Evaluating Current Density Modeling of Non-Invasive Eye and Brain Electrical Stimulation Using Phosphene Thresholds

Because current flow cannot be measured directly in the intact retina or brain, current density distribution models were developed to estimate it during magnetic or electrical stimulation. A paradigm is now needed to evaluate if current flow modeling can be related to physiologically meaningful signs of true current distribution in the human brain. We used phosphene threshold measurements (PTs) as surrogate markers of current-flow to determine if PTs, evoked by transcranial alternating current stimulation (tACS), can be matched with current density estimates generated by head model-based computer simulations. Healthy, male subjects (n=15) were subjected to three-staged PT measurements comparing six unilateral and one bilateral stimulation electrode montages according to the 10/20 system: Fp2-Suborbital right (So), Fp2-right shoulder (rS), Fp2-Cz, Fp2- O2, So-rS, Cz-F8 and F7-F8. The stimulation frequency was set at 16 Hz. Subjects were asked to report the appearance and localization of phosphenes in their visual field for every montage. Current density models were built using multi-modal imaging data of a standard brain, meshed with isotropic conductivities of different tissues of the head using the SimBio and SCIRun software packages. We observed that lower PTs were associated with higher simulated current levels in the unilateral montages of the model head, and shorter electrode distances to the eye had lower PTs. The lowest mean PT and the lowest variability were found in the F7-F8 montage (95±33 μA). Our results confirm the hypothesis that phosphenes are primarily of retinal origin, and they provide the first in vivo evidence that computer models of current flow using head models are a valid tool to estimate real current flow in the human eye and brain.

[The 2-Scale Model of the National Eye Institute Visual Function Questionnaire (NEI-VFQ) to Assess Vision-Related Quality of Life]

Aim This study addresses the examination of the factorial validity of the National Eye Institute Visual Function Questionnaire 39 (NEI-VFQ 39) and the neuro-ophthalmological supplement in a German sample. Method Eighty-one patients with visual field defects affecting at least one eye answered the NEI-VFQ 39 and the supplement. Theoretical factor structures reported in the manuals were examined in confirmatory factor analysis. Because of a misfit, items retained after item analysis were subjected to exploratory factor analysis. Results The originally postulated factor structures could not be replicated. Many items revealed floor effects. The 21 remaining items could be assigned to two factors - "visual functioning" and "socio-emotional impairment". Conclusion The weakness of the theoretical factors can be avoided by using the 2-scale model.

Repetitive Transcorneal Alternating Current Stimulation Reduces Brain Idling State After Long-term Vision Loss

BACKGROUND

Deafferentation of visual system structures following brain or optic nerve injury leaves cortical areas deprived of visual input. Deprived cortical areas have a reduced sensory information processing and are characterized with localized enhanced or synchronized rhythms believed to represent an "idling state".

OBJECTIVE/HYPOTHESIS

We hypothesized that cortical idling can be modified with transcorneal alternating current stimulation (tACS) known to modulate cortical oscillations and thus change the functional state of the deafferented areas.

METHODS

tACS was applied in rat model of severe optic nerve crush using a protocol similar to our clinical studies (200 μA, 2-8 Hz) for 5 treatment days right after the lesion and at the chronic stage (3 months later). EEG and VEP were recorded over the visual cortices. In vivo confocal neuroimaging of the retina and histology of the optic nerves were performed.

RESULTS

Morphological investigations showed massive retinal ganglion cells death and degeneration of the optic nerves after crush. Visual loss was associated with increased EEG spectral power and lower coherence, indicating an "idling state". Stimulation induced a significant decrease of EEG power towards normal values. These effects were especially pronounced in the chronic stage.

CONCLUSION

Our results suggest that alternating current injected via the eye is able to modulate visually deprived brain areas and thus reduce cortical idling.

Structural abnormalities in early Tourette syndrome children: a combined voxel-based morphometry and tract-based spatial statistics study

Tourette Syndrome (TS) is characterized with chronic motor and vocal tics beginning in childhood. Abnormality of both gray (GM) and white matter (WM) has been observed in cortico-striato-thalamo-cortical circuits and sensory-motor cortex of adult TS patient. It is not clear if these morphological changes are also present in TS children and if there are any microstructural changes of WM. To understand the developmental cause of such changes, we investigated volumetric changes of GM and WM using VBM and microstructural changes of WM using DTI, and correlated these changes with tic severity and duration. T1 images and Diffusion Tensor Images (DTI) from 21 TS children were compared with 20 age and gender matched health control children using a 1.5T Philips scanner. All of the 21 TS children met the DSM-IV-TR criteria. T1 images were analyzed using DARTEL-VBM in conjunction with statistical parametric mapping (SPM). Diffusion tensor imaging (DTI) analysis was performed using Tract-Based Spatial Statistics (TBSS). Brain volume changes were found in left superior temporal gyrus, left and right paracentral gyrus, right precuneous cortex, right pre- and post- central gyrus, left temporal occipital fusiform cortex, right frontal pole, and left lingual gyrus. Significant axial diffusivity (AD) and mean diffusivity (MD) increases were found in anterior thalamic radiation, right cingulum bundle projecting to the cingulate gurus and forceps minor. Decreases in white matter volume (WMV) in the right frontal pole were inversely related with tic severity (YGTSS), and increases in AD and MD were positively correlated with tic severity and duration, respectively. These changes in TS children can be interpreted as signs of neural plasticity in response to the experiential demand. Our findings may suggest that the morphological and microstructural measurements from structural MRI and DTI can potentially be used as a biomarker of the pathophysiologic pattern of early TS children.

Altered white matter integrity in adolescents with prelingual deafness: a high-resolution tract-based spatial statistics imaging study

BACKGROUND AND PURPOSE

Prelingual deafness is a hearing loss that occurs before language is acquired and may result in brain structural alterations. We studied microstructural WM alterations in prelingually deaf adolescents by using DTI. We hypothesized that any morphologic alterations are mainly located in the auditory association areas. Furthermore, considering that the developing brain is both more vulnerable to deprivation and more plastic than the adult brain, we speculated that the affected areas should be larger than those previously reported in adult deafness.

MATERIALS AND METHODS

Diffusion tensor images were obtained from 16 prelingually deaf adolescents (age range, 10-18 years) and 16 healthy control adolescents matched for age and sex. Both groups were compared in fractional anisotropy and radial diffusivity by tract-based spatial statistics. In addition, we examined the correlation between the structural data (FA, RD) differences and the duration of sign language use and hearing aid experience.

