Proteomic analysis of rat plasma following transient focal cerebral ischemia

AIM

This study aimed to identify plasma protein changes in a rat model of ischemic stroke using a proteomic approach.

MATERIALS & METHODS

Four male Sprague-Dawley rats (3-6 months old) were subjected to 90 min of left middle cerebral artery occlusion under anesthesia with 1.5% isoflurane in O(2)/air followed by 24-h reperfusion. Blood samples (~100 µl) were collected at baseline, at the end of 90-min middle cerebral artery occlusion and at 24-h postreperfusion. Brain injuries were assessed by MRI at 24-h postreperfusion. Quantitative comparison of global plasma protein expression was performed using 2D differential in-gel electrophoresis. Differentially expressed protein spots were identified using peptide sequencing tandem mass spectrometry.

RESULTS

These rats had clear brain infarction in the left hemisphere detected by MRI. Thirty-three protein spots of plasma samples were differentially expressed following focal cerebral ischemia/reperfusion. These protein spots belonged to eight proteins. Six of them (α2-macroglobulin, complement C3, inter-α- trypsin inhibitor heavy chain H3, serum albumin, haptoglobin and transthyretin), which are a class of acute-phase proteins, changed significantly.

CONCLUSION

This study describes the responses of young rats to focal cerebral ischemia and suggests that future studies should use aged animals to better mimic the clinical ischemic stroke setting.

Subthalamic nucleus neurones in slices from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned mice show irregular, dopamine-reversible firing pattern changes, but without synchronous activity

The loss of dopamine in idiopathic or animal models of Parkinson's disease induces synchronized low-frequency oscillatory burst-firing in subthalamic nucleus neurones. We sought to establish whether these firing patterns observed in vivo were preserved in slices taken from dopamine-depleted animals, thus establishing a role for the isolated subthalamic-globus pallidus complex in generating the pathological activity. Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) showed significant reductions of over 90% in levels of dopamine as measured in striatum by high pressure liquid chromatography. Likewise, significant reductions in tyrosine hydroxylase immunostaining within the striatum (>90%) and tyrosine hydroxylase positive cell numbers (65%) in substantia nigra were observed. Compared with slices from intact mice, neurones in slices from MPTP-lesioned mice fired significantly more slowly (mean rate of 4.2 Hz, cf. 7.2 Hz in control) and more irregularly (mean coefficient of variation of inter-spike interval of 94.4%, cf. 37.9% in control). Application of ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 2-amino-5-phosphonopentanoic acid (AP5) and the GABA(A) receptor antagonist picrotoxin caused no change in firing pattern. Bath application of dopamine significantly increased cell firing rate and regularized the pattern of activity in cells from slices from both MPTP-treated and control animals. Although the absolute change was more modest in control slices, the maximum dopamine effect in the two groups was comparable. Indeed, when taking into account the basal firing rate, no differences in the sensitivity to dopamine were observed between these two cohorts. Furthermore, pairs of subthalamic nucleus cells showed no correlated activity in slices from either control (21 pairs) or MPTP-treated animals (20 pairs). These results indicate that the isolated but interconnected subthalamic-globus pallidus network is not itself sufficient to generate the aberrant firing patterns in dopamine-depleted animals. More likely, inputs from other regions, such as the cortex, are needed to generate pathological oscillatory activity.

Using the BOLD MR signal to differentiate the stereoisomers of ketamine in the rat

RATIONALE

Ketamine is a chiral molecule that is reported to model aspects of schizophrenia.

OBJECTIVES

To investigate the stereospecificity of the isomers of ketamine using pharmacological magnetic resonance imaging (phMRI) in order to further understand ketamine's pharmacodynamic actions.

METHOD

Responses to 25 mg kg-1S(+) isomer, R(-) isomer and racemic ketamine in independent groups of Sprague-Dawley rats were investigated using a prepulse inhibition paradigm, locomotor observations, MRI and 2-deoxyglucose techniques.

RESULTS

Racemic ketamine and the S(+) isomer were both capable of disrupting sensorimotor gating as measured using prepulse inhibition and produced a longer period of hyperlocomotion comparative to the R(-) isomer. In contrast, large alterations in the BOLD MR signal were observed with R(-) isomer, whereas S(+) isomer and racemate precipitated more localized BOLD signal changes predominantly in cortical, hippocampal and hindbrain regions. Glucose utilization rates in conscious animals are in agreement with previously published data and verify the BOLD responses in the racemic group. However, no significant changes in glucose utilization were observed in the anesthetized cohort.

