A Cholecystokinin Analogue Ameliorates Cognitive Deficits and Regulates Mitochondrial Dynamics via the AMPK/Drp1 Pathway in APP/PS1 Mice

BACKGROUND

There are no drugs on the market that can reverse or slow Alzheimer's disease (AD) progression. A protease-resistant Cholecystokinin (CCK) analogue used in this study is based on the basic structure of CCK, which further increases the stability of the peptide fragment and prolongs its half-life in vivo. We observed a neuroprotective effect of CCK-8L in APPswe/PS1dE9 (APP/PS1) AD mice. However, its corresponding mechanisms still need to be elucidated.

OBJECTIVE

This study examined CCK-8L's neuroprotective effects in enhancing cognitive impairment by regulating mitochondrial dynamics through AMPK/Drp1 pathway in the APP/PS1 AD mice.

METHODS

Behavioural tests are applied to assess competence in cognitive functions. Transmission electron microscopy (TEM) was performed to observe the ultrastructure of mitochondria of hippocampal neurons, Immunofluorescent staining was employed to assay for Aβ1-42, APP, Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) and dynamin-related protein1 (Drp1). CRISPR/Cas9 was utilized for targeted knockout of the CCKB receptor (CCKBR) in the mouse APP/PS1 hippocampal CA1 region. A model of lentiviral vector-mediated overexpression of APP in N2a cells was constructed.

RESULTS

In vivo, experiments revealed that CCK analogue and liraglutide significantly alleviated cognitive deficits in APP/PS1 mice, reduced Aβ1-42 expression, and ameliorated l damage, which is associated with CCKBR activation in the hippocampal CA1 region of mice. In vitro tests showed that CCK inhibited mitochondrial fission and promoted fusion through AMPK/Drp1 pathway.

CONCLUSIONS

CCK analogue ameliorates cognitive deficits and regulates mitochondrial dynamics by activating the CCKB receptor and the AMPK/Drp1 pathway in AD mice.

Cultural determinants of the gap between self-estimated navigation ability and wayfinding performance: evidence from 46 countries

Cognitive abilities can vary widely. Some people excel in certain skills, others struggle. However, not all those who describe themselves as gifted are. One possible influence on self-estimates is the surrounding culture. Some cultures may amplify self-assurance and others cultivate humility. Past research has shown that people in different countries can be grouped into a set of consistent cultural clusters with similar values and tendencies, such as attitudes to masculinity or individualism. Here we explored whether such cultural dimensions might relate to the extent to which populations in 46 countries overestimate or underestimate their cognitive abilities in the domain of spatial navigation. Using the Sea Hero Quest navigation test and a large sample (N = 383,187) we found cultural clusters of countries tend to be similar in how they self-rate ability relative to their actual performance. Across the world population sampled, higher self-ratings were associated with better performance. However, at the national level, higher self-ratings as a nation were not associated with better performance as a nation. Germanic and Near East countries were found to be most overconfident in their abilities and Nordic countries to be most under-confident in their abilities. Gender stereotypes may play a role in mediating this pattern, with larger national positive attitudes to male stereotyped roles (Hofstede's masculinity dimension) associated with a greater overconfidence in performance at the national level. We also replicate, with higher precision than prior studies, evidence that older men tend to overestimate their navigation skill more than other groups. These findings give insight into how culture and demographics may impact self-estimates of our abilities.

The SUMOylation Pathway Restricts Gene Transduction by Adeno-Associated Viruses

Adeno-associated viruses are members of the genus dependoviruses of the parvoviridae family. AAV vectors are considered promising vectors for gene therapy and genetic vaccination as they can be easily produced, are highly stable and non-pathogenic. Nevertheless, transduction of cells in vitro and in vivo by AAV in the absence of a helper virus is comparatively inefficient requiring high multiplicity of infection. Several bottlenecks for AAV transduction have previously been described, including release from endosomes, nuclear transport and conversion of the single stranded DNA into a double stranded molecule. We hypothesized that the bottlenecks in AAV transduction are, in part, due to the presence of host cell restriction factors acting directly or indirectly on the AAV-mediated gene transduction. In order to identify such factors we performed a whole genome siRNA screen which identified a number of putative genes interfering with AAV gene transduction. A number of factors, yielding the highest scores, were identified as members of the SUMOylation pathway. We identified Ubc9, the E2 conjugating enzyme as well as Sae1 and Sae2, enzymes responsible for activating E1, as factors involved in restricting AAV. The restriction effect, mediated by these factors, was validated and reproduced independently. Our data indicate that SUMOylation targets entry of AAV capsids and not downstream processes of uncoating, including DNA single strand conversion or DNA damage signaling. We suggest that transiently targeting SUMOylation will enhance application of AAV in vitro and in vivo.

The incretin analogue D-Ala2GIP reduces plaque load, astrogliosis and oxidative stress in an APP/PS1 mouse model of Alzheimer's disease

Type 2 diabetes mellitus has been identified as a risk factor for Alzheimer's disease (AD). Insulin is a neuroprotective growth factor, and an impairment of insulin signalling has been found in AD brains. Glucose-dependent insulinotropic polypeptide (GIP), an incretin hormone, normalises insulin signalling and also acts as a neuroprotective growth factor. GIP plays an important role in memory formation, synaptic plasticity and cell proliferation. We have shown previously that the long-lasting incretin hormone analogue D-Ala(2)GIP protects memory formation and synaptic plasticity, reduces plaques, normalises the proliferation of stem cells, reduces the activation of microglia, and prevents the loss of synapses in the cortex of the APPswe/PS1deltaE9 mouse model of Alzheimer's disease. D-Ala(2)GIP was injected for 35 days at 25 nmol/kg i.p. once daily in APP/PS1 male mice and wild-type (WT) littermates aged 6, 12 and 19 months. In a follow-up study, we analysed plaque load, the activation of astrocytes as a means of chronic inflammation in the brain, and oxidative stress in the brains of these mice (8-oxoguanine levels). D-Ala(2)GIP reduced the amyloid plaque load in 12- and 19-month-old mice, and the inflammation response as shown in the reduction of activated astrocytes in 12- and 19-month old APP/PS1 mice. Chronic oxidative stress in the brain was reduced in 12- and 19-month-old mice as shown in the reduction of 8-oxoguanine levels in the cortex of D-Ala(2)GIP-injected APP/PS1 mice. The results demonstrate that D-Ala(2)GIP has neuroprotective properties on key markers found in Alzheimer's disease. This finding shows that novel GIP analogues have the potential to be developed as novel therapeutics for Alzheimer's disease.

