Chronic 17β‐estradiol or cholesterol prevents stress‐induced hippocampal CA3 dendritic retraction in ovariectomized female rats: Possible correspondence between CA1 spine properties and spatial acquisition

Chronic stress may have different effects on hippocampal CA3 and CA1 neuronal morphology and function depending upon hormonal status, but rarely are manipulations of stress and gonadal steroids combined. Experiment 1 investigated the effects of chronic restraint and 17β‐estradiol replacement on CA3 and CA1 dendritic morphology and spatial learning in ovariectomized (OVX) female Sprague–Dawley rats. OVX rats were implanted with 25% 17β‐estradiol, 100% cholesterol, or blank silastic capsules and then chronically restrained (6h/d/21d) or kept in home cages. 17β‐Estradiol or cholesterol prevented stress‐induced CA3 dendritic retraction, increased CA1 apical spine density, and altered CA1 spine shape. The combination of chronic stress and 17β‐estradiol facilitated water maze acquisition compared to chronic stress + blank implants and nonstressed controls + 17β‐estradiol. To further investigate the interaction between 17β‐estradiol and stress on hippocampal morphology, experiment 2 was conducted on gonadally intact, cycling female rats that were chronically restrained (6h/d/21d), and then euthanized at proestrus (high ovarian hormones) or estrus (low ovarian hormones). Cycling female rats failed to show chronic stress‐induced CA3 dendritic retraction at either estrous phase. Chronic stress enhanced the ratio of CA1 basal spine heads to headless spines as found in experiment 1. In addition, proestrous rats displayed increased CA1 spine density regardless of stress history. These results show that 17β‐estradiol or cholesterol protect against chronic stress‐induced CA3 dendritic retraction in females. These stress‐ and 17β‐estradiol‐induced morphological changes may provide insight into how dendritic complexity and spine properties contribute to spatial ability. © 2009 Wiley‐Liss, Inc.     

Slow‐pressor angiotensin II hypertension and concomitant dendritic NMDA receptor trafficking in estrogen receptor β–containing neurons of the mouse hypothalamic paraventricular nucleus are sex and age dependent

The incidence of hypertension increases after menopause. Similar to humans, “slow‐pressor” doses of angiotensin II (AngII) increase blood pressure in young males, but not in young female mice. However, AngII increases blood pressure in aged female mice, paralleling reproductive hormonal changes. These changes could influence receptor trafficking in central cardiovascular circuits and contribute to hypertension. Increased postsynaptic N‐methyl‐D‐aspartate (NMDA) receptor activity in the hypothalamic paraventricular nucleus (PVN) is crucial for the sympathoexcitation driving AngII hypertension. Estrogen receptors β (ERβs) are present in PVN neurons. We tested the hypothesis that changes in ovarian hormones with age promote susceptibility to AngII hypertension, and influence NMDA receptor NR1 subunit trafficking in ERβ‐containing PVN neurons. Transgenic mice expressing enhanced green fluorescent protein (EGFP) in ERβ‐containing cells were implanted with osmotic minipumps delivering AngII (600 ng/kg/min) or saline for 2 weeks. AngII increased blood pressure in 2‐month‐old males and 18‐month‐old females, but not in 2‐month‐old females. By electron microscopy, NR1‐silver–intensified immunogold (SIG) was mainly in ERβ‐EGFP dendrites. At baseline, NR1‐SIG density was greater in 2‐month‐old females than in 2‐month‐old males or 18‐month‐old females. After AngII infusion, NR1‐SIG density was decreased in 2‐month‐old females, but increased in 2‐month‐old males and 18‐month‐old females. These findings suggest that, in young female mice, NR1 density is decreased in ERβ‐PVN dendrites thus reducing NMDA receptor activity and preventing hypertension. Conversely, in young males and aged females, NR1 density is upregulated in ERβ‐PVN dendrites and ultimately leads to the neurohumoral dysfunction driving hypertension. J. Comp. Neurol. 522:3075–3090, 2014. © 2014 Wiley Periodicals, Inc.     

