Dendritic morphology of neurons in medial prefrontal cortex, hippocampus, and nucleus accumbens in adult SH rats

Harmful Effects on the Hippocampal Morpho-Histology and on Learning and Memory in the Offspring of Rats with Streptozotocin-Induced Diabetes

Learning alterations in the child population may be linked to gestational diabetes as a causal factor, though this remains an open and highly controversial question. In that sense, it has been reported that maternal hyperglycemia generates a threatening condition that affects hippocampal development in offspring. The pyramidal cells of the CA3 subfield, a key structure in learning and memory processes, are particularly important in cognitive deficiencies. We evaluate the effect of the hyperglycemic intrauterine environment on hippocampal histomorphometry in offspring, correlating it with spatial learning and memory, as well as the morphology of dendrites and spines in 30-day-old pups (P30). The maternal hyperglycemia affected the body weight, height, and brain size of fetuses at 21 days of gestation (F21), newborn pups (P0) and P30 pups from diabetic rats, which were smaller compared to the control group. Consequently, this resulted in a decrease in hippocampal size, lower neuronal density and cytoarchitectural disorganization in the CA3 region of the hippocampus in the offspring at the three ages studied. The behavioral tests performed showed a direct relationship between morpho-histological alterations and deficiencies in learning and memory, as well as alterations in the morphology of the dendrites and spines. Therefore, knowing the harmful effects caused by gestational diabetes can be of great help to establish therapeutic and educational strategies that can help to improve learning and memory in children.

Differential Effects of Neonatal Ventral Hippocampus Lesion on Behavior and Corticolimbic Plasticity in Wistar-Kyoto and Spontaneously Hypertensive Rats

Dysfunction of the corticolimbic system, particularly at the dendritic spine level, is a recognized core mechanism in neurodevelopmental disorders such as schizophrenia. Neonatal ventral hippocampus lesion (NVHL) in Sprague-Dawley rats induces both a schizophrenia-related behavioral phenotype and dendritic spine pathology (reduced total number and mature spines) in corticolimbic areas, which is mitigated by antipsychotics. However, there is limited information on the impact of rat strain on NVHL outcomes and antipsychotic effects. We compared the behavioral performance in the open field, novel object recognition (NORT), and social interaction tests, as well as structural neuroplasticity with the Golgi-Cox stain in Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) male rats with and without NVHL. Additionally, we explored the effect of the atypical antipsychotic risperidone (RISP). WKY rats with NVHL displayed motor hyperactivity without impairments in memory and social behavior, accompanied by dendritic spine pathology in the neurons of the prefrontal cortex (PFC) layer 3 and basolateral amygdala. RISP treatment reduced motor activity and had subtle and selective effects on the neuroplasticity alterations. In SH rats, NVHL increased the time spent in the border area during the open field test, impaired the short-term performance in NORT, and reduced social interaction time, deficits that were corrected after RISP administration. The NVHL caused dendritic spine pathology in the PFC layers 3 and 5 of SH rats, which RISP treatment ameliorated. Our results support the utility of the NVHL model for exploring neuroplasticity mechanisms in schizophrenia and understanding pharmacotherapy.

Hippocampus under Pressure: Molecular Mechanisms of Development of Cognitive Impairments in SHR Rats

Data from clinical trials and animal experiments demonstrate relationship between chronic hypertension and development of cognitive impairments. Here, we review structural and biochemical alterations in the hippocampus of SHR rats with genetic hypertension, which are used as a model of essential hypertension and vascular dementia. In addition to hypertension, dysfunction of the hypothalamic-pituitary-adrenal system observed in SHR rats already at an early age may be a key factor of changes in the hippocampus at the structural and molecular levels. Global changes at the body level, such as hypertension and neurohumoral dysfunction, are associated with the development of vascular pathology and impairment of the blood-brain barrier. Changes in multiple biochemical glucocorticoid-dependent processes in the hippocampus, including dysfunction of steroid hormones receptors, impairments of neurotransmitter systems, BDNF deficiency, oxidative stress, and neuroinflammation are accompanied by the structural alterations, such as cellular signs of neuroinflammation micro- and astrogliosis, impairments of neurogenesis in the subgranular neurogenic zone, and neurodegenerative processes at the level of synapses, axons, and dendrites up to the death of neurons. The consequence of this is dysfunction of hippocampus, a key structure of the limbic system necessary for cognitive functions. Taking into account the available results at various levels starting from the body and brain structure (hippocampus) levels to molecular one, we can confirm translational validity of SHR rats for modeling mechanisms of vascular dementia.