The effect of mGlu8 deficiency in animal models of psychiatric diseases

The metabotropic glutamate receptor subtype 8 (mGlu(8)) is presynaptically located and regulates the release of the transmitter. Dysfunctions of this mechanism are involved in the pathophysiology of different psychiatric disorders. mGlu(8) deficient mice have been previously investigated in a range of studies, but the results are contradictory and there are still many open questions. Therefore, we tested mGlu(8)-deficient animals in different behavioral tasks that are commonly used in neuropsychiatric research. Our results show a robust contextual fear deficit in mGlu(8)-deficient mice. Furthermore, novel object recognition, chlordiazepoxide-facilitated extinction of operant conditioning and the acoustic startle response were attenuated by mGlu(8) deficiency. We found no changes in sensory processing, locomotor activity, prepulse inhibition, phencyclidine-induced changes in locomotion or prepulse inhibition, operant conditioning, conditioned fear to a discrete cue or in animal models of innate fear and post-traumatic stress disorder. We conclude that mGlu(8) might be a potential target for disorders with pathophysiological changes in brain areas where mGlu(8) modulates glutamate and gamma-amino butyric acid (GABA) transmission. Our data especially point to anxiety disorders involving exaggerated contextual fear, such as generalized anxiety disorders, and to conditions with disturbed declarative memory.

Rats are able to navigate in virtual environments

Virtual reality (VR) systems are useful tools that enable users to alter environmental settings and the location of landmarks in an accurate and fast way. Primates have been shown to be able to navigate in virtual environments. For rodents, however, all previous attempts to develop VR systems in which rats behave in the same way as in corresponding 3-D environments have failed. The question arises as to whether, in principle, rodents can be trained to navigate in a properly designed virtual environment (VE), or whether this peculiarity is limited to primates and humans. We built a virtual reality set-up that takes the wide-angle visual system of rats into account. We show for the first time that rats learn spatial tasks in this VE quite readily. This set-up opens up new opportunities for investigations of information processing in navigation (e.g. the importance of optic flow or vestibular input).

Effects of the isolation methodology on protein profiles of blood trypomastigotes of Trypanosoma cruzi

Blood trypomastigotes of Trypanosoma cruzi were isolated from infected athymic rnu/rnu rats and purified by an improved procedure of DEAE-Sephacel ion-exchange chromatography. Elution into a buffer supplemented with bovine serum albumin avoided column-induced changes on the surface of the parasites. Biotin-labelled bovine serum albumin, fluorescence microscopy, flow cytometry and Western blot analysis revealed a very intense binding of albumin to the parasite. Incubation and washing of cells without protein supplementation did not result in any damage or lysis of parasites but it did cause extensive shedding of cellular and surface proteins into the supernatant which could be prevented by using the protein-supplemented buffer. A decreasing yield of high molecular weight cellular proteins in relation to centrifugal force was a general phenomenon observed in scanning densitometry of SDS gels after isolation in either protein-supplemented buffer or protein-free buffer. The quantity of shed cellular components increased with increasing centrifugal force. In contrast, quantities of high molecular weight, biotin-labelled surface proteins increased with greater centrifugal force, indicating labelling of otherwise inaccessible residues. These data emphasize the importance of protein supplementation of buffers with proteins and of choosing low centrifugation forces (<400 g) during investigations of T. cruzi.

A protective and agonistic function of IL-12p40 in mycobacterial infection

IL-12p35(-/-)p40(-/-) mice are highly susceptible to Mycobacterium bovis bacillus Calmette-Guérin (BCG) or Mycobacterium tuberculosis infection. In this study IL-12p35(-/-) mice, which are able to produce endogenous IL-12p40, cleared M. bovis BCG and showed reduced susceptibility to pulmonary M. tuberculosis infection, which was in striking contrast to the outcome of mycobacterial infection in IL-12p35(-/-)p40(-/-) mice. Resistance in wild-type and IL-12p35(-/-) mice was accompanied by protective granuloma formation and Ag-specific delayed-type hypersensitivity responses, which were impaired in susceptible IL-12p35(-/- )p40(-/-) mice. Furthermore, IL-12p35(-/-) mice, but not IL-12p35(-/-)p40(-/-) mice, mounted Ag-specific Th1 and cytotoxic T cell responses. In vivo therapy with rIL-12p40 homodimer restored the impaired delayed-type hypersensitivity responses in M. bovis BCG-infected IL-12p35(-/-)p40(-/-) mice and reverted them to a more resistant phenotype. Together, these results show evidence for a protective and agonistic role of endogenous and exogenous IL-12p40 in mycobacterial infection, which is independent of IL-12p70.

IL-12-independent IFN-gamma production by T cells in experimental Chagas' disease is mediated by IL-18

IL-12p35-deficient (IL-12p35(-/-)) mice were highly susceptible to Trypanosoma cruzi infection and succumbed during acute infection, demonstrating the crucial importance of endogenous IL-12 in resistance to experimental Chagas' disease. Delayed immune responses were observed in mutant mice, although comparable IFN-gamma and TNF-alpha blood levels as in wild-type mice were detected 2 wk postinfection. In vivo and in vitro analysis demonstrated that T cells, but not NK cells, were recruited to infected organs. Analysis of mice double deficient in the recombinase-activating gene 2 (RAG2) and IL-12p35, as well as studies involving T cell depletion, identified CD4(+) T cells as the cellular source for IL-12-independent IFN-gamma production. IL-18 was induced in IL-12p35(-/-) mice and was responsible for IFN-gamma production, as demonstrated by in vivo IL-18 neutralization studies. In conclusion, evidence is presented for an IL-12-independent IFN-gamma production in experimental Chagas' disease that is T cell and IL-18 dependent.

