Impaired cognition, sensorimotor gating, and hippocampal long-term depression in mice lacking the prostaglandin E2 EP2 receptor.

Cyclooxygenase-2 (COX-2) is a neuronal immediate early gene that is regulated by N-methyl d aspartate (NMDA) receptor activity. COX-2 enzymatic activity catalyzes the first committed step in prostaglandin synthesis. Recent studies demonstrate an emerging role for the downstream PGE(2) EP2 receptor in diverse models of activity-dependent synaptic plasticity and a significant function in models of neurological disease including cerebral ischemia, Familial Alzheimer's disease, and Familial amyotrophic lateral sclerosis. Little is known, however, about the normal function of the EP2 receptor in behavior and cognition. Here we report that deletion of the EP2 receptor leads to significant cognitive deficits in standard tests of fear and social memory. EP2-/- mice also demonstrated impaired prepulse inhibition (PPI) and heightened anxiety, but normal startle reactivity, exploratory behavior, and spatial reference memory. This complex behavioral phenotype of EP2-/- mice was associated with a deficit in long-term depression (LTD) in hippocampus. Our findings suggest that PGE(2) signaling via the EP2 receptors plays an important role in cognitive and emotional behaviors that recapitulate some aspects of human psychopathology related to schizophrenia.

Alteration of BACE1-dependent NRG1/ErbB4 signaling and schizophrenia-like phenotypes in BACE1-null mice.

beta-Site APP-cleaving enzyme 1 (BACE1) is required for the penultimate cleavage of the amyloid-beta precursor protein (APP) leading to the generation of amyloid-beta peptides that is central to the pathogenesis of Alzheimer's disease. In addition to its role in endoproteolysis of APP, BACE1 participates in the proteolytic processing of neuregulin 1 (NRG1) and influences the myelination of central and peripheral axons. Although NRG1 has been genetically linked to schizophrenia and NRG1(+/-) mice exhibit a number of schizophrenia-like behavioral traits, it is not known whether altered BACE1-dependent NRG1 signaling can cause similar behavioral abnormalities. To test this hypothesis, we analyze the behaviors considered to be rodent analogs of clinical features of schizophrenia in BACE1(-/-) mice with impaired processing of NRG1. We demonstrate that BACE1(-/-) mice exhibit deficits in prepulse inhibition, novelty-induced hyperactivity, hypersensitivity to a glutamatergic psychostimulant (MK-801), cognitive impairments, and deficits in social recognition. Importantly, some of these manifestations were responsive to treatment with clozapine, an atypical antipsychotic drug. Moreover, although the total amount of ErbB4, a receptor for NRG1 was not changed, binding of ErbB4 with postsynaptic density protein 95 (PSD95) was significantly reduced in the brains of BACE1(-/-) mice. Consistent with the role of ErbB4 in spine morphology and synaptic function, BACE1(-/-) mice displayed reduced spine density in hippocampal pyramidal neurons. Collectively, our findings suggest that alterations in BACE1-dependent NRG1/ErbB4 signaling may participate in the pathogenesis of schizophrenia and related psychiatric disorders.

Cycloxygenase-2 activity promotes cognitive deficits but not increased amyloid burden in a model of Alzheimer's disease in a sex-dimorphic pattern.

Administration of non-steroidal anti-inflammatory agents reduces the risk of developing Alzheimer's disease in normal aging populations, an effect that may occur from inhibition of the cyclooxygenases, the rate-limiting enzymes in the formation of prostaglandins. In this study, we investigated whether increased activity of cyclooxygenase-2 (COX-2), the inducible isoform of cyclooxygenase, potentiates disease progression in a transgenic mouse model of Alzheimer's disease. To study the functional effects of COX-2 activity, male and female bigenic mice (amyloid precursor protein with Swedish mutation [APPswe]-presenilin-1 protein with deletion of exon 9 [PS1dE9] and trigenic COX-2/APPswe-PS1dE9) were behaviorally tested +/-administration of the selective COX-2 inhibitor celecoxib. Behavioral testing included a three-trial Y maze that measures spatial working and recognition memories and an open field task that tested levels of hyperactivity. Overexpression of COX-2 in APPswe-PS1dE9 mice resulted in specific deficits in spatial working memory in female but not male mice. These sex-specific deficits were abolished by pharmacological inhibition of COX-2 activity. Importantly, COX-2-associated deficits were dependent on co-expression of all three transgenes since COX-2 single transgenic and APPswe-PS1dE9 bigenic mice showed normal memory. Quantification of amyloid plaque load and total Abeta 40 and 42 peptides did not reveal significant differences in trigenic versus bigenic mice treated with either vehicle or celecoxib. Taken together, these data indicate an interaction between the effects of COX-2 and Abeta peptides on cognition that occurs in a sex-specific manner in the absence of significant changes in amyloid burden. These findings suggest that pathological activation of COX-2 may potentiate the toxicity of Abeta peptides, particularly in females, without significantly affecting Abeta accumulation.

