Assessment of Hippocampal Dendritic Complexity in Aged Mice Using the Golgi-Cox Method

Contralateral synaptic changes following severe unilateral brain injury

The brain is highly integrated and thus unilateral injury can impact the contralateral hemisphere. However, further research is needed to clarify the changes in the response of the contralateral homotopic area to ipsilateral injury. We hypothesized that severe unilateral brain injury would be accompanied by contralateral synaptic changes that are related to functional recovery. To test this, we divided rats into sham and experimental groups. In the experimental group, we performed right motor cortex resection. These rats were further divided into three subgroups according to post-injury time: 7 days, 14 days, and 30 days post-injury. Rats in each group were evaluated using a beam walking test to quantify the recovery of motor function, and all rats received an injection of adeno-associated virus-containing green fluorescent protein (GFP). Finally, we conducted morphological and histological analyses to identify synaptic changes. Over time, the behavior of the rats that underwent right motor cortex resection recovered. Furthermore, in contrast to the sham group, the experimental groups exhibited an increase in the spine density and expression of synaptic proteins in layer V of the contralateral motor cortex, which was consistent with the GFP-labeled neurons. Moreover, more immature spines were observed 7 days post-injury. Notably, spine morphology matured from 7 to 30 days, and the increase in Synapsin-1 intensity in layer V peaked 14 days after the resection, whereas PSD-95 intensity continued to increase until day 30. Our findings suggested that following motor function recovery from unilateral brain injury, spine morphology and synaptic proteins change dynamically in the contralateral hemisphere.

Testosterone Influence on Microtubule-Associated Proteins and Spine Density in Hippocampus: Implications on Learning and Memory

The thorny protrusions or spines increase the neuronal surface area, facilitate synaptic interconnections among neurons, and play an essential role in the hippocampus. Increasing evidence suggests that testosterone, the gonadal hormone, plays an important role in neurogenesis and synaptic plasticity. The role of testosterone on microtubule-associated proteins on dendritic neurite stability in the hippocampus and its impact on learning disability is not elucidated. Adult male Wistar albino rats were randomly selected for the control, castrated, castrated + testosterone, and control + testosterone groups. Bilateral orchidectomy was done, and the testosterone propionate was administered during the entire trial period, i.e., 14 days. The learning assessments were done using working/reference memory versions of the 8-arm radial maze and hippocampal tissues processed for histological and protein expressions. There were reduced expressions of microtubule-associated protein 2 (MAP2), postsynaptic density protein 95 (PSD95), and androgen receptor (AR) and increased expression of pTau in the castrated group. Conversely, the expression of MAP2, PSD95, and AR was increased, and the pTau expression was reduced in the hippocampus of the castrated rat administrated with testosterone. Androgen-depleted rats showed impaired synaptic plasticity in the hippocampus associated with contracted microtubule dynamics. Along with learning disability, there was an increased number of reference memory errors and working memory errors in castrated rats. Observations suggest that androgen regulates expression of neural tissue-specific MAPs and plays a vital role in hippocampus synaptic plasticity and that a similar mechanism may underlie neurological disorders in aging and hypogonadal men.

A New Approach to Model Sporadic Alzheimer's Disease by Intracerebroventricular Streptozotocin Injection in APP/PS1 Mice

Alzheimer's disease (AD) is the most common cause of dementia among elderly people. Majority of AD cases are sporadic (SAD) with unknown cause. Transgenic animal models closely reflect the familial (genetic) aspect of the disease but not the sporadic type. However, most new drug candidates which are tested positive in transgenic animal models failed in clinical studies so far. Herein, we aim to develop an AD animal model that combines most of the neuropathological features seen in sporadic AD in humans with amyloid plaques observed in transgenic mice. Four-month-old wild-type and APP/PS1 AD mice were given a single intracerebroventricular (ICV) injection of 3 mg/kg streptozotocin (STZ), a diabetogenic agent. Three weeks later, their cognitive behavior was assessed, and their brain tissues were collected for biochemical and histological analysis. STZ produced cognitive deficits in both non-transgenic mice and AD mice. Biochemical analysis showed a severe decline in synaptic proteins, increase in tau phosphorylation, oxidative stress, disturbed brain insulin signaling with extensive neuroinflammation, and cell death. Significant increase was also observed in the level of the soluble beta amyloid precursor protein (APP) fragments and robust accumulation of amyloid plaques in AD mice compared to the control. These results suggest that STZ ICV treatment causes disturbance in multiple metabolic and cell signaling pathways in the brain that facilitated amyloid plaque accumulation and tau phosphorylation. Therefore, this animal model can be used to evaluate new AD therapeutic agents for clinical translation.

