One-trial object recognition memory in the domestic rabbit (Oryctolagus cuniculus) is disrupted by NMDA receptor antagonists

Boldness affects novel object recognition in a gecko species

Individual animals exhibit considerable differences in cognitive characteristics associated with personality differences. The cognition-personality link was intensively investigated in the last decade though with mixed results. To grasp the general pattern, a common method should be applied to a wide range of animals. We tested novel object recognition (NOR) in the mourning gecko (Lepidodactylus lugubris) and investigated whether boldness, assessed in an anti-predator context, explained neophobia and how much attention animals pay to their surroundings. Boldness did not simply explain object neophobia but predicted attention to novel objects. Specifically, shy geckos showed shorter latency to approach the novel object than bold geckos only in the changed situation in which distinct types of objects were presented in two successive phases. However, no significant effect of boldness was detected in the unchanged situation in which the same object was presented twice. Our findings suggest that, in the mourning gecko, (1) boldness and object neophobia represent different aspects of personality traits and that (2) boldness underlies sensitivity to slight changes in the environment.

MK-801 and cognitive functions: Investigating the behavioral effects of a non-competitive NMDA receptor antagonist

RATIONALE

MK-801 (dizocilpine) is a non-competitive NMDA receptor antagonist originally explored for anticonvulsant potential. Despite its original purpose, its amnestic properties led to the development of pivotal models of various cognitive impairments widely employed in research and greatly impacting scientific progress. MK-801 offers several advantages; however, it also presents drawbacks, including inducing dose-dependent hyperlocomotion or ambiguous effects on anxiety, which can impact the interpretation of behavioral research results.

OBJECTIVES

The present review attempts to summarize and discuss the effects of MK-801 on different types of memory and cognitive functions in animal studies.

RESULTS

A plethora of behavioral research suggests that MK-801 can detrimentally impact cognitive functions. The specific effect of this compound is influenced by variables including developmental stage, gender, species, strain, and, crucially, the administered dose. Notably, when considering the undesirable effects of MK-801, doses up to 0.1 mg/kg were found not to induce stereotypy or hyperlocomotion.

CONCLUSION

Dizocilpine continues to be of significant importance in preclinical research, facilitating the exploration of various procognitive therapeutic agents. However, given its potential undesirable effects, it is imperative to meticulously determine the appropriate dosages and conduct supplementary evaluations for any undesirable outcomes, which could complicate the interpretation of the findings.

Protocols for the Evaluation of Neurodevelopmental Alterations in Rabbit Models In Vitro and In Vivo

The rabbit model is gaining importance in the field of neurodevelopmental evaluation due to its higher similarity to humans in terms of brain development and maturation than rodents. In this publication, we detailed 14 protocols covering toxicological relevant endpoints for the assessment of neurodevelopmental adverse effects in the rabbit species. These protocols include both in vitro and in vivo techniques, which also cover different evaluation time-points, the neonatal period, and long-term examinations at postnatal days (PNDs) 50–70. Specifically, the protocols (P) included are as follows: neurosphere preparation (GD30/PND0; P2) and neurosphere assay (P3), behavioral ontogeny (PND1; P4), brain obtaining and brain weight measurement at two different ages: PND1 (P5) and PND70 (P12), neurohistopathological evaluations after immersion fixation for neurons, astrocytes, oligodendrocytes and microglia (PND1; P6-9) or perfusion fixation (PND70; P12), motor activity (P11, open field), memory and sensory function (P11, object recognition test), learning (P10, Skinner box), and histological evaluation of plasticity (P13 and P14) through dendritic spines and perineuronal nets. The expected control values and their variabilities are presented together with the information on how to troubleshoot the most common issues related to each protocol. To sum up, this publication offers a comprehensive compilation of reliable protocols adapted to the rabbit model for neurodevelopmental assessment in toxicology.

Scopolamine and MK-801 impair recognition memory in a new spontaneous object exploration task in monkeys

The spontaneous object recognition (SOR) task is one of the most widely used behavioral protocols to assess visual memory in animals. However, only recently was it shown that nonhuman primates also perform well on this task. Here we further characterized this new monkey recognition memory test by assessing the performance of adult marmosets after an acute systemic administration of two putative amnesic agents: the competitive muscarinic acetylcholine receptor antagonist scopolamine (SCP; 0.05 mg/kg) and the noncompetitive N-methyl-d-aspartate glutamate receptor antagonist MK-801 (0.015 mg/kg). We also determined whether the acetylcholinesterase inhibitor donepezil (DNP; 0.50 mg/kg), a clinically-used cognitive enhancer, reverses memory deficits caused by either drug. The subjects had an initial 10 min sample trial where two identical neutral objects could be explored. After a 6 h retention interval, recognition was based on an exploratory preference for a new rather than familiar object during a 10 min test trial. Both SCP and MK-801 impaired the marmosets' performance on the SOR task, as both objects were explored equivalently. Co-administration of 0.50 mg/kg of DNP reversed the SCP- but not the MK-801-induced memory deficit. These results indicate that cholinergic and glutamatergic pathways mediate object recognition memory in the monkey SOR task.

Rigor and reproducibility in rodent behavioral research

Behavioral neuroscience research incorporates the identical high level of meticulous methodologies and exacting attention to detail as all other scientific disciplines. To achieve maximal rigor and reproducibility of findings, well-trained investigators employ a variety of established best practices. Here we explicate some of the requirements for rigorous experimental design and accurate data analysis in conducting mouse and rat behavioral tests. Novel object recognition is used as an example of a cognitive assay which has been conducted successfully with a range of methods, all based on common principles of appropriate procedures, controls, and statistics. Directors of Rodent Core facilities within Intellectual and Developmental Disabilities Research Centers contribute key aspects of their own novel object recognition protocols, offering insights into essential similarities and less-critical differences. Literature cited in this review article will lead the interested reader to source papers that provide step-by-step protocols which illustrate optimized methods for many standard rodent behavioral assays. Adhering to best practices in behavioral neuroscience will enhance the value of animal models for the multiple goals of understanding biological mechanisms, evaluating consequences of genetic mutations, and discovering efficacious therapeutics.