The cognitive effects of ovariectomy and estrogen replacement are modulated by aging.

Recent experimental and clinical studies suggest that estrogen may be an important factor influencing neuronal function during normal and pathological aging. Using different behavioral paradigms in rodents, estrogen replacement was shown to enhance learning and memory as well as attenuate learning deficits associated with cholinergic impairment. The goal of this study was to determine whether cognitive sensitivity to estrogen manipulations (short-term ovariectomy and chronic estrogen replacement) is affected by aging. Middle-aged and old female Fischer-344 rats were used to estimate the effects of estrogen manipulations at two different stages of reproductive aging. At middle age, when the females underwent an initial stage of reproductive aging (irregular cyclicity), ovariectomy did not significantly affect the acquisition of the T-maze active avoidance as compared with Sham rats, while estrogen replacement decreased behavioral vulnerability to scopolamine. However, when tested at more advanced stage of aging (consistent diestrus), old ovariectomized rats were more sensitive to scopolamine as compared with the control rats. Moreover, estrogen treatment at this age did not produce any protective effect against scopolamine. Contrasting findings of the effects of estrogen replacement in middle-aged and old rats suggest that the ability of estrogen to enhance the basal forebrain cholinergic function declines with age. These data indicate that aging processes may substantially modulate the mechanisms of estrogen action. A "time window" during which hormone replacement must be initiated in order to be effective could be determined in terms of the stages of reproductive senescence. This study is the first to clearly demonstrate that the cognitive effects of estrogen replacement are still preserved during the initial stages of reproductive aging (irregular cyclicity) and dramatically limited as aging progresses (cessation of proestrus).

Age-dependent cognitive deficits and neuronal apoptosis in cyclooxygenase-2 transgenic mice.

The cyclooxygenases catalyze the rate-limiting step in the formation of prostaglandins from arachidonic acid and are the pharmacological targets of (NSAIDs). In brain, cyclooxygenase-2 (COX-2), the inducible isoform of cyclooxygenase, is selectively expressed in neurons of the cerebral cortex, hippocampus, and amygdala. As an immediate-early gene, COX-2 is dramatically and transiently induced in these neurons in response to NMDA receptor activation. In models of acute excitotoxic neuronal injury, elevated and sustained levels of COX-2 have been shown to promote neuronal apoptosis, indicating that upregulated COX-2 activity is injurious to neurons. COX-2 may also contribute to the development of Alzheimer's disease, for which early administration of NSAIDs is protective against development of the disease. To test the effect of constitutively elevated neuronal COX-2, transgenic mice were generated that overexpressed COX-2 in neurons and produced elevated levels of prostaglandins in brain. In cross-sectional behavioral studies, COX-2 transgenic mice developed an age-dependent deficit in spatial memory at 12 and 20 months but not at 7 months and a deficit in aversive behavior at 20 months of age. These behavioral changes were associated with a parallel age-dependent increase in neuronal apoptosis occurring at 14 and 22 months but not at 8 months of age and astrocytic activation at 24 months of age. These findings suggest that neuronal COX-2 may contribute to the pathophysiology of age-related diseases such as Alzheimer's disease by promoting memory dysfunction, neuronal apoptosis, and astrocytic activation in an age-dependent manner.

Escape from shock versus escape from shock accompanied by a visual stimulus in rats.

Two groups of 15 rats each were trained in a shuttle box to escape foot-shock either unsignalled or presented in compound with a visual cue: darkness. The visual cue presented in shock compartment amplifies the behavioral tendency actually prevailing in the response repertory of the rat. During the 1st session the compound enhanced the species-specific flight resulting in shortening of the rat's escape latency. Thereafter, during subsequent sessions, darkness exaggerated resistance to enter the other compartment; thus escape latencies were longer under compounded than under unsignalled procedure. The darkness cue reduces the intertrial response rate relative to the unsignalled group. This latter finding supports the discrimination model of the effect, since the compound helps the animals to discriminate the illuminated "safe" period between trials from the aversive shock period. Our data seem to suggest that the darkness presented synchronously with escapable grid-shock acquires aversive properties.

[Delay inhibition of the active avoidance reflex and intertrial responses in rats in the shuttle box]. / Zapazdyvatel'noe tormozhenie reaktsii aktivnogo izbeganiia i mezhsignal'nye reaktsii v chelnochnoi kamere u krys.

