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 rim, the EB-positive cells emitted bright-red fluorescence at > 590 rim 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

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 hypoperfus ion-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

Effects of Dehydroepiandrosterone Sulfate on the Evoked Cortical Activity of Controls and of Brain-Injured Rats

Dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) are sex hormone precursors which exert marked neurotrophic and/or neuroprotective activity in the central nervous system (CNS). 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. 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. 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