Inputs from the olfactory bulb and olfactory cortex to the entorhinal cortex in the cat

Summary The spatial organization and laminar distribution of projections from the olfactory bulb and the anterior (PPCa) and posterior (PPCp) divisions of the prepiriform cortex to the entorhinal cortex were studied with anterograde (³H-leucine) and retrograde (WGA-HRP) tracing techniques. After ³H-leucine injections into the olfactory bulb transported labeling was seen over the lateral entorhinal area, except its most medial part, and over the rostral part of the medial entorhinal area. The labeling covers exclusively layer Ia. The lateral and medial entorhinal areas are also reached by fibers from the prepiriform cortex. The projection to the medial entorhinal area has not been described previously. Following injections of ³H-leucine into the PPCa transported labeling is present over the entire expanse of the entorhinal cortex and is located over layer Ib with the greatest density in its superficial part. Injections of ³H-leucine into the PPCp give rise to transported labeling over much of the entorhinal cortex. No labeling was found over the most medial parts of the medial subdivision (VMEA) of the lateral entorhinal area and the medial entorhinal area. Labeling occupies layer Ib, especially its middle part, and layers II and III. Both PPCa and PPCp appear to project most heavily to the dorsal (DLEA) and ventral (VLEA) subdivisions of the lateral entorhinal area. From the retrograde experiments it can be inferred that cells of layers II and III of the PPCa project predominantly to the DLEA, whereas those of the PPCp project predominantly to the VLEA. The MEA receives its heaviest projection from layer II of both PPCa and PPCp. In control experiments with ³H-leucine injections into the endopiriform nucleus it was found that this nucleus projects to the entire expanse of the entorhinal cortex. The fibers distribute to all layers with the exception of layer Ia.Abbreviations AI agranular insular cortex - AL lateral nucleus of the amygdala - BL basolateral nucleus of the amygdala - BM basomedial nucleus of the amygdala - C claustrum - CoA cortical nucleus of the amygdala - DLEA dorsal division of the lateral entorhinal cortex - END endopiriform nucleus - H hippocampus - I granular insular cortex - lot lateral olfactory tractus - MCL mitral cell layer of the olfactory bulb - MEA medial entorhinal area - OB olfactory bulb - PPCa anterior part of the prepiriform nucleus - PPCp posterior part of the prepiriform nucleus - VLEA ventral division of the lateral entorhinal cortex - VMEA ventromedial division of the lateral entorhinal cortex - 35 area 35 of the perirhinal cortex - 36 area 36 of the perirhinal cortex     

Afferents to the seizure-sensitive neurons in layer III of the medial entorhinal area: a tracing study in the rat

Neurons in layer III of the medial entorhinal area (MEA) in the rat are extremely vulnerable to local injections of amino-oxyacetic acid and to exprimentally induced limbic seizures. A comparable specific pathology has been noted in surgical specimens from patients with temporal lobe epilepsy. Efforts to understand this preferential neuronal vulnerability led us to study the neural input to this layer in the rat. Iontophoretic injection of the retrograde tracer fast blue, aimed at layer III of the MEA, resulted in retrogradely labeled neurons in the presubiculum in all the injected hemispheres. The nucleus reuniens thalami, the anteromedial thalamic nucleus, the ventral portion of the claustrum (endopiriform nucleus), the dorsomedial parts of the anteroventral thalamic nucleus, and the septum-diagonal band complex were labeled less frequently. In only one experiment, retrogradely labeled neurons were observed in the ventrolateral hypothalamus and in the brainstem nucleus raphe dorsalis. Since projections from claustrum to the entorhinal cortex has not been studied in the rat with modern sensitive anterograde tracing techniques, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were placed into the ventral portion of the claustrum. Anterogradely labeled fibers in the entorhinal area proved not to be confined to the MEA, since a prominent projection distributed to the lateral entorhinal area as well. In both areas, the densest terminal labeling was present in layers IV–VI, whereas layer III appeared to be only sparsely labeled. The present data indicate that of all potential afferents only those from the presubiculum distribute preferentially to layer III of the MEA. This, in turn, suggests a potentially important role of the presubiculum in the seizure-related degeneration of neurons in layer III of the MEA.     