A diminished probability of avoidance response in early phases of a warning signal was revealed with salient signals given after short intertrial intervals. The inhibition of the delay in avoidance response is due to an interaction of the safety state conditioning and the excitation elicited by onset of warning signal.

Defensive conditioning-related functional heterogeneity among nuclei of the rat amygdala revealed by c-Fos mapping.

The amygdala is a complex forebrain structure proposed to play a pivotal role in fear conditioning circuitry. In this study, c-Fos immunomapping was applied to investigate the functional activation of particular amygdalar nuclei following a 50-trial training session of two-way active avoidance reaction. To dissect distinctive responses displayed by the animals and to cluster them into groups of correlated behaviors, factor analysis was employed. The training procedure resulted in an increase of c-Fos expression within the cortical, medial, lateral and basolateral, but not central, nuclei. The expression in the cortical nucleus correlated negatively with grooming behavior, whereas c-Fos immunolabeling of the other three subdivisions of the amygdala could be associated with the number of intertrial responses. No correlation was observed between c-Fos expression and avoidance reactions performed or the amount of shock received by the animal. The results obtained with c-Fos mapping of various regions of rat amygdala, combined with a fine dissection of behavioral repertoire, imply that there are specific functional links between particular parts of the structure and distinctive behaviors that reflect various emotional states of the animal.

Studies of individual differences as a method for discriminating the stages of acquisition of a conditioned reflex.

Learning of a two-way active avoidance response in a shuttle box, which reflects the establishment of a complex reflex, was characterized by a high level of individual variability for learning measures. Our previous report (Savonenko and Zelin'ski, 1997) showed that rats with different rates of learning have different parameters for the freezing response, demonstrating that the animals' behavior shows a conflicting drive not to enter into the other half of the box. We analyze here the sequence of freezing, avoidance, and escape responses in groups of rats with different rates of learning. The results support the hypothesis that the need to overcome conflict is a separate stage of learning, occurring before the stage at which the avoidance response forms and stabilizes.

How do rats cope with the two-way escape problem in a homogeneous shuttle box?

The behavior of 25 rats trained in a homogeneous shuttle box to escape unsignalled grid-shock was analyzed. Three categories of escape were distinguished: (1) species-specific fly away from the charged grid, (2) long-latency crossing preceded and accompanied by other behaviors that compete with the escape response, and (3) short-latency escape which followed an anticipatory postural pose. The animals displayed species-specific fly away only during the initial trials of a session. Subsequently long-latency crossings develops, reflecting a resistance to enter the opposite compartment. A measure based on a comparison of escape latency distributions in the two halves of the 1st session discriminates between good and poor learners. Subgroups of good and poor learners differed in performance efficiency in all five training sessions. Good learners were able to overcome the resistance to enter the opposite compartment and recall the learned short-latency escape.

Defensive conditioning-related increase in AP-1 transcription factor in the rat cortex.

In the studies reported herein, electrophoretic mobility shift assay (EMSA) and immunocytochemistry have been applied to document increased levels of AP-1 transcription factor, and its major component, c-Fos in the rat brain following behavioral training of two-way active avoidance. A single training session (50 trials) provoked elevation of AP-1 in the visual, sensory and limbic cortex but not in the hippocampus. A session following long term training (10 sessions, up to asymptotic level of performance) had much smaller effect on AP-1 levels in the visual cortex than single training session. The long term training was used to ensure that observed effects were related to acquisition of the reaction rather than simply to behavioral performance. Supershift EMSA analysis with antibodies directed at individual AP-1 components revealed that AP-1 extracted from the brains of trained as well as naive animals is composed of the same proteins, i.e., in order of relative level within the protein family: c-Fos, Fos B, Fra-2, and Jun D, Jun B, c-Jun. These studies reinforce the notion that transcription factors as regulators of gene expression-and AP-1 in particular-may respond to behavioral stimulation and furthermore may play a role in acquisition of behavioral reactions.

[The dependence of learning an active avoidance reaction on overcoming a problem-solving situation in a shuttle box]. / Zavisimost' obucheniia reaktsii aktivnogo izbeganiia ot preodoleniia problemnoi situatsii v chelnochnoi kamere.

The two-way avoidance procedure dramatically differs from the one-way procedure in rate of learning. The present study was conducted to prove that retardation of the two-way avoidance acquisition resulted from development of the behavioral conflict tendency not to reenter the previous shock compartment. Cluster analysis of avoidance response indices divided rats into three distinctive classes. The occurrence of avoidance, escape, and freezing responses in the first session was analyzed in these three groups. Freezing during the shock action reflected the conflict tendency and showed a negative correlation with avoidance response indices. Only the rats which overcame the conflict and performed at least one avoidance reaction toward the end of the first session significantly improved their avoidance score in the following session. Discriminant analysis of indices of the three reaction types in the first session revealed sufficiency of these indices for prediction of the success in avoidance learning in subsequent sessions. Our results proved the hypothesis formulated previously that the conflict situation inherent to the two-way shuttle box procedure retarded the active avoidance acquisition. A number of trials have to be reserved in the first session for solving the conflict situation (direct effect on the rate of learning). The conflict intensity which directly effects the avoidance performance in the first session, presumably, influences learning in subsequent sessions (secondary effect on learning).