TIP60 mediates stress-induced hypertension via promoting glutamatedmPFC-to-vCA1 release

Hypertension is well-known to be influenced by genetic and environmental factors. Managing stress is one of the non-pharmacologic approaches to treating hypertension. It is, therefore, imperative to unravel the molecular mechanism by which stress conditions influence hypertension. In this study, TIP60 expressions in human blood samples and cell lines, glutamatedmPFC-to-vCA1 release, and receptor expressions in the Stress-induced hypertension mice were determined using western blotting, CSF (obtained by microdialysis), and ELISA. The study reports increased protein expressions of TIP60 in the peripheral blood of hypertensive patients and in cell lines representing hypertension. In Chronic restraint stress (CRS) conditions TIP60 expression and vCA1 glutamate release were found to be up-regulated, with high SBP and DSP indicating hypertension was induced. After electrical stimulation at the dmPFC, release of glutamate in the vCA1 increased, indicating that activity within the dmPFC drives the release of glutamate in the vCA1, which was blocked by injecting MG149 (a TIP60 inhibitor) into dmPFC. To further determine whether TIP60 was involved in glutamate release and eventually results in hypertension, MG149 was also injected i.p. alongside CRS modeling. The increased glutamate release, NR2B, and IL-18 expressions as well as the CRS-induced hypertension was therefore reversed by chronic application with MG149. Altogether, these results suggest that TIP60 influences the glutamatedmPFC-to-vCA1 release and receptor expressions. This study, therefore, proposes that stressful condition induces increased expression of TIP60 which lead to the transcription of genes that result in conditions that favors glutamate release and receptor expressions hence triggering hypertension.

Exercise Normalized the Hippocampal Renin-Angiotensin System and Restored Spatial Memory Function, Neurogenesis, and Blood-Brain Barrier Permeability in the 2K1C-Hypertensive Mouse

Hypertension is associated with blood-brain barrier alteration and brain function decline. Previously, we established the 2-kidney,1-clip (2K1C) hypertensive mice model by renin-angiotensin system (RAS) stimulating. We found that 2K1C-induced hypertension would impair hippocampus-related memory function and decrease adult hippocampal neurogenesis. Even though large studies have investigated the mechanism of hypertension affecting brain function, there remains a lack of efficient ways to halt this vicious effect. The previous study indicated that running exercise ameliorates neurogenesis and spatial memory function in aging mice. Moreover, studies showed that exercise could normalize RAS activity, which might be associated with neurogenesis impairment. Thus, we hypothesize that running exercise could ameliorate neurogenesis and spatial memory function impairment in the 2K1C-hypertension mice. In this study, we performed 2K1C surgery on eight-weeks-old C57BL/6 mice and put them on treadmill exercise one month after the surgery. The results indicate that running exercise improves the spatial memory and neurogenesis impairment of the 2K1C-mice. Moreover, running exercise normalized the activated RAS and blood-brain barrier leakage of the hippocampus, although the blood pressure was not decreased. In conclusion, running exercise could halt hypertension-induced brain impairment through RAS normalization.

Curcumin induces cortico-hippocampal neuronal reshaping and memory improvements in aged mice

Aging induces cognitive decline, reduces of synaptic plasticity and increases oxidative reactive species (ROS) in the central nervous system. Traditional medicine has long benefitted from naturally occurring molecules such as curcumin (diferuloymethane). Curcumin is extracted from the plant Curcuma longa and is known for its synaptic and antioxidant-related benefits. In this study, we tested the hypothesis that chronic curcumin treatment reduces cognitive and cellular effects of aging. Curcumin-treated mice showed improved learning and memory using the Morris Water Maze and novel object recognition task. In addition, using the Golgi-Cox stain, curcumin treatment increased spine density in all evaluated regions and increased dendritic arborization in the prefrontal cortex (PFC) layer 3 and CA3 subregion of the hippocampus. Moreover, chronic curcumin exposure increased synaptophysin and actin expression and reduced glial fibrillary acidic protein expression, a marker of astrocytes, in the hippocampus (CA1 and CA3 subregions), while simultaneously reducing the ROS-related molecule, metallothionein 3 expression in the PFC and hippocampus. Collectively, these novel findings suggest that curcumin reduces cognitive, neuronal and astrocytic signs of aging in mice.

Large-scale functional connectivity predicts cognitive impairment related to type 2 diabetes mellitus

BACKGROUND

Large-scale functional connectivity (LSFC) patterns in the brain have unique intrinsic characteristics. Abnormal LSFC patterns have been found in patients with dementia, as well as in those with mild cognitive impairment (MCI), and these patterns predicted their cognitive performance. It has been reported that patients with type 2 diabetes mellitus (T2DM) may develop MCI that could progress to dementia. We investigated whether we could adopt LSFC patterns as discriminative features to predict the cognitive function of patients with T2DM, using connectome-based predictive modeling (CPM) and a support vector machine.

AIM

To investigate the utility of LSFC for predicting cognitive impairment related to T2DM more accurately and reliably.

METHODS

Resting-state functional magnetic resonance images were derived from 42 patients with T2DM and 24 healthy controls. Cognitive function was assessed using the Montreal Cognitive Assessment (MoCA). Patients with T2DM were divided into two groups, according to the presence (T2DM-C; n = 16) or absence (T2DM-NC; n = 26) of MCI. Brain regions were marked using Harvard Oxford (HOA-112), automated anatomical labeling (AAL-116), and 264-region functional (Power-264) atlases. LSFC biomarkers for predicting MoCA scores were identified using a new CPM technique. Subsequently, we used a support vector machine based on LSFC patterns for among-group differentiation. The area under the receiver operating characteristic curve determined the appearance of the classification.