RESULTS

Prelingually deaf adolescents had significantly lower FA and increased RD in the bilateral superior temporal gyri, Heschl gyrus, planum polare, and the splenium of the corpus callosum. Only RD values in the right superior temporal gyrus correlated significantly and negatively (r = -0.518; P = .040) with duration of sign language use. These alterations were larger than those previously reported in adult deafness.

CONCLUSIONS

As expected, we found severe morphologic changes of decreased FA and increased RD in multiple auditory association areas and in the corpus callosum. These changes are signs of development impairments in prelingually deaf adolescents, possibly reflecting axonal loss or lack of myelination.

Visual field enlargement after computer training in brain-damaged patients with homonymous deficits: an open pilot trial

Brain damage is often accompanied by homonymous hemianopia, but few therapeutic approaches exist for visual field deficits. In this open pilot study we describe a computerized training program which may possibly reduce the size of the 'blind' visual field in patients with homonymous visual field deficits. Various stimuli to test light perception and discrimination of colors and shapes were presented on a monitor which permitted the examination or training of the central section of the visual field up to about 25° vertical and 40° horizontal eccentricity. Eleven patients trained at home for 1 h each day for a total of 80-300 h. Their results were compared with those of three patients who opted not to participate in the training procedure or those with very little therapy. These latter subjects had a slight decrease in the visual field size after about 1 year. In contrast, the treatment group displayed a reliable enlargement of visual field size. This was revealed by a significant improvement in the detection of small light stimuli, an increase in the ability to discriminate colors and a minor, but notable, improvement of shape discrimination in the blind areas of the visual field. Additional training of shape recognition led to further improvement of shape discriminations, even when the patients trained with very different kinds of shapes, e.g. lines or letters. Outcome depended on age of the patients and the size of the lesion, but it was independent of on-set of treatment and cause of the lesion. Only two of the 11 patients with treatment showed no significant improvement. This study suggests that regular home training of the 'blind' visual field with computer-controlled stimuli may lead to improvement in vision. However, because of the following methodological limitations results are only preliminary: (1) the trial did not contain a true placebo group, (2) the patients were not assigned randomly to a control or treatment condition, (3) the lack of defined inclusion criteria considerably increased the variance in neuropsychological performance, (4) because the experimental design was not double blind, experimenter bias cannot be ruled out, and (5) the conditions of the home training could not be standardized. The results warrant a larger randomized, double-blind controlled trial.

Quantification of the human lateral geniculate nucleus in vivo using MR imaging based on morphometry: volume loss with age

BACKGROUND AND PURPOSE

Because it is a small subcortical structure, the precise measurement of the human LGN is still a technical challenge. In this article, we identify the LGN in vivo, measure its volume based on high-resolution MR imaging, and then relate its volume to subject age to evaluate the potential clinical application.

MATERIALS AND METHODS

A semiautomatic LGN isolation method was developed on scans obtained with 1.5T MR imaging, which involves highlighting the surrounding landmarks, obtaining candidate LGN voxels with a region-growing algorithm, and isolating the LGN from the ventral diencephalon. The method was accessed with a test-retest reliability on the results from 55 healthy subjects at different ages.

RESULTS

This method showed high test-retest within-subject reliability (ICC, 0.950 and 0.948 in left and right hemispheres, respectively) among 3 independent measurements in each subject. The unilateral volume was highly variable, ranging from 52 to 102 mm(3) in the left and 66 to 105 mm(3) in the right hemisphere, with significantly larger volumes on the right (86 mm(3)) than on the left (77 mm(3)). The combined bilateral volumes (controlled for ICV) significantly decreased in size with progressing age from 20 to 65 years (r = -0.512, P = .000). There was no sex difference in bilateral LGN volumes (male/female: 163.1 ± 18.2/162.2 ± 21.4 mm(3)).

CONCLUSIONS

Using our new technique, we were able to reliably determine the human LGN volume in vivo, which was found to decline with age. The volumes obtained by our method corresponded well with previously reported postmortem values, so our method may be considered to be superior for investigating the pathology of LGN.

Restoration of vision after optic nerve lesions with noninvasive transorbital alternating current stimulation: a clinical observational study

BACKGROUND

Non-invasive current stimulation can induce neuroplastic changes in the normal brain, including visual system structures. Because it is not known if such plasticity is of clinical value, we wished to learn if vision restoration can be induced after optic nerve damage.

METHODS

In an open-label, clinical observational study 446 patients with optic nerve lesions were treated with non-invasive repetitive transorbital alternating current stimulation (rtACS). Current bursts (<1000 μA, 5-20 Hz) were applied to induce phosphenes for one or two 10-day stimulation periods. Efficacy was assessed by monocular measurements of visual acuity and visual field (VF) size. EEG recordings at rest (n = 68) were made before and after treatment and global power spectra changes were analyzed.

RESULTS

rtACS improved VF size in the right and left eye by 7.1% and 9.3% (p < 0.001), respectively. VF enlargements were present in 40.4% of right and 49.5% of left eyes. Visual acuity (VA) significantly increased in both eyes (right = 0.02, left = 0.015; p < 0.001). A second 10-day course was conducted 6 months in a subset of 62 patients and resulted in additional significant improvements of VA. Analysis of EEG power spectra revealed that VA and VF improvements were associated with increased alpha power. Increased theta power was observed in patients that had only VF enlargements but no VA change. In contrast, non-responders had increased delta power spectra in frontal and occipital areas.

CONCLUSIONS

rtACS leads to long-lasting improvements in VA and VF size and after-effects in EEG power spectra. Because physiological and clinical parameters are correlated we hypothesize that rtACS enhances plasticity by inducing synchronization in different cortical regions, but the precise mechanisms needs further clarification. These encouraging results require confirmation by controlled clinical trials.

Special issues in brain plasticity, repair and rehabilitation: 20 years of a publishing strategy

The journal Restorative Neurology and Neuroscience (RNN) is focused on the emerging field of brain plasticity, repair and rehabilitation, including original and review papers both in basic research (in vitro studies, animal experiments) and in the clinical domain, including brain imaging studies. The publication of special issues on vital topics, summarizing the work of leading experts in the field of restoration and plasticity has become a major strategy of RNN and has attracted worldwide attention. Special issues are typically organized by specialized guest-editors familiar with the respective science field. Special issues cover a particular sub-discipline and often contain laboratory review papers. The first special issue appeared in 1990, and until today RNN has published a total of 25 special issues on a variety of basic science and clinical matters. In this way, RNN promotes the dissemination of information in the field of neuroplasticity, repair and rehabilitation, providing the reader with up-to-date information prepared by leading experts in the field.