Prion protein contains a second endoplasmic reticulum targeting signal sequence located at its C terminus

Prion protein (PrP) is synthesized at the membrane of the endoplasmic reticulum (ER) in three different topological forms as follows: a fully translocated one ((sec)PrP) and two with opposite orientations in the membrane ((Ntm)PrP and (Ctm)PrP). We asked whether other signal sequences exist in the PrP, other than the N-terminal signal sequence, that contribute to its topological diversity. In vitro translocation assays showed that PrP lacking its N-terminal signal sequence could still translocate into ER microsomes, although at reduced efficiency. Deletion of each of the two hydrophobic regions in PrP revealed that the C-terminally located hydrophobic region (TM2) can function as second signal sequence in PrP. Translocation mediated by the TM2 alone can occur post-translationally and yields mainly (Ctm)PrP, which is implicated in some forms of neurodegeneration in prion diseases. We conclude that, in vitro, PrP can insert into ER membranes co- and post-translationally and can use two different signal sequences. We propose that the unusually complex topology of PrP results from the differential utilization of two signal sequences in PrP.

Development of high numbers of blood trypomastigotes of Trypanosoma cruzi in nude rats

The development and pathogenicity of a Trypanosoma cruzi strain ("Chile 5") of low virulence were studied after infection of nude rats with different doses of blood trypomastigotes (10-10(7) parasites/rat). Peak parasitemias were correlated with the infection dose, which also influenced the mean survival times (26-36 days post-infection). Within 26 or 27 days, a subcutaneous injection of 10(7) blood trypomastigotes developed to about 8-20 x 10(7) parasites/ml.

Tumor necrosis factor alpha-mediated toxic shock in Trypanosoma cruzi-infected interleukin 10-deficient mice

Using interleukin-10 (IL-10)-deficient (IL-10(-/-)) mice, previous studies revealed a pathological immune response after infection with Trypanosoma cruzi that is associated with CD4(+) T cells and overproduction of proinflammatory cytokines. In this study we further investigate the pathology and potential mediators for the mortality in infected animals. T. cruzi-infected IL-10(-/-) mice showed reduced parasitemia accompanied by increased systemic release of gamma interferon (IFN-gamma), IL-12, and reactive nitrogen intermediates and overproduction of tumor necrosis factor alpha (TNF-alpha). Despite this early resistance, IL-10(-/-) mice died within the third week of infection, whereas all control mice survived acute infection. The clinical manifestation with weight loss, hypothermia, hypoglycemia, hyperkalemia, and increased liver-derived enzymes in the blood together with hepatic necrosis and intravascular coagulation in moribund mice indicated a toxic shock-like syndrome, possibly mediated by the systemic TNF-alpha overproduction. Indeed, high production of systemic TNF-alpha significantly correlated with mortality, and moribund mice died with critically high TNF-alpha concentrations in the blood. Consequent treatment with anti-TNF-alpha antiserum attenuated pathological changes in T. cruzi-infected IL-10(-/-) mice and significantly prolonged survival; the mice died during the fourth week postinfection, again with a striking correlation between regaining high systemic TNF-alpha concentrations and the time of death. Since elevated serum IL-12 and IFN-gamma concentrations were not affected by the administration of antiserum, these studies suggest that TNF-alpha is the direct mediator of this toxic shock syndrome. In conclusion, induction of endogenous IL-10 during experimentally induced Chagas' disease seems to be crucial for counterregulating an overshooting proinflammatory cytokine response resulting in TNF-alpha-mediated toxic shock.

Synaptic plasticity and learning and memory: LTP and beyond

Long-term potentiation (LTP) of synaptic activity is by far the most popular and widely researched model of synaptic plastic changes that might occur during learning. Numerous recent reports, however, have not found a correlation between the inducibility of LTP in the hippocampus and the ability of animals to learn hippocampus-dependent tasks. For example, some experiments with gene deletion (knockout) mice strains have shown that in some strains LTP is not inducible in the dentate gyrus, in area CA3, or CA1, but the animals are still able to learn spatial tasks. This apparent mismatch has rejuvenated the discussion concerning whether LTP is a good model for mechanisms that underlie memory formation in the nervous system. This review analyzes the conditions under which LTP is induced or learning takes place and suggests reasons for the mismatches that can occur and what we can learn from them. High-frequency stimulation protocols and in vitro assays cannot be seen to resemble natural firing patterns or conditions found in the brain. More physiological experimental conditions, especially in vivo recording in awake animals, could lead the way to the development of improved models of learning mechanisms that better correlate with learning abilities of animals.

Long term substitution and specific immune responses after transfer of bovine peripheral blood lymphocytes into severe combined immunodeficient mice

The long term immune responsiveness of bovine peripheral blood lymphocytes engrafted into severe combined immunodeficient mice (bovine PBL SCID mice) was analyzed. After intraperitoneal transfer (i.p.) of 2x10(7) bovine PBL into SCID mice, FACS analysis revealed successful engraftment of bovine CD4 and CD8+ T cells in the peritoneal cavity, the peripheral blood, spleen, lymph nodes, bone marrow, and thymus of reconstituted mice for up to 13 weeks. As shown by immunocytochemistry in sections of spleens from SCID mice 16 weeks after substitution, bovine T and B cells were localized perivasculary forming pseudofollicular structures. Nevertheless, histopathology of spleen and liver from bovine PBL SCID mice revealed pathological alterations indicating rejection of xenogenic cells or graft versus host disease (GVHD). On the functional level, i.p. transfer of bovine PBL into SCID mice induced increasing levels of bovine IgM and IgG in the sera of recipients. Bovine Ig could be detected up to 20 weeks. Immunization of SCID mice reconstituted with PBL of normal donors with dinitrophenol (DNP)-edestin induced a weak specific bovine antibody response in recipient mice. In contrast, a secondary specific bovine IgG response was observed after antigen restimulation of SCID mice reconstituted with PBL from calves preimmunized either with DNP-edestin or keyhole limpet hemocyanin (KLH) showing functional T cell-independent and -dependent antibody responses of bovine PBL SCID mice. Our data demonstrate that transfer of bovine PBL into SCID mice leads to a long term engraftment of bovine cells in lymphatic and non-lymphatic organs inducing a functional substitution of T and B cell immune response of SCID mice. Therefore, bovine PBL SCID chimera can serve as a small animal model for the analysis of bovine lymphopoiesis and infectious diseases of cattle.

