OBX Mice Research Articles

Butea superba–Induced Amelioration of Cognitive and Emotional Deficits in Olfactory Bulbectomized Mice and Putative Mechanisms Underlying Its Actions

This study investigated the effects of alcoholic extract of Butea superba (BS) on cognitive deficits and depression-related behavior using olfactory bulbectomized (OBX) mice and the underlying molecular mechanisms of its actions. OBX mice were treated daily with BS (100 and 300 mg/kg, p.o.) or reference drugs, tacrine (2.5 mg/kg, i.p.) and imipramine (10 mg/kg, i.p.) from day 3 after OBX. OBX impaired non-spatial and spatial cognitive performances, which were elucidated by the novel object recognition test and modified Y maze test, respectively. These deficits were attenuated by tacrine and BS but not imipramine. OBX animals exhibited depression-like behavior in the tail suspension test in a manner reversible by imipramine and BS but not tacrine. OBX down-regulated phosphorylation of synaptic plasticity–related signaling proteins: NMDA receptor, AMPA receptor, calmodulin-dependent kinase II, and cyclic AMP-responsive element-binding protein. OBX also reduced choline acetyltransferase in the hippocampus. BS and tacrine reversed these neurochemical alterations. Moreover, BS inhibited ex vivo activity of acetylcholinesterase in the brain. These results indicate that BS ameliorates not only cognition dysfunction via normalizing synaptic plasticity–related signaling and facilitating central cholinergic systems but also depression-like behavior via a mechanism differing from that implicated in BS amelioration of cognitive function in OBX animals.

CaMKII activity is essential for improvement of memory‐related behaviors by chronic rivastigmine treatment

Because the cholinergic system is down-regulated in the brain of Alzheimer's disease patients, cognitive deficits in Alzheimer's disease patients are significantly improved by rivastigmine treatment. To address the mechanism underlying rivastigmine-induced memory improvements, we chronically treated olfactory bulbectomized (OBX) mice with rivastigmine. The chronic rivastigmine treatments for 12-13 days starting at 10 days after OBX operation significantly improved memory-related behaviors assessed by Y-maze task, novel object recognition task, passive avoidance task, and Barnes maze task, whereas the single rivastigmine treatment failed to improve the memory. Consistent with the improved memory-related behaviors, long-term potentiation in the hippocampal CA1 region was markedly restored by rivastigmine treatments. In immunoblotting analyses, the reductions of calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and calcium/calmodulin-dependent protein kinase IV (CaMKIV) phosphorylation in the CA1 region in OBX mice were significantly restored by rivastigmine treatments. In addition, phosphorylation of AMPAR subunit glutamate receptor 1 (GluA1) (Ser-831) and cAMP-responsive element-binding protein (Ser-133) as downstream targets of CaMKII and CaMKIV, respectively, in the CA1 region was also significantly restored by chronic rivastigmine treatments. Finally, we confirmed that rivastigmine-induced improvements of memory-related behaviors and long-term potentiation were not obtained in CaMKIIα(+/-) mice. On the other hand, CaMKIV(-/-) mice did not exhibit the cognitive impairments. Taken together, the stimulation of CaMKII activity in the hippocampus is essential for rivastigmine-induced memory improvement in OBX mice.

Immunization with either prion protein fragment 95–123 or the fragment-specific antibodies rescue memory loss and neurodegenerative phenotype of neurons in olfactory bulbectomized mice

