Hippocampus-related Behaviors Research Articles

Interplay of MeCP2/REST/Synaptophysin-BDNF and intranasal oxytocin influence on Aβ-induced memory and cognitive impairments

BackgroundAlzheimer's disease (AD) is linked to the accumulation of Aβ, increased tau hyperphosphorylation, persistent neuroinflammation, and a decline in neurotrophic factors, neurogenesis, and synaptic plasticity. Oxytocin (OT) has a significant impact on memory and learning. We examined the influence of intranasal (IN) OT on synaptic plasticity, neurogenesis, histone acetylation, and spatial and cognitive memories in rats. MethodsAβ25–35 (5 µg/2.5 µl) was administered bilaterally in the CA1 of male Wistar rats for four consecutive days. After seven days of recovery, OT (2 µg/µl, 10 µl in each nostril) was administered IN for seven consecutive days. Working, spatial, and cognitive memories, and gene expression of neurogenesis- and synaptic plasticity-involved factors were measured in the hippocampus. Histone acetylation (H3K9 and H4K8) was also measured using western blotting. ResultsIN administration of OT significantly improved working and spatial memory impairment induced by Aβ and increased the factors involved in synaptic plasticity (MeCP2, REST, synaptophysin, and BDNF) and neurogenesis (Ki67 and DCX). We also found an enhancement in the levels of H3K9ac and H4K8ac following OT administration. ConclusionThese findings indicated that IN OT could improve hippocampus-related behaviors by increasing synaptic plasticity, stimulating neurogenesis, and chromatin plasticity.

Postnatal calpeptin treatment causes hippocampal neurodevelopmental defects in neonatal rats.

Our previous studies showed that the early use of calpain inhibitors reduces calpain activity in multiple brain regions, and that postnatal treatment with calpeptin may lead to cerebellar motor dysfunction. However, it remains unclear whether postnatal calpeptin application affects hippocampus-related behaviors. In this study, Sprague-Dawley rats were purchased from the Animal Center of Anhui Medical University of China. For the experiments in the adult stage, rats were intraperitoneally injected with calpeptin, 2 mg/kg, once a day, on postnatal days 7-14. Then on postnatal day 60, the Morris water maze test was used to evaluate spatial learning and memory abilities. The open field test was carried out to assess anxiety-like activities. Phalloidin staining was performed to observe synaptic morphology in the hippocampus. Immunohistochemistry was used to count the number of NeuN-positive cells in the hippocampal CA1 region. DiI was applied to label dendritic spines. Calpeptin administration impaired spatial memory, caused anxiety-like behavior in adulthood, reduced the number and area of apical dendritic spines, and decreased actin polymerization in the hippocampus, but did not affect the number of NeuN-positive cells in the hippocampal CA1 region. For the neonatal experiments, neonatal rats were intraperitoneally injected with calpeptin, 2 mg/kg, on postnatal days 7 and 8. Western blot assay was performed to analyze the protein levels of Akt, Erk, p-Akt, p-Erk1/2, Erk1/2, SCOP, PTEN, mTOR, p-mTOR, CREB and p-CREB in the hippocampus. SCOP expression was increased, and the phosphorylation levels of Akt, mTOR and CREB were reduced in the hippocampus. These findings show that calpeptin administration after birth affects synaptic development in neonatal rats by inhibiting the Akt/mTOR signaling pathway, thereby perturbing hippocampal function. Therefore, calpeptin administration after birth is a risk factor for neurodevelopmental defects.