Effects of 16O charged-particle irradiation on cognition, hippocampal morphology and mutagenesis in female mice

The effects of radiation in space on human cognition are a growing concern for NASA scientists and astronauts as the possibility for long-duration missions to Mars becomes more tangible. Oxygen (¹⁶O) radiation is of utmost interest considering that astronauts will interact with this radiation frequently. ¹⁶O radiation is a class of galactic cosmic ray (GCR) radiation and also present within spacecrafts. Whole-body exposure to high linear energy transfer (LET) radiation has been shown to affect hippocampal-dependent cognition. To assess the effects of high-LET radiation, we gave 6-month-old female C57BL/6 mice whole-body exposure to ¹⁶O at 0.25 or 0.1 Gy at NASA's Space Radiation Laboratory. Three months following irradiation, animals were tested for cognitive performance using the Y-maze and Novel Object Recognition paradigms. Our behavioral data shows that ¹⁶O radiation significantly impairs object memory but not spatial memory. Also, dendritic morphology characterized by the Sholl analysis showed that ¹⁶O radiation significantly decreased dendritic branch points, ends, length, and complexity in 0.1 Gy and 0.25 Gy dosages. Finally, we found no significant effect of radiation on single nucleotide polymorphisms in hippocampal genes related to oxidative stress, inflammation, and immediate early genes. Our data suggest exposure to heavy ion ¹⁶O radiation modulates hippocampal neurons and induces behavioral deficits at a time point of three months after exposure in female mice.

Cranial irradiation impairs juvenile social memory and modulates hippocampal physiology

Cranial and craniospinal irradiation are the oldest central nervous system prophylaxis treatments considered for pediatric patients with acute lymphoblastic leukemia (ALL). However, survivors of childhood ALL that received cranial radiotherapy are at increased risk for deficits in neurocognitive skills. The continuous and dynamic response of normal tissue after irradiation has been identified as one of the causative factors for cognitive changes after cranial radiation therapy. The aim of our study was to investigate the radiation effects on social behavior and neuronal morphology in the hippocampus of adult mice. Twenty-oneday-old male C57BL/6 mice were irradiated with the small-animal radiation research platform (SARRP). Animals were given a single 10-Gy dose of radiation of X-ray cranial radiation. One month following irradiation, animals underwent behavioral testing in the Three-Chamber Sociability paradigm. Radiation affected social discrimination during the third stage eliciting an inability to discriminate between the familiar and stranger mouse, while sham successfully spent more time exploring the novel stranger. Proteomic analysis revealed dysregulation of metabolic and signaling pathways associated with neurocognitive dysfunction such as mitochondrial dysfunction, Rac 1 signaling, and synaptogenesis signaling. We observed significant decreases in mushroom spine density in the Cornu Ammonis 2 of the hippocampus, which is associated with sociability processing.

Late Effects of 1H + 16O on Short-Term and Object Memory, Hippocampal Dendritic Morphology and Mutagenesis

The space extending beyond Earth’s magnetosphere is subject to a complex field of high-energy charged nuclei, which are capable of traversing spacecraft shielding and human tissues, inducing dense ionization events. The central nervous system is a major area of concern for astronauts who will be exposed to the deep-space radiation environment on a mission to Mars, as charged-particle radiation has been shown to elicit changes to the dendritic arbor within the hippocampus of rodents, and related cognitive-behavioral deficits. We exposed 6-month-old male mice to whole-body ¹H (0.5 Gy; 150 MeV/n; 18–19 cGy/minute) and an hour later to ¹⁶O (0.1Gy; 600 MeV/n; 18–33 Gy/min) at NASA’s Space Radiation Laboratory as a galactic cosmic ray-relevant model. Animals were housed with bedding which provides cognitive enrichment. Mice were tested for cognitive behavior 9 months after exposure to elucidate late radiation effects. Radiation induced significant deficits in novel object recognition and short-term spatial memory (Y-maze). Additionally, we observed opposing morphological differences between the mature granular and pyramidal neurons throughout the hippocampus, with increased dendritic length in the dorsal dentate gyrus and reduced length and complexity in the CA1 subregion of the hippocampus. Dendritic spine analyses revealed a severe reduction in mushroom spine density throughout the hippocampus of irradiated animals. Finally, we detected no general effect of radiation on single-nucleotide polymorphisms in immediate early genes, and genes involved in inflammation but found a higher variant allele frequency in the antioxidants thioredoxin reductase 2 and 3 loci.

