Evidence for the origin of the binaural interaction component of the auditory brainstem response

The binaural interaction component (BIC) represents the mismatch between auditory brainstem responses (ABR) obtained with binaural stimulation and the sum of ABRs obtained with monaural left and right stimulation. It is generally assumed that the BIC reflects binaural integration. Its potential use as a diagnostic tool, however, is hampered by the lack of direct evidence about its origin. While an origin at the initial site of binaural integration seems likely, there is no general agreement on the contribution of the two primary candidate nuclei, the lateral and medial superior olives (LSO and MSO, respectively). Here, we recorded local field potentials (LFP) and responses of units in the LSO and MSO of Mongolian gerbils (Meriones unguiculatus), presenting clicks with an interaural time or level difference (ITD and ILD, respectively), while simultaneously recording ABR. We determined the BIC from the ABR and, importantly, from LFP and responses of units in the LSO and MSO. If stimulus‐induced changes in the ABR‐derived BIC have their source in the LSO and/or MSO, we expect coherent changes in the unit‐derived and the ABR‐derived BIC. We find that BIC obtained from LSO units exhibits the same ITD and ILD dependence as the ABR‐derived BIC. Neither BIC obtained from MSO units nor LFP‐derived BIC recorded in either LSO or MSO did. The data thus strongly suggest that it is the activity of LSO units in the gerbil that is decisive for the generation of the ABR‐derived BIC, determining its properties.     

The Stapedial Artery in the Mongolian Gerbil (Meriones unguiculatus)

The persistent stapedial artery is a component of the main arterial roads of the head in some animal groups (Fr?ckowiak: Roczn Akad Roln Poznań 336 (2003) 1–81). This type of vascularization occurs in the Mongolian gerbil, among others. The stapedial artery is common in a variety of forms in rodents. It has been described, for example, in Sciuridae, Muridae, Heteromyidae, Geomyidae, Splacidae, Cricetidae, Arvicolinae, and in genus Jaculus (Cox and Hautier: Evolution of the Rodents: Advances in phylogeny, Functional Morphology and Development, 2015). The aim of this study was the analysis of morphology, and of course, of the stapedial artery in this species. Investigations were performed on 10 animals of both sexes, weighing 50–60 g. After lethal anesthesia, the vascular system of every animal was filled with colored latex. After latex coagulation and decalcification of skull bones, fixed tissues were delicately prepared, and the head vascular system was exposed. The stapedial artery separates from the internal carotid artery, runs toward the auditory bulb and passes through the stapes. After the branching of the medial meningeal artery, the stapedial artery runs rostrally, forming its infraorbital branch. This branch, in the further course, gives the branch forming the short trunk of the ophthalmic artery, which supplies orbital structures (muscles, lacrimal gland, Harderian gland, and eyeball). The performed investigations revealed that the maintained infraorbital branch of the stapedial artery is the only source of arterial supply of the orbit in this species. Anat Rec, 301:1131–1137, 2018. © 2018 Wiley Periodicals, Inc.     

Morphological characteristics of eosinophilic neuronal death after transient unilateral forebrain ischemia in Mongolian gerbils

Various types of eosinophilic neurons (ENs) are found in the post‐ischemic brain. The aim of the present study was to elucidate the temporal and spatial profile of ENs, the expression of TUNEL staining and ultrastructural characteristics in the core and peripheral regions of the cortex post‐ischemia. Unilateral forebrain ischemia was induced in Mongolian gerbils by transient common carotid artery occlusions, and the brains from 3 h to 2 weeks post‐ischemia were prepared for morphometric, electron microscopy (EM) and TUNEL staining of the ENs. Light microscopy showed that ENs with minimally abnormal nuclei and swollen cell bodies appeared at 3 h in the ischemic core and at 12 h in the periphery. Thereafter, ENs with pyknosis and irregular atrophic cytoplasm peaked at 12 h, pyknosis with scant cytoplasm peaked at 4 days, and TUNEL‐positive staining was observed in the ischemic core. In the ischemic periphery, ENs had slightly atrophic cytoplasm and sequentially developed pyknosis, karyorrhexis and karyolysis over 1 week. These cells were also positive for TUNEL. In EM, severe organelle dilation and vacuolization preceded chromatin fragmentation in the ischemic core, while chromatin fragmentation and homogenization were the vital characteristics in the ischemic periphery. There might be two region‐dependent pathways for EN changes in the post‐ischemic brain: pyknosis with cytoplasmic shrinkage in the core and nuclear disintegration with slightly atrophic cytoplasm in the periphery. These pathways were comparable to necrosis and proceeded from non‐classical apoptosis to necrosis, respectively.     

Ion Transport and Energy Metabolism in Brain

Abstract

The kinetics of extracellular K⁺ activity was compared to the availability of energy in the cortex of rats and gerbils exposed to anoxia, hypoxia, spreading depression, and ischemia.

