Oxaloacetate decreases the infarct size and attenuates the reduction in evoked responses after photothrombotic focal ischemia in the rat cortex.

A traumatic brain injury or a focal brain lesion is followed by acute excitotoxicity caused by the presence of abnormally high glutamate (Glu) levels in the cerebrospinal and interstitial fluids. It has recently been demonstrated that this excess Glu in the brain can be eliminated into the blood following the intravenous administration of oxaloacetate (OxAc), which, by scavenging the blood Glu, induces an enhanced and neuroprotective brain-to-blood Glu efflux. In this study, we subjected rats to a photothrombotic lesion and treated them after the illumination with a single 30-min-long administration of OxAc (1.2 mg/100 g, i.v.). Following induction of the lesion, we measured the infarct size and the amplitudes of the somatosensory evoked potentials (SEPs) as recorded from the skull surface. The photothrombotic lesion resulted in appreciably decreased amplitudes of the evoked potentials, but OxAc administration significantly attenuated this reduction, and also the infarct size assessed histologically. We suggest that the neuroprotective effects of OxAc are due to its blood Glu-scavenging activity, which, by increasing the brain-to-blood Glu efflux, reduces the excess Glu responsible for the anatomical and functional correlates of the ischemia, as evaluated by electrophysiological evoked potential (EP) measurements.

Evans Blue fluorescence permits the rapid visualization of non-intact cells in the perilesional rim of cold-injured rat brain.

A focal cold lesion-induced injury, i.e., a model of focal vasogenic brain edema, enhances the permeability of the blood-brain barrier and cell membrane in the perilesional rim. However, non-intact cells can be detected, e.g. by markers of apoptosis, only hours or even days after the injury. The early membrane dysfunction allows extravasated serum proteins to enter the injured cells, which can be readily visualized if the plasma albumin was previously bound to fluorescent tracers, such as Evans Blue (EB). The aim of this study was to demonstrate injured cells that take up the EB/albumin conjugate in the perilesional rim. This tracer was administered 3.5 h after the induction of the injury and the animals were sacrificed 30 min later. With an excitation wavelength of 530-550 nm, the EB-positive cells emitted bright-red fluorescence at > 590 nm and were easy to count. No positive cells were observed in the controls. This method provides more information than the classical 2,3,5-triphenyltetrazolium chloride reaction, because it permits an assessment of the density and distribution of cells with non-intact cell membranes in the perilesional area following cerebrocortical injury.

Dehydroepiandrosterone sulfate is neuroprotective when administered either before or after injury in a focal cortical cold lesion model.

Dehydroepiandrosterone and its sulfate (DHEAS) are sex hormone precursors that exert marked neurotrophic and/or neuroprotective activity in the central nervous system. The present study evaluated the effects of DHEAS and 17beta-estradiol (E2) in a focal cortical cold lesion model, in which DHEAS (50 mg/kg, sc) and E2 (35 mg/kg, sc) were administered either as pretreatment (two subsequent injections 1 d and 1 h before lesion induction) or posttreatment (immediately after lesion induction). The focal cortical cold lesion was induced in the primary motor cortex by means of a cooled copper cylinder placed directly onto the cortical surface. One hour later, the animals were killed, the brains cut into 0.4-mm-thick slices, and the sections stained with 1% triphenyltetrazolium chloride. The volume of the hemispheric lesion was calculated for each animal. The results demonstrated that the lesion area was significantly attenuated in both the DHEAS- and E2- pre- and posttreated groups and that in the presence of letrozole, a nonsteroidal aromatase inhibitor, no neuroprotection was observed, suggesting that the beneficial effect of DHEAS on the cold injury might depend on the conversion of DHEAS to E2 within the brain. It is concluded that even a single posttraumatic administration of DHEAS may be of substantial therapeutic benefit in the treatment of focal brain injury with vasogenic edema.

Hippocampal (CA1) activities in Wistar rats from different vendors. Fundamental differences in acute ischemia.

Two-vessel occlusion, a frequently used model of global cerebral ischemia in rats, results in a dysfunction predominantly within the CA1 field of the hippocampus; it induces many processes with different time-scales. However, the great divergence in the results of the studies reported in the literature suggests valuable differences in response to hypoperfusion-induced ischemia among the laboratory rats used in these studies. In the present work, the acute effects of two-carotid occlusion-induced global ischemia (2VO) on the CA3 stimulation-evoked population spike activity in the CA1 region of Wistar rats from different suppliers (Charles-River and Harlan) were compared. In the acute electrophysiological experiments, the hippocampal CA1 responses revealed that the Charles-River rats immediately compensated the 2VO much better than did the Harlan rats. However, 3 days later, no difference could be observed between the CA1 activities of these rats. The presented data show that the Wistar rats from different vendors represent an important source of variability in the results of acute experiments on the hippocampal ischemia. These observations draw attention to the importance of the careful choice of the laboratory rats (both strains and breeds) used in such experiments.