Determining factors for optimal neuronal and glial Golgi-Cox staining

Golgi staining allows for the analysis of neuronal arborisations and connections and is considered a powerful tool in basic and clinical neuroscience. The fundamental rules for improving neuronal staining using the Golgi-Cox method are not fully understood; both intrinsic and extrinsic factors may control the staining process. Therefore, various conditions were tested to improve the Golgi-Cox protocol for vibratome-cut rat brain sections. Optimal staining of cortical neurons was achieved after 72 h of impregnation. Well-stained neurons in both cortical and subcortical structures were observed after 96 h of impregnation. The dendritic arborisation pattern of cortical neurons derived from the 72-h impregnation group was comparable to those of the 96 and 168-h impregnation groups. The entire brain was stained well when the pH of the Golgi-Cox solution was 6.5 and that of the sodium carbonate solution was 11.2. Lack of brain perfusion or perfusion with 0.9% NaCl did not influence optimal neuronal staining. Perfusion with 37% formaldehyde, followed by impregnation, only resulted in glial staining, but perfusion with 4% formaldehyde facilitated both glial and neuronal staining. Whole brains required longer impregnation times for better staining. Although every factor had a role in determining optimal neuronal staining, impregnation time and the pH of staining solutions were key factors among them. This modified Golgi-Cox protocol provides a simple and economical procedure to stain both neurons and glia separately.

Assessing the Effects of Redox Modifier MnTnBuOE-2-PyP 5+ on Cognition and Hippocampal Physiology Following Doxorubicin, Cyclophosphamide, and Paclitaxel Treatment

Background: Chemotherapy treatment for breast cancer can induce cognitive impairments often involving oxidative stress. The brain, as a whole, is susceptible to oxidative stress due to its high-energy requirements, limited anaerobic respiration capacities, and limited antioxidant defenses. The goal of the current study was to determine if the manganese porphyrin superoxide dismutase mimetic MnTnBuOE-2-PyP (MnBuOE) could ameliorate the effects of doxorubicin, cyclophosphamide, and paclitaxel (AC-T) on mature dendrite morphology and cognitive function. Methods: Four-month-old female C57BL/6 mice received intraperitoneal injections of chemotherapy followed by subcutaneous injections of MnBuOE. Four weeks following chemotherapy treatment, mice were tested for hippocampus-dependent cognitive performance in the Morris water maze. After testing, brains were collected for Golgi staining and molecular analyses. Results: MnBuOE treatment preserved spatial memory during the Morris water-maze. MnBuOE/AC-T showed spatial memory retention during all probe trials. AC-T treatment significantly impaired spatial memory retention in the first and third probe trial (no platform). AC-T treatment decreased dendritic length in the Cornu Ammonis 1 (CA1) and dentate gyrus (DG) areas of the hippocampus while AC-T/MnBuOE maintained dendritic length. Comparative proteomic analysis revealed affected protein networks associated with cell morphology and behavior functions in both the AC-T and AC-T/MnBuOE treatment groups.

Loss of C/EBPδ Exacerbates Radiation-Induced Cognitive Decline in Aged Mice due to Impaired Oxidative Stress Response

Aging is characterized by increased inflammation and deterioration of the cellular stress responses such as the oxidant/antioxidant equilibrium, DNA damage repair fidelity, and telomeric attrition. All these factors contribute to the increased radiation sensitivity in the elderly as shown by epidemiological studies of the Japanese atomic bomb survivors. There is a global increase in the aging population, who may be at increased risk of exposure to ionizing radiation (IR) as part of cancer therapy or accidental exposure. Therefore, it is critical to delineate the factors that exacerbate age-related radiation sensitivity and neurocognitive decline. The transcription factor CCAAT enhancer binding protein delta (C/EBPδ) is implicated with regulatory roles in neuroinflammation, learning, and memory, however its role in IR-induced neurocognitive decline and aging is not known. The purpose of this study was to delineate the role of C/EBPδ in IR-induced neurocognitive decline in aged mice. We report that aged Cebpd^−/− mice exposed to acute IR exposure display impairment in short-term memory and spatial memory that correlated with significant alterations in the morphology of neurons in the dentate gyrus (DG) and CA1 apical and basal regions. There were no significant changes in the expression of inflammatory markers. However, the expression of superoxide dismutase 2 (SOD2) and catalase (CAT) were altered post-IR in the hippocampus of aged Cebpd^−/− mice. These results suggest that Cebpd may protect from IR-induced neurocognitive dysfunction by suppressing oxidative stress in aged mice.