Binge Alcohol Exposure Causes Neurobehavioral Deficits and GSK3\u03b2 Activation in the Hippocampus of Adolescent Rats

Heavy alcohol exposure causes profound damage to the adolescent brain, particularly the hippocampus, which underlie some behavioral deficits. However, the underlying molecular mechanisms remain inconclusive. The current study sought to determine whether binge alcohol exposure affects the hippocampus-related behaviors and key signaling proteins that may mediate alcohol neurotoxicity in adolescent rats. Alcohol exposure reduced the number of both NeuN-positive and doublecortin-positive cells in the hippocampus. Alcohol also induced neurodegeneration which was confirmed by ultrastructural analysis by electronic microscopy and was accompanied with the activation of microglia. Binge alcohol exposure impaired spatial learning and memory which was evaluated by the Morris water maze. However, alcohol did not alter the spontaneous locomotor activity which was determined by the open field test. GSK3β is a multi-function serine/threonine protein kinase regulating both neuronal survival and neurogenesis and plays an important role in various neurodegenerative disorders. We have previously shown that GSK3β is a key mediator of alcohol-induced neuron apoptosis in the developing brain. We showed here binge alcohol exposure caused GSK3β activation by inducing dephosphorylation at Ser9 without affecting the phosphorylation of Tyr216 in the hippocampus. Thus, GSK3β may be involved in binge alcohol exposure-induced neuronal damage to the adolescent hippocampus.

Altered aspects of anxiety-related behavior in kisspeptin receptor-deleted male mice

The roles of kisspeptin signaling outside the hypothalamus in the brain are unknown. We examined here the impact of Kiss1r-deletion on hippocampus-related behaviors of anxiety and spatial learning in adult male mice using two mouse models. In the first, global Kiss1r-null and control mice were gonadectomized (GDX KISS1R-KO). In the second, KISS1R signalling was rescued selectively in gonadotropin-releasing hormone neurons to generate Kiss1r-null mice with normal testosterone levels (intact KISS1R-KO). Intact KISS1R-KO rescue mice were found to spend twice as much time in the open arms of the elevated plus maze (EPM) compared to controls (P < 0.01). GDX KISS1R-KO mice showed a similar but less pronounced trend. No differences were detected between intact KISS1R-KO mice and controls in the open field test (OFT), although a marked reduction in time spent in the centre quadrant was observed for all GDX mice (P < 0.001). No effects of KISS1R deletion or gonadectomy were detected in the Morris water maze. These observations demonstrate that KISS1R signalling impacts upon anxiogenic neural circuits operative in the EPM, while gonadal steroids appear important for anxiety behaviour observed in the OFT. The potential anxiogenic role of kisspeptin may need to be considered in the development of kisspeptin analogs for the clinic.

A sex difference in oxidative stress and behavioral suppression induced by ethanol withdrawal in rats

Ethanol withdrawal (EW) is referred to the abrupt termination of long-term heavy drinking, and provokes oxidative brain damage. Here, we investigated whether the cerebellum and hippocampus of female rats are less affected by prooxidant EW than male rats due to the antioxidant effect of 17β-estradiol (E2). Female and male rats received a four-week ethanol diet and three-week withdrawal per cycle for two cycles. Some female rats were ovariectomized with E2 or antioxidant (Vitamin E+Co-Q10) treatment. Measurements were cerebellum (Rotarod) and hippocampus (water-maze)-related behaviors, oxidative markers (O2−, malondialdehyde, protein carbonyls), mitochondrial membrane swelling, and a key mitochondrial enzyme, cytochrome c oxidase (CcO). Separately, HT22 (hippocampal) cells were subjected to ethanol-exposure and withdrawal for two cycles to assess the effect of a CcO inhibitor on E2’s protection for mitochondrial respiration and cell viability. Ethanol-withdrawn female rats showed a smaller increase in oxidative markers in cerebellum and hippocampus than male rats, and E2 treatment decreased the oxidative markers. Compared to male counterparts, ethanol-withdrawn female rats showed better Rotarod but poorer water-maze performance, accompanied by more severe mitochondrial membrane swelling and CcO suppression in hippocampus. E2 or antioxidant treatment improved Rotarod but not water-maze performance. In the presence of a CcO inhibitor, E2 treatment failed to protect mitochondrial respiration and cell viability from EW. These data suggest that antioxidant E2 contributes to smaller oxidative stress in ethanol-withdrawn female than male rats. They also suggest that EW-induced severe mitochondrial damage in hippocampus may blunt E2’s antioxidant protection for hippocampus-related behavior.