The effects of IL‐1 receptor antagonist on beta amyloid mediated depression of LTP in the rat CA1 in vivo

Beta‐amyloid (Aβ) is a neuro‐peptide implicated in the pathogenesis of Alzheimer's disease (AD). Aβ‐peptide is known to disrupt cellular processes, including synaptic plasticity. To date, the precise mechanisms leading to the Aβ‐mediated impairment of normal neurophysiological function still remains elusive. A rise in the pro‐inflammatory cytokine interleukin‐1‐β (IL‐1β) has been previously reported, following Aβ peptide insult. IL‐1β in turn, activates a cascade of pro‐apoptotic markers, gradually leading to cell death. In this work, we have investigated the possible protective effects of interleukin‐1 receptor antagonist (IL‐1ra) on the effects of Aβ‐peptide on long‐term potentiation (LTP) in the CA1 region of the rat hippocampus in vivo. We observed a significant depression of LTP in the group of animals that received intracerebroventricular (icv) injection of Aβ‐peptide (1–40) compared with control animals injected with vehicle. Administration of IL‐1ra alone (icv) also resulted in a depression of LTP; however, there was no change in the baseline synaptic response. Combined injection of Aβ(1–40) + IL‐1ra caused an attenuation of the effects observed with Aβ(1–40) alone for a period of up to 15 min following LTP induction; rescuing post‐tetanicpotentiation (PTP). Gradually however, EPSP‐values declined to produce a level of LTP similar to that observed following treatment with Aβ(1–40) alone. These results suggest that the acute Aβ‐mediated impairment of PTP and LTP may be partial as a result of activation of an inflammatory response and the release of IL‐1β. The attenuation of plasticity by IL‐1ra alone supports the theory that low levels of IL‐1β are required for normal synaptic plasticity. The limited rescue of the Aβ‐mediated effects on LTP, in the presence of IL‐1ra, may represent the short half life found with this receptor antagonist in vivo. © 2008 Wiley‐Liss, Inc.     

Hippocampal subfields alterations in adolescents with post‐traumatic stress disorder

Reexperiencing symptoms in adolescent Post‐Traumatic Stress Disorder (PTSD) are characterized by the apparition of vivid intrusive images of the traumatic event. The emergence of these intrusions is thought to be related to a deficiency in context processing and could then be related to hippocampal alterations. The hippocampus is a complex structure which can be divided into several subfields, namely, the Cornu Ammonis (CA1, CA2, and CA3), the subiculum, and the dentate gyrus (DG). As each subfield presents different histological characteristics and functions, it appears more relevant to consider hippocampal subfields, instead of only assessing the whole hippocampus, to understand the neurobiology of PTSD. Hence, this study presents the first investigation of structural alterations within hippocampal subfields and their links to reexperiencing symptoms in adolescent PTSD. Hippocampal subfields were manually delineated on high‐resolution MRI images in 15 adolescents (13–18 years old) with PTSD and 24 age‐matched healthy controls. The volume of the region CA2‐3/DG region was significantly smaller in the PTSD group compared to controls in both hemispheres. No other significant difference was found for other subfields. Moreover, the volume of the left CA2‐3/DG was negatively correlated with the intrusion score (as measured by the Impact of Events Scale‐Revised) in the PTSD group. To conclude, an alteration in the hippocampal subregion CA2‐3/DG, known to resolve interferences between new and similar stored memories, could participate in the apparition of intrusive trauma memories in adolescents with PTSD.     

Longitudinal trajectory of Amyloid‐related hippocampal subfield atrophy in nondemented elderly

Hippocampal atrophy and abnormal β‐Amyloid (Aβ) deposition are established markers of Alzheimer's disease (AD). Nonetheless, longitudinal trajectory of Aβ‐associated hippocampal subfield atrophy prior to dementia remains unclear. We hypothesized that elevated Aβ correlated with longitudinal subfield atrophy selectively in no cognitive impairment (NCI), spreading to other subfields in mild cognitive impairment (MCI). We analyzed data from two independent longitudinal cohorts of nondemented elderly, including global PET‐Aβ in AD‐vulnerable cortical regions and longitudinal subfield volumes quantified with a novel auto‐segmentation method (FreeSurfer v.6.0). Moreover, we investigated associations of Aβ‐related progressive subfield atrophy with memory decline. Across both datasets, we found a converging pattern that higher Aβ correlated with faster CA1 volume decline in NCI. This pattern spread to other hippocampal subfields in MCI group, correlating with memory decline. Our results for the first time suggest a longitudinal focal‐to‐widespread trajectory of Aβ‐associated hippocampal subfield atrophy over disease progression in nondemented elderly.     