A combined K⁺/DC surface electrode was used alone or together with a fiber optic light guide in various experiments. All experiments were done on slightly anesthetized animals that were practically awake. The results can be summarized in the following conclusions: (1) Under conditions such as hypoxia or ischemia, K⁺₀ showed a two-phase efflux kinetics, and a transition or critical point was reached where the response proceeds at a higher rate. This critical point was in the range of 10-16 mEq/1 potassium. (2) Availability of oxygen is necessary but not sufficient for a full rate of recovery from a long-term oxygen-deprivation insult. (3) There is an energy debt or energy-transduction bottleneck fonned during a prolonged O₂ insufficiency. This debt is reversed slowly during the recovery phase even when full restitution of O₂ supply and blood flow has occurred.     

Long-term observations in gerbil brain following transient cerebral ischemia: Autoradiographic and histological study

We investigated the long-term changes that occur in the gerbil brain following transient cerebral ischemia using histology and receptor autoradiography. Transient ischemia was induced for 3 and 10 min, and animals were allowed to survive for 8 months. A histological study showed that 3-min ischemia caused neuronal damage and mild atrophy only in the hippocampal CA1 sector, and that 10-min ischemia produced severe neuronal damage and marked shrinkage in the hippocampal CA1 and CA3 sectors. Furthermore, severe neuronal damage was seen in the striatum after 10-min ischemia. Autoradiography study revealed that 3-min ischemia caused a significant reduction in [³H] naloxone binding in the frontal cortex, striatum, dentate gyrus, and thalamus, whereas [³H]SCH 23390 and [³H] forskolin binding was not significantly altered in all regions, In contrast, 10-min ischemia produced marked alteration in these binding sites in the striatum, hippocampus, thalamus, and substantia nigra. The alteration was especially notable in the hippocampal region and substantia nigra. These results indicate that hippocampal damage after transient ischemia, compared with that in other regions, is not static, but particularly progressive. Furthermore, they demonstrate a reduction in adenylate cyclase system in the striatum and substantia nigra after transient ischemia. Moreover, our results suggest that long-term survival after ischemia may induce synaptic modification of neurotransmitter and adenylate cyclase system in the hippocampus.     

沙鼠全脑缺血再灌注后海马神经营养保护作用研究

目的 沙鼠全脑缺血再灌注后给予神经营养保护,观察海马神经元细胞中凋亡相关蛋白表达变化.方法 通过夹闭沙鼠双侧颈总动脉法制作全脑缺血再灌注模型54只,随机分为神经营养因子治疗组、丹参治疗组以及生理盐水对照组3组.在沙鼠全脑缺血30 min再灌注后,分别在6 h、连续3 d、连续7 d给予腹腔注射神经营养因子、丹参以及生理盐水,采用免疫组化法观察海马神经元细胞胞浆中凋亡相关蛋白表达的变化.结果 生理盐水组中,B细胞淋巴瘤2蛋白表达无论是在第6小时,还是第3天或者第7天,都明显最低,而丹参组次之,神经营养因子治疗组表达最高;同组内不同时间相比,B细胞淋巴瘤2蛋白在第6 小时表达最高.B细胞淋巴瘤2相关X蛋白无论是在第6小时,还是第3天或者第7天,在生理盐水对照组中都有阳性表达;但在神经营养因子治疗组及丹参治疗组,B细胞淋巴瘤2相关X蛋白几乎没有表达或者表达极低;在同组内不同时间,B细胞淋巴瘤2相关X蛋白表达没有明显的差异.结论 神经营养因子和中药丹参对全脑缺血再灌注所致的神经细胞损伤具有一定的保护作用且6 h内神经营养保护效果较好.     

A better method for confirming <Emphasis Type="Italic">Helicobacter pylori</Emphasis> infection in Mongolian gerbils

Background. Our aim was to evaluate the accuracy of the stool antigen test and the optimal time point for detecting Helicobacter pylori infection in a Mongolian gerbil model. Methods. We inoculated 8-week-old Mongolian gerbils with H. pylori (Vac A (+)/CagA(+)). The gerbil-infected model was developed as follows: H. pylori was put into broth (about 10⁹ CFU/ml), and 50 gerbils were then fed with 1 ml intragastrically twice within a 3-day interval. Another ten gerbils were fed broth only. Twenty-six weeks after the inoculation, the gerbils were killed. The gastric mucosa was sampled for a series of examinations including culture, histology, rapid urease test, and polymerase chain reaction. Stool samples for a stool antigen test, H. pylori-specific stool antigen assay (HpSA), were collected during weeks 4, 6, 8, 12, and 26 after inoculation. Of the 50 gerbils inoculated with H. pylori, the inoculation was successful in 88%. Severe active gastritis, ulceration, and intestinal metaplasia were obvious. Results. The HpSA test results were sensitivity, 88.6%; specificity, 100%; positive predictive value (PPV), 100%; negative predictive value (NPV), 54.5%, and accuracy, 90%. The HpSA test began to be more sensitive and accurate (P < 0.05) beginning during week 6 after inoculation. We also found that H. pylori could be detected earlier and more easily in the group with high H. pylori density. Conclusions. HpSA seems to be suitable for confirming colonization of gerbils with H. pylori. The optimal testing time point is around 6 weeks after inoculation. This test is a good choice for long-term observation of H. pylori infection in Mongolian gerbils.     