Control of glycosylation of MHC class II-associated invariant chain by translocon-associated RAMP4

Protein translocation across the membrane of the endoplasmic reticulum (ER) proceeds through a proteinaceous translocation machinery, the translocon. To identify components that may regulate translocation by interacting with nascent polypeptides in the translocon, we used site-specific photo-crosslinking. We found that a region C-terminal of the two N-glycosylation sites of the MHC class II-associated invariant chain (Ii) interacts specifically with the ribosome-associated membrane protein 4 (RAMP4). RAMP4 is a small, tail-anchored protein of 66 amino acid residues that is homologous to the yeast YSY6 protein. YSY6 suppresses a secretion defect of a secY mutant in Escherichia coli. The interaction of RAMP4 with Ii occurred when nascent Ii chains reached a length of 170 amino acid residues and persisted until Ii chain completion, suggesting translocational pausing. Site-directed mutagenesis revealed that the region of Ii interacting with RAMP4 contains essential hydrophobic amino acid residues. Exchange of these residues for serines led to a reduced interaction with RAMP4 and inefficient N-glycosylation. We propose that RAMP4 controls modification of Ii and possibly also of other secretory and membrane proteins containing specific RAMP4-interacting sequences. Efficient or variable glycosylation of Ii may contribute to its capacity to modulate antigen presentation by MHC class II molecules.

Stress impairs performance in spatial water maze learning tasks

The water maze task has been developed to test spatial learning abilities in rats or mice, and is widely used. Though it has been reported before that numerous cognitive abilities are of importance for learning this task, poor performance is usually interpreted as an impairment of spatial memory formation. Previous investigations that tried to correlate long-term potentiation (LTP) of synaptic transmission with spatial learning abilities in rats reported that injection of drugs or specific gene deletions which blocked the expression of LTP correlated with learning impairments of spatial tasks in a water maze. Recent studies, however, have shown that pretraining enables these animals to learn such spatial tasks even though LTP was still found to be blocked. I investigated to what degree altered fear condition and stress perception could account for the impaired spatial learning when no pretraining is given. In a fear habituation task, unhandled rats preferred a dark over a well lit chamber more than handled animals did, but unhandled rats favoured the lit chamber more in an active avoidance task. They also performed poorly in a spatial water maze task compared with handled rats. Rats pretrained in a radial arm maze performed better in a water maze than non-pretrained rats. No difference between groups was found in a non-spatial water maze task. On the other hand, when pretrained in a water maze, rats performed only marginally better in a radial arm maze compared to non-pretrained animals. Since animals have to be handled to learn a radial arm maze, the difference in this task was not due to stress but most probably due to getting accustomed to the room dimensions prior to learning the spatial task. The results suggest that impaired learning of spatial tasks in the water maze can be due to increased stress and decreased fear conditioning without actually affecting spatial learning abilities. These results question the interpretations of the results of some previously published results of spatial water maze tasks.

Metabotropic glutamate receptor activation and blockade: their role in long-term potentiation, learning and neurotoxicity

Metabotropic glutamate receptors represent a fairly recent addition to the family of glutamate receptors. These receptors have the distinguishing feature of being coupled to G-proteins rather than ion channels and they appear to have a variety of functional characteristics. These receptors play a vital role, for example, in the induction and maintenance of long-term potentiation, the most popular current model of the biological correlates of learning and memory. Blockade of metabotropic glutamate receptors prevents long-term potentiation induction and learning in a variety of tasks in different species. Chronic metabotropic glutamate receptor activation is also associated with neurodegeneration and selective neuronal loss when agonists of these receptors are injected in high concentrations directly into the brain. Metabotropic glutamate receptors also play a role in the normal development of the nervous system and these sites within the central nervous system offer possible routes for drug therapies; selective receptor antagonists, for example, may prove to have the very desirable feature of endowing neuroprotection during ischaemic episodes whilst allowing normal excitatory neurotransmission to occur.

Nitric oxide is required for expression of LTP that is induced by stimulation phase-locked with theta rhythm

Long-term potentiation (LTP) can be induced by giving only one burst (five stimuli at 200 Hz) on the positive phase of sensory-induced theta rhythm in awake or anaesthetized rats, a stimulation protocol that mimics naturally occurring neuronal activity. Nitric oxide has been discussed as an important neuronal messenger in the induction of LTP. However, experiments testing inhibitors of nitric oxide synthase (NOS) in vitro produced contradictory results. The non-specific NOS inhibitor Nitro-L-arginine (L-NARG) impaired LTP induced by high-frequency stimulation (HFS) [from 155 +/- 7% to 122 +/- 8%), but completely blocked theta-dependent LTP induction (161 +/- 8% to 102 +/- 5%). NOS inhibitors, e.g. 7-nitro indazole (7-NI) or 1-(2-trifluoromethylphenyl) imidazole (TRIM) that are more selective for neuronal NOS and affect blood pressure less also impaired HFS-induced LTP (186 +/- 11% to 135 +/- 9% for TRIM) but completely blocked theta-dependent LTP (154 +/- 7 to 91 +/- 8). L-Arginine reversed the effects of the NOS inhibitors tested. Therefore, NO appears to be a modulator that is important for synaptic plasticity in this more physiological stimulation technique in vivo. NO is not released in slice preparations in sufficient quantities or at the right timing. Instead, the unphysiologically strong HFS protocol appears to induce an NO-independent type of LTP in some cases.

Possible causes of Alzheimer's disease: amyloid fragments, free radicals, and calcium homeostasis

Alzheimer's disease (AD) is a form of dementia in which patients develop neurodegeneration and complete loss of cognitive abilities and die prematurely. No treatment is known for this condition. Evidence points toward beta-amyloid as one of the main causes for cytotoxic processes. The cascade of biochemical events that lead to neuronal death appears to be interference with intracellular calcium homeostasis via activation of calcium channels, intracellular calcium stores, and subsequent production of free radicals by calcium-sensitive enzymes. The glutamatergic system seems to be implicated in mediating the toxic processes. Several strategies promise amelioration of neurodegenerative developments as judging from in vitro experiments. Glutamate receptor-selective drugs, antioxidants, inhibitors of nitric oxide synthase, calcium channel antagonists, receptor or enzyme inhibitors, and growth factors promise help. Especially combinations of drugs that act at different levels might prolong patients' health.