Reelin-immunoreactivity in the hippocampal formation of 9-month-old wildtype mouse: effects of APP/PS1 genotype and ovariectomy

Reelin, an extracellular matrix protein has an important role in the migration, correct positioning and maturation of neurons during development. Though it is generally down-regulated in the postnatal period, expression of this large glycoprotein continues in the adult brain in some cell populations. In the present study, we examined the distribution of reelin-immunoreactivity (-ir) in the hippocampal formation of 9-month-old wildtype mice (WT). Then, reelin-ir in normal mice was compared to that of transgenic mice (APP/PS1) carrying mutated human APP and PS1 genes, which are linked to the familial form of Alzheimer's disease (AD). The APP/PS1 mice were additionally burdened with a second risk factor for AD, namely depletion of circulating gonadal hormones by ovariectomy (APP/PS1 + OVX). The analyses revealed that in adult WT reelin-ir is expressed by Cajal-Retzius cells and a subgroup of interneurons throughout the hippocampal formation. In addition, layer II projection neurons in the lateral entorhinal subfields are reelin-ir. Interestingly, ovariectomy decreases the number of reelin-ir cells in the hilus in WT mice, whereas AD-related genotype alone induces only a non-significant reduction. Unexpectedly, additional stress, e.g., depletion of gonadal hormones, does not aggravate the slight reduction in the reelin cell number in the APP/PS1 mice. We propose that the changes in normal reelin-ir are linked to disturbances in repair mechanisms in which APP/PS1 and gonadal hormones are involved and which are perturbed in neurodegenerative conditions, namely AD.     

Effects of combined entorhinal cortex-hippocampal lesions on locomotor behavior, spontaneous alternation and spatial maze learning in the rat

Male Sprague-Dawley rats with combined lesions to the dorsal and lateral aspects of the entorhinal cortex in one hemisphere and of the contralateral dorsolateral hippocampal formation were compared with both operated and unoperated controls on three different behaviors, monitored across a 53 day postoperative period. The rats with the combined entorhinal cortex-hippocampal lesions (EH) showed transient hyperactivity in the open field, transient reduction in spontaneous alternation levels in an unbaited T-maze and persistent deficits in learning spatial maze problems. The results of the present experiment are discussed in comparison with those from experiments on rats with bilateral hippocampal lesions and those from experiments on rats with bilateral entorhinal cortex lesions. Although some similarities among these findings suggest that these two brain regions probably function in a coordinated fashion with respect to these behaviors, differences in the various syndromes are also discussed.     

Selective cytotoxic lesions of the retrohippocampal region produce a mild deficit in social recognition memory

Although a number of studies have implicated the hippocampal formation in social recognition memory in the rat, a recent study in this laboratory has demonstrated that selective cytotoxic lesions, confined to the hippocampus proper (encompassing the four CA subfields and the dentate gyrus), are without effect on this behaviour. This finding suggests that the hippocampus proper does not subserve social recognition memory in the rat, but does not preclude the possibility that other areas of the hippocampal formation, such as the entorhinal cortex or subiculum, could support this form of learning. The present study addressed this issue by examining the effects of selective cytotoxic retrohippocampal (RHR) lesions (including both the entorhinal cortex and subiculum) on social recognition memory in the rat. RHR lesions produced a mild social recognition memory impairment, although lesioned animals still displayed a reduction in investigation time between the first and second exposure to the juvenile. This result is consistent with other studies which have implicated the retrohippocampal or parahippocampal area in olfactory recognition memory processes. It also suggests, however, that other areas, out with the retrohippocampal region, are also likely to play an important role in social recognition memory.     