Epidemiological studies demonstrated association between head injury (HI) and the subsequent development of Alzheimer’s disease (AD). Certain hallmarks of AD, e.g. amyloid-β (Aβ) containing deposits, may be found in patients following traumatic BI (TBI). Recent studies uncover the cellular prion protein, PrPC, as a receptor for soluble polymeric forms of Aβ (sAβ) which are an intermediate of such deposits. We aimed to test the hypothesis that targeting of PrPC can prevent Aβ related spatial memory deficits in olfactory bulbectomized (OBX) mice utilized here to resemble some clinical features of AD, such as increased level of Aβ, memory loss and deficit of the CNS cholin- and serotonin-ergic systems. We demonstrated that immunization with the a.a. 95–123 fragment of cellular prion (PrP-I) recovered cortical and hippocampus neurons from OBX induced degeneration, rescued spatial memory loss in Morris water maze test and significantly decrease the Aβ level in brain tissue of these animals. Affinity purified anti-PrP-I antibodies rescued pre-synaptic biomarker synaptophysin eliciting similar effect on memory of OBX mice, and protected hippocampal neurones from Aβ25–35-induced toxicity in vitro. Immunization OBX mice with a.a. 200–213 fragment of cellular prion (PrP-II) did not reach a significance in memory protection albeit having similar to PrP-I immunization impact on Aβ level in brain tissue. The observed positive effect of targeting the PrP-I by either active or passive immunization on memory of OBX mice revealed the involvement of the PrPC in AD-like pathology induced by olfactory bulbectomy. This OBX model may be a useful tool for mechanistic and preclinical therapeutic investigations into the association between PrPC and AD.

Bacopa monnieri Ameliorates Memory Deficits in Olfactory Bulbectomized Mice: Possible Involvement of Glutamatergic and Cholinergic Systems

This study investigated the effects of alcoholic extract of Bacopa monnieri (L.) Wettst. (BM) on cognitive deficits using olfactory bulbectomized (OBX) mice and the underlying molecular mechanisms of its action. OBX mice were treated daily with BM (50 mg/kg, p.o.) or a reference drug, tacrine (2.5 mg/kg, i.p.), 1 week before and continuously 3 days after OBX. Cognitive performance of the animals was analyzed by the novel object recognition test, modified Y maze test, and fear conditioning test. Brain tissues of OBX animals were used for neurochemical and immunohistochemical studies. OBX impaired non-spatial short-term memory, spatial working memory, and long-term fair memory. BM administration ameliorated these memory disturbances. The effect of BM on short-term memory deficits was abolished by a muscarinic receptor antagonist, scopolamine. OBX downregulated phosphorylation of synaptic plasticity-related signaling proteins: NR1 subunit of N-methyl-D-aspartate receptor, glutamate receptor 1 (GluR1), and calmodulin-dependent kinase II but not cyclic AMP-responsive element binding protein (CREB), and reduced brain-derived neurotrophic factor (BDNF) mRNA in the hippocampus. OBX also reduced choline acetyltransferase in the hippocampus and cholinergic neurons in the medial septum, and enlarged the size of lateral ventricle. BM administration reversed these OBX-induced neurochemical and histological alterations, except the decrease of GluR1 phosphorylation, and enhanced CREB phosphorylation. Moreover, BM treatment inhibited ex vivo activity of acetylcholinesterase in the brain. These results indicate that BM treatment ameliorates OBX-induced cognition dysfunction via a mechanism involving enhancement of synaptic plasticity-related signaling and BDNF transcription and protection of cholinergic systems from OBX-induced neuronal damage.

Stimulation of the sigma-1 receptor by DHEA enhances synaptic efficacy and neurogenesis in the hippocampal dentate gyrus of olfactory bulbectomized mice.