Novel stress increases hypothalamic-pituitary-adrenal activity in mice with a raised bite

Background and objectiveIn humans, occlusal disharmony may cause various physical complaints, including head and neck ache, stiffness in the shoulder and neck, and arthrosis of the temporomandibular joints. Occlusal disharmony induced by raising the bite in rodents, increases plasma corticosterone levels, which leads to morphologic changes in the hippocampus and altered hippocampus-related behavior. The paraventricular nucleus (PVN) of the hypothalamus regulates the hypothalamic-pituitary-adrenal system. Chronically stressed animals exposed to a novel stress exhibit higher adrenocorticotropic hormone levels than naive control animals. We hypothesized that there would be different response of the corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) to a novel acute stress with occlusal disharmony. DesignIn order to investigate how exposure of mice with occlusal disharmony to a novel acute stress (restraint stress) affects the PVN, we induced occlusal disharmony by raising the vertical dimension of the bite (bite-raised condition) and examined the expression of corticotrophin releasing hormone (CRH) mRNA and arginine vasopressin (AVP) mRNA in mouse PVN. ResultsCRH mRNA expression was increased in the PVN of the bite-raised group 90min after the bite-raising procedure, but the expression was recovered to the control level at 14days. AVP mRNA expression in the PVN was normal at 90min, and increased significantly 14days after the bite-raising procedure. Exposure to restraint stress in the bite-raised mice induced a significant increase in CRH mRNA expression in the PVN. ConclusionsThe bite-raising procedure induced a rapid CRH mRNA response and a slower AVP mRNA response in the parvocellular PVN of the hypothalamus. Exposure to a novel stress following the bite-raising procedure further reinforced the CRH stress response. Thus, occlusal disharmony, such as that induced by raising the bite, may be a risk factor for hypersensitivity to a novel stress.

Total Levels of Hippocampal Histone Acetylation Predict Normal Variability in Mouse Behavior

BackgroundGenetic, pharmacological, and environmental interventions that alter total levels of histone acetylation in specific brain regions can modulate behaviors and treatment responses. Efforts have been made to identify specific genes that are affected by alterations in total histone acetylation and to propose that such gene specific modulation could explain the effects of total histone acetylation levels on behavior — the implication being that under naturalistic conditions variability in histone acetylation occurs primarily around the promoters of specific genes.Methods/ResultsHere we challenge this hypothesis by demonstrating with a novel flow cytometry based technique that normal variability in open field exploration, a hippocampus-related behavior, was associated with total levels of histone acetylation in the hippocampus but not in other brain regions.ConclusionsResults suggest that modulation of total levels of histone acetylation may play a role in regulating biological processes. We speculate in the discussion that endogenous regulation of total levels of histone acetylation may be a mechanism through which organisms regulate cellular plasticity. Flow cytometry provides a useful approach to measure total levels of histone acetylation at the single cell level. Relating such information to behavioral measures and treatment responses could inform drug delivery strategies to target histone deacetylase inhibitors and other chromatin modulators to places where they may be of benefit while avoiding areas where correction is not needed and could be harmful.

Implications of p75NTR for dentate gyrus morphology and hippocampus-related behavior revisited