Facial nerve injury induces facilitation of responses in both trigeminal and facial nuclei of rat.

A study was made of the effects of facial nerve transection on trigeminal stimulation- evoked field potentials in the principal trigeminal (Pr5) and facial nuclei (7) in rats. Although the transected branch of the facial nerve contains pure motoric efferents, it resulted in enhanced responses in both Pr5 and 7. These electrophysiological results suggest a functional circuitry involving the whiskers, trigeminal nerve, Pr5 and 7 and the facial nerve as efferent. The disconnection (opening) of this loop results in enhanced responsiveness of the neurons in both Pr5 and 7.

Oxaloacetate restores the long-term potentiation impaired in rat hippocampus CA1 region by 2-vessel occlusion.

Various acute brain pathological conditions are characterized by the presence of elevated glutamate concentrations in the brain interstitial fluids. It has been established that a decrease in the blood glutamate level enhances the brain-to-blood efflux of glutamate, removal of which from the brain may prevent glutamate excitotoxicity and its contribution to the long-lasting neurological deficits seen in stroke. A decrease in blood glutamate level can be achieved by exploiting the glutamate-scavenging properties of the blood-resident enzyme glutamate-oxaloacetate transaminase, which transforms glutamate into 2-ketoglutarate in the presence of the glutamate co-substrate oxaloacetate. The present study had the aim of an evaluation of the effects of the blood glutamate scavenger oxaloacetate on the impaired long-term potentiation (LTP) induced in the 2-vessel occlusion ischaemic model in rat. Transient (30-min) incomplete forebrain ischaemia was produced 72 h before LTP induction. Although the short transient brain hypoperfusion did not induce histologically identifiable injuries in the CA1 region (Fluoro-Jade B, S-100 and cresyl violet), it resulted in an impaired LTP function in the hippocampal CA1 region without damaging the basal synaptic transmission between the Schaffer collaterals and the pyramidal neurons. This impairment could be fended off in a dose-dependent manner by the intravenous administration of oxaloacetate in saline (at doses between 1.5 mmol and 0.1 mumol) immediately after the transient hypoperfusion. Our results suggest that oxaloacetate-mediated blood and brain glutamate scavenging contributes to the restoration of the LTP after its impairment by brain ischaemia.

Effects of dehydroepiandrosterone sulfate on the evoked cortical activity of controls and of brain-injured rats.

1. Dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) are sex hormone precursors which exert marked neurotrophic and/or neuroprotective activity in the central nervous system (CNS). 2. In the present electrophysiological experiments, we studied the effects of peripherally administered DHEAS on responses of the primary somatosensory (SSI) and motor cortices (MI) of (i) anesthetized controls and (ii) MI focal cold-lesioned rats. (iii) The effects of DHEAS on the field excitatory postsynaptic potentials (fEPSPs) were also studied in vitro brain slices. DHEAS (50 mg/kg) was injected subcutaneously 12 h before and immediately after cold lesion induction. The anesthetized rats were fixed in a stereotaxic frame, the SSI and MI were exposed, and control SSI and MI responses were evoked by contralateral whisker pad stimulation. After registration of the evoked responses for a 35-min period, a copper cylinder (2 mm in diameter) cooled with a mixture of acetone and dry ice (-78 degrees C) was applied to produce a lesion in the MI and the registration of the evoked responses was then continued for an additional 360 min. 3. In the controls, DHEAS administration resulted in slight increases in amplitude of both the SSI and the MI responses. After focal cold lesion induction, the most significant reduction in amplitude was observed at the focus of the lesion in the primary MI, but the amplitudes of the SSI responses were also decreased. After 3-5 h of lesion induction, the amplitudes started to increase around the injury in the primary MI, while the SSI response had already started to recover 2 h after induction of the MI lesion. In the course of the postlesion recovery period, the MI responses peripherally to the center of the lesion frequently exhibited extremely high and low amplitudes. The paired-pulse paradigm revealed changing, but basically high levels of disinhibition and facilitation in extended cortical areas after focal cortical cold lesion induction. The deviations (e.g., the extremely augmented responses) in cortical functioning of the anesthetized rats were unambiguously diminished by DHEAS administration, and the period required for the cortical responses to recover was significantly shorter after the steroid treatment. In the in vitro studies, however, DHEAS administration resulted in an enhanced level of disinhibition in extended cortical areas of both the hemispheres. 4. This observation draws attention to the possible differences between the results obtained in different models (in vitro vs. in situ). Nevertheless, all the presented data suggest that DHEAS treatment might have neuroprotective effect on the neocortex at least at a short-time scale.