Dehydroepiandrosterone (DHEA) is the most abundant neurosteroid synthesized de novo in the central nervous system. We previously reported that stimulation of the sigma-1 receptor by DHEA improves cognitive function by activating calcium/calmodulin-dependent protein kinase II (CaMKII), protein kinase C and extracellular signal-regulated kinase in the hippocampus in olfactory bulbectomized (OBX) mice. Here, we asked whether DHEA enhances neurogenesis in the subgranular zone of the hippocampal dentate gyrus (DG) and improves depressive-like behaviors observed in OBX mice. Chronic treatment with DHEA at 30 or 60 mg/kg p.o. for 14 days significantly improved hippocampal LTP impaired in OBX mice concomitant with increased CaMKII autophosphorylation and GluR1 (Ser-831) phosphorylation in the DG. Chronic DHEA treatment also ameliorated depressive-like behaviors in OBX mice, as assessed by tail suspension and forced swim tests, while a single DHEA treatment had no affect. DHEA treatment also significantly increased the number of BrdU-positive neurons in the subgranular zone of the DG of OBX mice, an increase inhibited by treatment with NE-100, a sigma-1 receptor antagonist. DHEA treatment also significantly increased phosphorylation of Akt (Ser-473), Akt (Ser-308) and ERK in the DG. Furthermore, GSK-3β (Ser-9) phosphorylation increased in the DG of OBX mice possibly accounting for increased neurogenesis through Akt activation. Finally, we confirmed that DHEA treatment of OBX mice increases the number of BrdU-positive neurons co-expressing β-catenin, a downstream GSK-3βtarget. Overall, we conclude that sigma-1 receptor stimulation by DHEA ameliorates OBX-induced depressive-like behaviors by increasing neurogenesis in the DG through activation of the Akt/GSK-3β/β-catenin pathway.

Social isolation differentially affects anxiety and depressive-like responses of bulbectomized mice

Social isolation in rodents may interfere in their behavioural responses on paradigms used to test anxiety- and depressive-like states. Herein we study the influence of social isolation upon the behavioural responses of olfactory bulbectomized mice (OBX). In the open-field test (OFT), social isolation enhanced OBX-induced hyperactivity and exploratory behaviour. However, OBX-induced anxiety in the OFT (central activity) was less apparent after isolation, due to the increased level of anxiety showed by the sham-isolated counterparts. In the novelty-suppressed feeding (NSF), isolation derived in an increased latency to feeding of both OBX and sham mice. The isolation did not affect the response of OBX mice and sham mice in the forced-swimming test (FST). Interestingly, OBX animals exhibited an increased immobility time during the FST, though a dramatic decrease in the climbing scores. Finally, OBX-induced anhedonia in the sucrose intake test was not affected by housing conditions. Our findings demonstrate that social isolation influences the performance of OBX mice in some behavioural paradigms, thus facilitating the characterization of depressive-like states, and by contrast, hindering anxiety-related behaviours. This fact should be taken into account in order to minimize economical and time-consuming efforts when assessing potential antidepressant and anxiolytic drugs.

Novel nootropic drug sunifiram improves cognitive deficits via CaM kinase II and protein kinase C activation in olfactory bulbectomized mice

Alzheimer's disease (AD) shows degeneration of the cholinergic system in the medial septum, thereby eliciting down-regulation of the olfactory function in patients. We have previously reported that olfactory bulbectomized (OBX) mice show hippocampus-dependent memory impairment as assessed by memory-related behavioral tasks and hippocampal long-term potentiation (LTP). In the present study, we focused whether novel pyrrolidone nootropic drug sunifiram improves both memory impairment and depression observed in OBX mice. OBX mice were administered once a day for 7–12 days with sunifiram (0.01–1.0mg/kg p.o.) from 10 days after operation with or without gavestinel (10mg/kg i.p.), which is glycine-binding site inhibitor of N-methyl-d-aspartate receptor (NMDAR). The spatial reference memory assessed by Y-maze and short-term memory assessed by novel object recognition task were significantly improved by sunifiram treatment in OBX mice. Sunifiram also restored hippocampal LTP injured in OBX mice without treatment with gavestinel. By contrast, sunifiram treatment did not ameliorate the depressive behaviors assessed by tail suspension task in OBX mice. Notably, sunifiram treatment restored CaMKIIα (Thr-286) autophosphorylation and GluR1 (Ser-831) phosphorylation in the hippocampal CA1 region from OBX mice to the levels of control mice. Likewise, sunifiram treatment improved PKCα (Ser-657) autophosphorylation and NR1 (Ser-896) phosphorylation to the control levels. Stimulation of CaMKII and PKC autophosphorylation by sunifiram was significantly inhibited by pre-treatment with gavestinel. However, sunifiram treatment did not affect the phosphorylation of CaMKIV (Thr-196) and ERK. Taken together, sunifiram ameliorates OBX-induced deficits of memory-related behaviors and impaired LTP in the hippocampal CA1 region via stimulation of glycine-binding site of NMDAR.

