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The odour span task: a novel paradigm for assessing working memory in mice.

Impoverished odour recognition and memory are amongst the earliest symptoms observed in mild cognitive impairment, Alzheimer's disease and schizophrenia, and have been advocated as early disease bio-markers. Although transgenic animals modelling disease pathologies continually emerge, there remains a paucity of tasks to examine olfactory working memory in mice. The present studies describe a mouse odour span task, which assesses the ability to remember increasing numbers of odours. Since caspase-3 is highly expressed throughout the olfactory system, we postulated that mice over-expressing this apoptogenic protein would exhibit impaired performance in the odour span task. Mice over-expressing human caspase-3 (Tg) exhibited age-independent deficits in olfactory working memory (6-18 months) compared with wild-type littermates, requiring longer for task acquisition and exhibiting impaired asymptotic performance, with reduced span lengths, lower accuracy and increased error rates. These impairments appeared to be selective for working memory, as Tg mice had no deficits in odour discriminatory ability or in locomotor measures. Importantly, nicotine, which improves working memory span in man, reversed the deficits exhibited by Tg mice. In conclusion, the mouse odour span task can detect subtle changes in olfactory working memory induced by genetic manipulation and drug administration and therefore should be applied to animal models of neurological disease.

Analysis of Variance↗

Acoustic startle and open-field behavior in mice bred for magnitude of swim analgesia.

Acoustic startle response (ASR) and open-field activity was examined in the 46th generation of mice that have been selectively bred for high analgesia (HA) and for low analgesia (LA) induced by 3-min swimming in 20 degrees C water. These lines were earlier found to differ in brain opioid receptor density and in the expression of opioid-mediated phenomena, as analgesic sensitivity to opiates and reversibility of swim stress-induced analgesia (SSIA) by naloxone. For comparison, a randomly bred control (C) line was used. To measure the amplitude of ASR, the mice were exposed to 110-dB acoustic stimuli in a Coulbourn apparatus. In saline-injected mice, the ASR force was found significantly lower in the LA than in the HA, as well in the C line, but did not differ between the two last lines. Naltrexone hydrochloride (10 mg/kg IP 30 min before ASR testing) augmented the startle in the opioid receptor-dense HA line, but had no effect in the opioid receptor-deficient LA line, as well in the C line; therefore, the ASR magnitude in naltrexone-injected HA mice was significantly higher compared to the C line. HA mice displayed less activity in an open-field test; that is, they remained immobile longer in the center of the field, and thereafter performed less ambulation and less rearing against the wall compared to the LA line. Naltrexone failed to modify the open-field activity in any line. The results confirm that the pattern of ASR depends on the genetic makeup of the animals. The higher amplitude of ASR, taken together with the lower open-field activity of HA mice, can be interpreted in terms of higher anxiety level, compared to the LA line. It is suggested that the higher ASR in HA mice relies on a nonopioid mechanism, which is tonically inhibited by the opioid system.

Acoustic Stimulation↗

Tracking the displacement of objects: a series of tasks with great apes (Pan troglodytes, Pan paniscus, Gorilla gorilla, and Pongo pygmaeus) and young children (Homo sapiens).

The authors administered a series of object displacement tasks to 24 great apes and 24 30-month-old children (Homo sapiens). Objects were placed under 1 or 2 of 3 cups by visible or invisible displacements. The series included 6 tasks: delayed response, inhibition test, A not B, rotations, transpositions, and object permanence. Apes and children solved most tasks performing at comparable levels except in the transposition task, in which apes performed better than children. Ape species performed at comparable levels in all tasks except in single transpositions, in which chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) performed better than gorillas (Gorilla gorilla) and orangutans (Pongo pygmeaus). All species found nonadjacent trials and rotations especially difficult. The number of elements that changed locations, the type of displacement, and having to inhibit predominant reaching responses were factors that negatively affected the subjects' performance.

Animals↗

Cocaine self-administration increases the incentive motivational properties of the drug in rats.