The pan-neurotrophin receptor p75NTR is expressed in the adult brain in a discrete pattern. Although numerous studies have addressed its implications for hippocampal functions, the generated sets of data are surprisingly conflicting. We have therefore set out to re-investigate the impact of a deletion of the full-length p75NTR receptor on several parameters of the dentate gyrus (DG), including neurogenesis and hippocampus-related behavior by using p75NTR(ExIII) knockout mice. Moreover, we investigated further parameters of the DG (cholinergic innervation, dendritic spines). In addition, we analyzed on the morphological level the impact of aging by comparing adult and aged p75NTR(ExIII) mice and their age-matched littermates. Adult (4-6 months old), but not aged (20 months old), p75NTR(ExIII) knockout mice display an enhanced volume of the DG. However, adult neurogenesis within the adult DG was unaffected in both adult and aged p75NTR(ExIII) knockout mice. We could further demonstrate that the change in the volume of the DG was accompanied by an increased cholinergic innervation and increased spine densities of granule cells in adult, but not aged p75NTR deficient mice. These morphological changes in the adult p75NTR deficient mice were accompanied by specific alterations in their behavior, including altered behavior in the Morris water maze test, indicating impairments in spatial memory retention.

Genetic analysis reveals polygenic influences on iron, copper, and zinc in mouse hippocampus with neurobiological implications

Fe, Cu, and Zn are of widespread neurobiological importance, but must be regulated closely as too much or too little of these metals can have adverse effects on brain function. Recent evidence from nutritional models notes that the hippocampus is particularly vulnerable to Fe and Zn deficiencies. We recently performed a quantitative trait loci (QTL) analysis as a preliminary step in identifying genes that contribute to natural variation in hippocampal Fe, Cu, and Zn content. We used ICP-MS to measure the concentrations of these metals in 120-day-old mice from 30 strains of the BXD/TY panel. The BXD/Ty recombinant inbred strain panel is well-suited for complex trait analysis, as all strains are genotyped with a dense marker set and have been phenotyped extensively for neurobehavioral traits and hippocampal gene expression. We observed a wide-range of hippocampal Fe, Cu, and Zn concentrations across the BXD strains. These concentrations were related to systemic Fe status, but not to Fe, Cu, and Zn elsewhere in the brain. The three metals also showed strong covariance, suggestive of overlap in their regulatory pathways. We identified two QTL, on chromosomes 14 and 9, most strongly associated with Cu but also suggestively associated with Fe (chr. 14) and Zn (chr. 9). We also performed genetic correlational analyses with existing data on these strains and revealed associations with cognitive, anxiety-related, and alcohol-related phenotypes. Covariance of these metals with gene expression is also discussed. This work shows that hippocampal Fe, Cu, and Zn are under polygenic influence and that trace metal regulation is associated with hippocampus-related behaviors. Future work will elucidate the genes underlying the two QTL identified, to aid in identifying homologous genetic variants in human populations, which may underlie altered trace metal homeostasis and related neurological disease.

Alterations in hippocampal hemicholinium-3 binding and related behavioural and biochemical changes after prenatal phenobarbitone exposure.

Previous studies demonstrated postsynaptic septohippocampal cholinergic alterations after early exposure to phenobarbital. The present study was designed to ascertain possible corresponding presynaptic alterations while confirming the known behavioral deficits and extending previous findings on postsynaptic cholinergic alterations. Pregnant heterogeneous mice received milled mouse food containing 3 g/kg phenobarbital on gestation days 9-18. At age 50 days, [3H]hemicholinium-3 binding, which labels the presynaptic transporter for high affinity choline uptake, was increased in treated mice by 100% (P < 0.001). This change was not accompanied by a change in the affinity of the transporter to the ligand. Another group of offspring was tested for hippocampus-related behaviors. Consistent with our previous studies in the Morris maze, treated animals took longer to reach the platform in the place test as compared to control, and swam fewer times over the missing platform location in the spatial probe test. In the eight-arm maze, the treated offspring needed more entries than control to visit all the arms. In the spontaneous alternation test, the treated mice showed fewer alternations than controls. Biochemically, as in our previous results, prenatal phenobarbital exposure resulted in an increase in the degree of stimulation of inositol phosphate formation by carbachol (P < 0.05), an action presumed to occur at postsynaptic muscarinic receptors. While the present results show that the effect of a combination of raised K+ in the presence of physostigmine and carbachol was significantly greater in barbiturate-treated mice (P < 0.05), the action of K+ in the presence of physostigmine, but without carbachol, was not affected by the phenobarbital treatment. The results point to the uniqueness of outcome of early insults where alterations along nerve conduction cascades do not necessarily follow the common rules in that upregulation could simultaneously occur both pre- and post synaptically.