Donepezil rescues the medial septum cholinergic neurons via nicotinic ACh receptor stimulation in olfactory bulbectomized mice

Olfactory bulbectomy (OBX) causes cognitive dysfunction by degeneration of cholinergic neurons in the medial septum. Here, we define an involvement of nicotinic acetylcholine receptor (nAChR) in neuroprotective effect of donepezil in the septum neurons of OBX mice. Neuroprotective effects on the medial septal cholinergic neurons were assessed after chronic donepezil administration in OBX mice. We also measured Akt and ERK phosphorylation to define the neuroprotective mechanism of donepezil. We found that treatment with donepezil (1 - 3 mg/kg) for 15 consecutive days completely rescued cholinergic neurons in the OBX mice with concomitant improved memory. Reduction of both protein kinase B (Akt) and extracellular signal-regulated kinase (ERK) phosphorylation were restored by chronic donepezil administration (1 - 3 mg/kg) in OBX mouse medial septum. Both phosphorylated Akt and ERK immunoreactivities were localized in cell bodies of choline acetyltransferase (ChAT)-positive cholinergic cells in the medial septum. Enhancement of Akt and ERK phosphorylation seen following donepezil administration was totally blocked by pre-administration of mecamylamine (10 μM), a nicotinic acetylcholine receptor antagonist. Donepezil increases phosphorylation of Akt and ERK via nAChR stimulation in the medial septum cholinergic neurons. The Akt and ERK stimulation by donepezil is associated with its ability of neuroprotection in the medial septum and memory improvement.

Ameliorative Effects ofAcanthopanax trifoliatuson Cognitive and Emotional Deficits in Olfactory Bulbectomized Mice: An Animal Model of Depression and Cognitive Deficits

Acanthopanax trifoliatus is a plant that has been traditionally used in Thailand as a vegetable and a tonic. This study investigated effects of the aqueous extract of its leaves (ATL) on cognitive and emotional deficits using an olfactory bulbectomized mouse (OBX) model. OBX mice were treated daily with ATL (250 and 500 mg/kg, p.o.) 3 days after OBX. Antidementia drug tacrine (2.5 mg/kg/day) and antidepressant drug imipramine (10 mg/kg/day) were given i.p. as reference drugs. OBX significantly impaired cognitive behavior in a novel object recognition test and a modified Y-maze test and induced depression-like behavior in a tail suspension test. ATL and tacrine treatment attenuated OBX-induced cognitive deficits, whereas ATL and imipramine improved OBX-induced depression-like behavior. Neurochemical studies conducted after completing behavioral experiments demonstrated that OBX downregulated the expression levels of cholinergic marker genes encoding choline acetyltransferase and muscarinic M1 receptor in a manner reversed by ATL and tacrine. Moreover, ATL and tacrine administration inhibited the ex vivo activity of acetylcholinesterase in the brain. These findings suggest that ATL is beneficial for the treatment of cognitive and emotional deficits related to dementia with depressive symptoms and that the antidementia effect of ATL is mediated by normalizing the function of central cholinergic systems.

The Novel Cognitive Enhancer ST101 Enhances Acetylcholine Release in Mouse Dorsal Hippocampus Through T-type Voltage-Gated Calcium Channel Stimulation