A progressive increase in the frequency and intensity of drug use is one of the major behavioural phenomena characterizing the development of addiction. The nature of the drug-induced adaptations involved in this escalating drug intake remains unknown. Some theories propose that this escalation is due to a progressive decrease (tolerance) in the reinforcing or incentive effects of the drug. Alternative views posit that with chronic use the reinforcing or incentive effects of drugs increase, by a sensitization or a learning mechanism. In this report, we address the question of whether escalating cocaine intake is paralleled by an increase or a decrease in the reinforcing and incentive effects of the drug. Using the experimental model of intravenous drug self-administration with a within-session dose-response paradigm, we first studied the course of cocaine intake over 14 sessions in rats. After acquisition of cocaine self-administration, cocaine intake progressively increased at each dose tested. Then rats, previously allowed to self-administer cocaine during either six or 29 sessions, were compared in three different tests of the incentive and reinforcing effects of cocaine: cocaine-induced reinstatement of self-administration, cocaine-induced runway and cocaine-induced place conditioning. As compared with rats briefly exposed to cocaine self-administration (six sessions), rats with the longer experience (29 sessions) exhibited a higher intake of cocaine paralleled by a higher responsiveness in the cocaine-induced reinstatement and runway tests. Both groups of rats were similarly sensitive to the rewarding effects of the drug as evaluated by the threshold dose of cocaine inducing place conditioning. Our results demonstrate that escalating cocaine intake is paralleled by an increase in the motivational properties of the drug in the absence of apparent signs of tolerance to the reinforcing or incentive effects of cocaine.

Animals↗

Sequential decision-making in a variable environment: modeling elk movement in Yellowstone National Park as a dynamic game.

We develop a suite of models with varying complexity to predict elk movement behavior during the winter on the Northern Range of Yellowstone National Park (YNP). The models range from a simple representation of optimal patch choice to a dynamic game, and we show how the underlying theory in each is related by the presence or absence of state- and frequency-dependence. We compare predictions from each of the models for three variables that are of basic and applied interest: elk survival, aggregation, and use of habitat outside YNP. Our results suggest that despite low overall forage depletion in the winter, frequency-dependence is crucial to the predictions for elk movement and distribution. Furthermore, frequency-dependence interacts with mass-dependence in the predicted outcome of elk decision-making. We use these results to show how models that treat single movement decisions in isolation from the seasonal sequence of decisions are insufficient to capture landscape scale behavior.

Animal Migration↗

Behavioural effects of prenatal exposure to carbon disulphide and to aromatol in rats.

The neurotoxic effects of prenatal organosolvent inhalation were studied in rats, because of the expectation that a developing organism may be more sensitive than the adult to the induction of functional deficits. The aim was to determine whether prenatal exposure to the new organosolvent mixture, Aromatol, and the well known neurotoxic carbon disulphide, would impair reflex ontogeny or produce neurobehavioural dysfunctions in the offspring. Development of gait, motor coordination, and activity, avoidance learning and swimming were tested in the offspring of CFY rat mothers, exposed to CS2 inhalation (0, less than 10, 700 and 2000 mg/m3) and to Aromatol (0, 600, 1000 and 2000 mg/m3) on days 7-15 gestation. Prenatal CS2 inhalation induced dose related perinatal mortality of pups. Eye opening and the auditory startle were retarded. There were immature gait, motor incoordination, diminished open field activity and altered behavioural patterns on day 21 and 36 but they were nearly age-appropriate on day 90. As signs of disturbed learning ability, there were diminished performance and lengthened latency of the conditioned avoidance response, related to the concentrations administered. Contrary to expectations, prenatal Aromatol inhalation had no effect on maturation of gait, behaviour patterns, or learning ability.

Animals↗

A behavior profile of the MRL/Mp lpr/lpr mouse and its association with hydrocephalus.

Since the NZB and BXSB autoimmune mouse strains have cortical ectopias and associated behavioral changes, mice from the MRL/l (MRL/Mp lpr/lpr) autoimmune strain were given a series of behavioral tests followed by anatomical analyses of their brains and immune assays of plasma. No cortical ectopias were found, but this strain was discovered to have a high incidence of hydrocephalus: 46% had severe dilatation of the lateral and third ventricles, 30% had moderate dilatation, and 24% had minimal or no enlargement of the ventricles (total N = 57). Those mice in the severe hydrocephalus group were poorer in a nonspatial discrimination learning task, had less paw asymmetry, and were less active in a swimming task. No association was found between degree of hydrocephalus and any immune parameter.