Behavioral deficits and related septohippocampal cholinergic alterations after prenatal exposure to heroin

Pregnant female mice were exposed to heroin on gestation days 9–18. On postnatal day 50, offspring showed marked deficits in the hippocampus related behaviors, eight-arm and Morris mazes. Alterations in the septohippocampal cholinergic innervations were studied as the possible mechanisms. We have found, presynaptically, that the binding of [ 3H]hemicholinium-3 (HC-3) (a reliable indicator of presynaptic cholinergic innervation) increased in the heroin exposed animals. The B max values of binding to muscarinic receptors (an indicator of postsynaptic cholinergic activity) increased as well. In agreement with this observation, carbachol induced formation of inositol phosphates (IP) similarly increased. Interestingly, we have also observed an increase in the levels of a subunit of several GTP binding proteins (Gai and Gaq). In addition, the basal level of Protein Kinase C (PKC) increased. However, PKC activity was unresponsive to acetylcholine agonist stimulation in the heroin treated animals, pointing to a possible explanation for the behavioral deficits.

Alterations in hippocampal cholinergic receptors and hippocampal behaviors after early exposure to nicotine

Mice were exposed to nicotine prenatally by injecting the mother with 1.5 mg/kg nicotine SC twice daily on gestation days 9–18 (PreN mice) or neonatally by daily SC injections of 1.5 mg/kg nicotine on postnatal days 2–21 (NeoN mice). At age 50 days, hippocampal muscarinic receptors S max of PreN and NeoN mice were 58% and 79% above control, respectively ( p < 0.01); K d was unaffected by early nicotine exposure. Eight-arm maze performance of nicotine-exposed animals fell behind control level. Both PreN and NeoN made approximately 10% less correct responses in the first eight trials than controls throughout the test period ( p < 0.01). By the last day of testing, PreN needed 23% and NeoN 31% more trials than controls to enter all arms ( p < 0.001). In addition, PreN needed 35 and NeoN 42% more days than controls to reach criterion ( p < 0.05). Similarly, while 61% of controls reached criterion by day 6 only 17% of PreN and 25% of NeoN reached criterion ( p < 0.01). In the Morris maze, PreN needed from 43–119% more time to reach the platform ( p < 0.001). In the spatial probe test, PreN animals made 35% fewer crosses over the area of the missing platform ( p < 0.001). The study suggests that nicotine administered to the fetus or neonate alters septohippocampal chemistry and induces deficits in hippocampus-related behaviors. The possible reversal of the behavioral changes by manipulating the cholinergic innervations should be the subject of future investigations.

Hippocampal cholinergic alterations and related behavioral deficits after early exposure to phenobarbital

Mice were exposed to phenobarbital(PhB) prenatally and neonatally. Prenatal exposure was accomplished by feeding the mother PhB (3 g/kg milled food) on gestation days 9–18. Neonatal exposure was accomplished by daily injections of 50 mg/kg sodium PhB directly to the pups on days 2–21. Long-term biochemical alterations in the pre- and postsynaptic septohippocampal system, as well as related behavioral deficits, were assessed in the treated animals. Significant increase in B max values for binding of [ 3H]QNB to muscarinic cholinergic receptors was obtained on both ages 22 and 50 in prenatally (40–90%, respectively, p < 0.001) and neonatally exposed (58–89%, p < 0.001) mice whereas K d remained normal. Similarly, a significant increase of inositol phosphate (IP) formation in response to carbachol was found after both prenatal and neonatal exposure to PhB ( p < 0.05). No alterations in choline acetyltransferase (ChAT) activity were observed in the prenatally or neonatally treated animals. The early exposed mice showed deficits in the performance in Morris water maze, a behavior related to the septohippocampal pathway. The results suggest that early exposure to PhB induces alterations in postsynaptic components of the hippocampal cholinergic system and concomitantly to impairment in hippocampus-related behavior.