Cellular and subcellular localization of estrogen and progestin receptor immunoreactivities in the mouse hippocampus

Estrogen receptor‐α (ERα), estrogen receptor‐β (ERβ), and progestin receptor (PR) immunoreactivities are localized to extranuclear sites in the rat hippocampal formation. Because rats and mice respond differently to estradiol treatment at a cellular level, the present study examined the distribution of ovarian hormone receptors in the dorsal hippocampal formation of mice. For this, antibodies to ERα, ERβ, and PR were localized by light and electron immunomicroscopy in male and female mice across the estrous cycle. Light microscopic examination of the mouse hippocampal formation showed sparse nuclear ERα and PR immunoreactivity (‐ir) most prominently in the CA1 region and diffuse ERβ‐ir primarily in the CA1 pyramidal cell layer as well as in a few interneurons. Ultrastructural analysis additionally revealed discrete extranuclear ERα‐, ERβ‐, and PR‐ir in neuronal and glial profiles throughout the hippocampal formation. Although extranuclear profiles were detected in all animal groups examined, the amount and types of profiles varied with sex and estrous cycle phase. ERα‐ir was highest in diestrus females, particularly in dendritic spines, axons, and glia. Similarly, ERβ‐ir was highest in estrus and diestrus females, mainly in dendritic spines and glia. Conversely, PR‐ir was highest during proestrus, mostly in axons. Except for very low levels of extranuclear ERβ‐ir in mossy fiber terminals in mice, the labeling patterns in the mice for all three antibodies were similar to the ultrastructural labeling found previously in rats, suggesting that regulation of these receptors is well conserved across the two species. J. Comp. Neurol. 518:2729–2743, 2010. © 2010 Wiley‐Liss, Inc.     

Caffeine prevents sleep loss‐induced deficits in long‐term potentiation and related signaling molecules in the dentate gyrus

We have previously reported that caffeine prevented sleep deprivation‐induced impairment of long‐term potentiation (LTP) of area CA1 as well as hippocampus‐dependent learning and memory performance in the radial arm water maze. In this report we examined the impact of long‐term (4‐week) caffeine consumption (0.3 g/L in drinking water) on synaptic plasticity ( Alhaider et al., 2010 ) deficit in the dentate gyrus (DG) area of acutely sleep‐deprived rats. The sleep deprivation and caffeine/sleep deprivation groups were sleep‐deprived for 24 h by using the columns‐in‐water technique. We tested the effect of caffeine and/or sleep deprivation on LTP and measured the basal levels as well as stimulated levels of LTP‐related molecules in the DG. The results showed that chronic caffeine administration prevented the impairment of early‐phase LTP (E‐LTP) in the DG of sleep‐deprived rats. Additionally, chronic caffeine treatment prevented the sleep deprivation‐associated decreases in the basal levels of the phosphorylated calcium/calmodulin‐dependent protein kinase II (P‐CaMKII) and brain derived neurotrophic factor (BDNF) as well as in the stimulated levels of P‐CaMKII in the DG area. The results suggest that chronic use of caffeine prevented anomalous changes in the basal levels of P‐CaMKII and BDNF associated with sleep deprivation and as a result contributes to the revival of LTP in the DG region.     

Roles for γ‐aminobutyric acid in the development of the paraventricular nucleus of the hypothalamus

The development of the hypothalamic paraventricular nucleus (PVN) involves several factors that work together to establish a cell group that regulates neuroendocrine functions and behaviors. Several molecular markers were noted within the developing PVN, including estrogen receptors (ER), neuronal nitric oxide synthase (nNOS), and brain‐derived neurotrophic factor (BDNF). By contrast, immunoreactive γ‐aminobutyric acid (GABA) was found in cells and fibers surrounding the PVN. Two animal models were used to test the hypothesis that GABA works through GABA_A and GABA_B receptors to influence the development of the PVN. Treatment with bicuculline to decrease GABA_A receptor signaling from embryonic day (E) 10 to E17 resulted in fewer cells containing immunoreactive (ir) ERα in the region of the PVN vs. control. GABA_BR1 receptor subunit knockout mice were used to examine the PVN at P0 without GABA_B signaling. In female but not male GABA_BR1 subunit knockout mice, the positions of cells containing ir ERα shifted from medial to lateral compared with wild‐type controls, whereas the total number of ir ERα‐containing cells was unchanged. In E17 knockout mice, ir nNOS cells and fibers were spread over a greater area. There was also a significant decrease in ir BDNF in the knockout mice in a region‐dependent manner. Changes in cell position and protein expression subsequent to disruption of GABA signaling may be due, in part, to changes in nNOS and BDNF signaling. Based on the current study, the PVN can be added as another site where GABA exerts morphogenetic actions in development. J. Comp. Neurol. 518:2710–2728, 2010. © 2010 Wiley‐Liss, Inc.     

