a real-time, frameless, stereotactic navigation device to facilitate the removal of seizure foci in children suffering from intractable epilepsy. Using this system, the location of subdural grid and strip electrodes is recorded on the 3D model to facilitate focus localization and resection. Ten operations were performed, including 2 girls and 8 boys ranging in age from 3 to 17, during which 3D reconstruction and surgical instrument tracking navigation was used. In all the cases, the patients tolerated the procedure well and showed no postoperative neurological deficits. We believe this to be a valuable tool for a complete and safe resection of seizure foci, thereby reducing the incidence of postoperative neurological deficits and significantly improving the overall quality of life of the patients.