We recently developed a novel cognitive enhancer, ST101 (spiro[imidazo[1,2-a] pyridine-3,2-indan]-2(3H)-one), that activates T-type voltage-gated calcium channels (VGCCs). Here, we address whether T-type VGCC activation with ST101 mediates its cognitive effects in vivo and the relevance of T-type VGCC activation to acetylcholine (ACh) release in the hippocampus. Acute intraperitoneal administration of ST101 (1 mg/kg, i.p.) improved memory-related behaviors in both olfactory bulbectomized (OBX) and scopolamine-treated mice. Effects of ST101 administration were abolished by both intraperitoneal and intracerebroventricular pre-administration of the T-type VGCC inhibitor mibefradil. Acute administration of ST101 enhanced basal and nicotine-induced ACh release in the dorsal hippocampus in both OBX and sham-treated mice. Enhanced ACh release was abolished by infusion with mibefradil (10 μM) but not with the L-type VGCC inhibitor nifedipine (10 μM). As expected, significantly reduced CaMKIIα, PKCα, and ERK phosphorylation was restored by acute ST101 administration in the OBX mouse hippocampal CA1 region. Enhancement of CaMKIIα and PKCα but not ERK phosphorylation was inhibited by mibefradil (20 mg/kg, i.p.) pre-administration. Increased CaMKIIα and PKCα phosphorylation was confirmed by increased phosphorylation of GluR1, synapsin I, and NR1. Taken together, stimulation of T-type VGCCs is critical for the enhanced hippocampal ACh release and improved cognitive function seen following ST101 administration.

Chronic fluvoxamine treatment changes 5-HT2A/2C receptor-mediated behavior in olfactory bulbectomized mice

AimsOlfactory bulbectomy (OBX) in rodents represents a valuable experimental model of depression. This study was designed to shed further light on the impact of putative serotonergic neuronal degeneration in OBX mice and to assess the effect of a widely used antidepressant on serotonergic related behavioral changes induced by OBX. Main methodsAdult male ddY mice were subject to bilateral OBX or sham surgery. The serotonin (5-HT)2A/2C receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) enhanced a head-twitch response (HTR) in OBX mice. Effects of 5-HT2A, 5-HT2C antagonists and fluvoxamine were observed in OBX mice following DOI administration. Key findingsThe HTR elicited by the administration of DOI (0.5mg/kg and 1mg/kg, i.p.) was increased about twofold in OBX mice when compared with controls on the 14th day after the surgery. The injection of ketanserin (0.025mg/kg, i.p.), a 5-HT2A receptor antagonist, inhibited the enhancement of the DOI-induced HTR after OBX. Likewise, the administration of SB 242084 (1mg/kg, s.c.), a 5-HT2C receptor antagonist, also inhibited the DOI-induced HTR in OBX mice. Chronic but not acute treatment with the antidepressant fluvoxamine, a selective serotonin reuptake inhibitor (SSRI), suppressed the enhancement of DOI-induced HTR after OBX. SignificanceThese findings indicate that OBX, and the subsequent degeneration of neurons projecting from the olfactory bulb, caused a supersensitivity of 5-HT2A/2C receptors which may be involved in symptoms of depression.

Dynamics of endogenous Hsp70 synthesis in the brain of olfactory bulbectomized mice

Numerous epidemiological studies have established acute brain injury as one of the major risk factors for the Alzheimer's disease (AD). However, the lack of animal models of AD-like degeneration triggered by a defined injury hampered the development of adequate therapies. Here we report that the surgical damage of the olfactory bulbs triggers the development of several pathologies, including amyloid-β accumulation and strong decrease of neuron density in the cortex and hippocampus as well as significant disturbance of spatial memory. Characteristically, these harmful consequences of the olfactory bulbectomy (OBX) have a peculiar dynamics in time with maximal manifestation in periods of 1-1.5 months and 8 months after the surgery and, hence, exhibit biphasic pattern with almost complete recovery period taking place at 5-6 months after the operation. The quantitative determination of endogenous inducible form of Hsp70 in different brain areas of OBX mice demonstrated characteristic fluctuations of Hsp70 levels depending on the time after the operation and age of mice. Interestingly, maximal induction of Hsp70 synthesis in the hippocampus exhibits clear-cut coincidence with the recovery period in OBX animals. The observed correlation enables to suggest curing effect of Hsp70 synthesis at an earlier period of pathology development and establishes it as a possible therapeutic agent for secondary grave consequences of brain injury, such as AD-like degeneration, for which neuroprotective therapy is urgently needed.