Novel encoding and updating of positional,or directional,spatial cues are processed by distinct hippocampal subfields: Evidence for parallel information processing and the “what” stream

The specific roles of hippocampal subfields in spatial information processing and encoding are, as yet, unclear. The parallel map theory postulates that whereas the CA1 processes discrete environmental features (positional cues used to generate a “sketch map”), the dentate gyrus (DG) processes large navigation‐relevant landmarks (directional cues used to generate a “bearing map”). Additionally, the two‐streams hypothesis suggests that hippocampal subfields engage in differentiated processing of information from the “where” and the “what” streams. We investigated these hypotheses by analyzing the effect of exploration of discrete “positional” features and large “directional” spatial landmarks on hippocampal neuronal activity in rats. As an indicator of neuronal activity we measured the mRNA induction of the immediate early genes (IEGs), Arc and Homer1a. We observed an increase of this IEG mRNA in CA1 neurons of the distal neuronal compartment and in proximal CA3, after novel spatial exploration of discrete positional cues, whereas novel exploration of directional cues led to increases in IEG mRNA in the lower blade of the DG and in proximal CA3. Strikingly, the CA1 did not respond to directional cues and the DG did not respond to positional cues. Our data provide evidence for both the parallel map theory and the two‐streams hypothesis and suggest a precise compartmentalization of the encoding and processing of “what” and “where” information occurs within the hippocampal subfields.     

Melatonin protects against amyloid‐β‐induced impairments of hippocampal LTP and spatial learning in rats

Alzheimer's disease (AD), the most prevalent neurodegenerative disease in the elderly, leads to progressive loss of memory and cognitive deficits. Amyloid‐β protein (Aβ) in the brain is thought to be the main cause of memory loss in AD. Melatonin, an indole hormone secreted by the pineal gland, has been reported to produce neuroprotective effects. We examined whether melatonin could protect Aβ‐induced impairments of hippocampal synaptic plasticity, neuronal cooperative activity, and learning and memory. Rats received bilateral intrahippocampal injection of Aβ1‐42 or Aβ31‐35 followed by intraperitoneal application of melatonin for 10 days, and the effects of chronic melatonin treatment on in vivo hippocampal long‐term potentiation (LTP) and theta rhythm and Morris water maze performance were examined. We showed that intrahippocampal injection of Aβ1‐42 or Aβ31‐35 impaired hippocampal LTP in vivo, while chronic melatonin treatment reversed Aβ1‐42‐ or Aβ31‐35‐induced impairments in LTP induction. Intrahippocampal injection of Aβ31‐35 impaired spatial learning and decreased the power of theta rhythm in the CA1 region induced by tail pinch, and these synaptic, circuit, and learning deficits were rescued by chronic melatonin treatment. These results provide evidence for the neuroprotective action of melatonin against Aβ insults and suggest a strategy for alleviating cognition deficits of AD. Synapse 67:626–636, 2013 . © 2013 Wiley Periodicals, Inc.     

Caffeine treatment prevents rapid eye movement sleep deprivation‐induced impairment of late‐phase long‐term potentiation in the dentate gyrus

The CA1 and dentate gyrus (DG) are physically and functionally closely related areas of the hippocampus, but they differ in various respects, including their reactions to different insults. The purpose of this study was to determine the protective effects of chronic caffeine treatment on late‐phase long‐term potentiation (L‐LTP) and its signalling cascade in the DG area of the hippocampus of rapid eye movement sleep‐deprived rats. Rats were chronically treated with caffeine (300 mg/L drinking water) for 4 weeks, after which they were sleep‐deprived for 24 h. L‐LTP was induced in in anaesthetized rats, and extracellular field potentials from the DG area were recorded in vivo. The levels of L‐LTP‐related signalling proteins were assessed by western blot analysis. Sleep deprivation markedly reduced L‐LTP magnitude, and basal levels of total cAMP response element‐binding protein (CREB), phosphorylated CREB (P‐CREB), and calcium/calmodulin kinase IV (CaMKIV). Chronic caffeine treatment prevented the reductions in the basal levels of P‐CREB, total CREB and CaMKIV in sleep‐deprived rats. Furthermore, caffeine prevented post‐L‐LTP sleep deprivation‐induced downregulation of P‐CREB and brain‐derived neurotrophic factor in the DG. The current findings show that caffeine treatment prevents acute sleep deprivation‐induced deficits in brain function.     