RESULTS

CPM could predict the MoCA scores in patients with T2DM (Pearson’s correlation coefficient between predicted and actual MoCA scores, r = 0.32, P=0.0066 [HOA-112 atlas]; r = 0.32, P=0.0078 [AAL-116 atlas]; r = 0.42, P=0.0038 [Power-264 atlas]), indicating that LSFC patterns represent cognition-level measures in these patients. Positive (anti-correlated) LSFC networks based on the Power-264 atlas showed the best predictive performance; moreover, we observed new brain regions of interest associated with T2DM-related cognition. The area under the receiver operating characteristic curve values (T2DM-NC group vs. T2DM-C group) were 0.65-0.70, with LSFC matrices based on HOA-112 and Power-264 atlases having the highest value (0.70). Most discriminative and attractive LSFCs were related to the default mode network, limbic system, and basal ganglia.

CONCLUSION

LSFC provides neuroimaging-based information that may be useful in detecting MCI early and accurately in patients with T2DM.

Treadmill Exercise Prevents Decline in Spatial Learning and Memory in 3×Tg-AD Mice through Enhancement of Structural Synaptic Plasticity of the Hippocampus and Prefrontal Cortex

Alzheimer’s disease (AD) is characterized by deficits in learning and memory. A pathological feature of AD is the alterations in the number and size of synapses, axon length, dendritic complexity, and dendritic spine numbers in the hippocampus and prefrontal cortex. Treadmill exercise can enhance synaptic plasticity in mouse or rat models of stroke, ischemia, and dementia. The aim of this study was to examine the effects of treadmill exercise on learning and memory, and structural synaptic plasticity in 3×Tg-AD mice, a mouse model of AD. Here, we show that 12 weeks treadmill exercise beginning in three-month-old mice improves spatial working memory in six-month-old 3×Tg-AD mice, while non-exercise six-month-old 3×Tg-AD mice exhibited impaired spatial working memory. To investigate potential mechanisms for the treadmill exercise-induced improvement of spatial learning and memory, we examined structural synaptic plasticity in the hippocampus and prefrontal cortex of six-month-old 3×Tg-AD mice that had undergone 12 weeks of treadmill exercise. We found that treadmill exercise led to increases in synapse numbers, synaptic structural parameters, the expression of synaptophysin (Syn, a presynaptic marker), the axon length, dendritic complexity, and the number of dendritic spines in 3×Tg-AD mice and restored these parameters to similar levels of non-Tg control mice without treadmill exercise. In addition, treadmill exercise also improved these parameters in non-Tg control mice. Strengthening structural synaptic plasticity may represent a potential mechanism by which treadmill exercise prevents decline in spatial learning and memory and synapse loss in 3×Tg-AD mice.

Losartan enhances cognitive and structural neuroplasticity impairments in spontaneously hypertensive rats

Hypertension is a risk factor for vascular dementia, which is the second most prevalent type of dementia, just behind Alzheimer's disease. This highlights the brain vulnerability due to hypertension, which may increase with aging. Thus, studying how hypertension affects neural cells and behavior, as well as the effects of antihypertensives on these alterations, it's important to understand the hypertension consequences in the brain. The spontaneously hypertensive rat (SHR) has been useful for the study of hypertension alterations in diverse organs, including the brain. Thus, we studied the losartan effects on cognitive and structural neuroplasticity impairments in SHR of 10 months of age. In the first instance, we evaluated the losartan effects on exploratory behavior and novel object recognition test (NORT) in the SHR. Then, we assessed the density and morphology of dendritic spines of pyramidal neurons from the prefrontal cortex (PFC) layers 3 and 5, and CA1 of the dorsal Hp (dHp). Our results indicate that in SHR, losartan treatment (2 months, 15 mg/Kg/day) reduces high blood pressure to age-matched vehicle-treated Wistar-Kyoto (WKY) rat levels. Moreover, losartan improved long-term memory in SHR compared with age-matched vehicle-treated WKY rats, without affecting the locomotor and anxiety behaviors. The behavioral improvement of the SHR can be associated with the increase in the number of dendritic spines and the mushroom spine population in the PFC and the dHp. In conclusion, losartan enhances cognitive impairments by controlling the high blood pressure and improving neuroplasticity in animals with chronic hypertension.

A multimodal meta-analysis of regional structural and functional brain alterations in type 2 diabetes

Neuroimaging studies have identified brain structural and functional alterations of type 2 diabetes mellitus (T2DM) patients; however, there is no systematic information on the relations between abnormalities in these two domains. We conducted a multimodal meta-analysis of voxel-based morphometry and regional resting-state functional MRI studies in T2DM, including fifteen structural datasets (693 patients and 684 controls) and sixteen functional datasets (378 patients and 358 controls). We found, in patients with T2DM compared to controls, conjoint decreased regional gray matter volume (GMV) and altered intrinsic activity mainly in the default mode network including bilateral superior temporal gyrus/Rolandic operculum, left middle and inferior temporal gyrus, and left supramarginal gyrus; decreased GMV alone in the limbic system; and functional abnormalities alone in the cerebellum, insula, and visual cortex. This meta-analysis identified complicated patterns of conjoint and dissociated brain alterations in T2DM patients, which may help provide new insight into the neuropathology of T2DM.