Beta-amyloid induced reduction in synaptic transmission is reversed by inhibitors of nitric oxide synthase

beta-Amyloid has been shown to be neurotoxic in vivo and in vitro. Free radical production and subsequent lipid oxidation after beta-amyloid application have been observed in vitro and are considered to be factors that contribute to the neurotoxicity. Field recordings in the area CA1 for 3 weeks showed a dose-dependent effect on amplitude after intracerebroventricular (i.c.v.) injections of 1, 5 or 10 nmol beta-amyloid (25-35). The nitric oxide synthase inhibitors 7-nitro indazole (30 mg/kg, i.p.) and 1-(2-trifluoromethylphenyl)imidazole (150 nmol, i.c.v.) which preferentially inhibit the neuronal isoform prevented this beta-amyloid-induced decay of synaptic transmission. The protective effect of these inhibitors was reversed by L-arginine (200 mg/kg, i.p.). The results support the theory that nitric oxide production contributes to beta-amyloid-induced neuronal degeneration or reduction of neurotransmission.

Defective nitric oxide effector functions lead to extreme susceptibility of Trypanosoma cruzi-infected mice deficient in gamma interferon receptor or inducible nitric oxide synthase

Trypanosoma cruzi, the causative agent of Chagas' disease, induces an innate and adaptive host immune response during the acute phase of infection. These responses were analyzed by comparing mouse lines deficient for the gamma interferon (IFN-gamma) receptor (IFN-gammaR(-/-)) or deficient for inducible nitric oxide synthase (iNOS(-/-)). Both lines were highly susceptible, with similar and dramatically increased parasite burdens and severe histopathology and were incapable of surviving even very low doses, exhibiting similar mortality kinetics. This pathophysiological correlation has a common cause, since both mutant mouse strains were unable to respond to infection by producing nitric oxide (NO) with the consequence that mutant macrophages had impaired trypanocidal activities. These in vivo and subsequent in vitro studies further demonstrated that an IFN-gamma-dependent pathway of iNOS induction is crucial for efficient NO production and mandatory for resisting acute infection with T. cruzi. Despite this defect, both mutant mouse strains had a rather normal proinflammatory cytokine response (interleukin-12 [IL-12], IFN-gamma, IL-6), with the exception of an impaired tumor necrosis factor alpha and IL-1alpha response in IFN-gammaR(-/-) mice, demonstrating that only the latter two cytokines are dependent on IFN-gamma activation. Moreover, polarization of T cells in type 1 and type 2 T-helper (Th1/Th2) and cytotoxic T (Tc1/Tc2) cells as well as T. cruzi-specific antibody responses were normal in IFN-gammaR(-/-) mice, demonstrating that IFN-gamma is not necessary for the promotion of T-cell differentiation and T. cruzi-specific antibody responses.

Overexpression of nonconvertible PrPc delta114-121 in scrapie-infected mouse neuroblastoma cells leads to trans-dominant inhibition of wild-type PrP(Sc) accumulation

One hallmark of prion diseases is the accumulation of the abnormal isoform PrP(Sc) of a normal cellular glycoprotein, PrPc, which is characterized by a high content of beta-sheet structures and by its partial resistance to proteinase K. It was hypothesized that the PrP region comprising amino acid residues 109 to 122 [PrP(109-122)], which spontaneously forms amyloid when it is synthesized as a peptide but which does not display significant secondary structure in the context of the full-length PrPc molecule, should play a role in promoting the conversion into PrP(Sc). By using persistently scrapie-infected mouse neuroblastoma (Sc+-MNB) cells as a model system for prion replication, we set out to design dominant-negative mutants of PrPc that are capable of blocking the conversion of endogenous, wild-type PrPc into PrP(Sc). We constructed a deletion mutant (PrPc delta114-121) lacking eight codons that span most of the highly amyloidogenic part, AGAAAAGA, of PrP(109-122). Transient transfections of mammalian expression vectors encoding either wild-type PrPc or PrPc delta114-121 into uninfected mouse neuroblastoma cells (Neuro2a) led to overexpression of the respective PrPc versions, which proved to be correctly localized on the extracellular face of the plasma membrane. Transfection of Sc+-MNB cells revealed that PrPc delta114-121 was not a substrate for conversion into a proteinase K-resistant isoform. Furthermore, its presence led to a significant reduction in the steady-state levels of PrP(Sc) derived from endogenous PrPc. Thus, we showed that the presence of amino acids 114 to 121 of mouse PrPc plays an important role in the conversion process of PrPc into PrP(Sc) and that a deletion mutant lacking these codons indeed behaves as a dominant-negative mutant with respect to PrP(Sc) accumulation. This mechanism could form a basis for a new gene therapy and/or a prevention concept for prion diseases.

Block of theta-burst-induced long-term potentiation by (1S,3S)-1-aminocyclopentane-1,3-dicarboxylic acid: further evidence against long-term potentiation as a model for learning

It has been previously reported that block of high-frequency stimulation-induced long-term potentiation of synaptic transmission in the hippocampus does not necessarily lead to impairment of spatial learning. Here we show that (1S,3S)-1-aminocyclopentane-1,3-dicarboxylic acid, an agonist at group II metabotropic glutamate receptors, completely blocked long-term potentiation induced by a theta-burst type of stimulation protocol (five pulses at 75 Hz per train, 200 ms inter-train interval) in the CA1 region in vivo. The drug did not significantly affect synaptic responses during each train whereas inter-train facilitation of excitatory postsynaptic potentials was slightly reduced. It also produced a large reduction in paired-pulse facilitation (50 ms inter-stimulus interval), possibly indicating that an increase in inhibition might be involved in the block of long-term potentiation. The drug dose used (5 microliters of a 10 mM solution i.c.v.) was half the dose which inhibited high-frequency stimulation-induced long-term potentiation in earlier experiments but which did not prevent learning of spatial tasks. We conclude that long-term potentiation induced by a more physiological stimulation protocol which uses theta-like inter-train intervals does not appear to accurately model the synaptic changes which are believed to occur during learning either.