Animals↗

Effects of neonatal lesions of the medial prefrontal cortex on adult rat behaviour.

While prefrontal lesions in rodents serve as models for frontal lobe syndromes, neonatal lesions are considered as models for disconnection syndromes, such as schizophrenia. We investigated the effect of neonatal lesions of the rat medial prefrontal cortex (mPFC) together with pubertal dexamethasone-challenge on adult rat behaviour and on apomorphine-induced behavioural changes. Adult lesions were used as controls. Rats with neonatal (postnatal day 7) or adult excitotoxic lesions or sham-lesions of the mPFC were tested 9 weeks after surgery. At postnatal day 49 one group of neonatal operated rats were systemically injected with the glucocorticoid receptor agonist dexamethasone (20 mg/kg), in order to simulate stress-induced glucocorticoid receptor activation. Working memory and perseveration was tested in T-maze tasks (continuous delayed alternation and reversal learning). Additionally, locomotor activity and prepulse inhibition (PPI) of startle was tested with and without apomorphine-treatment. Brain tissue damage was assessed using Nissl-staining and parvalbumine-immunocytochemistry. Pronounced thinning of the prelimbic-infralimbic subregion of the mPFC accompanied by altered cytoarchitecture and reduced number of parvalbumine-immunopositive neurones was found after neonatal lesions while adult lesions resulted in loss of neurones accompanied by gliosis. Neonatal lesions increased perseveration in the T-maze tasks and enhanced PPI, while adult lesions induced a working memory deficit. This differential behavioural outcome presumably reflects neurodevelopmentally induced alterations in neuronal circuits after neonatal lesions versus damage to mPFC alone after adult lesions. Dexamethasone-injection at day 49 did not alter behaviour in these tasks. Motor activity was not affected by neonatal or adult lesions but dexamethasone reduced apomorphine-induced hyperlocomotion.

Analysis of Variance↗

Development and temporal organization of compulsive checking induced by repeated injections of the dopamine agonist quinpirole in an animal model of obsessive-compulsive disorder.

Rats treated chronically with the dopamine D2/D3 receptor agonist quinpirole develop locomotor sensitization and exhibit compulsive checking of specific places in an open-field arena, a behavioral profile that may represent an animal model of obsessive-compulsive disorder. However, it is not known how compulsive checking develops across quinpirole injections nor whether checking behavior possesses a particular temporal structure. Male rats received quinpirole (0.5mg/kg, twice weekly x 10) or an equivalent regimen of saline and were placed in a large open field for 55 min where their behavior was digitally tracked for subsequent analysis of checking behavior using existing and newly developed computer software. Results showed that the measures of compulsive checking did not follow a singular profile across injections: some remained constant and others changed monotonically reaching their near-maximum levels after about 5-7 quinpirole injections. Moreover, results showed that checking behavior was organized into bouts of checking, with the number of bouts, as well as the rate of checking within a bout, increasing across injections to reach near maximal levels after about 5-7 administrations of quinpirole. Finally, quinpirole-treated rats showed a paucity of long inter-bout intervals. These results suggest that (a) compulsive checking emerges from the operation of at least two underlying processes: a regulated process and a process of sensitization that intensifies the performance of checking behavior; and (b) quinpirole treatment may attenuate a sense of satiety that could underlie the compulsive nature of checking. Finally, because key variables measured using the newly developed algorithms showed the expected profile, the present study provides validation for the use of this methodology for the analysis of checking behavior.

Analysis of Variance↗

Estrogen selectively increases tryptophan hydroxylase-2 mRNA expression in distinct subregions of rat midbrain raphe nucleus: association between gene expression and anxiety behavior in the open field.