Publishing in the field of brain plasticity, repair and rehabilitation: The 20th Anniversary issue of Restorative Neurology and Neuroscience

The journal Restorative Neurology and Neuroscience (RNN) now celebrates its 20th anniversary. Since 1989 RNN has published scientific findings in the emerging fields of brain plasticity, repair and rehabilitation via original scientific publications and review papers in basic research (animal experiments, in vitro studies) and clinical science. During the last decade RNN had a steady progress in reference value and scientific impact, reaching an ISI-impact factor of 1.978 (2008) and has published a total of 717 papers. The journal's success can be explained by different factors: (1) neuroplasticity, regeneration, recovery and rehabilitation have developed to main stream subjects with a worldwide increase in the number of publications and their citation rate, (2) RNN has published numerous special issues which summarize the work of leading experts in specialized sub-fields, (3) a dedicated, highly qualified editorial board (4) the quality of papers submitted to RNN has increased over time. RNN has now become a visible and leading source of original scientific information in the space of brain plasticity, rehabilitation and repair.

[Do patients undergo changes of their personality due to visual field defects? An investigation with FPI-R and NEI-VQ]

BACKGROUND

Visual restrictions can lead to anxiety and possibly to social retirement. Therefore it makes sense to assess the patients' degree of handicap. The goal of the present study was to investigate if patients show changes in their personality or a reduced quality of life as a result of their visual field defect.

METHODS

15 patients with visual field defects were asked to fill out the revised version of the Freiburger Persönlichkeitsinventar (FPI-R) and the National Eye Institute Visual Function Questionnaire (NEI-VFQ). The FPI-R encompasses the standardised recording of many personality traits whereas the NEI-VFQ addresses the visual quality of life.

RESULTS

In the total sample all FPI-R scales were appropriate for the study in the inconspicuous standard range. Slight shifts resulted toward increased willingness to make contacts (scale 4, ST 4.2), reduced physical strain (scale 7, ST 4.3) and lower physical discomfort (scale 8, ST 3.7). The size of the visual field defect does not correlate with the satisfaction with life, with the physical discomfort and with the state of health but with the dependency on others (p = 0.047) and with the exertion of their social roles (p = 0.043). The scale "satisfaction with life" of the FPI-R correlated with the scale "psychic condition" of the NEI-VFQ (p = 0.028) and the physical discomfort showed a significant correlation with the scale "eye strain" (p = 0.006) in the NEI-VFQ.

DISCUSSION

Contrary to our presumptions, patients with visual field defects did not show any changes in their personality. It is supposed that they have learned to compensate for their reduced visual functions.

Two faces of calcium activation after optic nerve trauma: life or death of retinal ganglion cells in vivo depends on calcium dynamics

Calcium elevations after neurotrauma are not only implicated in cell death but may contribute to adaptive plasticity. We now wished to resolve this contradiction by following calcium dynamics after optic nerve crush in vivo. Adult rats received no injury (n = 5), unilateral mild (n = 10) or moderate optic nerve crush (n = 10) (ONC), or axotomy (n = 5). Before surgery, retinal ganglion cells (RGCs) were retrogradely labelled with Oregon Green BAPTA-dextran, a fluorescent calcium marker. Calcium-related fluorescence intensity (FI) was repeatedly measured in individual RGCs in vivo using the in vivo confocal neuroimaging (ICON) method. Four different RGC types were found. Normal RGCs without FI change were found in sham rats and also in both ONC groups. RGCs with mild damage were seen only after mild ONC, showing an initial calcium depression of 26% at day 4 followed by a 169% increase 15 days after ONC. RGCs with moderate damage were found only after moderate ONC and showed calcium hypoactivation followed by a slower return toward baseline and a delayed calcium increase of 72% above baseline. Sixty to sixty-five per cent of the RGCs in both ONC groups and all RGCs in the axotomy group died within 6 days following a fast and massive calcium increase of 316% with a concomitant 156% soma size increase. In conclusion rapid calcium elevation leads to cell death, while an initial calcium depression followed by a delayed and moderate calcium hyperactivation is associated with cell survival. We propose that immediate, massive calcium activation is maladaptive whereas delayed and moderate hyperactivation of surviving cells is adaptive. Implications for pharmacotherapy are discussed.

Visual hallucinations during spontaneous and training-induced visual field recovery

Visual hallucinations after post-geniculate visual system lesions were shown to be associated with spontaneous recovery of visual functions. We investigated the occurrence of hallucinations during spontaneous recovery and additionally tested whether hallucinations were re-instated in a phase of vision restoration therapy (VRT). Nineteen patients with post-geniculate lesions and homonymous visual loss participated in a prospective study, and 121 patients with various lesions were included in a retrospective study using a questionnaire including verbal descriptions as well as drawings of hallucinations experienced by the patients. In both samples, visual-field size was determined before and after 6 months of VRT. Many patients in both groups experienced post-lesion hallucinations (mostly colors, objects, motion) which subsided after spontaneous recovery of visual functions (increase of visual field size, recovery of more complex visual function) was ended. Hallucinations re-emerged during training. However, the majority of patients reported simple, unformed visual hallucinations (uncolored phosphenes, spots, flashes), especially when visual field recovery was most intense. Hallucinations were mainly found in patients with large shifts of the visual field border. They occurred in blind areas, particularly in areas of residual vision where recovery was predominantly observed. Hallucinations may reflect functional recovery in partially lesioned brain areas. While the colored/formed hallucinations during spontaneous recovery may represent non-specific activation of higher visual areas, the simple, unformed training-related hallucinations may indicate recovery in the primary visual cortex during treatment. Hallucinations should not generally be discarded as pathological or unimportant symptoms, but they may be functional indicators of visual system plasticity.