CONCLUSIONS

Ketamine and its isomers have stereospecific effects on sensorimotor gating and locomotion that correlate with the enantiomer's affinity for the NMDA receptor. It would appear that anesthesia, as required for preclinical MRI procedures, may interact with and potentially attenuate the drug's response. Although analysis of the main effect of isomers in comparison to each other or the racemate offers an alternative analysis method that should be less susceptible to anesthetic interactions, only the R(-) isomer comparative to the racemate offers significant differences of interest.

Mapping transplanted stem cell migration after a stroke: a serial, in vivo magnetic resonance imaging study

Preferential migration of stem cells toward the site of a lesion is a highly desirable property of stem cells that allows flexibility in the site of graft implantation in the damaged brain. In rats with unilateral stroke damage, neural stem cells transplanted into the contralateral hemisphere migrate across to the lesioned hemisphere and populate the area around the ischaemic infarct. To date, the migration of neural stem cells in the damaged brain has been mainly inferred from snapshot histological images. In this study, we demonstrate that by pre-labelling neural stem cells with the bimodal contrast agent Gadolinium-RhodamIne Dextran [GRID, detectable by both magnetic resonance imaging (MRI) and fluorescent microscopy], the transhemispheric migration of transplanted neural stem cells contralateral to a stroke lesion can be followed in vivo by serial MRI and corroborated by subsequent histological analyses. Our results indicate that neural stem cells migrated from the injection tract mainly along the corpus callosum within 7 days of transplantation and extensively re-populated the peri-lesion area by 14 days following implantation. In contrast, neural stem cells transplanted into sham controls did not show any substantial migration outside of the injection tract, suggesting that the transcallosal migration observed in the stroke-lesioned animals is due to neural stem cells being attracted by the lesion site. In vivo tracking of the migration of neural stem cells responding to damage will greatly enhance our understanding of optimal transplantation strategies as well as how neural stem cells promote functional and anatomical recovery in neurological disorders.

Simultaneous PET and NMR

There is currently great interest in combining data from different imaging modalities, either by image registration methods that are performed after the data has been acquired or using new devices that can acquire data from two modalities simultaneously, or near simultaneously. In this paper a small prototype NMR-compatible PET scanner capable of acquiring PET images simultaneously with either NMR images or NMR spectra is described. In an associated paper [1], Pamela Garlick describes some investigations of cardiac metabolism that have been made using this system. One of the main challenges in constructing an NMR-compatible PET scanner is that photomultiplier tubes, which are an essential element of nearly all current PET systems, will not function in a high magnetic field. In collaboration with Simon Cherry and the Crump Institute of Biomedical Imaging at UCLA Medical School, a small (5.4 cm diameter) NMR-compatible PET scanner that will operate within the bore of an NMR magnet has been developed. Long optical fibres are used to transport light from the scintillation crystals that form the detector head to photomultiplier tubes situated in a low magnetic field region several metres from the magnet. This system has been used to perform simultaneous PET and NMR spectroscopy measurements with a 9.4T spectroscopy system, and has also been used to obtain simultaneous PET and MR images in several MRI scanners including a 4.7T small bore animal imaging system. Current efforts in the development of this technology are directed at experimental studies on small animals, both because this is less demanding technically and because it is in this area that applications are likely to appear first. However, there is no reason in principle why human PET-MR would not be feasible. Below, work with the prototype system and the next stage in its development are described, and some of the future possibilities and challenges are discussed.

Tracking transplanted stem cell migration using bifunctional, contrast agent-enhanced, magnetic resonance imaging

The ability to track stem cell transplants in the brain by in vivo neuroimaging will undoubtedly aid our understanding of how these cells mediate functional recovery after neural transplantation. One major challenge for the development and refinement of stem cell transplantation is to map the spatial distribution and rate of migration in situ. Here we report a method for tracking transplanted stem cells in the ischemia-damaged rat hippocampus by magnetic resonance imaging (MRI). Before transplantation, stem cells were labeled in vitro either with a novel bifunctional contrast agent, gadolinium rhodamine dextran (GRID), identifiable by both MRI and fluorescence microscopy, or with PKH26, visible exclusively under fluorescence microscopy. At different time points following engraftment, the brains were evaluated by both histology and ex vivo MR imaging. Transplanted stem cells were identified by MRI only if prelabeled with GRID, whereas fluorescence microscopy detected transplanted cells using either label. The distribution of GRID-labeled stem cells identified by MRI corresponded to those detected using fluorescence microscopy. These results demonstrate that GRID-enhanced MRI can reliably identify transplanted stem cells and their migration in the brain.