Memory and dendritic spines loss, and dynamic dendritic spines changes are age-dependent in the rat

Brain aging is a widely studied process, but due to its complexity, much of its progress is unknown. There are many studies linking memory loss and reduced interneuronal communication with brain aging. However, only a few studies compare young and old animals. In the present study, in male rats aged 3, 6, and 18 months, we analyzed the locomotor activity and also short and long-term memory using the novel object recognition test (NORT), in addition to evaluating the dendritic length and the number of dendritic spines in the prefrontal cortex (PFC) and in the CA1, CA3 and DG regions of the dorsal hippocampus using Golgi-Cox staining. We also analyzed the types of dendritic spines in the aforementioned regions. 6- and 18-month old animals showed a reduction in locomotor activity, while long-term memory deficit was observed in 18-month old rats. At 18 months old, the dendritic length was reduced in all the studied regions. The dendritic spine number was also reduced in layer 5 of the PFC, and the CA1 and CA3 of the hippocampus. The dynamics of dendritic spines changed with age, with a reduction of the mushroom spines in all the studied regions, with an increase of the stubby spines in all the studied regions except from the CA3 region, that showed a reduction. Our data suggest that age causes changes in behavior, which may be the result of morphological changes at the dendrite level, both in their length and in the dynamics of their spines.

Natural products present neurotrophic properties in neurons of the limbic system in aging rodents

Aging is a complex process that can lead to neurodegeneration and, consequently, several pathologies, including dementia. Physiological aging leads to changes in several body organs, including those of the central nervous system (CNS). Morphological changes in the CNS and particularly the brain result in motor and cognitive deficits affecting learning and memory and the circadian cycle. Characterizing neural modifications is critical to designing new therapies to target aging and associated pathologies. In this review, we compared aging to the changes occurring within the brain and particularly the limbic system. Then, we focused on key natural compounds, apamin, cerebrolysin, Curcuma longa, resveratrol, and N-PEP-12, which have shown neurotrophic effects particularly in the limbic system. Finally, we drew our conclusions delineating future perspectives for the development of novel natural therapeutics to ameliorate aging-related processes.

Phenylbutyrate ameliorates prefrontal cortex, hippocampus, and nucleus accumbens neural atrophy as well as synaptophysin and GFAP stress in aging mice

Recent reports on brain aging suggest that oxidative stress and inflammatory processes contribute to aging. Interestingly, sodium phenylbutyrate (PBA) is an inhibitor of histone deacetylase, which has anti-inflammatory properties. Several reports have suggested the effect of PBA on learning and memory processes, however there are no studies of the effect of this inhibitor of histone deacetylase on aging. Consequently, in the present study, the effect of PBA was studied in 18-month-old mice. The animals were administered PBA for 2 months after locomotor activity treatment and Morris water maze tests were performed. The Golgi-Cox staining technique and immunohistochemistry for glial fibrillary acidic protein (GFAP) and synaptophysin were performed for the morphological procedures. The administration of PBA improves learning and memory according to the Morris water maze test compared to vehicle-treated animals, which had unchanged locomotor activity. Using Golgi-Cox staining, dendritic length and the number of dendritic spines were measured in limbic regions, such as the nucleus accumbens (NAcc), prefrontal cortex (PFC) layer 3, and the CA1 of the dorsal hippocampus. In addition, PBA increased the number of dendritic spines in the PFC, NAcc, and CA1 subregions of the hippocampus with an increase in dendritic length only in the CA1 region. Moreover, PBA reduced the levels of the GFAP and increased the levels of synaptophysin in the studied regions. Thus, PBA can be a useful pharmacological tool to prevent or delay synaptic plasticity damage and cognitive impairment caused by age.

Cerebrolysin ameliorates prefrontal cortex and hippocampus neural atrophy of spontaneous hypertensive rats with hyperglycemia

Hyperglycemia of diabetes mellitus causes damage at the vascular level, which at the renal level represents diabetic nephropathy. In this pathology, there is arterial hypertension. In addition, several reports suggest that hyperglycemia and arterial hypertension affect interneuronal communication at the level of dendritic morphology. We studied these changes in an animal model with streptozotocin-induced diabetes mellitus in the spontaneous hypertensive (SH) rat. Recent reports from our laboratory have demonstrated that cerebrolysin (CBL), a preparation of neuropeptides with protective and repairing properties, reduces dendritic deterioration in both pathologies, in separate studies. In the present study, we evaluated the effect of CBL using the animal model with hyperglycemia and arterial hypertension and assessed the dendritic morphology using a Golgi-Cox staining procedure. Our results suggest that CBL ameliorated the reduction in the number of dendritic spines in the PFC and hippocampus caused by hyperglycemia in the SH rat. In addition, CBL also increased distal dendritic length in the PFC and hippocampus in hyperglycemic SH rats. Consequently, the CBL could be a therapeutic tool used to reduce the damage at the level of dendritic communication present in both pathologies.