不同认知功能障碍程度阿尔茨海默病患者海马、内嗅皮层体积变化及其与MMSE评分的关系

目的 探讨不同认知功能障碍程度的患者阿尔兹海默病（AD）海马、内嗅皮层体积的变化,及其与简易精神状态检查表（MMSE）评分的相关性。方法 横断面研究。纳入2017年9月—2021年9月联保部队第九六〇医院淄博院区86例AD患者临床和影像学资料,其中男54例、女32例,年龄55~87（73.9±8.1）岁。根据临床痴呆评定量表（CDR）评分将86例患者分为3组,其中36例CDR评分0.5分患者为轻度认知障碍（MCI）组,21例1分患者为轻度AD组,29例2~3分患者为中重度AD组。患者均应用MRI测量双侧海马体积、内嗅皮层体积,采用MMSE评分评估患者认知功能。观察指标：（1）比较3组患者性别、年龄、受教育年限等临床基线资料,以及MMSE评分;（2）比较3组患者海马体积和内嗅皮层体积;（3）分析AD患者MMSE评分与海马、内嗅皮层体积的相关性。结果 （1）3组患者性别、年龄、受教育年限等临床基线资料比较差异均无统计学意义（P值均>0.05）。MCI组、轻度AD组、中重度AD组患者MMSE评分依次降低,差异有统计学意义（F=113.29,P<0.001）。（2）MCI组、轻度AD组、中重度AD组左右侧海马体积MRI测量值分别为（3.24±0.32）cm³和（3.22±0.31）cm³、（2.72±0.53）cm³和（2.84±0.56）cm³、（2.31±0.55）cm³和（2.46±0.54）cm³,左右侧内嗅皮层体积分别为（1.42±0.26）cm³和（1.39±0.27）cm³、（1.28±0.24）cm³和（1.24±0.25）cm³、（1.04±0.31）cm³和（1.06±0.34）cm³。3组患者左右侧海马体积、内嗅皮层体积MRI测量值比较,均为MCI组>轻度AD组>中重度AD组,差异均有统计学意义（P值均<0.05）。（3）86例AD患者MMSE评分10~27（20.9±5.2）分,与左右两侧海马体积、内嗅皮层体积MRI测量值均呈正相关（r=0.82、0.81、0.73、0.72,P值均<0.001）。结论 随着认知功能障碍程度的加重,AD患者海马、内嗅皮层体积MRI测量值逐渐减小,且MMSE评分与海马、内嗅皮层体积存在相关性。     

内嗅皮质萎缩评价糖尿病患者认知功能

目的 探讨2型糖尿病（T2DM）伴轻度认知功能损害（MCI）患者与单纯T2DM患者、健康对照者间各脑区皮质体积的差异,并分析其与认知下降的关联程度。方法 收集30例单纯T2DM患者、30例T2DM伴MCI患者和30名健康对照者,通过高分辨率MR T1WI采集大脑结构像数据,应用FreeSurfer软件处理获得各脑区体积参数。3组间各脑区体积的比较采用方差分析,对差异有统计学意义的脑区与心理学量表进行相关分析。结果 T2DM与T2DM伴MCI患者的听觉词语学习测验、复杂图形20 min回忆测验、数字符号编码测验、连线测验A、连线测验B、蒙特利尔认知评估量表分数差异有统计学意义（P均<0.05）。与T2DM患者比较,T2DM伴MCI患者的左侧内嗅皮质、左侧外侧眶额皮层、左侧后扣带回皮质、右侧外侧眶额皮质、右侧眶部皮质、右侧岛叶皮质体积均降低（P均<0.05）;T2DM伴MCI患者的左侧内嗅皮质体积与听觉词语学习测验评分（即刻）呈正相关（r=0.452,P=0.018）。结论 T2DM伴MCI患者出现多个脑区皮质体积降低,其中左侧内嗅皮质体积可作为诊断和衡量T2DM伴MCI的潜在生物学指标。     

Reduced plasticity and mild cognitive impairment-like deficits after entorhinal lesions in hAPP/APOE4 mice

Mild cognitive impairment (MCI) is a clinical condition that often precedes Alzheimer disease (AD). Compared with apolipoprotein E-ε3 (APOE3), the apolipoprotein E-ε4 (APOE4) allele is associated with an increased risk of developing MCI and spatial navigation impairments. In MCI, the entorhinal cortex (EC), which is the main innervation source of the dentate gyrus, displays partial neuronal loss. We show that bilateral partial EC lesions lead to marked spatial memory deficits and reduced synaptic density in the dentate gyrus of APOE4 mice compared with APOE3 mice. Genotype and lesion status did not affect the performance in non-navigational tasks. Thus, partial EC lesions in APOE4 mice were sufficient to induce severe spatial memory impairments and synaptic loss in the dentate gyrus. In addition, lesioned APOE4 mice showed no evidence of reactional increase in cholinergic terminals density as opposed to APOE3 mice, suggesting that APOE4 interferes with the ability of the cholinergic system to respond to EC input loss. These findings provide a possible mechanism underlying the aggravating effect of APOE4 on the cognitive outcome of MCI patients.     