BACKGROUND: Ovarian steroids modulate anxiety behavior, perhaps by regulating the serotonergic neurons in the midbrain raphe nucleus. The regulation of the brain-specific isoform of rat tryptophan hydroxylase (TPH2) by ovarian hormones has not yet been investigated. Therefore, we examined the effects of estrogen and progesterone on TPH2 mRNA in the rat dorsal and median raphe nuclei (DRN and MRN, respectively) and whether TPH2 mRNA levels correlated with anxiety behavior. METHODS: Ovariectomized rats were treated for two weeks with placebo, estrogen or estrogen plus progesterone, exposed to the open field test, and TPH2 mRNA was quantified by in situ hybridization histochemistry. RESULTS: Estrogen increased TPH2 mRNA in the mid-ventromedial and caudal subregions of the DRN and the caudal MRN. Combined estrogen and progesterone treatment did not change TPH2 mRNA relative to ovariectomized controls. TPH2 mRNA in caudal DRN was associated with lower anxiety-like behavior, whereas TPH2 mRNA in rostral dorsomedial DRN was associated with increased anxiety-like behavior. CONCLUSIONS: These results suggest that estrogen may increase the capacity for serotonin synthesis in discrete subgroups of raphe neurons, and reinforce previous observations that different subregions of DRN contribute to distinct components of anxiety behavior.

Animals↗

Intraaccumbens injections of substance P, morphine and amphetamine: effects on conditioned place preference and behavioral activity.

The nucleus accumbens of the rat plays a critical role in behavioral activation and appetitive motivation. Within the nucleus accumbens, the shell subarea may be especially relevant, since this site is anatomically related to other brain areas that are considered to play a critical role in the processing of motivation. We investigated the behavioral effects of local drug treatments aimed at the shell of the nucleus accumbens and tested the indirect dopamine agonist d-amphetamine, the opiate agonist morphine, and the neurokinin substance P. These substances are known to exert positive reinforcing effects, and can affect behavioral activity; effects that are physiologically closely related to the nucleus accumbens and its inputs and outputs. Our results show that unilateral microinjections of amphetamine (1.0 microg, 10.0 microg) into the shell of the nucleus accumbens dose-dependently stimulated behavioral activity (locomotion, rears, sniffing), and led to conditioned place preference. Furthermore, the effect of amphetamine on place preference was negatively related to the psychomotor stimulant action on rears. Morphine injections (5.0 microg) also stimulated behavioral activity and elicited contraversive turning, but were ineffective with respect to place preference. Finally, the neuropeptide substance P, injected in a dose range of 0.1-10.0 ng, had no significant behavioral effects. These findings are discussed with respect to the role of dopaminergic, peptidergic and cholinergic mechanisms in the nucleus accumbens. It is suggested that dopamine, opiates, and neurokinins in the shell of the nucleus accumbens are differentially involved in mediating behavioral activity and appetitive motivation.

Acute Disease↗

The neurosteroid 3alphaDIOL modulates place preference when infused in the basolateral amygdala according to sex.

Three different behavioral tasks were used to study the role of the neurosteroid 5alpha -androstane-3alpha, 17beta-diol (3alphaDIOL) in affective components of behavior when infused into the basolateral amygdala (BLA) of both sexes. Female rats were ovariectomized; half received implants containing estradiol benzoate (OVX-EB), whereas the other half received empty implants (OVX). Male rats were gonadally intact. No differences were noted in male behavior according to the conditioned place preference (CPP) test, the modified Vogel conflict test (VCT), or the elevated plus maze (EPM) upon infusion of 3alphaDIOL. In contrast, 3alphaDIOL modulated CPP and VCT performance among female rats. Therefore, the authors propose that 3alphaDIOL modulates affect through the BLA via a sex-specific mechanism.

Amygdala↗

Estimating wall guidance and attraction in mouse free locomotor behavior.

In this study, we estimate the influence exerted by the wall of the Open Field on the trajectory of the mouse. The wall exerts two types of influence on the mouse's path: one of guidance and one of attraction. The guiding influence is expressed by the tendency of mice to progress in parallel to the wall. This tendency wanes with increasing distance from the wall but is observed at large distances from it. The more parallel the mouse is to the wall the higher is its speed, even when distant from the wall. This association between heading direction and speed shows that the mouse controls its heading in reference to the wall. It is also observed in some blind strains, revealing that wall-guidance is not based exclusively on vision. The attraction influence is reflected by movement along the wall and by the asymmetry between speed during movement toward, and during movement away from the wall: sighted mice move faster toward the wall, whereas blind mice use similar speeds in both directions. Measures characterizing these influences are presented for five inbred strains, revealing heritable components that are replicable across laboratories. The revealed structure can lead to the identification of distinct groups of genes that mediate the distinct influences of guidance and attraction exerted by the wall. It can also serve as a framework for the decoding of electrophysiological data recorded in free moving rodents in the Open Field.