P.2.017 Size does matter: environmental enrichment rescues cognitive and synaptic deficits following olfactory bulbectomy in mice

Environmental enrichment (EE) has been shown to improve cognitive performance and enhance synaptic plasticity in various neurodegenerative animal models. Antidepressant efficacy of environmental enrichment, however, remains unclear. To investigate the effect of EE on cognitive and depressive symptoms, and on structural plasticity, we used olfactory bulbectomy (OBX) in mice. OBX is primarily known as a model for predicting antidepressant activity, since its hyperactivity is normalized by chronic antidepressant administration; however, the ablation of olfactory bulbs in a rodent also results in progressive neurodegeneration, behavioral disturbances, and cognitive impairments − symptoms reminiscent of those of Alzheimer’s and depressed patients [1]. Four weeks after the bulbectomy, mice were exposed to EE, consisting of tunnel, toys and nesting material, for 4 weeks. The animals’ locomotor activity was observed, using the open-field paradigm and their cognitive ability was measured throughout the study using passive avoidance (assessing fear memory) and T-maze (assessing spatial memory). Compared to sham-operated controls, OBX mice showed significantly increased locomotor activity (F(3,20) = 4.38, p< 0.05), impaired shortand long-term fear memory in the passive avoidance test, and hindered spatial memory in the T-maze. EE-treated OBX mice demonstrated significantly increased fear (both short and long-term) ((H(4) = 14.11, p< 0.01 and (H(4) = 7.15, p< 0.05, respectively) and spatial memory when compared to the non-enriched bulbectomized mice (H(4) = 8.12, p< 0.05). There was no antidepressant effect of EE on the OBX mice. The brain weights of the EE-OBX mice were significantly larger in comparison to the standard housed bulbectomized mice (F(3,20) = 5.73, p< 0.05) and coincided with improved cognitive functioning. Furthermore, preliminary data demonstrated EE treatment reversed the bulbectomy-induced reduction in dendritic spine density in hippocampus (F(3,8) = 18.86, p< 0.01) without affecting the OBX-mediated decrease in the number of neurons. Thus, despite a substantial neuronal loss, EE induced a refinement of the synaptic network, which may underlie the improved cognitive functioning in the OBX mice following EE, suggesting that the beneficial effects of enrichment on memory stems mainly from enhanced synaptic plasticity rather than impediment of general brain atrophy. Interestingly, in rats, bulbectomy also results in a loss of dendritic spines in hippocampus [2], and although EE recovers the reduced hippocampal weights in the OBX rat, it is unable to alleviate OBX-induced cognitive deficits, yet it exerts antidepressant effects in rats [3]. The lack of EE efficacy on the OBX mediated cognitive impairments in the rat compared to the mouse, may be due to differences in the ability of these species to rewire their brain after severe neurodegeneration. Why EE induced antidepressant effect in the OBX rat but not in mice remains to be elucidated. In addition to possible implications for the development of novel therapeutic agents that enhance the beneficial effects of EE, our findings raise an important question of translational value in animal research: is the mouse or the rat a better animal model for human neurodegenerative disorders and for testing therapeutic interventions for their efficacy? It appears that, after all, size does matter both at the level of the animal strain, brain size and dendritic spines.

ChemInform Abstract: Neurochemical Mechanisms of a Novel Alzheimer′s Disease Therapeutics on Improvement of Cognition and Depressive Behavior

AbstractReview: 42 refs.