Neuroprotective effect of aminoguanidine on transient focal ischaemia in the rat brain

Using serial magnetic resonance imaging we have evaluated the effectiveness of aminoguanidine (AG) as a neuroprotective agent in a rat model of transient middle cerebral artery occlusion (MCAO). Because aminoguanidine's neuroprotective properties have primarily been ascribed to its action as iNOS inhibitor, we also performed a biochemical analysis of nitric oxide metabolites and NOS isoforms in our model of ischaemia. Daily injections of AG (100 mg/kg) or saline, were started at 6 h after the occlusion and the effects of this treatment on lesion progression monitored by T(2)-weighted MRI at 6 (pre-treatment scan), 24 and 72 h. Measurements of lesion volumes showed that between 6 and 72 h post-MCAO, lesion growth was slower in AG-treated rats than in control rats. This difference was most pronounced between 24 and 72 h post-MCAO when AG halted the lesion volume expansion observed in control rats. Measurements of plasma NOx (nitrite plus nitrate) at 0, 24, 48 and 72 h after MCAO, showed that NO levels did not differ significantly between the AG- and saline-treated groups at any time-point. Moreover, NOS activity assays revealed that no iNOS activity was present in any of the brains tested and that constitutive neuronal NOS activity was similar across the two hemispheres between both groups. The absence of iNOS protein in the ischaemic and contralateral hemispheres at 48 and 72 h after MCAO (control group only) was confirmed by Western blot analysis. These results suggest that AG treatment reduces the rate of growth of ischaemic lesions, perhaps preserving the functioning of perifocal neurons. Our observations contradict suggestions that high levels of NO generated by iNOS are partially responsible for exacerbating the neuronal damage in the postischaemic phase of MCAO. Although this does not rule out a role for AG as a neuroprotective agent via its ability to inhibit iNOS, these findings indicate that neuroprotective actions of AG may also be mediated via other cellular targets.

Sensitivity to urea fertilization in three amphibian species

Forest fertilization with granular urea is a well-established management practice in many forested regions of the world. We hypothesize that chemical forest fertilizers may be affecting forest-dwelling wildlife. In the laboratory, we studied the effects of fertilization doses of granular urea on three species of forest-dwelling amphibians (Plethodon vehiculum, Rhyacotriton variegatus, and Taricha granulosa). In avoidance experiments, the three species avoided a substrate treated with a dose of 225 kg N/ha urea. In toxicity experiments, we exposed amphibians to urea at doses of 225 kg N/ha and 450 kg N/ha for 4 days. The observed effects increased with time and dose, and there were significant differences in sensitivity among the species. Both treatment levels had an acute effect on survival of P. vehiculum and R. variegatus. At 24 h, mortality at the highest dose was 67% for P. vehiculum, and 47% for R. variegatus. In contrast, there was no mortality for T. granulosa at these concentrations. We suggest that environmental levels of urea could be affecting behavior and survival of some amphibians species in fertilized forests.

A CAT-derived one to three session intervention for repeated deliberate self-harm: a description of the model and initial experience of trainee psychiatrists in using it

We describe a new Cognitive Analytic Therapy (CAT)-based intervention for those who repeatedly self-harm. It is specifically designed to be deliverable by staff with no training in psychotherapy. The intervention is simply manualized into sequential tasks that are mediated by new CAT-style standardized tools. A particular feature of this intervention is the deliberate use of feelings elicited in the therapist ('counter-transference') as (a) a guide to how professional poise is being threatened or lost and (b) an indicator of the appropriate focus for this very brief therapy. The psychiatrists' reflection on their elicited feelings is mediated by a new CAT tool, the 'Assessor's Response File' developed in this project. Audiotape analysis suggested that following a very brief learning period, trainee psychiatrists were able to adhere to the structure of the model and arrive at an appropriate reformulation in the first session but tended to be collusive in reciprocating the patients' dysfunctional coping styles.

A quantitative analysis of the development of the central nervous system in juvenile Aplysia californica

The marine mollusc Aplysia californica has proved to be a useful preparation for analyzing the development of learning and memory on both behavioral and cellular levels. An important issue in this analysis concerns the anatomical substrate upon which learning is superimposed during development. As a first step in examining this question, in the present study we have determined the number of neurons in all the major central ganglia at each stage during juvenile development, a time when several forms of learning first emerge in Aplysia. We found that a large and highly nonlinear proliferation of neurons occurs during juvenile development, with the greatest increase in cell number occurring during a specific juvenile stage: Stage 12. The neuronal proliferation is system-wide, occurring in each of the central ganglia simultaneously, suggesting the action of a general developmental signal or trigger (perhaps a hormone). Accompanying the increase in neuron number in Stage 12 there is a large increase in neuropilar volume (150-fold), which significantly increases the opportunity for synaptic interactions late in juvenile development.