Bexarotene treatment increases dendritic length in the nucleus accumbens without change in the locomotor activity and memory behaviors, in old mice

The aged brain has biochemical and morphological alterations in the dendrites of the pyramidal neurons of the limbic system, which consequently trigger motor and cognitive deficits. Bexarotene 4-[1-(3,5,5,8,8-pentamethyl-6,7-dihydronaphthalen-2-yl)ethenyl]benzoic acid is a selective agonist of X-retinoid receptors which acts by binding to the intracellular retinoic acid receptors (RAR). It decreases oxidative and inflammatory activity, in addition to the transport of lipids, mechanisms that together could have a neuroprotective effect. Our objective was to evaluate the effect of bexarotene on the motor and cognitive processes, as well as its influence on the dendritic morphology of neurons in the limbic system of elderly mice. Dendritic morphology was evaluated with the Golgi-Cox staining procedure followed by the Sholl analysis. Bexarotene was administered at different doses: 0.0; 0.5; 2.5 and 5.0 mg/kg for 60 days in 18-month-old mice. After the treatment, locomotor activity in a novel environment and spatial memory in the water labyrinth were evaluated. Mice treated with bexarotene did not show significant changes in their behavior. Moreover, bexarotene-treated mice only showed a significant increase in the density of the dendritic spines and the dendritic length in the nucleus accumbens (NAcc) neurons. In conclusion, the administration of bexarotene improves the plasticity of the NAcc of aged mice, and therefore could be a pharmacological alternative to prevent or delay neuroplasticity disruptions in brain aging.

Hypertension and Its Impact on Stroke Recovery: From a Vascular to a Parenchymal Overview

Hypertension is the first modifiable vascular risk factor accounting for 10.4 million deaths worldwide; it is strongly and independently associated with the risk of stroke and is related to worse prognosis. In addition, hypertension seems to be a key player in the implementation of vascular cognitive impairment. Long-term hypertension, complicated or not by the occurrence of ischemic stroke, is often reviewed on its vascular side, and parenchymal consequences are put aside. Here, we sought to review the impact of isolated hypertension or hypertension associated to stroke on brain atrophy, neuron connectivity and neurogenesis, and phenotype modification of microglia and astrocytes. Finally, we discuss the impact of antihypertensive therapies on cell responses to hypertension and functional recovery. This attractive topic remains a focus of continued investigation and stresses the relevance of including this vascular risk factor in preclinical investigations of stroke outcome.

Consequences of diabetes mellitus on neuronal connectivity in limbic regions

Diabetes mellitus (DM) is characterized by high levels of blood glucose. In recent years, its prevalence has increased, which was 422 million in the world in 2014. In elderly patients, DM is associated with deficits in memory and learning processes. The cognitive deficits lead to dementia. With the development of animal models in DM, it has been possible to better understand quantitative morphological changes in numerous neuronal structures belonging to the limbic system, such as the prefrontal cortex (PFC), the hippocampus and basolateral amygdala (BLA). These structures are in close relationship with processes of memory and learning. Several reports have demonstrated that chronic hyperglycemia reduces spinogenesis and dendritic arborization in the aforementioned regions along with a decline in memory and learning processes, especially in streptozotocin (STZ)-induced diabetic rats. In the present review, we discuss animal models, the effects of chronic hyperglycemia on dendritic morphology of limbic regions and memory and learning processes, the effect on neural transmission in these regions, the pathologic mechanisms involved, and the relevance of dendritic morphology in diabetes. All of this information can help us to have a better understanding of dementia in diabetes mellitus and propose strategies for its prevention and treatment.

Curcuma longa L. extract improves the cortical neural connectivity during the aging process

Turmeric or Curcuma is a natural product that has anti-inflammatory, antioxidant and anti-apoptotic pharmacological properties. It can be used in the control of the aging process that involves oxidative stress, inflammation, and apoptosis. Aging is a physiological process that affects higher cortical and cognitive functions with a reduction in learning and memory, limited judgment and deficits in emotional control and social behavior. Moreover, aging is a major risk factor for the appearance of several disorders such as cerebrovascular disease, diabetes mellitus, and hypertension. At the brain level, the aging process alters the synaptic intercommunication by a reduction in the dendritic arbor as well as the number of the dendritic spine in the pyramidal neurons of the prefrontal cortex, hippocampus and basolateral amygdala, consequently reducing the size of these regions. The present review discusses the synaptic changes caused by the aging process and the neuroprotective role the Curcuma has through its anti-inflammatory, antioxidant and anti-apoptotic actions

Selective Oestrogen Receptor Agonists Rescued Hippocampus Parameters in Male Spontaneously Hypertensive Rats

Spontaneously hypertensive rats (SHR) show pronounced hippocampus alterations, including low brain-derived neurotrophic factor (BDNF) expression, reduced neurogenesis, astrogliosis and increased aromatase expression. These changes are reverted by treatment with 17β-oestradiol. To determine which oestradiol receptor (ER) type is involved in these neuroprotective effects, we used agonists of the ERα [propylpyrazole triol (PPT)] and the ERβ [diarylpropionitrite (DPN)] given over 2 weeks to 4-month-old male SHR. Wistar Kyoto normotensive rats served as controls. Using immunocytochemistry, we determined glial fibrillary protein (GFAP)+ astrocytes in the CA1, CA3 and hilus of the dentate gyrus of the hippocampus, aromatase immunostaining in the hilus, and doublecortin (DCX)+ neuronal progenitors in the inner granular zone of the dentate gyrus. Brain-derived neurotrophic factor mRNA was also measured in the hippocampus by the quantitative polymerase chain reaction. In SHR, PPT had no effect on blood pressure, decreased astrogliosis, slightly increased BDNF mRNA, had no effect on the number of DCX+ progenitors, and increased aromatase staining. Treatment with DPN decreased blood pressure, decreased astrogliosis, increased BDNF mRNA and DCX+ progenitors, and did not modify aromatase staining. We hypothesise that, although both receptor types may participate in the previously reported beneficial effects of 17β-oestradiol in SHR, receptor activation with DPN may preferentially facilitate BDNF mRNA expression and neurogenesis. The results of the present study may help in the design of ER-based neuroprotection for the encephalopathy of hypertension.