Animals↗

The role of the dorsal hippocampus in the acquisition and retrieval of context memory representations.

It is argued that the hippocampus contributes to contextual fear conditioning by supporting the acquisition of a conjunctive memory representation of context, which associates with shock. This function was examined by studying the context pre-exposure facilitation effect (CPFE). A rat that is shocked immediately after being placed into a context subsequently displays almost no fear of that context. However, if it is pre-exposed to the context the day before immediate shock, it displays significant freezing to that context. By using 5-aminomethyl-3-hydroxysoxazole to temporarily inactivate the dorsal hippocampus (DH) at three different phases of the procedure, which produces the CPFE, we show that the hippocampus is necessary for the following: (1) acquisition of the context memory, (2) retrieval of this memory at the time of immediate shock, and (3) retrieval of the context-shock memory at the time of testing. In contrast, inactivating the DH before a standard contextual shock experience had no effect on contextual fear conditioning. These results support the view that two processes can support contextual fear conditioning: (1) conditioning to the conjunctive representation, which depends on the hippocampus, and (2) conditioning to the features that make up the context, which does not.

Animals↗

Reversible memory loss in a mouse transgenic model of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative condition, believed to be irreversible, characterized by inexorable deterioration of memory and intellect, with neuronal loss accompanying amyloid plaques and neurofibrillary tangles. In an amyloid precursor protein transgenic mouse model, Tg2576, little or no neuronal loss accompanies age-related memory impairment or the accumulation of Abeta, a 40-42 aa polypeptide found in plaques. Recently, we have shown inverse correlations between brain Abeta and memory in Tg2576 mice stratified by age (Westerman et al., 2002). Broadening the age range examined obscured this relationship, leading us to propose that small, soluble assemblies of Abeta disrupt cognitive function in these mice. Here we show that memory loss can be fully reversed in Tg2576 mice using intraperitoneally administered BAM-10, a monoclonal antibody recognizing the N terminus of Abeta. The beneficial effect of BAM-10 was not associated with a significant Abeta reduction, but instead eliminated the inverse relationship between brain Abeta and memory. We postulate that BAM-10 acts by neutralizing Abeta assemblies in the brain that impair cognitive function. Our results indicate that a substantial portion of memory loss in Tg2576 mice is not permanent. If these Abeta assemblies contribute significantly to memory loss in AD, then successfully targeting them might improve memory in some AD patients.

Aging↗

Lesions of the tegmental pedunculopontine nucleus block the rewarding effects and reveal the aversive effects of nicotine in the ventral tegmental area.

Nicotine, the primary psychoactive component of tobacco smoke, is known to possess potent rewarding and aversive stimulus properties. The mammalian ventral tegmental area (VTA) is involved importantly in the mediation of the motivational effects of nicotine. However, the neural outputs from the VTA that may be involved in the transmission of the rewarding and aversive motivational effects of nicotine are not well understood. We report that bilateral lesions of the tegmental pedunculopontine nucleus (TPP) double dissociate the rewarding and aversive motivational effects of nicotine. Using a conditioned place preference paradigm, bilateral TPP lesions blocked a nicotine reward signal and revealed the aversive motivational properties of intra-VTA nicotine. These same TPP lesions did not block an aversive nicotine signal, as measured in a conditioned taste aversion paradigm. TPP lesions also produce an attenuation in nicotine-induced locomotor activity; however, neither learning nor performance deficits can account for these observed effects, because TPP-lesioned animals still showed clear aversive nicotine conditioning in two separate behavioral paradigms. Our results suggest that the rewarding effects of nicotine in the VTA are dependent on a nondopaminergic, descending reward pathway to the brainstem TPP.

Animals↗