Sigma-1 receptor stimulation by dehydroepiandeosterone (DHEA) ameliorates the cognitive deficits via CaMKII, PKC and ERK activities in olfactory bulbectomized mice

Yokukansan (YKS) is a Japanese traditional herbal medicine and has been used for the treatment of the behavioral and psychological symptoms of dementia (BPSD). The present study aimed to clarify the effects of YKS on learning and memory impairments, and its mechanisms of action in olfactory bulbectomized (OBX) mice, one of the animal models of Alzheimer's disease (AD).OBX or sham-operated ddY mice were treated with YKS or donepezil (DPZ), a reference drug, and their cognitive performances were tested by the modified Y-maze test, novel object recognition test, and fear conditioning test to elucidate the spatial working memory, non-spatial short-term memory, and long-term memory, respectively. After completing the behavioral experiments, the expression level of cholinergic marker proteins and the activity of acetylcholinesterase (AChE) in the brain were analyzed by western blotting and Ellman's method, respectively.OBX caused spatial working memory and non-spatial working memory impairments that were reversed by YKS and also by DPZ; however, YKS failed to affect the long-term memory deficits. Amelioration of the spatial working memory by YKS was reversible by scopolamine, a muscarinic receptor antagonist. YKS treatment reversed OBX-induced down-regulation of choline acetyltransferase and muscarinic muscarinic M1 receptor expression without affecting muscarinic M3 receptor expression or AChE activity.These results demonstrate that YKS improves short-term memory deficit caused by OBX and that the effect is at least partly mediated by muscarinic receptor stimulation and the normalization of central cholinergic systems. The present findings also suggest that YKS has a therapeutic effect not only on BPSD, but also on memory impairment of AD.

Sigma-1 receptor stimulation by dehydroepiandrosterone ameliorates cognitive impairment through activation of CaM kinase II, protein kinase C and extracellular signal-regulated kinase in olfactory bulbectomized mice

Dehydroepiandrosterone (DHEA) is one of the most abundant neurosteroids synthesized de novo in the CNS. We here found that sigma-1 receptor stimulation by DHEA improves cognitive function through phosphorylation of synaptic proteins in olfactory bulbectomized (OBX) mouse hippocampus. We have previously reported that calcium/calmodulin-dependent protein kinase II (CaMKII), protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) were impaired in OBX mouse hippocampus. OBX mice were administered once a day for 7-8 days with DHEA (30 or 60 mg/kg p.o.) 10 days after operation. The spatial, cognitive and conditioned fear memories in OBX mice were significantly improved as assessed by Y-maze, novel object recognition and passive avoidance task, respectively. DHEA also improved impaired hippocampal long-term potentiation in OBX mice. Notably, DHEA treatment restored PKCα (Ser-657) autophosphorylation and NR1 (Ser-896) and myristoylated alanine-rich protein kinase C substrate (Ser-152/156) phosphorylation to the control levels in the hippocampal CA1 region. Likewise, DHEA treatment improved CaMKIIα (Thr-286) autophosphorylation and GluR1 (Ser-831) phosphorylation to the control levels in the CA1 region. Furthermore, DHEA treatment improved ERK and cAMP-responsive element-binding protein (Ser-133) phosphorylation to the control levels. Finally, NE-100, sigma-1 receptor antagonist, significantly inhibited the DHEA-induced improvement of memory-related behaviors and CaMKII, PKC and ERK phosphorylation in CA1 region. Taken together, sigma-1 receptor stimulation by DHEA ameliorates OBX-induced impairment in memory-related behaviors and long-term potentiation in the hippocampal CA1 region through activation of CaMKII, PKC and ERK.

Ameliorative effects of yokukansan on learning and memory deficits in olfactory bulbectomized mice

Yokukansan (YKS) is a Japanese traditional herbal medicine and has been used for the treatment of the behavioral and psychological symptoms of dementia (BPSD). The present study aimed to clarify the effects of YKS on learning and memory impairments, and its mechanisms of action in olfactory bulbectomized (OBX) mice, one of the animal models of Alzheimer's disease (AD). OBX or sham-operated ddY mice were treated with YKS or donepezil (DPZ), a reference drug, and their cognitive performances were tested by the modified Y-maze test, novel object recognition test, and fear conditioning test to elucidate the spatial working memory, non-spatial short-term memory, and long-term memory, respectively. After completing the behavioral experiments, the expression level of cholinergic marker proteins and the activity of acetylcholinesterase (AChE) in the brain were analyzed by western blotting and Ellman's method, respectively. OBX caused spatial working memory and non-spatial working memory impairments that were reversed by YKS and also by DPZ; however, YKS failed to affect the long-term memory deficits. Amelioration of the spatial working memory by YKS was reversible by scopolamine, a muscarinic receptor antagonist. YKS treatment reversed OBX-induced down-regulation of choline acetyltransferase and muscarinic muscarinic M₁ receptor expression without affecting muscarinic M₃ receptor expression or AChE activity. These results demonstrate that YKS improves short-term memory deficit caused by OBX and that the effect is at least partly mediated by muscarinic receptor stimulation and the normalization of central cholinergic systems. The present findings also suggest that YKS has a therapeutic effect not only on BPSD, but also on memory impairment of AD.