Publishing in the field of brain plasticity, repair and rehabilitation: an emerging neuroscience niche journal

The journal Restorative Neurology and Neuroscience (RNN) is now published in its 25th volume since its inception in 1989. RNN focuses on the emerging field of brain plasticity, repair and rehabilitation, including original and review papers both in basic research (animal experiments, in vitro studies) and in the clinical domain, including brain imaging studies. During the last decade RNN has experienced a steady progress in its reference value and scientific impact. The ISI-impact factor has risen from 1.117 (1997) to 2.862 (2006). This places the journal at the 81st rank among all 200 neuroscience journals, i.e. 60% of all neuroscience journals have a lower impact factor. When compared to other journals in the field of rehabilitation, RNN ranks number 1. Causes for this positive development are, among others: (1) the field of neuroplasticity, regeneration, recovery and rehabilitation is an emerging field in medicine and therefore the number of publications and their citation rate overall increases, (2) the special issues strategy, (3) a top level editorial board, and (4) the quality of papers submitted to RNN continuously improves as RNN is gaining increasing acceptance in the scientific community. Thus, in the space of neuroscience in general, and rehabilitation in particular, RNN has become a visible, high impact journal and a leading source of original scientific information pertaining to brain plasticity , rehabilitation and repair. RNN is likely to gain more momentum as the field matures further.

Does visual restitution training change absolute homonymous visual field defects? A fundus controlled study

AIM

To examine whether visual restitution training (VRT) is able to change absolute homonymous field defect, assessed with fundus controlled microperimetry, in patients with hemianopia.

METHODS

17 patients with stable homonymous visual field defects before and after a 6 month VRT period were investigated with a specialised microperimetric method using a scanning laser ophthalmoscope (SLO). Fixation was controlled by SLO fundus monitoring. The size of the field defect was quantified by calculating the ratio of the number of absolute defects and the number of test points; the training effect E was defined as the difference between these two ratios before and after training. A shift of the entire vertical visual field border by 1 degrees would result in an E value of 0.14.

RESULTS

The mean training effect of all right eyes was E = 0.025 (SD 0.052) and all left eyes E = 0.008 (SD 0.034). In one eye, a slight non-homonymous improvement along the horizontal meridian occurred.

CONCLUSIONS

In one patient, a slight improvement along the horizontal meridian was found in one eye. In none of the patients was an explicit homonymous change of the absolute field defect border observed after training.

L-type calcium channel antagonist nifedipine reduces neurofilament restitution following traumatic optic nerve injury

BACKGROUND

The aim of the present study was to observe if the use of the L-type calcium channel antagonist nifedipine would offer advantages for the retinal ganglion cells and the restitution of the axonal cytoskeleton after optic nerve crush.

METHODS

Retinal ganglion cells were retrogradely labeled with a fluorescent calcium marker. With the in vivo confocal neuroimaging (ICON) method we observed the fluorescent cell metabolism marker Oregon Green BAPTA in the same retinal ganglion cells over 3 weeks after optic nerve crush. 2 micromol nifedipine were injected intraocularly 30 minutes following optic nerve crush.

FINDINGS

Investigation of the optic nerve immunostained for NF-H presented decreased restitution of the neurofilaments in the axonal cytoskeleton after 3 weeks in the optic nerve crush group treated with nifedipine as compared to the optic nerve crush only group.

INTERPRETATION

These results show that a single injection of the calcium L-type antagonist nifedipine shortly after optic nerve injury has long-lasting negative effects on the recovery of the retinal ganglion cells.

Protease-activated receptor subtype expression in developing eye and adult retina of the rat after optic nerve crush

Protease-activated receptors (PARs), 7-transmembrane domain G protein-coupled receptors, are involved in tissue degeneration and repair upon injury. We demonstrate the expression of all four PAR subtypes in the postnatal eye and in retina of the adult rat by reverse transcription-polymerase chain reaction (RT-PCR). PAR-1 is regulated developmentally in the eye, with a decrease from P1, P9, to P16, whereas levels for PAR-2, PAR-3, and PAR-4 remain unchanged throughout. In the retina of the adult rat, PAR-1 is highly expressed, whereas PAR-2 and PAR-3 are moderately expressed, compared to low PAR-4 expression. To elucidate possible roles of PARs after trauma, we carried out semiquantitative RT-PCR analysis of expression of all 4 PAR subtypes, beginning 6 hr after partial optic nerve crush (ONC) in the adult rat until 3 weeks after the mild trauma. Levels of PAR mRNA for all four subtypes were upregulated as early as 6 hr after unilateral ONC, except PAR-3, which showed a delayed upregulation. PAR-1, PAR-3, and PAR-4 mRNA levels returned to almost basal levels at 3 weeks post-crush, whereas PAR-2 mRNA level was still high by the end of 3 weeks after crush. Although the lesion was unilateral, PAR mRNA expression in the contralateral, uninjured side was affected to levels almost comparable to those in the injured side. Previous studies have shown an increase in thrombin levels at the site of injury, retinal ganglion cell degeneration by necrosis and apoptosis, and PAR activation as consequences of nerve crush. PAR upregulation because of nerve crush in the mild trauma model could act as an effector of early cell death. Eventual return of receptor mRNA to basal levels is consistent with neuroprotection.

Editorial: Residual vision and plasticity after visual system damage

This is an introduction to a special issue of the journal Restorative Neurology and Neuroscience which contains a series of papers presented at a satellite symposium held in conjunction with the European Forum of Neuroscience, Berlin, July 1-2, 1998, entitled "Visual System Damage: Residual Vision and Plasticity". The symposium highlighted research findings both from animals and humans which sustained brain injury in early development and in adulthood. The findings demonstrate the degree of residual vision the injured brain possesses and summarize the effects of drugs and training on the plasticity of the visual system. As this conference demonstrated, the visual system is able to respond in many ways in an adaptive manner to lesions inflicted early in life and in adulthood. These changes may bring about spontaneous recovery of visual functions as long as the brain contains a sufficient capacity of residual vision. Both in children and in adults, systematic visual training can help patients to regain some visual functions which have previously been considered to be irrevocably lost. By carefully assessing residual vision it is proposed that the potential for plasticity of the visual system can be utilized to achieve clinical improvement using appropriate training paradigms.