Astrocytic Aβ1‐42 uptake is determined by Aβ‐aggregation state and the presence of amyloid‐associated proteins

Intracerebral accumulation of amyloid‐β (Aβ) leading to Aβ plaque formation, is the main hallmark of Alzheimer's disease and might be caused by defective Aβ‐clearance. We previously found primary human astrocytes and microglia able to bind and ingest Aβ1‐42 in vitro, which appeared to be limited by Aβ1‐42 fibril formation. We now confirm that astrocytic Aβ‐uptake depends on size and/or composition of Aβ‐aggregates as astrocytes preferably take up oligomeric Aβ over fibrillar Aβ. Upon exposure to either fluorescence‐labelled Aβ1‐42 oligomers (Aβ_oligo) or fibrils (Aβ_fib), a larger (3.7 times more) proportion of astrocytes ingested oligomers compared to fibrils, as determined by flow cytometry. Aβ‐internalization was verified using confocal microscopy and live‐cell imaging. Neither uptake of Aβ_oligo nor Aβ_fib, triggered proinflammatory activation of the astrocytes, as judged by quantification of interleukin‐6 and monocyte‐chemoattractant protein‐1 release. Amyloid‐associated proteins, including α1‐antichymotrypsin (ACT), serum amyloid P component (SAP), C1q and apolipoproteins E (ApoE) and J (ApoJ) were earlier found to influence Aβ‐aggregation. Here, astrocytic uptake of Aβ_fib increased when added to the cells in combination with SAP and C1q (SAP/C1q), but was unchanged in the presence of ApoE, ApoJ and ACT. Interestingly, ApoJ and ApoE dramatically reduced the number of Aβ_oligo‐positive astrocytes, whereas SAP/C1q slightly reduced Aβ_oligo uptake. Thus, amyloid‐associated proteins, especially ApoJ and ApoE, can alter Aβ‐uptake in vitro and hence may influence Aβ clearance and plaque formation in vivo. © 2010 Wiley‐Liss, Inc.     

Fluorescent Visualisation of Oxytocin in the Hypothalamo‐neurohypophysial/‐spinal Pathways After Chronic Inflammation in Oxytocin‐Monomeric Red Fluorescent Protein 1 Transgenic Rats

Oxytocin (OXT) is a well‐known neurohypophysial hormone that is synthesised in the paraventricular (PVN) and supraoptic nuclei (SON) of the hypothalamus. The projection of magnocellular neurosecretory cells, which synthesise OXT and arginine vasopressin in the PVN and SON, to the posterior pituitary plays an essential role in mammalian labour and lactation through its peripheral action. However, previous studies have shown that parvocellular OXTergic cells in the PVN, which project to the medulla and spinal cord, are involved in various physiological functions (e.g. sensory modulation and autonomic). In the present study, we examined OXT expression in the PVN, SON and spinal cord after chronic inflammation from adjuvant arthritis (AA). We used transgenic rats that express OXT and the monomeric red fluorescent protein 1 (mRFP1) fusion gene to visualise both the magnocellular and parvocellular OXTergic pathways. OXT‐mRFP1 fluorescence intensity was significantly increased in the PVN, SON, dorsal horn of the spinal cord and posterior pituitary in AA rats. The levels of OXT‐mRFP1 mRNA were significantly increased in the PVN and SON of AA rats. These results suggested that OXT was up‐regulated in both hypothalamic magnocellular neurosecretory cells and parvocellular cells by chronic inflammation, and also that OXT in the PVN‐spinal pathway may be involved in sensory modulation. OXT‐mRFP1 transgenic rats are a very useful model for visualising the OXTergic pathways from vesicles in a single cell to terminals in in vitro preparations.     