Stimulation on the positive phase of hippocampal theta rhythm induces long-term potentiation that can Be depotentiated by stimulation on the negative phase in area CA1 in vivo

Long-term potentiation (LTP) of synaptic transmission induced by high-frequency stimulation (HFS) is considered to be a model for learning processes; however, standard HFS protocols consisting of long trains of HFS are very different from the patterns of spike firing in freely behaving animals. We have investigated the ability of brief bursts of HFS triggered at different phases of background theta rhythm to mimic more natural activity patterns. We show that a single burst of five pulses at 200 Hz given on the positive phase of tail pinch-triggered theta rhythm reliably induced LTP in the stratum radiatum of the hippocampus of urethane-anesthetized rats. Three of these bursts saturated LTP, and 10 bursts occluded the induction of LTP by long trains of HFS. Burst stimulation on the negative phase or at zero phase of theta did not induce LTP or long-term depression. In addition, stimulation with 10 bursts on the negative phase of theta reversed previously established LTP. The results show that the phase of sensory-evoked theta rhythm powerfully regulates the ability of brief HFS bursts to elicit either LTP or depotentiation of synaptic transmission. Furthermore, because complex spike activity of approximately five pulses on the positive phase of theta rhythm can be observed in freely moving rats, LTP induced by the present theta-triggered stimulation protocol might model putative synaptic plastic changes during learning more closely than standard HFS-induced LTP.

Nitric oxide, the enigmatic neuronal messenger: its role in synaptic plasticity

The discovery of the intercellular messenger nitric oxide (NO) stimulated new concepts of how synaptic plasticity could be induced in the nervous system. While initial reports found evidence that NO is of importance for the formation of long-term potentiation of synaptic transmission (LTP) and spatial learning in rats, later reports failed to confirm these results. Novel approaches such as deletion of the gene that encodes NO synthase in mice showed that the neuronal and the endothelial isoforms are expressed in neurones. Deletion of both isoforms reduced the inducibility of LTP. Furthermore, novel selective inhibitors of NO synthase impaired spatial learning. These results support the hypothesis that NO plays an important role in synaptic transmission and explain some but not all previously contradictory results.

Spontaneous imitation of fundamental frequency and speech rate by nonstutterers and stutterers

Speech can be described either in terms of acoustics, as a perceptual outcome, or as a motor event. Central to theories of speech perception and production is an attempt to describe how these aspects of speech are interrelated. The present experiment investigated how the nonstutterers' and stutterers' reproductions of acoustically presented interrogative sentences were influenced by experimental variations of intonation (sentence initial vs. sentence final) and speech rate (normal vs. time compressed). We studied the effects of these stimulus manipulations on the speech rate and fundamental frequency (F0) of 10 adult German-speaking nonstutterers and seven stutterers. Experimental manipulations of intonation and speech rate significantly influenced the syllable duration and speech rate of both normal speakers and stutterers. The fundamental frequency of the subjects' responses were also significantly influenced by the intonation of the stimulus. But the stutterers' increase in F0 for stressed syllables was generally less pronounced than that of nonstutterers. These results imply that (a) the subject not only extract linguistic meaning from intonation but that they also store extragrammatical speech rate information, and (b) the speakers adopt these speech rate variations for their own productions. Generally, these results demonstrate that speech perception is not limited to extracting linguistically invariant information. The results show that speakers actively generate their own prosody and that this generative process is influenced by the prosodic structure of another speaker's antecedent speech. The implications of these results for theories of speech production are discussed.

Activation of group-II metabotropic glutamate receptors blocks induction of long-term potentiation and depotentiation in area CA1 of the rat in vivo

The metabotropic glutamate receptor group-II agonist (1S,3S)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3S-ACPD; 5 microliters/10 mM, i.c.v.) prevented the induction of long-term potentiation and depotentiation in the CA1 area of the hippocampus in urethane-anaesthetised rats. These effects were prevented by the group-II metabotropic glutamate receptor antagonists alpha-methyl-(2S,3S,4S)-alpha-(carboxycyclopropyl)glycine (MCCG; 5 microliters/100 mM) and (RS)-alpha-methyl-4-tetrazolylphenylglycine (MTPG; 5 microliters/500 mM). The group-I antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA; 5 microliters/200 mM) or the group-III antagonist alpha-methyl-L-2-amino-4-phosphonobutyrate (MAP4; 5 microliters/100 mM) did not affect the block of the induction of long-term potentiation by 1S,3S-ACPD. It is concluded that activation of group-II metabotropic glutamate receptors can block both high-frequency stimulation-induced long term potentiation and low-frequency stimulation-induced depotentiation in the CA1 area in vivo.

HFS-induced long-term potentiation and LFS-induced depotentiation in area CA1 of the hippocampus are not good models for learning

Spatial learning in rats has been shown to be dependent on the intact hippocampus and lesioning this region impairs learning performance. Long-term potentiation (LTP) and depotentiation (DP) of synaptic transmission have been suggested to model memory formation at the neuronal level. Recently it was shown that LTP in the dentate gyrus or area CA3 of the hippocampus is not essential for the ability to learn a spatial water maze task. Here we show that the metabotropic glutamate receptor agonist (1S,3S)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3S-ACPD), which acts predominantly at presynaptic sites, only marginally impaired spatial learning in a water maze or radial arm maze (three out of eight arms baited) when injected ICV (5 microliters of a 20 mM solution). There also were small impairments in non-spatial and visual discrimination tasks, indicating that the small learning impairments were due to nonselective effects of the drug. The same dose depressed field EPSPs and completely blocked LTP induced by high-frequency stimulation (HFS, 200 Hz) in the CA1 region of the rat hippocampus in vivo. A lower (5 microliters of a 10 mM solution) dose did not depress baseline but still blocked LTP. Injecting the same dose after induction of LTP blocked DP induced by low-frequency stimulation (LFS, 10 Hz). These results indicate that neither HFS-induced LTP nor LFS-induced DP in area CA1 are good models for the induction of synaptic changes that might underlie spatial learning in the rat.

Block of HFS-induced LTP in the dentate gyrus by 1S,3S-ACPD: further evidence against LTP as a model for learning

We have previously shown that block of high-frequency stimulation (HFS) induced long-term potentiation (LTP) of synaptic transmission in area CA1 by (1S,3S)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3S-ACPD; 5 microliters of a 20 mM solution), an agonist at group II metabotropic glutamate receptors, did not prevent animals from learning a spatial task. Here we show that the same dose of 1S,3S-ACPD also blocked the induction of HFS-induced LTP of the slope of the excitatory postsynaptic potential and of the amplitude of the population spike in the dentate gyrus. We conclude that HFS-induced LTP in the dentate gyrus is not a good model for memory formation.

Long-term potentiation: a good model for learning and memory?