Restoration of vision I: neurobiological mechanisms of restoration and plasticity after brain damage - a review

Lesions in the central nervous system often lead to loss of vision due to visual system involvement. In the course of weeks or months, some vision can recover in rats, cats, monkeys, and humans, though it is mostly incomplete. This paper reviews the current knowledge of the under-lying neurobiological mechanism of recovery of vision, particularly those observed in adult rats with partial optic nerve crush (ONC). Immediately after ONC, rats are almost completely blind, evident by their inability to perform visual tasks such as brightness and pattern discrimination and they fail to orient towards small, moving targets. Within about two weeks, however, rats significantly recover some of their lost visual functions despite the fact that only about 10 % of the retinal ganglion cells (RGCs) maintain a viable connection with their brain tar-gets. Molecular, anatomical and physiological studies have identified some of the neurobiological determinants of this visual restitution. Immediately following ONC there is a massive soma swelling of about 80 % of the RGCs with subsequent cell death due to apoptosis and necrosis. The remaining 20 % survive with or without axonal connection to their target and undergo marked changes: (i) about half of these RGCs experience a moderate, reversible soma swelling, (ii) there is a loss of anterograde axonal transport in the optic nerve which partially recovers after several weeks, and (iii) many of the surviving RGCs undergo alterations in gene expression, particularly that of the NR1 receptor and the immediate early gene, c-jun. While these changes may be part of an adaptive program of the cells to cope with the trauma, cell survival in the retina does not correlate well with subsequent recovery of vision. We have therefore also studied plasticity in the down stream denervated brain structures which are innervated by retinofugal pathways, particularly the superior colliculus. Here we found (i) recovery of metabolic activity and (ii) changes in gene expression, such as an up-regulation of the enhancer of split (R esp-1) gene. When viewed together with studies on recovery of vision and neuronal reorganization done in other laboratories it is clear that recovery of vision involves simultaneous plasticity in the damaged structure itself and, transsynaptically, in down-stream structures such as the tectum, the lateral geniculate nucleus and visual cortex. Considering both pre-clinical and clinical evidence, I propose the biological substrate underlying restoration of vision as follows: surviving neurons within areas of partial damage - which corresponds clinically to "transition zones" located between intact and deficient visual field sectors - act in concert with down-stream areas, which themselves undergo dramatic reorganization to cope with a condition of reduced, but residual input. Restitution of vision is therefore a multifactorial event of within-systems plasticity, involving neurobiological alterations along the entire retinofugal axis. It is likely that these mechanisms are also responsible for visual improvements that are seen both in animals and patients after prolonged visual restitution training.

Recovery of metabolic activity in retinofugal targets after traumatic optic nerve injury is independent of retinofugal input

Traumatic injury of the adult optic nerve causes a progressive degeneration of retinal ganglion cells. Despite this ongoing degeneration, a partial recovery of visual behavioral function and of local cerebral glucose use (LCGU) has been observed. To evaluate whether this partial recovery of LCGU is due to a recovery of visual conductance (extrinsic) or intrinsic neuronal activity, visual stimulation alone and combined with physostigmine,an acetylcholinesterase inhibitor, were used to activate the retinofugal pathway. LCGU was determined in 30 male adult rats with or without physostigmine treatment 2 or 9 days after crush or 8 days after cut of the right optic nerve. Analysis of LCGU in contralateral first-order projection areas revealed no differences 8 days after cut and 9 days after optic nerve crush. Furthermore, LCGU in the contralateral areas could not be stimulated by the treatment with physostigmine. We therefore conclude that the increase in LCGU from 2 to 9 days after crush is not due to a recovery in the conductance of visual input. We hypothesize a relief of an injury-dependent active suppression (diaschisis) of LCGU. This reversal of diaschisis may, in part, account for the return of visual functions after mild optic nerve injury.

Restoration of vision II: residual functions and training-induced visual field enlargement in brain-damaged patients

PURPOSE

Brain damage is often accompanied by visual field defects which have been considered to be non-treatable. In recent years, however, new diagnostic methods have revealed hitherto unknown residual vision, which was found, for instance, in transition zones near the blind visual field sectors and in spared islands of vision within the blind regions ("blindsight"). Furthermore, animal studies revealed a high degree of plasticity in the visual system suggesting the possibility that recovery of vision may be induced by systematic visual training.

METHODS

Here we summarize a series of studies with patients suffering from visual field defects after brain lesion using some most recently developed computer-based programs for the diagnosis and treatment of visual field defects. Specifically, high-resolution perimetry (HRP) was applied to first diagnose residual function in or near the "blind" sector of the visual field. Thereafter, visual restitution training (VRT, see Kasten et al., Nature med. 4, 1998, p. 1083) was used daily for 6 months to provide systematic stimulation of these areas of residual vision.

RESULTS

In a number of studies, we have observed not only residual visual functions within or near the field defect, but we were also able to follow the course of spontaneous recovery of visual functions within weeks or months after visual system damage. Furthermore, even long after spontaneous recovery is complete, computer-based visual restitution training (VRT) in or near the areas of residual vision results in a significant enlargement of intact areas, both after optic nerve damage and postchiasmatic lesions. Using VRT, we found a border shift of about 5 degrees of visual angle which cannot be explained by eye movements or eccentric fixation. We observed a transfer of this training effects to other tasks such as form and color detection, as well as to tests of visual exploration which were not specifically trained. Moreover, 72 % of the patients reported subjective improvements of vision. Training-induced visual field enlargement persisted for at least one year, even in the absence of training beyond 6 months of treatment.

CONCLUSIONS

The visual system possesses a remarkable plasticity which becomes apparent in visual field enlargement during spontaneous recovery and specific visual training. Animal studies indicate that a minimum number of residual neurons surviving the lesion, in the order of 10%, provides a sufficient substrate for recovery of vision. Though the precise mechanisms of training-induced visual field enlargement need to be further explored, VRT can be introduced for routine clinical treatment of patients with visual field defects.

Restoration of vision IV: role of compensatory soma swelling of surviving retinal ganglion cells in recovery of vision after optic nerve crush

PURPOSE

Diffuse axonal injury following partial optic nerve crush (ONC) leads to severe visual deficits from which rats can partially recover within 2-3 weeks. To evaluate tbc role of surviving retinal ganglion cells (RGCS) in recovery, we have observed their morphology repeatedly in vivo with ICON-microscopy and correlated cell size changes with recovery of vision which we observed in parallel in the same animals.

METHODS

After rats had learned a visual contrast discrimination task using an automated, computer-based test, RGCs were labeled retrogradely with fluorescent beads. Animals then received either no lesion, a complete axotomy or bilateral mild, moderate or severe ONC. Before surgery and for 40 days post-operatively, ROC number and soma size was repeatedly quantified every five days with tbc in vivo confocal neuroimaging method (Sabel et al., Nature med. 3, 1997, p. 244). In parallel, visual function was quantified with the contrast-discrimination task.