Desacyl‐ghrelin and synthetic GH‐secretagogues modulate the production of inflammatory cytokines in mouse microglia cells stimulated by β‐amyloid fibrils

Data from Alzheimer's disease (AD) patients and AD animal models demonstrate the accumulation of inflammatory microglia at sites of insoluble fibrillar β‐amyloid protein (fAβ) deposition. It is known that fAβ binds to CD36, a type B scavenger receptor also involved in internalization of oxidized low‐density lipoprotein (LDL), and initiate a signaling cascade that regulates microglial recruitment, activation, and secretion of inflammatory mediators leading to neuronal dysfunction and death. The recent demonstration of a binding site for the growth hormone secretagogues (GHS) on CD36 prompted us to ascertain whether ghrelin and synthetic GHS could modulate the synthesis of inflammatory cytokines in fAβ‐activated microglia cells. We demonstrate that N9 microglia cells express the CD36 and are a suitable model to study the activation of inflammatory cytokines synthesis. In fact, in N9 cells exposed to fAβ_25–35 for 24 hr, the expression of interleukin (IL)‐1β and IL‐6 mRNA significantly increased. Interestingly, 10^?7 M desacyl‐ghrelin, hexarelin, and EP80317 in the nanomolar range effectively counteracted fAβ_25–35 stimulation of IL‐6 mRNA levels, whereas ghrelin was ineffective. Similarly, the effects of fAβ_25–35 on IL‐1β mRNA levels were attenuated by desacyl‐ghrelin, hexarelin, and EP80317, but not ghrelin. Because we have observed that the specific GHS receptor GHS‐R1a is not expressed in N9 cells, the actions of GHS should be mediated by different receptors. Reportedly, hexarelin and EP80317 are capable of binding the CD36 in mouse macrophages and reducing atherosclerotic plaque deposition in mice. We conclude that desacyl‐ghrelin, hexarelin, and EP80317 might interfere with fAβ activation of CD36 in microglia cells. © 2009 Wiley‐Liss, Inc.     

Interleukin‐1β protects astrocytes against oxidant‐induced injury via an NF‐κB‐Dependent upregulation of glutathione synthesis

Astrocytes produce and export the antioxidant glutathione (GSH). Previously, we found that interleukin‐1β (IL‐1β) enhanced the expression of astrocyte system x_c^?, the transporter that delivers the rate‐limiting substrate for GSH synthesis—cyst(e)ine. Herein, we demonstrate directly that IL‐1β mediates a time‐dependent increase in extracellular GSH levels in cortical astrocyte cultures, suggesting both enhanced synthesis and export. This increased GSH production was blocked by inhibition of nuclear factor‐κB (NF‐κB) activity but not by inhibition of p38 MAPK. To determine whether this increase could provide protection against oxidative stress, the oxidants tert‐butyl hydroperoxide (tBOOH) and ferrous sulfate (FeSO₄) were employed. IL‐1β treatment prevented the increase in reactive oxygen species produced in astrocytes following tBOOH exposure. Additionally, the toxicity induced by tBOOH or FeSO₄ exposure was significantly attenuated following treatment with IL‐1β, an effect reversed by concomitant exposure to l ‐buthionine‐S,R‐sulfoximine (BSO), which prevented the IL‐1β‐mediated rise in GSH production. IL‐1β failed to increase GSH or to provide protection against t‐BOOH toxicity in astrocyte cultures derived from IL‐1R1 null mutant mice. Overall, our data indicate that under certain conditions IL‐1β may be an important stimulus for increasing astrocyte GSH production, and potentially, total antioxidant capacity in brain, via an NF‐κB‐dependent process. GLIA 2015;63:1568–1580     

Crocin improved amyloid beta induced long‐term potentiation and memory deficits in the hippocampal CA1 neurons in freely moving rats

Extracellular beta‐amyloid (Aβ) accumulation and deposition is the main factor, which causes synaptic loss and eventually cells death in Alzheimer's disease (AD). Memory loss and long‐term potentiation (LTP) dysfunction in the hippocampus are involved in the AD. The involvement of crocin, as the main and active constituent of saffron extract in learning and memory processes, has been proposed. Here we investigated the probable therapeutic effect of crocin on memory, LTP, and neuronal apoptosis using in vivo Aβ models of the AD. The Aβ peptide (1–42) was bilaterally administered into the frontal‐cortex using stereotaxic apparatus. Five hours after surgery, rats were given intraperitoneal crocin (30 mg/kg) daily, which repeated for 12 days. Barnes maze results showed that administration of crocin significantly improves spatial memory indicators such as latency time to achieving the target hole and the number of errors when compared to Aβ‐group. Passive avoidance test revealed that crocin significantly increased the step‐through‐latency compared to Aβ‐treated alone. These learning deficits in Aβ‐treated animals correlated with a reduction of LTP in hippocampal CA1 synapses in freely moving rats, which crocin improved population spike amplitude and mean field excitatory postsynaptic potentials (fEPSP) slope reduction induced by Aβ. Neuronal apoptosis was detected by TUNEL assay and the expression levels of c‐Fos proteins were examined by Western blotting. Crocin significantly reduced the number of TUNEL‐positive cells in the CA1 region and decreased c‐Fos in the hippocampus compared to Aβ‐group. In vivo Aβ treatment altered significantly the electrophysiological properties of CA1 neurons and crocin further confirmed a neuroprotective action against Aβ toxicity.     