Late Effects of 16O-Particle Radiation on Female Social and Cognitive Behavior and Hippocampal Physiology

The radiation environment in space remains a major concern for manned space exploration, as there is currently no shielding material capable of fully protecting flight crews. Additionally, there is growing concern for the social and cognitive welfare of astronauts, due to prolonged radiation exposure and confinement they will experience on a mission to Mars. In this artice, we report on the late effects of ¹⁶O-particle radiation on social and cognitive behavior and neuronal morphology in the hippocampus of adult female mice. Six-month-old mice received ¹⁶O-particle whole-body irradiation at doses of either 0.25 or 0.1 Gy (600 MeV/n; 18-33 cGy/min) at the NASA's Space Radiation Laboratory in Upton, NY. At nine months postirradiation, the animals underwent behavioral testing in the three-chamber sociability, novel object recognition and Y-maze paradigms. Exposure to 0.1 or 0.25 Gy ¹⁶O significantly impaired object memory, a 0.25 Gy dose impaired social novelty learning, but neither dosage impaired short-term spatial memory. We observed significant decreases in mushroom spine density and dendrite morphology in the dentate gyrus, cornu ammonis 3, 2 and 1 of the hippocampus, which are critical areas for object novelty and sociability processing. Our data suggest exposure to ¹⁶O modulates hippocampal pyramidal and granular neurons and induces behavioral deficits at a time point of nine months after exposure in females.

Long-Term Changes in Cognition and Physiology after Low-Dose 16O Irradiation

Astronauts traveling to Mars will be exposed to high levels of ionizing radiation upon leaving low-Earth orbit. During prolonged space travel, astronauts are exposed to galactic cosmic rays (GCRs) composed of protons; oxygen molecules; and high energy, high mass charged particles. Notably, oxygen molecules can travel through the shielding of spacecraft, potentially impacting 25% of the hippocampus. The aim of the current study was to assess whether ¹⁶O-particle radiation induced a behavioral deficit and histological changes in mice. Mice were sent to the National Aeronautics and Space Administration (NASA) Space Radiation Laboratory at Brookhaven National Laboratory and exposed to particulate ¹⁶O radiation at doses of 0 and 0.05 Gy. Nine months after irradiation, the mice were tested for novel object recognition and in the Y-maze, after which the animals were sacrificed. The brains were then dissected along the midsagittal plane for Golgi staining. Exposure to 0.05 Gy significantly impaired novel object recognition. However, short term memory and exploratory activity in the Y-maze were not affected. Micromorphometric analysis revealed significant decreases in mushroom spine density in the dentate gyrus and cornu Ammonis-1 and -3 of the hippocampus. Sholl analysis revealed a significant decrease in dendritic complexity in the dentate gyrus. The present data provide evidence that space radiation has deleterious effects on mature neurons associated with hippocampal learning and memory.

NR2B-Tyr phosphorylation regulates synaptic plasticity in central sensitization in a chronic migraine rat model

Background

Although the mechanism of chronic migraine (CM) is unclear, it might be related to central sensitization and neuronal persistent hyperexcitability. The tyrosine phosphorylation of NR2B (NR2B-pTyr) reportedly contributes to the development of central sensitization and persistent pain in the spinal cord. Central sensitization is thought to be associated with an increase in synaptic efficiency, but the mechanism through which NR2B-pTyr regulates synaptic participation in CM-related central sensitization is unknown. In this study, we aim to investigate the role of NR2B-pTyr in regulating synaptic plasticity in CM-related central sensitization.

Methods

Male Sprague-Dawley rats were subjected to seven inflammatory soup (IS) injections to model recurrent trigeminovascular or dural nociceptor activation, which is assumed to occur in patients with CM. We used the von Frey test to detect changes in mechanical withdrawal thresholds, and western blotting and immunofluorescence staining assays were performed to detect the expression of NR2B-pTyr in the trigeminal nucleus caudalis (TNC). NR2B-pTyr was blocked with the Src family kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)-pyrazolo [3,4-d] pyrimidine (PP2) and the protein tyrosine kinase inhibitor genistein to detected the changes in calcitonin gene-related peptide (CGRP), substance P (SP), and the synaptic proteins postsynaptic density 95 (PSD95), synaptophysin (Syp), synaptotagmin1 (Syt-1). The synaptic ultrastructures were observed by transmission electron microscopy (TEM), and the dendritic architecture of TNC neurons was observed by Golgi-Cox staining.

Results

Statistical analyses revealed that repeated infusions of IS induced mechanical allodynia and significantly increased the expression of NR2B Tyr-1472 phosphorylation (pNR2B-Y1472) and NR2B Tyr-1252 phosphorylation (pNR2B-Y1252) in the TNC. Furthermore, the inhibition of NR2B-pTyr by PP2 and genistein relieved allodynia and reduced the expression of CGRP, SP, PSD95, Syp and Syt-1 and synaptic transmission.

Conclusions

These data indicate that NR2B-pTyr might regulate synaptic plasticity in central sensitization in a CM rat model. The inhibition of NR2B tyrosine phosphorylation has a protective effect on threshold dysfunction and migraine attacks through the regulation of synaptic plasticity in central sensitization.