RESULTS

After ONC about 70 % of the ROCs died after having undergone a fast and massive soma swelling. The extent of cell death was independent of crush severity. RGCs surviving the injury did not change their body size over time in the severe group and these animals also did not recover their vision. In contrast, after a mild or moderate crush, about half of the surviving RGCs experienced a slow and moderate, "compensatory" cell soma swelling and the rats showed partial recovery of vision. Both the number of RGCs showing such compensatory soma swelling and the extent of the swelling correlated highly (r = 0.96) with recovery of contrast discrimination performance at post-operative days 23 and 38.

CONCLUSIONS

Depending en the time course and extent, soma swelling after neurotrauma may be associated either with cell death or recovery of function. Because of the very high correlation between extent of recovery and amount of soma swelling, moderate soma swelling contributes in a prominent way to recovery of vision. We believe that these cells provide an important structural substrate for neuronal tissue repair and therefore term these cells "compensatory neurons".

Anatomical correlations of intrinsic axon repair after partial optic nerve crush in rats

About 15% of retinal ganglion cells survive diffuse axonal injury of the optic nerve in adult rats. Following initial blindness, discrimination of visual stimuli in behavioral tests recovers within three weeks. To investigate the mechanisms promoting this functional recovery the axonal transport and the neurofilaments were studied. Intraocularly applied MiniRuby is transported until the place of crush and accumulated in enlarged axon terminals. Three weeks after lesion the anterograde transport of MiniRuby recovers distal to the place of crush. At the same point in time the retrograde transport of surviving retinal ganglion cells is restored which was visualized by horseradish peroxidase injected into the superior colliculus. The heavy neurofilament was stained immunohistochemically and analyzed statistically up to three weeks after optic nerve crush. The stained filaments in the axon fibers of retinal ganglion cells appear wavelike and/or fragmented up to day 8, but first signs of heavy neurofilament restitution in the fibers of the optic nerve are seen at day 12 after axonal injury. Because these results cannot be explained by longlasting axon regeneration, the present results provide convincing evidence for intrinsic axon repair soon after diffuse axonal injury that correlates in time with recovery of vision.

Deficits of respiratory-cardiac coupling in heavy drinkers

1. Physiological evidence of chronic alcohol abuse prior to the onset of clinical signs of alcohol dependence is difficult to obtain The purpose of this study was to search for possible non-invasive indicators for chronic alcohol consumption yielding information in addition to conventional biological markers. 2. The authors investigated the relationship between respiratory-cardiac coupling and blood alcohol concentration (BAC) in male subjects who lost their driver's license from drunk driving. 3. We found that subjects who had a high BAC level (0.16-0.31% at the time of offense) show altered respiratory sinus arrhythmia (RSA) and, in particular, an altered heart-rate response to auditory stimulation and compared them to a control group of social drinkers. Normal subjects showed a pronounced acoustic heart-rate response, i.e., particularly during expiration there was a difference between the interbeat-interval (IBI) traces with and without auditory stimulation. Subjects who had lost their driver's license from drunk driving had an overall severely reduced heart-rate response, that was even absent particularly in the subgroup having high BAC values (0.21-0.31%). The authors also found some evidence that in the latter subgroup IBI, RSA, and acoustic heart-rate responses partially recover after a six-month period of abstinence. 4. Specific parameters of the acoustic heart-rate response are changed in our group of alcohol abusers presumably, due to impairment of vagal function. These parameters may therefore be useful to serve as a non-invasive measure of alcohol abuse.

Stability of visual field enlargements following computer-based restitution training -- results of a follow-up

In a previous randomized placebo-controlled clinical trial, we observed significant visual field enlargements induced by computer-based restitution training in patients with cerebral lesions (Kasten et al., Nature med., 4, 1998, 1083-87). Now we asked the question whether this effect is stable after training was discontinued? Here we report data of a follow-up study after a training-free interval (mean 23.5 +/- 2.3 months after end of therapy). 16 patients of the original restitution group and 6 patients of the placebo group were re-examined. On average, in high resolution computer campimetry (stimulus detection: PeriMa, form recognition: PeriForm, color perception: PeriColor) as well as in conventional automatic perimetry (TAP-2000) both groups showed no significant decline in the number of correctly detected stimuli after training was discontinued. However, cluster analysis revealed three different types of patients, who showed either increase (Type-I), decrease (Type-II) or stability (Type-III) in performance. We propose that many patients learn to use the regained visual capacities not only in the setting of a computer training but also in every day life, while other patients do not use the areas of restored vision and show a decrease of visual functions after the end of training. The Type-I group does not need continuous training, while the Type-II group may benefit from phases of refreshment exercises.

Acute effects of alcohol on divided and covert attention in men

RATIONALE

While several studies identified divided attention to be sensitive to alcohol effects, the impact of alcohol on covert visual attention is still not clear, despite the latter's important role in perception.

OBJECTIVES

The study tests the effect of acute moderate doses of alcohol on divided and covert attention in right-handed, male volunteers.

METHODS

The design of the study involved a double-blind trial with an alcohol and a placebo condition; measurements were taken before and after an oral dose of 0.6 g/kg alcohol versus placebo. In the divided-attention task, simultaneous visuo-spatial and auditory stimulation was applied. In a test of covert attention, subjects had to shift their attentional focus according to a central cue, from one location in the visual field to another.

RESULTS

Under the divided-attention condition, reaction times were significantly prolonged after alcohol ingestion compared to placebo. Covert attention pre-post change was also significantly different between the alcohol and placebo groups. There is a reduction of false-cueing disturbance for left-appearing stimuli under moderate alcohol but an increase of disturbance for rightward stimuli, i.e. we found a lateralised pattern of reaction for spatial orienting. In the placebo group, no significant differences in right-left performance were obtained.

CONCLUSION

The results suggest that sensory-attentional mechanisms play a key role in altered visual perceptual performance after alcohol ingestion. Furthermore, differences between the right and left visual field in the cued target-detection task indicate that alcohol exerts an influence on right-hemispheric attentional priming.

Unusual spontaneous and training induced visual field recovery in a patient with a gunshot lesion

Over a period of more than 3 years, changes in visual and neuropsychological functions were examined in a patient with a visual field defect caused by a cerebral gunshot lesion. Initially, the patient had been completely blind, but after 6 months of spontaneous recovery, he showed a homonymous bilateral lower quadrantanopia and impairment of higher visual functions. Unexpectedly, recovery still continued after the first 6 months. This process was documented in detail by visual field examinations using high resolution perimetry. When visual field size had stabilised almost 16 months after the lesion, further improvement could be achieved by visual restitution training. The duration and extent of spontaneous recovery were unusual. In spontaneous as well as in training induced recovery, progress was mainly seen in partially defective areas (areas of residual vision) along the visual field border. Thus, it is speculated that modulation of perceptual thresholds in transition zones of visual field defects contributes to spontaneous and training induced recovery.