[The study of individual differences as a method for dividing into stages the acquisition of a complex reflex]. / Izuchenie individual'nykh razlichii kak metod vychleneniia étapov vyrabotki slozhnogo refleksa.

Two-way active avoidance learning is a complex task characterized by a high level of interindividual variability. We have demonstrated in our previous paper that rats with different rate of learning vary in expression of freezing responses, which reflects a conflict tendency not to re-enter the previous chock compartment [4]. In the present work we analyzed as main indices the proportions of avoidance, rapid escape, and freezing responses and their distribution within a session. Sequences of occurrence of these three types of responses were examined in groups of rats with different success of avoidance learning. The obtained results confirmed a hypothesis that overcoming the conflict tendency was a separate stage of learning which preceded avoidance response appearance and subsequent stabilization. Only in rats which failed to learn and develop avoidance responses within the first session, freezing responses were observed in successive session being indicative of reappearance of the conflict tendency. The intensity of the conflict tendency did not depend on the type of the first response of an animal (fleeing or freezing) to an unexpected aversive stimulus.

Morphochemical features of sensorimotor cortex and neostriatum neurons in rats with different levels of alcohol preference.

This paper reports interferometric studies of the contents and concentrations of proteins in the cellular structures of neurons of the sensorimotor cortex (layers III, V) and in the region of the caudate nucleus of the neostriatum (Golgi type II cells) in Wistar rats with high, intermediate, and low levels of ethanol preference. The greatest differences between groups of animals in terms of cell size and protein metabolism were seen in the cortex. Along with measures correlating with initial ethanol preference (cell body size, nucleus size, and cytoplasm size of cortical neurons, cytoplasmic protein content, etc.), a number of measures were found to show statistically significant differences which did not correlate with preference (nuclear protein contents and concentrations in cortical neurons of layers III and V). These data may suggest the existence of another significant measure responsible for the difference between the groups and, possibly, more closely correlated with the analytical-synthetic functions of the central nervous system.

[Weak magnetic fields and cognitive activity]. / Slabye magnitnye polia i poznavatel'naia deiatel'nost'.

The influence of natural level of uniform magnetic field (to 200 microT) on Wistar rat cognition was studied in this work. It was found that influence of disturbed Earth magnetic field has caused a long depression of explorative activity only in the presence of information loading. Such depression was removed only after short external stimulation. After this stimulation rats were able to learn by themselves and it took them twice less time than in the control (nootropic effect). It is suggested that a weak magnetic field disturbances may be considered as a negative psychogenic factor which distorts normal conditions for cognitive activity.

[The morphochemical characteristics of the neurons of the sensorimotor cortex and neostriatum in rats with differing degrees of alcohol preference]. / Morfokhimicheskie osobennosti neironov sensomotornoi kory i neostriatuma krys s razlichnoi stepen'iu predpochteniia alkogolia.

Cytochemical techniques revealed that the content of the cytoplasm albumins and the size of the cortex neurons depended on the level of alcohol preference in rats. The neurons nucleus' proteins, however, do not depend on the alcohol preference and are associated with their cognitive characteristics rather.

[The normal characteristics of erythrocyte Na, K-ATPase in rats with different behaviors to ethanol and after chronic alcoholization]. / Kharakteristika Na, K-ATFazy éritrotsitov krys s raznym otnosheniem k étanolu v norme i posle khronicheskoi alkogolizatsii.

The relationship of Na,K-ATPase of erythrocytes and MgCl2 concentration in the incubation medium was studied in rats preferring ethanol (PE) and rejecting ethanol (RE) normally and 3 months after chronic alcoholization. The dependence of erythrocyte Na,K-ATPase on MgCl2 in PE and RE animals before alcoholization was similar. The chronic effect of alcohol on rats resulted in increase of Na,K-ATPase both in PE and RE rats; however, Mg(2+)-dependence of increase of Na,K-ATPase differed in animals with different response to alcohol: in PE rats, the per cent of increasing activity of Na,K-ATPase declined with the growth of MgCl2 concentration and in RE rats increased. It is concluded that the reaction to alcohol of the functional activity of plasma membranes differs in rats with different alcohol motivation.