1. Long-term potentiation (LTP), long-term depression (LTD), and depotentiation of synaptic activity have been suggested to model synaptic plastic changes that occur during learning. Recent reports however show that neither LTP induced by high frequency stimulation (HFS) in the dentate, CA3, or CA1, nor depotentiation in area CA1 of the hippocampus, are reliable models of the learning abilities of rats or mice. LTD cannot reliably be obtained in the hippocampus in vivo and might be an artefact caused by altered inhibitory transmission. 2. Experiments with gene deletion ('knock out') mice strains show that mice that do not express HFS-induced LTP in the dentate are able to learn spatial tasks. 3. Studies of the effect of NMDA receptor blockers also showed that HFS-induced LTP in the dentate is not a model for processes that occur during learning. Studies using drugs that act on metabotropic glutamate receptors showed that HFS-induced LTP or depotentiation of LTP in area CA1 are not models for learning mechanisms either. 4. Neither in vivo recording of naturally-occurring LTP in the dentate nor synaptic saturation experiments in the hippocampus was able to support the theory that LTP occurs during learning. 5. While in vitro experiments are essential tools to investigate cellular and subcellular mechanisms that underlay synaptic transmission, measurements of LTP, LTD, or DP are not reliable models for learning processes and cannot replace experiments with intact animals that learn spatial tasks.

L-AP4 (L-(+)-2-amino-4-phosphonobutyric acid) induced impairment of spatial learning in the rat is antagonized by MAP4 ((S)-2-amino-2-methyl-4-phosphonobutanoic acid)

L-AP4, an agonist at the metabotrophic glutamate receptors 4, 6, 7, 8 and 9 produced a selective spatial learning impairment in a water maze as well as in an 8-arm maze task when injected i.c.v. (5 microliters of a 80 mM solution), a dose previously reported to block consolidation of long-term potentiation in vivo. Acquisition and recall of the spatial water-maze task, as measured by escape latency and quadrant bias, respectively, were impaired, whereas swim speed was not affected. In contrast, ability to perform a non-spatial control task was not impaired; latency to reach a visible escape platform was not delayed in L-AP4-treated animals. No behavioral difference was visible in the open field. MAP4, an antagonist of mGluRs mediating L-AP4 induced reduction of transmitter release, when administered pretraining i.c.v. (5 microliters of an 80 mM solution) did not affect motor activity in the open field test but did impair learning of both spatial tasks. In addition, swim speed was increased. However, injecting L-AP4 and MAP4 in combination at equimolar concentrations had no effect on learning in both spatial tasks or on swim speed in the water maze. Neither latency in the visible-platform test nor behavior in the open field was affected. We conclude that L-AP4 sensitive metabotropic glutamate receptors play a selective role in learning and memory formation of the rat.

7-Nitro indazole, a selective neuronal nitric oxide synthase inhibitor in vivo, impairs spatial learning in the rat

Nitric oxide (NO) is an intercellular messenger that has been suggested to have a role in learning and memory formation. Previous studies with nonselective NO synthase inhibitors have produced contradictory results in learning experiments. However, these drugs also produced blood pressure changes, as NO is an endothelial-derived relaxing factor. A novel NO synthase inhibitor, 7-nitro indazole (7-NI), as a dose (30 mg/kg i.p.) shown previously to inhibit neuronal NO synthase by 85% without affecting blood pressure, produced amnesic effects both in a water maze and in an 8-arm radial maze. Latency as well as distance was greater in the 7-NI group in the water maze while swim speed was not affected. Latency, working memory (WM), and reference memory (RF) errors were also higher in the 7-NI group in the 8-arm maze. At the end of the second training day, these differences were no longer apparent. However, on the fourth training day, a transfer test in the water maze showed that 7-NI had produced a spatial memory deficit, reducing quadrant bias and the number of annulus crossings. Learning of a visual cue task was not affected. No difference between groups was visible in an open field test. We conclude that neuronal NO synthase activity plays a role in learning and memory formation in the rat.

The selective neuronal NO synthase inhibitor 7-nitro-indazole blocks both long-term potentiation and depotentiation of field EPSPs in rat hippocampal CA1 in vivo

The membrane-permeant gas NO is a putative intercellular messenger that has been proposed on the basis of previous in vitro studies to be involved in synaptic plasticity, especially the induction of long-term potentiation (LTP) of excitatory synaptic transmission in the hippocampus and cortex. In the present study, the role of NO in synaptic plasticity has been investigated in vivo. In particular, the action of the novel and selective neuronal NO synthase (nNOS) inhibitor 7-nitro-indazole (7-NI) has been investigated on the induction of LTP and depotentiation (DP) of field EPSPs in CA1 of the hippocampus in vivo. Unlike previously studied nonselective NOS inhibitors, 7-NI does not increase arterial blood pressure. In vehicle-injected rats, high-frequency stimulation consisting of a series of trains at 200 Hz induced LTP. However, LTP induction was strongly inhibited in 7-NI (30 mg/kg, i.p.)-treated animals. The inhibitory effect of 7-NI on the induction of LTP was prevented by pretreatment with L-arginine, the substrate amino acid used by NOS. In control animals, low-frequency stimulation consisting of 900 stimuli at 10 Hz induced DP of previously established LTP, whereas in 7-HI-treated animals only a short-term depression was induced. This effect of 7-NI also was prevented by D-arginine. The LTP and DP induced in control animals in this study were NMDA receptor-dependent, the NMDA receptor antagonist 3-(R,S)-2-carboxypiperazin-4-yl-propyl-1- phosphonic acid inhibiting the induction of both forms of synaptic plasticity. The present experiments are the first to demonstrate that an NOS inhibitor blocks the induction of the synaptic component of LTP and DP in vivo and, therefore, these results strengthen evidence that the production of NO is necessary for the induction of LTP and DP.

Prostaglandins play a role in memory consolidation in the chick

Previous studies showed that inhibitors of cyclooxygenases have amnesic effects in chicks in a passive avoidance task. The onset of amnesia has a delay of 2 h post-training. To investigate if this effect is due to the inhibition of induction of the enzyme during learning, the release of cyclooxygenase products into the extracellular fluid was measured at 1, 2 and 3 h post-training. A cyclooxygenase inhibitor, ibuprofen, inhibited the training-dependent increase of cyclooxygenase products only 2 h and 3 h after learning when injected pre-training, as did dexamethasone which prevents cyclooxygenase induction, and SC58125 (1,2-diarylcyclopentene), an inhibitor of inducible cyclooxygenase. Injections 30 min post-training showed the same effect with the exception of dexamethasone. Injecting SC58125, ibuprofen, indomethacin, or dexamethasone i.c. before training showed amnesic effects for training on a one-trial passive avoidance task at 2 h but not 1 h after training. Injections 30 min post-training produced the same effects with the exception of dexamethasone. I conclude that cyclooxygenases are induced during training and that cyclooxygenase products are of importance in memory formation of the chick.