Restoration of vision by training of residual functions

A new paradigm emerges: visual field defects after optic nerve or brain injury are partially reversible. Using high-resolution visual field tests, areas of residual vision can be identified which are characterized by impaired vision (relative defect) with some residual capacities. By repetitively stimulating these partially damaged areas with daily computer-based visual restitution training it is now possible to enlarge the visual field. Average border shifts of 5 degrees (range, 0 to 20 degrees) have been found in clinical trials, and training is effective even when started years after the injury. Visual restitution training is useful for the treatment of patients with stroke, head injury, or partial optic nerve damage, as long as the patient presents some residual vision. The improved vision is maintained in most patients after training is discontinued. Brain plasticity is likely to provide the substrate for restoration of vision, opening new opportunities to treat partial blindness, which has been considered irreversible.

Computer-based training of stimulus detection improves color and simple pattern recognition in the defective field of hemianopic subjects

In a previously conducted randomized placebo-controlled trial, we were able to demonstrate significant visual field enlargement induced by restitution therapy in patients with cerebral lesions [Kasten, E., Wuest, S., Behrens-Bamann, W., & Sabel, B. A. (1998c). Computer-based training for the treatment of partial blindness. Nature Medicine, 4, 1083-1087.]. Visual field training was performed on a computer monitor for 1 hr per day over a period of 6 months. Since the procedure included only stimulation with white light, in the present study we investigated if this simple detection training had a transfer effect on color or form recognition in the trained area (i.e., in the absence of modality specific training). Answering this question would be crucial for planning optimal restitution therapy: In case there is no transfer of training effects to other visual modalities, a specific treatment of each visual function must be performed in order to achieve maximum benefit. Therefore, we analyzed the data from 32 patients with visual field defects who had participated in the original trial and whose form and color recognition had been investigated. The experimental group (n = 19, restitution training) experienced not only an increase of 12.8% correctly detected stimuli (PeriMa program, p <.05), but also an improvement of 5.6% in pattern recognition (PeriForm) and of 6.1% in color perception (PeriColor), respectively. In contrast, the placebo group (n = 13, fixation training) showed no significant changes from baseline to final outcome in any of the visual modalities (PeriMa: 0.3%; PeriForm: -0.3%; PeriColor: 0.4%). Conventional perimetry yielded an increase of 7.8% detected stimuli in the experimental group, but only of 1.2% in the placebo group (p <.05). For form recognition and color perception, the differences between the results of the experimental and the placebo groups narrowly missed significance. However, correlations of diagnostic results showed that mainly those patients who had achieved visual field enlargement also improved in color and form perception: r =.67 (p <.05) between PeriMa and PeriForm and r =.32 between PeriMa and PeriColor. We conclude that visual restitution training using a simple white light stimulus has at least some influence on improving other visual functions such as color and pattern recognition. This result supports the "bottleneck theory" of visual restitution, i.e., training effects can be explained as a process of perceptual learning and increased processing of information by residual structures surviving lesions of the primary visual pathways.

Influence of nanoparticles on the brain-to-serum distribution and the metabolism of valproic acid in mice

The suitability of nanoparticles as a drug-carrier system for the antiepileptic valproic acid has been studied in mice. The aim of the study was to increase the brain-to-serum ratio of the drug to reduce dose-related side effects in the periphery. The influence of nanoparticles on the metabolism of valproic acid was also investigated. The serum kinetics and the brain tissue levels of valproic acid were not altered by administration with nanoparticles. However, the nanoparticles did inhibit the metabolic degradation of valproic acid via mitochondrial beta-oxidation but did not influence any other metabolic pathway. It can be concluded that nanoparticles loaded with valproic acid may help to reduce the toxic side effects of valproate therapy, not by reducing the therapeutically necessary dosage but by inhibition of formation of toxic metabolites. Using their ability to selectively block a pathway nanoparticles may serve as a tool to investigate the metabolic origin of metabolites and their contribution to therapeutic efficacy and side effects.

Quinolinic acid released from polymeric brain implants causes behavioral and neuroanatomical alterations in a rodent model of Huntington's disease

Quinolinic acid (QA) is an N-methyl-d-aspartate agonist that has been shown to produce neurotoxic effects that mimic certain neurodegenerative diseases when administered to laboratory animals. Intrastriatal injections of QA in rats have been used extensively to produce some of the neuropathological and behavioral deficits that are analogous to Huntington's disease (HD). However, acute intrastriatal injections of QA produce symptoms that are not analogous to the progressive nature of HD. Thus far, models using chronic administration of QA that produce HD-like behavioral and neuroanatomical changes have necessitated the use of a relatively bulky and fragile microdialytic pump apparatus. The present study tested an alternative way of chronically administering QA. Specifically, this study tested whether gradual release of QA from ethylene vinylacetate (EVA) polymers could produce symptoms analogous to HD. Rats received either no implants or bilateral intrastriatal implants of polymers with or without QA. Subsequent tests for spontaneous motor activity (SMA), grip strength, balance, and learning ability in a radial-arm-water-maze task revealed QA-induced impairments in balance and learning ability, but did not affect grip strength or SMA. Histological analysis revealed QA-induced enlargement of lateral ventricles, striatal atrophy, and striatal neuronal loss, with relative sparing of NADPH-diaphorase-positive neurons. These results suggest that QA released from polymers can produce behavioral and neuropathological profiles analogous to early stages of HD and that EVA polymers offer a useful means of chronically delivering QA in rodent models of neurodegeneration.

Body distribution of 3H-labelled dalargin bound to poly(butyl cyanoacrylate) nanoparticles after i.v. injections to mice

The blood-brain barrier (BBB) limits the penetration of substances into the brain. Because many drugs, particularly peptides, therefore can not be delivered to the brain, carrier systems were developed to overcome this problem. In earlier studies we demonstrated central analgesic effects of a peptide, dalargin (dal), after systemic administration when this substance was bound onto the surface of polybutylcyanoacrylate nanoparticles and coated with polysorbate 80 but not when it was given alone. The aim of the present study was to investigate the body distribution of 3H-labelled dal bound to nanoparticles compared to unbound dal after i.v. injection in mice. The radioactivity in several tissues, including the brain, was separated in subcellular preparations and was measured after a single i.v. injection over time. Dal radioactivity level in brain preparations was 3 times higher when the drug was bound to nanoparticles whereas the first pass pathway in liver was reduced. The results support previous data that nanoparticles can be used to transport peptides across the BBB.