Neurochemical Mechanisms of a Novel Alzheimer's Disease Therapeutics on Improvement of Cognition and Depressive Behavior

Loss of cholinergic neurons and/or dysfunction of the glutamatergic system in the central nervous system cause learning impairment in experimental Alzheimer's (Alz) disease animals and Alz patients. Furthermore, the impaired cholinergic system is likely implicated in depressive behaviors in Alz patients. Neurogenesis persistently occurs in the forebrain subventricular zone (SVZ) and hippocampal subgranular zone (SGZ) in rodent and human brains. Notably, impaired neurogenesis in those regions is implicated not only in memory deficits but also in depressive behaviors. We have recently found that olfactory bulbectomized (OBX) mice reveal memory impairment and depressive behaviors. Using this attractive OBX mice model, we discovered a novel cognitive enhancer, spiro[imidazo[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446/ST101), that is a new azaindolizinone derivative without inhibitory action on acetylcholine esterase (AChE). Interestingly, ZSET1446 improved learning and memory by potentiating nicotine-induced ACh release in the hippocampus of amyloid-beta infused rats. In addition, ZSET1446 restored OBX-induced cognitive deficits in mice. Furthermore, chronic ZSET1446 administration significantly rescues decreased neuronal precursor cell proliferation seen in the dentate gyrus of OBX mice. Consistent with enhanced neurogenesis, chronic ZSET1446 administration improved depressive behavior assessed using the tail suspension test in OBX mice. Protein kinase B (Akt) and extracellular signal-regulated kinase pathways likely mediate ZSET1446-induced neurogenesis. These results suggest that ZSET1446 action via stimulation of the cholinergic system elicits improvement of the depression and cognitive impairment observed in Alz disease patients.

ChemInform Abstract: Donepezil‐Induced Neuroprotection of Acetylcholinergic Neurons in Olfactory Bulbectomized Mice

AbstractReview: 34 refs.

Influence of olfactory bulbectomy on maternal behavior and dopaminergic function in nucleus accumbens in mice

Olfactory bulbectomy (OBX) induces behavioral, physiological, and neurochemical alterations resembling clinical depression and is widely used as an animal model of depression. It has been reported that depression is a critical cause of child abuse and neglect and that maternal behavior involves dopaminergic neurons of the mesolimbic pathway. In a previous study we found that OBX mice show maternal behavior deficits which are improved by administration of apomorphine, a non-selective dopamine agonist. Therefore, in this study, we investigated the effect of l-3,4-dihydroxyphenylalanine ( l-DOPA) on maternal behavior deficits to examine the influence of pre-synaptic dopaminergic function in OBX mice. Furthermore, we measured tyrosine hydroxylase (TH) levels using microphotometry and quantified dopamine D1- and D2-like receptors using autoradiography in the nucleus accumbens (NAc). As a result, 25 mg/kg l-DOPA with 12.5 mg/kg benserazide improved disrupted maternal behavior in OBX mice and there are no changes in TH levels or number of D1- and D2-like receptors between sham and OBX mothers. The behavioral data support the hypothesis that changed dopaminergic function may contribute to maternal behavior deficits in OBX mice. However, our findings concerning dopaminergic function suggest that the deficits in OBX mice are not simply due to changes in TH levels or dopamine receptor number in the NAc.