Hypertension impairs hippocampus-related adult neurogenesis, CA1 neuron dendritic arborization and long-term memory

Hypertension is associated with neurodegenerative diseases and cognitive impairment. Several studies using spontaneous hypertensive rats to study the effect of hypertension on memory performance and adult hippocampal neurogenesis have reached inconsistent conclusions. The contradictory findings may be related to the genetic variability of spontaneous hypertensive rats due to the conventional breeding practices. The objective of this study is to examine the effect of hypertension on hippocampal structure and function in isogenic mice. Hypertension was induced by the '2 kidneys, 1 clip' method (2K1C) which constricted one of the two renal arteries. The blood pressures of 2K1C mice were higher than the sham group on post-operation day 7 and remained high up to day 28. Mice with 2K1C-induced hypertension had impaired long-term, but not short-term, memory. Dendritic complexity of CA1 neurons and hippocampal neurogenesis were reduced by 2K1C-induced hypertension on post-operation day 28. Furthermore, 2K1C decreased the levels of hippocampal brain-derived neurotrophic factor, while blood vessel density and activation status of astrocytes and microglia were not affected. In conclusion, hypertension impairs hippocampus-associated long-term memory, dendritic arborization and neurogenesis, which may be caused by down-regulation of brain-derived neurotrophic factor signaling pathways.

Impulsivity and Concussion in Juvenile Rats: Examining Molecular and Structural Aspects of the Frontostriatal Pathway

Impulsivity and poor executive control have been implicated in the pathogenesis of many developmental and neuropsychiatric disorders. Similarly, concussions/mild traumatic brain injuries (mTBI) have been associated with increased risk for neuropsychiatric disorders and the development of impulsivity and inattention. Researchers and epidemiologists have therefore considered whether or not concussions induce symptoms of attention-deficit/hyperactivity disorder (ADHD), or merely unmask impulsive tendencies that were already present. The purpose of this study was to determine if a single concussion in adolescence could induce ADHD-like impulsivity and impaired response inhibition, and subsequently determine if inherent impulsivity prior to a pediatric mTBI would exacerbate post-concussion symptomology with a specific emphasis on impulsive and inattentive behaviours. As these behaviours are believed to be associated with the frontostriatal circuit involving the nucleus accumbens (NAc) and the prefrontal cortex (PFC), the expression patterns of 8 genes (Comt, Drd2, Drd3, Drd4, Maoa, Sert, Tph1, and Tph2) from these two regions were examined. In addition, Golgi-Cox staining of medium spiny neurons in the NAc provided a neuroanatomical examination of mTBI-induced structural changes. The study found that a single early brain injury could induce impulsivity and impairments in response inhibition that were more pronounced in males. Interestingly, when animals with inherent impulsivity experienced mTBI, injury-related deficits were exacerbated in female animals. The single concussion increased dendritic branching, but reduced synaptic density in the NAc, and these changes were likely associated with the increase in impulsivity. Finally, mTBI-induced impulsivity was associated with modifications to gene expression that differed dramatically from the gene expression pattern associated with inherent impulsivity, despite very similar behavioural phenotypes. Our findings suggest the need to tailor treatment strategies for mTBI in light of an individual's premorbid characteristics, given significant differences in molecular profiles of the frontostriatal circuits that depend upon sex and the etiology of the behavioural phenotype.

Biphasic plasticity of dendritic fields in layer V motor neurons in response to motor learning

Motor learning is associated with plastic reorganization of neural networks in primary motor cortex (M1) that advances through stages. An initial increment in spine formation is followed by pruning and maturation one week after training ended. A similar biphasic course was described for the size of the forelimb representation in M1. This study investigates the evolution of the dendritic architecture in response to motor skill training using Golgy-Cox silver impregnation in rat M1. After learning of a unilateral forelimb-reaching task to plateau performance, an increase in dendritic length of layer V pyramidal neurons (i.e. motor neurons) was observed that peaked one month after training ended. This increment in dendritic length reflected an expansion of the distal dendritic compartment. After one month dendritic arborization shrinks even though animals retain task performance. This pattern of evolution was observed for apical and basal dendrites alike - although the increase in dendritic length occurs faster in basal than in apical dendrites. Dendritic plasticity in response to motor training follows a biphasic course with initial expansion and subsequent shrinkage. This evolution takes fourth as long as the biphasic reorganization of spines or motor representations.