High-level expression of adeno-associated virus (AAV) Rep78 or Rep68 protein is sufficient for infectious-particle formation by a rep-negative AAV mutant

Adeno-associated virus (AAV) codes for four closely related nonstructural proteins (Rep) required for AAV DNA replication and gene regulation. In vitro studies have revealed that either Rep78 or Rep68 alone is sufficient for AAV DNA replication. Rep52 and Rep40 are not required for DNA replication but have been reported to enhance the efficiency of accumulation of single-stranded progeny DNA. Previous studies on rep-expressing cell lines had indicated that only a subset of the four Rep proteins are required for the production of infectious AAV. We therefore set out to determine the minimal set of Rep proteins sufficient for the generation of infectious AAV. Transient cotransfections in HeLa cells of constructs for high-level expression of individual Rep proteins with a rep-negative AAV genome revealed that either Rep78 or Rep68 alone could complement for a full replication cycle yielding infectious virus. This result was confirmed by transfection studies in the cell line HeM2, which selectively expresses Rep78 at rather low levels under the control of the glucocorticoid-responsive mouse mammary tumor virus long terminal repeat (C. Hölscher, M. Hörer, J. A. Kleinschmidt, H. Zentgraf, A. Bürkle, and R. Heilbronn, J. Virol. 68:7169-7177, 1994). Increasing the level of Rep78 expression by transfection of a glucocorticoid receptor expression construct resulted in a higher level of DNA replication of a cotransfected rep-negative AAV genome and in the production of infectious rep-negative AAV particles. We further report on the generation of a new rep-expressing cell line, HeCM1, which was obtained by stable supertransfection of a construct for constitutive Rep40 expression into HeM1 cells (Hölscher et al., J. Virol. 68:7169-7177). Transfection of rather large amounts of rep-negative AAV DNA led to detectable virus production in HeCM1 cells even in the absence of the cotransfected glucocorticoid receptor expression construct, but higher yields were obtained after increasing the Rep78 level by coexpression of the glucocorticoid receptor. These data demonstrate that all Rep functions required for the productive replication of AAV in HeLa cells are contained within both Rep78 and Rep68.

Inhibitors of cyclooxygenases produce amnesia for a passive avoidance task in the chick

Arachidonic acid is a putative messenger in synaptic transmission which presumably plays a role in learning and memory. Previous experiments showed that inhibitors of phospholipase A2-dependent release of arachidonic acid cause amnesia in a one-trial passive avoidance task in the chick. To test if arachidonic acid is metabolized to other messengers, the effects of inhibitors of enzymes which metabolize arachidonic acid were tested in the same task. The cyclooxygenase inhibitors indomethacin, naproxen and ibuprofen caused amnestic effects at all concentrations tested when injected intracerebrally before training. Injections were 5 microliters of 5-20 mmolar solutions per hemisphere. The onset of amnestic effects was always 2 h after training, independently of drug type, concentration, and injection time before training. The delay of 2 h after training suggests that the drugs prevent induction of cyclooxygenase synthesis. Post-training injections had no effect. Control tests showed little effect of the drugs on motor control and motivation. Caffeic acid and esculetin, inhibitors of lipoxygenases, and sodium furegrelate, a thromboxane synthase inhibitor, had no effect on performance of chicks in the task at all concentrations or time points tested. The results indicate that cyclooxygenase products, but not lipoxygenase or thromboxane synthase products, play a role in memory consolidation in the chick when learning this task.

Inhibitors of PLA2 and NO synthase cooperate in producing amnesia of a spatial task

Both nitric oxide and arachidonic acid have been suggested to play a role as a retrograde messenger in synaptic plastic changes which underlie memory formation. However, inhibitors of nitric oxide (NO) synthesis or of arachidonic acid release have produced contradictory results. We suggest a model which involves simultaneous release of both messenger types which can compensate for the loss of one type. To test this theory, rats were injected either with a drug that inhibits release of arachidonic acid, or a drug that inhibits synthesis of NO, or with both drugs. Acquisition of a water maze task was not different between groups. In the test sessions, however, animals injected with both drugs showed marked amnesic symptoms, while the groups injected with a low dose of nordihydroguaiaretic acid (NDGA) or with nitro-L-arginine (L-NARG) showed a trend towards amnesia. The effect of both drugs appears to be additive. The results support the proposed theory.

Quinacrine acts like an acetylcholine receptor antagonist rather than like a phospholipase A2 inhibitor in a passive avoidance task in the chick

Quinacrine (QU) is an inhibitor of phospholipase A2 (PLA2). However, QU has antagonistic properties at the acetylcholine receptor as well. To investigate if PLA2 activity is of importance in memory formation, QU was tested in a passive avoidance task in the chick. Injecting QU pretraining caused amnestic effects 45 min post-training. When comparing this result with results obtained with other PLA2 inhibitors, it became apparent that QU is not acting primarily as an inhibitor of PLA2. Scopolamine, an acetylcholine receptor antagonist, was tested and produced the same onset of amnesia as QU. I conclude that QU is acting functionally as an antagonist of acetylcholine receptors rather than of PLA2.

7-Nitro indazole, a neuron-specific nitric oxide synthase inhibitor, produces amnesia in the chick

7-Nitro indazole (7-NI), which is selective for the neuronal isoform of nitric oxide synthase (NOS), was tested in a passive avoidance task in the chick. Injection of 50 mg/kg i.p. pretraining had amnesic effects for the task when tested 30 min, 2 or 24 hr after training. Injections post-training had no effect. Because 7-NI does not inhibit the endothelial isoform of NOS, it does not affect blood vessel relaxation, as nonspecific inhibitors do. This effect on blood vessels could explain the amnestic effects produced by nonspecific NOS inhibitors. The results support the theory that NO is a neuronal transmitter that is important in processes of synaptic plasticity and learning.