The pattern of ATP‐sensitive K+ channel subunits,Kir6.2 and SUR1 mRNA expressions in DG region is different from those in CA1‐3 regions of chronic epilepsy induced by picrotoxin in rats

ATP‐sensitive K⁺ (K_ATP) channel's function is a key determinant of both excitability and viability of neurons. In the present report, in situ hybridization histochemistry and Western blot were used to examine whether picrotoxin (PTX)‐kindling convulsions involved the changes in distribution of K_ATP channels. The data demonstrated that the formation of kindling state was associated with a decreased amount of Kir6.2 mRNAs and proteins both in cerebral cortex and dentate gyrus (DG) as well as with a decreased amount of (regulatory subunit) SUR 1 mRNAs in DG. In contrast, resulting from a PTX re‐induced seizure insult, both subunits were transiently up‐modulated but not exactly paralleled between them and among different regions. In DG, Kir6.2 mRNAs increased toward normal levels at 12 h, followed a gradual decrease from 1 day to 3 days, being distinct from that detected in CA1‐3 regions in which no significant change was shown. Further, SUR1 mRNAs markedly increased at 12 h, decreased significantly at 1 day, and even went down to a faint level at 3 days which was similar to that of CA1‐3 regions, and there was no significant change in CA1‐3 regions of SUR1 mRNAs. Also, at 7 days after a PTX re‐treatment, Kir6.2 proteins increased significantly in the cortex, CA1, CA3 and DG (increasing 49.52%, 39.36%, 33.41%, and 54.79%, respectively) as well, SUR1 proteins increased significantly in DG (increasing 3.42 times), as compared with kindling rats without PTX retreatments (P < 0.05). These results indicated that K_ATP channels in brain particularly in DG are likely related to enhanced seizure susceptibility and dynamic controls of seizure propagation of chronic epilepsy induced by PTX in rats.     

17α‐Oestradiol‐Induced Neuroprotection in the Brain of Spontaneously Hypertensive Rats

17β‐oestradiol is a powerful neuroprotective factor for the brain abnormalities of spontaneously hypertensive rats (SHR). 17α‐Oestradiol, a nonfeminising isomer showing low affinity for oestrogen receptors, is also endowed with neuroprotective effects in vivo and in vitro. We therefore investigated whether treatment with 17α‐oestradiol prevented pathological changes of the hippocampus and hypothalamus of SHR. We used 20‐week‐old male SHR with a blood pressure of approximately 170 mmHg receiving s.c. a single 800 μg pellet of 17α‐oestradiol dissolved in cholesterol or vehicle only for 2 weeks Normotensive Wistar–Kyoto (WKY) rats were used as controls. 17α‐Oestradiol did not modify blood pressure, serum prolactin, 17β‐oestradiol levels or the weight of the testis and pituitary of SHR. In the brain, we analysed steroid effects on hippocampus Ki67+ proliferating cells, doublecortin (DCX) positive neuroblasts, glial fibrillary acidic protein (GFAP)+ astrocyte density, aromatase immunostaining and brain‐derived neurotrophic factor (BDNF) mRNA. In the hypothalamus, we determined arginine vasopressin (AVP) mRNA. Treatment of SHR with 17α‐oestradiol enhanced the number of Ki67+ in the subgranular zone and DCX+ cells in the inner granule cell layer of the dentate gyrus, increased BDNF mRNA in the CA1 region and gyrus dentatus, decreased GFAP+ astrogliosis in the CA1 subfield, and decreased hypothalamic AVP mRNA. Aromatase expression was unmodified. By contrast to SHR, normotensive WKY rats were unresponsive to 17α‐oestradiol. These data indicate a role for 17α‐oestradiol as a protective factor for the treatment of hypertensive encephalopathy. Furthermore, 17α‐oestradiol is weakly oestrogenic in the periphery and can be used in males.