Sex differences in NMDA GluN1 plasticity in rostral ventrolateral medulla neurons containing corticotropin-releasing factor type 1 receptor following slow-pressor angiotensin II hypertension

There are profound, yet incompletely understood, sex differences in the neurogenic regulation of blood pressure. Both corticotropin signaling and glutamate receptor plasticity, which differ between males and females, are known to play important roles in the neural regulation of blood pressure. However, the relationship between hypertension and glutamate plasticity in corticotropin-releasing factor (CRF)-receptive neurons in brain cardiovascular regulatory areas, including the rostral ventrolateral medulla (RVLM) and paraventricular nucleus of the hypothalamus (PVN), is not understood. In the present study, we used dual-label immuno-electron microscopy to analyze sex differences in slow-pressor angiotensin II (AngII) hypertension with respect to the subcellular distribution of the obligatory NMDA glutamate receptor subunit 1 (GluN1) subunit of the N-methyl-D-aspartate receptor (NMDAR) in the RVLM and PVN. Studies were conducted in mice expressing the enhanced green fluorescence protein (EGFP) under the control of the CRF type 1 receptor (CRF1) promoter (i.e., CRF1-EGFP reporter mice). By light microscopy, GluN1-immunoreactivity (ir) was found in CRF1-EGFP neurons of the RVLM and PVN. Moreover, in both regions tyrosine hydroxylase (TH) was found in CRF1-EGFP neurons. In response to AngII, male mice showed an elevation in blood pressure that was associated with an increase in the proportion of GluN1 on presumably functional areas of the plasma membrane (PM) in CRF1-EGFP dendritic profiles in the RVLM. In female mice, AngII was neither associated with an increase in blood pressure nor an increase in PM GluN1 in the RVLM. Unlike the RVLM, AngII-mediated hypertension had no effect on GluN1 localization in CRF1-EGFP dendrites in the PVN of either male or female mice. These studies provide an anatomical mechanism for sex-differences in the convergent modulation of RVLM catecholaminergic neurons by CRF and glutamate. Moreover, these results suggest that sexual dimorphism in AngII-induced hypertension is reflected by NMDA receptor trafficking in presumptive sympathoexcitatory neurons in the RVLM.

Female protection from slow-pressor effects of angiotensin II involves prevention of ROS production independent of NMDA receptor trafficking in hypothalamic neurons expressing angiotensin 1A receptors

Renin–angiotensin system overactivity, upregulation of postsynaptic NMDA receptor function, and increased reactive oxygen species (ROS) production in the hypothalamic paraventricular nucleus (PVN) are hallmarks of angiotensin II (AngII)-induced hypertension, which is far more common in young males than in young females. We hypothesize that the sex differences in hypertension are related to differential AngII-induced changes in postsynaptic trafficking of the essential NMDA receptor GluN1 subunit and ROS production in PVN cells expressing angiotensin Type 1a receptor (AT1aR). We tested this hypothesis using slow-pressor (14-day) infusion of AngII (600 ng/kg/min) in mice, which elicits hypertension in males but not in young females. Two-month-old male and female transgenic mice expressing enhanced green fluorescent protein (EGFP) in AT1aR-containing cells were used. In males, but not in females, AngII increased blood pressure and ROS production in AT1aR–EGFP PVN cells at baseline and following NMDA treatment. Electron microscopy showed that AngII increased cytoplasmic and total GluN1–silver-intensified immunogold (SIG) densities and induced a trend toward an increase in near plasmalemmal GluN1–SIG density in AT1aR–EGFP dendrites of males and females. Moreover, AngII decreased dendritic area and diameter in males, but increased dendritic area of small (<1 µm) dendrites and decreased diameter of large (>1 µm) dendrites in females. Fluorescence microscopy revealed that AT1aR and estrogen receptor β do not colocalize, suggesting that if estrogen is involved, its effect is indirect. These data suggest that the sexual dimorphism in AngII-induced hypertension is associated with sex differences in ROS production in AT1aR-containing PVN cells but not with postsynaptic NMDA receptor trafficking.

Estrogens are neuroprotective factors for hypertensive encephalopathy

Estrogens are neuroprotective factors for brain diseases, including hypertensive encephalopathy. In particular, the hippocampus is highly damaged by high blood pressure, with several hippocampus functions being altered in humans and animal models of hypertension. Working with a genetic model of primary hypertension, the spontaneously hypertensive rat (SHR), we have shown that SHR present decreased dentate gyrus neurogenesis, astrogliosis, low expression of brain derived neurotrophic factor (BDNF), decreased number of neurons in the hilus of the dentate gyrus, increased basal levels of the estrogen-synthesizing enzyme aromatase, and atrophic dendritic arbor with low spine density in the CA1 region compared to normotensive Wistar Kyoto (WKY) ratsl. Changes also occur in the hypothalamus of SHR, with increased expression of the hypertensinogenic peptide arginine vasopressin (AVP) and its V1b receptor. Following chronic estradiol treatment, SHR show decreased blood pressure, enhanced hippocampus neurogenesis, decreased the reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus, increased neuronal number in the hilus of the dentate gyrus, further increased the hyperexpression of aromatase and replaced spine number with remodeling of the dendritic arbor of the CA1 region. We have detected by qPCR the estradiol receptors ERα and ERβ in hippocampus from both SHR and WKY rats, suggesting direct effects of estradiol on brain cells. We hypothesize that a combination of exogenously given estrogens plus those locally synthesized by estradiol-stimulated aromatase may better alleviate the hippocampal and hypothalamic encephalopathy of SHR. This article is part of a Special Issue entitled "Sex steroids and brain disorders".