Studies into the mechanisms of strain differences in hippocampus-related behaviors.

The heterogeneous mouse stocks HS/Ibg and SABRA/HUC and the inbred strains C57BL/6J, CBA/LAC, and BALB/Crgl were employed in an investigation of strain differences in delayed spontaneous alteration (SA) and eight-arm maze performance (EAM). Intact male mice were tested for SA at age 41 days for 2 consecutive days and for EAM at age 50-54 days, under conditions of water deprivation that commenced on day 43. In SA, BALB mice had a lower score than all other strains on day 1 but differed significantly only from SABRA; performance on day 2 was not consistent with that on day 1. In EAM, HS was first, CBA second, C57 third, SABRA fourth, and BALB fifth. HS was superior to the other strains, while BALB fell far below all other strains in both tests. Except for these two strains, the correlation between the two tests across the other strains was low. A study was undertaken to investigate the role of the hippocampus in the deficits in the performance of BALB mice in the two behaviors. Noradrenergic neurons were transplanted to hippocampus or cortex, and cholinergic neurons to their hippocampus. There were no significant differences in performance between the control and transplanted mice. The possibility was discussed that the behavioral differences are the outcome of variability in the neurotransmitters systems of the hippocampus but probably not the noradrenergic system.

Early phenobarbital-induced alterations in hippocampal acetylcholinesterase activity and behavior

Early exposure to phenobarbital (PhB) causes marked destruction of large neurons which are then forming both in the hippocampus and in the cerebellum. Such exposure to PhB also reduces the achievements of mice in hippocampus-related behaviors such as radial 8-arm maze performance. Experimental evidence suggests that these behaviors are partially mediated by cholinergic transmission. We studied the performance of mice, exposed to PhB prenatally or neonatally, in radial 8-arm maze. Both treatments caused significant impairments in the animals' performance in the maze. Acetylcholinesterase (AChE) and pseudocholinesterase (pChE) activities were studied in the hippocampus and cerebellum of mice who were exposed to PhB prenatally or neonatally. These enzymes are involved both in cholinergic transmission and in neuronal development. A significant decrease (13-16%, P less than 0.01) in hippocampal AChE specific activity was found between days 15 and 22 in animals exposed to PhB neonatally. The total hippocampal activity of AChE was also greatly reduced (25-39%, P less than 0.01) during that period as a result of both the reduction in specific activity and a reduction in hippocampal weight of the treated animals. These alterations were transient and were not detected in adulthood. No changes in hippocampal AChE or pChE activities were found in animals treated prenatally. Cerebellar AChE and pChE activities were not altered after prenatal nor after neonatal exposure to PhB. It is possible that the short-term effect of neonatal treatment on AChE specific activity might mediate the long-term impairments in hippocampus-related behaviors.

Parallel but independent effects of pentobarbital and scopolamine on hippocampus-related behavior

In Wistar-derived rats subanesthetic doses of pentobarbital were found to abolish spontaneous alternation, a form of exploratory behavior selectively sensitive to hippocampal damage and (until now) anticholinergic drugs. A dose of 15 mg/kg of pentobarbital completely abolished the behavior, as did a scopolamine dose of 0.3 mg/kg. Dose-response curves for the two drugs could be closely superimposed on the assumption that the potency ratio was about 45:1. Combined injections of the two drugs, with each employed at barely subthreshold dosage, did not reliably reduce the alternation rate, although a superthreshold combination of the two drugs did completely abolish alternation. All effects were predicted on the basis of electrophysiological-pharmacological studies showing each drug to affect hippocampal electrical activity in a different way. Pentobarbital, scopolamine, and massive hippocampal lesions have now been found to have the same behavioral effects on at least five different and highly diagnostic responses.