Brain Neuronal Degeneration Caused by Episodic Alcohol Intoxication in Rats: Effects of Nimodipine, 6,7-Dinitro-quinoxaline-2,3-dione, and MK-801

Rats repeatedly intoxicated with alcohol (ethanol, three times daily) over a 4-day period display neuronal degeneration in the dentate gyrus; entorhinal, piriform, insular, orbital, and perirhinal cortices; and in the olfactory nerve fibers and terminals in the olfactory bulb. Postulating a role for excitotoxicity, we have attempted to prevent the degeneration using antagonists that are neuroprotective in this type of brain damage. In an initial study, continuous subcutaneous infusion of a high dose of the glutamate/NMDA receptor antagonist MK-801 (2 mg/kg/day) by itself caused extensive neuronal degeneration in several brain regions and severe behavioral intoxication that precluded survival if combined with high blood alcohol levels (～300 mg/dl). Moreover, the lower, nonneurotoxic blood alcohol levels (～150 mg/dl) that were compatible with survival worsened the MK-801-induced brain damage. In a subsequent experiment, daily intraperitoneal injections of a lower dose of MK-801 (1 mg/kg/day) resulted in no MK-801 toxicity and, when combined with neurotoxic levels of alcohol, no reduction in alcohol-induced neurotoxicity. Nimodipine, a voltage-gated Ca²⁺ channel blocker, reduced the neuronal damage in the dentate gyrus, but greatly increased it in the piriform cortex when administered intragastrically at 600 mg/kg/day; it provided no protection from alcohol-dependent degeneration when given intragastrically at 100 mg/kg/day. Continuous intracere-broventricular delivery of 0.24 to 0.29 mg/day of 6,7-dinitro-quinoxa-line-2,3-dione, a glutamate/α-amino-3-hydroxy-5-methyl-4-isoxazole receptor antagonist, failed to diminish alcohol-dependent neuronal damage in any brain region. We conclude that brain damage from episodic “binge” alcohol intoxication is not primarily mediated by excitotoxic mechanisms, implying that other, nonexcrtotoxic pathophysiological mechanisms, are involved. Furthermore, MK-801, far from protecting from the alcohol-induced damage, at high doses causes widespread neuropathology that is significantly potentiated by alcohol.     

Behavioral Effects of Deep Brain Stimulation of the Anterior Nucleus of Thalamus,Entorhinal Cortex and Fornix in a Rat Model of Alzheimer's Disease

Background:

Recent clinical and preclinical studies have suggested that deep brain stimulation (DBS) can be used as a tool to enhance cognitive functions. The aim of the present study was to investigate the impact of DBS at three separate targets in the Papez circuit, including the anterior nucleus of thalamus (ANT), the entorhinal cortex (EC), and the fornix (FX), on cognitive behaviors in an Alzheimer''s disease (AD) rat model.

Methods:

Forty-eight rats were subjected to an intrahippocampal injection of amyloid peptides 1-42 to induce an AD model. Rats were divided into six groups: DBS and sham DBS groups of ANT, EC, and FX. Spatial learning and memory were assessed by the Morris water maze (MWM). Recognition memory was investigated by the novel object recognition memory test (NORM). Locomotor and anxiety-related behaviors were detected by the open field test (OF). By using two-way analysis of variance (ANOVA), behavior differences between the six groups were analyzed.

Results:

In the MWM, the ANT, EC, and FX DBS groups performed differently in terms of the time spent in the platform zone (F_(2,23) = 6.04, P < 0.01), the frequency of platform crossing (F_(2,23) = 11.53, P < 0.001), and the percent time spent within the platform quadrant (F_(2,23) = 6.29, P < 0.01). In the NORM, the EC and FX DBS groups spent more time with the novel object, although the ANT DBS group did not (F_(2,23) = 10.03, P < 0.001). In the OF, all of the groups showed a similar total distance moved (F_(1,42) = 1.14, P = 0.29) and relative time spent in the center (F_(2,42) = 0.56, P = 0.58).

Conclusions:

Our results demonstrated that DBS of the EC and FX facilitated hippocampus-dependent spatial memory more prominently than ANT DBS. In addition, hippocampus-independent recognition memory was enhanced by EC and FX DBS. None of the targets showed side-effects of anxiety or locomotor behaviors.