Adopted cognitive tests for gerbils: Validation by studying ageing and ischemia

Transient occlusion of common carotid arteries in gerbils is a simple and widely used model for assessing histological and functional consequences of transient forebrain ischemia and neuroprotective action of pharmaceuticals. In the present study we aimed to introduce additional behavioural tests as novel object recognition and food-motivated hole-board learning in order to measure attention and learning capacity in gerbils. For validating these cognitive tests the effects of ageing (4, 9 and 18 months) and those of transient forebrain ischemia induced by bilateral carotid occlusion at 9 months of age were investigated. Neuronal cell death was estimated in the hippocampus using TUNEL and caspase-3 double fluorescence labelling and confocal microscopy.Ageing within the selected range although influenced ambulatory activity, did not considerably change attention and memory functions of gerbils. As a result of transient ischemia a selective neuronal damage in CA1 and CA2 regions of the hippocampus has been observed and tested 4 days after the insult. Ischemic gerbils became hyperactive, but showed decreased attention and impaired spatial memory functions as compared to sham-operated controls. According to our results the novel object recognition paradigm and the hole-board spatial learning test could reliably be added to the battery of conventional behavioural tests applied previously in this species. The novel tests can be performed within a wide interval of adult age and provide useful additional methods for assessing ischemia-induced cognitive impairment in gerbils.     

Two region‐dependent pathways of eosinophilic neuronal death after transient cerebral ischemia

Various types of eosinophilic neurons (ENs) are found in the post‐ischemic brain. We examined the temporal profile of ENs in the core and peripheral regions of the ischemic cortex, and analyzed the relationship to the expression of various cell death‐related factors. Unilateral forebrain ischemia was induced in Mongolian gerbils by transient common carotid artery occlusions, and the brains from 3 h to 2 weeks post‐ischemia were prepared for morphometric and immunohistochemical analysis of ENs. ENs with minimally abnormal nuclei and swollen cell bodies appeared at 3 h in the ischemic core and at 12 h in the periphery. In both locations multiple cell death‐related factors including calcium, µ‐calpain, cathepsin D, 78 kDa glucose‐regulated protein (GRP78) and ubiquitin were activated. In the ischemic core, pyknosis and irregularly atrophic cytoplasm peaked at 12 h, which was associated with significant increases in staining for calcium and µ‐calpain. ENs with pyknosis and scant cytoplasm peaked at 4 days and were positive for TUNEL and calcium staining. In the ischemic periphery, ENs had slightly atrophic cytoplasm and sequentially developed pyknosis, karyorrhexis and karyolysis over 1 week. These cells were positive for TUNEL and calcium staining. All types of EN were negative for caspase 3. There may be two region‐dependent pathways of EN changes in the post‐ischemic brain: pyknosis with cytoplasmic shrinkage in the core, and nuclear disintegration with slightly atrophic cytoplasm in the periphery. This difference coordinates different activation patterns of cell death‐related factors in ENs.     

The neuronal apoptotic death in global cerebral ischemia in gerbil: Important role for sodium channel modulator

Global ischemia was induced in gerbil by bilateral occlusion of the common carotid arteries for 5 min. Sodium ionophore monensin or sodium channel blocker tetrodotoxin (TTX) was administered at doses of 10 μg/kg, i.p., 30 min before ischemia induction; the dose was repeated after 22 hr. Subsequently, brain infarct occurred, determined at 24 hr after occlusion. Large, well‐demarcated infarcts were observed in both hemispheres, an important observation because it critically influences the interpretation of the data. Because nitric oxide (NO) production is thought to be related to ischemic neuronal damage, we examined increases in Ca²⁺ influx, which lead to the activation of nitric oxide synthase (NOS). Then we evaluated the contributions of neuronal NOS, endothelial NOS, and inducible NOS to NO production in brain cryosections. The cytosolic release of apoptogenic molecules like cytochrome c and p53 were confirmed after 24 hr of reflow. TUNEL (terminal deoxynucleotidyl transferase dUTP nick‐end labeling) labeling detected the apoptotic cells, which were confirmed in neuron‐rich cell populations. After 24 hr, all the ischemic changes were amplified by monensin and significantly attenuated by TTX treatment. Additionally, the nesting behavior and histological outcomes were examined after 7 day of reflow. The neuronal damage in the hippocampal area and significant decrease in nesting scores were observed with monensin treatment and reduced by TTX pretreatment after day 7 of reflow. To our knowledge, this report is the first to highlight the involvement of the voltage‐sensitive Na⁺ channel in possibly regulating in part NO system and apoptosis in a cytochrome c–dependent manner in global ischemia in the gerbil, and thus warrants further investigation. © 2008 Wiley‐Liss, Inc.