In vivo microdialysis in the visual cortex of awake cat. III: histological verification

Postictal alterations induced by intrahippocampal injection of pilocarpine in C57BL/6 mice

Temporal lobe epilepsy (TLE) is the most common form of epilepsy in adults. The pilocarpine (PILO) experimental model of TLE portrays behavioral and pathophysiological changes in rodents that are very similar to those found in humans with TLE. However, this model is associated with an unfortunate high mortality rate. Studies have shown that intrahippocampal injection of PILO, while having a much smaller mortality rate, induces status epilepticus (SE) that secondarily leads to TLE. To the best of our knowledge, the present study was the first to evaluate the cognitive and histological alterations 72h after intrahippocampal microinjection of PILO in C57BL/6 mice. Seventy percent of mice developed status epilepticus (SE) after PILO administration, and all animals survived after SE. Seventy-two hours after SE, mice presented memory impairment in both Novel Object Recognition (recognition index - vehicle: 67.57±4.46% vs PILO: 52.33±3.29%) and Contextual Fear Conditioning (freezing time - vehicle: 203±20.43 vs PILO: 107.80±25.17s) tasks. Moreover, using Nissl and NeuN staining, we observed in PILO-treated mice a significant decrease in cell viability and an increase in neuronal loss in all three hippocampal regions analyzed, cornus ammonis (CA) 1, CA3, and dentate gyrus (DG), in comparison with the control group. Additionally, using Iba-1 staining, we observed in PILO-treated mice a significant increase in microglial proliferation in CA1, CA3, and DG of the hippocampus. Therefore, intrahippocampal PILO microinjection is an efficient route to induce SE and acute postictal epileptogenic-like alterations in C57BL/6 mice.

[Microdialysis and brain injury: importance of animal study]

Brain microdialysis allows the exploration of brain extracellular medium. This review discusses the main contribution of brain microdialysis for the knowledge of the pathophysiology of brain ischemia and trauma. We describe fundamental principle of microdialysis, limits, and validated metabolic parameters as the lactate/pyruvate ratio or glycerol. The interest to use microdialysis for testing metabolic hypothesis and potential scientific research ways will also be discussed.

Microdialysis—theoretical background and recent implementation in applied life-sciences

In the past decade microdialysis has become a method of choice in the study of unbound tissue concentrations of both endogenous and exogenous substances. Microdialysis has been shown to offer information about substances directly at the site of action while being well tolerable and safe. The large variety of its field of application has been demonstrated. However, a few challenges have to be met to make this method generally applicable in routine applications. This review will provide an overview over theoretical aspects that have to be considered during the implementation of microdialysis. Moreover, a comparison between microdialysis and other tissue sampling techniques will demonstrate advantages and limitations of the methods mentioned. Subsequently, it will present a critical synopsis of a variety of scientific/biomedical applications of this method with emphasis on the most recent literature, focussing on target tissues while giving examples of substances examined. It is concluded that microdialysis will be of great value in future investigations of pharmacokinetics, pharmacodynamics and in monitoring of disease status and progression.

Retinal lesions affect extracellular glutamate levels in sensory-deprived and remote non-deprived regions of cat area 17 as revealed by in vivo microdialysis

This study aimed at gaining insight into the role of the excitatory neurotransmitter glutamate in topographic map reorganization in the sensory systems of adult mammals after restricted deafferentations. Hereto, in vivo microdialysis was used to sample extracellular glutamate from sensory-deprived and non-deprived visual cortex of adult awake cats 18 to 53 days after the induction of restricted binocular retinal lesions, and in topographically corresponding cortical regions of control animals. A microbore HPLC-ED method was applied for the analysis of the microdialysates. In normal subjects, the visual cortex subserving central and peripheral vision showed similar extracellular fluid glutamate concentrations. In contrast, in animals with homonymous central retinal lesions, the extracellular glutamate concentration was significantly lower in central, sensory-deprived cortex compared to peripheral, non-deprived cortex. Compared to control regions in normal subjects, glutamate decreased in the extracellular fluid of deprived cortex but increased significantly in remote non-deprived visual cortex. These results not only suggest an activity-dependent regulation of the glutamate levels in visual cortex but also imply a role for perilesional cortical regions in topographic map reorganization following sensory deafferentation.