Repeated administration of a synthetic cannabinoid receptor agonist differentially affects cortical and accumbal neuronal morphology in adolescent and adult rats

Recent studies demonstrate a differential trajectory for cannabinoid receptor expression in cortical and sub-cortical brain areas across postnatal development. In the present study, we sought to investigate whether chronic systemic exposure to a synthetic cannabinoid receptor agonist causes morphological changes in the structure of dendrites and dendritic spines in adolescent and adult pyramidal neurons in the medial prefrontal cortex (mPFC) and medium spiny neurons (MSN) in the nucleus accumbens (Acb). Following systemic administration of WIN 55,212-2 in adolescent (PN 37-40) and adult (P55-60) male rats, the neuronal architecture of pyramidal neurons and MSN was assessed using Golgi-Cox staining. While no structural changes were observed in WIN 55,212-2-treated adolescent subjects compared to control, exposure to WIN 55,212-2 significantly increased dendritic length, spine density and the number of dendritic branches in pyramidal neurons in the mPFC of adult subjects when compared to control and adolescent subjects. In the Acb, WIN 55,212-2 exposure significantly decreased dendritic length and number of branches in adult rat subjects while no changes were observed in the adolescent groups. In contrast, spine density was significantly decreased in both the adult and adolescent groups in the Acb. To determine whether regional developmental morphological changes translated into behavioral differences, WIN 55,212-2-induced aversion was evaluated in both groups using a conditioned place preference paradigm. In adult rats, WIN 55,212-2 administration readily induced conditioned place aversion as previously described. In contrast, adolescent rats did not exhibit aversion following WIN 55,212-2 exposure in the behavioral paradigm. The present results show that synthetic cannabinoid administration differentially impacts cortical and sub-cortical neuronal morphology in adult compared to adolescent subjects. Such differences may underlie the disparate development effects of cannabinoids on behavior.

Estradiol increases dendritic length and spine density in CA1 neurons of the hippocampus of spontaneously hypertensive rats: a Golgi impregnation study

Increased neuronal vulnerability has been described in the brain of spontaneously hypertensive rats (SHR), models of primary hypertension. Previous data indicate that estradiol treatment corrects several dysfunctions of the hippocampus and hypothalamus of SHR. Considering this evidence we analyzed the dendritic arborization and spine density of the CA1 subfield in SHR and Wistar-Kyoto (WKY) normotensive rats with and without estradiol treatment. Five month old male SHR and WKY rats received single estradiol or cholesterol pellets (sham treatment) for 2 weeks. A substantial rise of circulating estradiol (>25 fold) and testicular atrophy was present in all estradiol-receiving rats. In both SHR and WKY rats, estradiol decreased blood pressure by ~20 mm Hg; however, a moderate hypertension persisted in SHR (164 mm Hg). Using a modified Golgi impregnation technique, apical and basal dendrites of the CA1 subfield were subjected to Sholl analysis. Spine density was also statistically analyzed. Apical dendritic length was significantly lower in SHR compared to WKY rats (p<0.01), whereas estradiol treatment increased dendritic length in the SHR group only (SHR vs SHR+estradiol; p<0.01). Apical dendritic length plotted against the shell distances 20-100, 120-200 and 220-300 μm, revealed that changes were more pronounced in the range 120-200 μm between SHR vs. WKY rats (p<0.05) and SHR vs. SHR+estradiol (p<0.05). Instead, basal dendrites were not significantly modified by hypertension or steroid treatment. Spine density of apical dendrites was lower in SHR than WKY (p<0.05) and was up-regulated in the SHR+estradiol group compared to the SHR group (p<0.001). Similar changes were obtained for basal dendritic spines. These data suggest that changes of neuronal processes in SHR are plastic events restorable by estradiol treatment. In conjunction with previous results, the present data reveal new targets of estradiol neuroprotection in the brain of hypertensive rats.

Dendritic morphology of neurons in medial prefrontal cortex and hippocampus in 2VO rats

Cerebral ischemia is the main cause of cognitive impairment. Changes in dendritic morphology and spines have been shown to occur with synaptic plasticity and cognitive function. Bilateral occlusion of the common carotid arteries (2VO) in rats was an effective model of chronic cerebral ischemia. In this experiment, SD rats were divided into model group (2VO) and sham-operated group. At 2, 4, 8 and 16 weeks, rats were tested in Morris water maze to observe learning and memory abilities, and then the brain tissue was stained by Golgi method to investigate the morphology of dendrites of pyramidal neurons under light microscope. Dendritic length and arborization and spine density of pyramidal neurons in medial prefrontal cortex (mPFC) and hippocampal CA1 were analyzed by ImageJ. Progressive learning and memory deficits appeared since 2 weeks. Compared to the sham-operated group, the dendritic length and arborization significantly decreased in the model group at 4, 8 and 16 weeks after 2VO in CA1, while there was no significant difference in mPFC. Dendritic spine density in hippocampal CA1 of the model group significantly decreased after 2 weeks, and it was decreased after 8 weeks in mPFC. The results suggest that under the condition of chronic cerebral ischemia, the alteration of dendritic morphology and spine density underlay cognitive impairment.