Neuroleptics ameliorate phencyclidine-induced impairments of short-term memory

1. Phencyclidine (PCP), a non-competitive NMDA-receptor antagonist, is able to induce schizophrenia-like symptoms in animals and in humans. It is known that schizophrenic patients have deficits in memory processes. 2. Therefore, it was investigated whether subchronic pulsatile or continuous application of 5.0 mg kg(-1) PCP over 5 days induce short-term memory deficits in holeboard learning and the action of two different neuroleptics on this behavioural test. 3. First, an impairment in the holeboard task was described when the animals were tested 24 h after the last application but not after 15 min or 1 h after the last injection. Secondly, the influence of haloperidol and risperidone on the PCP-induced short-term memory changes was tested. 4. The combined application of PCP and risperidone led to a complete antagonism of the short-term deficits, but the combined treatment with haloperidol was accompanied by a partial abolishment of the PCP-induced deficits. 5. PCP led to an upregulation of the glutamate binding sites in striatum and nucleus accumbens whereas the D(2) binding sites were reduced in striatum. The D(1) binding sites seem to be unchanged. The receptor protein expression of glutamate receptors mGluR1, GluR2, GluR5/7 and NMDAR1 were not modified in response to PCP treatment. 6. The determination of a subpopulation of GABAergic interneurons shows a decrease of the cells within the CA3 of the hippocampal formation. 7. These findings indicate that PCP induced impairments in short term memory can be detected by holeboard learning and may provide an interesting tool for the search of new neuroleptics.

Assessing spatial vision - automated measurement of the contrast-sensitivity function in the hooded rat

The contrast-sensitivity function (CSF) provides a concise and thorough description of an organism's spatial vision; it is widely used to describe vision in animals and humans, to track developmental changes in vision, and to compare vision among different species. Despite the predominance of rats in neuroscience research, their vision is not thoroughly studied due to the complexity of psychophysical measurement and a generally held notion that rat vision is poor. We therefore designed an economical and rapid method to assess the hooded rat's CSF, using a computer monitor to display stimuli and an infrared touch screen to record responses. A six-alternative forced-choice task presented trials in which a sine-wave grating (S+), varying in spatial frequency and contrast, was displayed at different locations along with five gray stimuli (S-). Nose pokes to the S+ but not the S- produced water reinforcers. Contrasts were tested at each spatial frequency with a simple adaptive procedure until stimulus detection fell below chance. Psychometric functions were obtained by maximum-likelihood fitting of a logistic function to the raw data, obtaining the threshold as the function's point of inflection. As in previous studies with rats, CSFs showed an inverse-U shape with peak sensitivity at 0.12 cyc/deg and acuity just under 1 cyc/deg. The results indicate the present computer-controlled behavioral testing device is a precise and efficient instrument to assess spatial visual function in rats.

Long-term stability of PBCA nanoparticle suspensions

In this study, the stability of poly(butyl cyanoacrylate) (PBCA) nanoparticle suspensions was examined for up to 1 year by measuring the nanoparticle sizes. The nanoparticles were prepared with different stabilizers (dextran 70.000, poloxamer 188, or polysorbate 85), and the particle size was determined before and after purification by centrifugation and after dilution with different solutions (0.1 N HCl, 0.01 N HCl, H2O, and PBS). The most constant sizes were with the untreated acidic nanoparticle suspensions. In all other cases, agglomeration of the particles occurred: the extent of this agglomeration and the time at which the agglomeration occurred depended on the experimental conditions. Nanoparticle polymer degradation, as indicated by size decrease, was not observed. Thus, PBCA nanoparticles can be stored as suspensions, making the lyophilization and the sometimes problematic resuspension by ultrasonication, unnecessary, which is advantageous for clinical applications.

Subchronically applied phencyclidine fails to disrupt prepulse inhibition in rats

To simulate psychosis in rats, the psychotomimetic agent phencyclidine (PCP, 5.0 mg/kg) was administered either by daily pulsatile injections or by continuous delivery with subcutaneously implanted, PCP-loaded controlled release polymers for a 5 day period. The acoustic startle response (ASR) and the prepulse inhibition (PPI) were then assessed 15 and 60 min as well as 24 h after the PCP application was discontinued. An impaired PPI occurred only under the acute influence of the last PCP injection, i.e. 15 and 60 min after last PCP treatment when it had previously been given in a pulsatile manner but not when it was administered continuously. The ASR to unpaired stimuli after PCP was not modified. These findings suggest that disruption of PPI occurs only under the acute influence of PCP and that PPI deficits are not primarily the consequence of structural brain damage which PCP produces.

Restoration of vision III: soma swelling dynamics predicts neuronal death or survival after optic nerve crush in vivo

Predicting neuron death or survival after axonal injury is important in neurotrauma research. We now used in vivo confocal neuroimaging microscopy to repeatedly visualize retinal ganglion cells after optic nerve crush and studied their morphological alterations and ultimate fate. An intracollicular injection of a retrograde fluorescent tracer was made before or after optic nerve crush. Retinal ganglion cell sizes were then determined at different time points up to post-surgery day 75. Cell death was inevitable when soma swelling was fast and massive (86% above baseline or higher), but when it was slower and moderate (32% above baseline) long-term neuron survival could be predicted with high accuracy as early as post-operative day 5. Moderate swelling continued until day 15 (64%) and after about 3 weeks these cells started shrinking again, as a sign of recovery. We propose that moderate soma swelling is an adaptive rather than pathogenic post-traumatic reaction to axonal injury.

R-esp1, a rat homologue of drosophila groucho, is differentially expressed after optic nerve crush and mediates NGF-induced survival of PC12 cells

The differential display reverse transcription polymerase chain reaction method was used to detect alterations in gene expression in the superior colliculus after optic nerve crush in adult rats. One of the most prominent changes observed was the selective induction of R-esp1, a homologue of the Drosophila enhancer of split locus (Groucho). Therefore, we studied the influence of R-esp1 on nerve growth factor (NGF)-induced cell survival of PC12 cells. Overexpression of R-esp1 promotes cell survival even in the absence of NGF and, conversely, it is reduced by antisense-mediated inhibition of R-esp1 expression. In conclusion, we propose a novel model in which R-esp1 protein mediates the NGF-signaling pathway.