Behavioral testing and litter effects in the rabbit

BACKGROUND

Behavioral testing provides an essential approach in further developing our understanding of brain structure and function. The aim of our study was to outline a more expanded approach to cognition- and anxiety-related behavior in the rabbit.

METHODS

Twenty-one 70-day old rabbits (13 female, 8 male) were exposed to open field test, dark-light box test and object recognition testing with variations in inter-trial-interval, olfactory recognition and object location testing. Independent T-tests were used to compare data by individual baseline characteristics, i.e. birth weight, weight at testing, sex, litter #, litter size.

RESULTS

In the open field test, median time spent in the center was 3.64 s (0.84-41.36) for the 9 rabbits who entered the center; median distance moved in the arena was 874.42 cm (54.20-3444.83). In the dark light box test, 12 rabbits entered the light compartment. In the object recognition task, rabbits spent significantly less time exploring the familiar object compared to the novel (0.40 s [0-2.8] vs. 3.17 s [1.30-32.69]; P = 0.003) when using a 30-min inter-trial interval, as well with a 90-min inter-trial interval: 0.87 s [0-7.8] vs. 7.65 s [0-37.6] (P = 0.008). However, recognition was lost when using a 24-h inter-trial interval (time spent exploring the familiar object: 3.33 [0-10.90]; novel object:3.87 [1.15-48.53]; n.s). In the object location task and in olfactory object recognition task, median discrimination indexes were 0.69 (-1 to 1) and 0.37 (-0.38 to 0.78) respectively, higher than level expected by chance (P < 0.001). Litter size >3 during the neonatal period was associated with increased explorative behavior in the dark light box test (P = 0.046) and in the visual object recognition task (P = 0.005), whereas body weight and sex were not.

CONCLUSIONS

Settings and outcome measures for multiple behavioral tests, providing reference values and considerations for future developmental studies are reported. Discrimination and memory in the rabbit appear to relate to litter characteristics, although a larger sample size is needed to confirm our findings.

The rabbit as a behavioral model system for magnetic resonance imaging

BACKGROUND

fMRI requires that subjects not move during image acquisition. This has been achieved by instructing people not to move, or by anesthetizing experimental animal subjects to induce immobility. We have demonstrated that a surgically implanted headbolt onto the skull of a rabbit allows their brain to be imaged comfortably while the animal is awake. This article provides a detailed method for the preparation.

NEW METHOD

We took advantage of the rabbit's tolerance for restraint to image the brain while holding the head at the standard stereotaxic angle. Visual stimulation was produced by flashing green LEDs and whisker stimulation was done by powering a small coil of wire attached to a fiber band. Blinking was recorded with an infrared emitter/detector directed at the eye with fiber-optic cabling.

RESULTS

Results indicate that a single daily session of habituation is sufficient to produce adequate immobility on subsequent days to avoid movement artifacts. Results include high resolution images in the stereotaxic plane of the rabbit.

COMPARISON WITH EXISTING METHOD(S)

We see no degradation or distortion of MR signal, and the headbolt provides a means for rapid realignment of the head in the magnet from day to day, and across subjects. The use of rabbits instead of rodents allows much shorter periods of habituation, and the rabbit allows behavior to be observed during the day while the animal is in its normal wake cycle.

CONCLUSIONS

The natural tolerance of the rabbit for restraint makes it a valuable subject for MRI studies of the brain.

Eyeblink Conditioning and Novel Object Recognition in the Rabbit: Behavioral Paradigms for Assaying Psychiatric Diseases

Analysis of data collected from behavioral paradigms has provided important information for understanding the etiology and progression of diseases that involve neural regions mediating abnormal behavior. The trace eyeblink conditioning (EBC) paradigm is particularly suited to examine cerebro-cerebellar interactions since the paradigm requires the cerebellum, forebrain, and awareness of the stimulus contingencies. Impairments in acquiring EBC have been noted in several neuropsychiatric conditions, including schizophrenia, Alzheimer's disease (AD), progressive supranuclear palsy, and post-traumatic stress disorder. Although several species have been used to examine EBC, the rabbit is unique in its tolerance for restraint, which facilitates imaging, its relatively large skull that facilitates chronic neuronal recordings, a genetic sequence for amyloid that is identical to humans which makes it a valuable model to study AD, and in contrast to rodents, it has a striatum that is differentiated into a caudate and a putamen that facilitates analysis of diseases involving the striatum. This review focuses on EBC during schizophrenia and AD since impairments in cerebro-cerebellar connections have been hypothesized to lead to a cognitive dysmetria. We also relate EBC to conditioned avoidance responses that are more often examined for effects of antipsychotic medications, and we propose that an analysis of novel object recognition (NOR) may add to our understanding of how the underlying neural circuitry has changed during disease states. We propose that the EBC and NOR paradigms will help to determine which therapeutics are effective for treating the cognitive aspects of schizophrenia and AD, and that neuroimaging may reveal biomarkers of the diseases and help to evaluate potential therapeutics. The rabbit, thus, provides an important translational system for studying neural mechanisms mediating maladaptive behaviors that underlie some psychiatric diseases, especially cognitive impairments associated with schizophrenia and AD, and object recognition provides a simple test of memory that can corroborate the results of EBC.

Clozapine and glycinamide prevent MK-801-induced deficits in the novel object recognition (NOR) test in the domestic rabbit (Oryctolagus cuniculus)

Studies in humans indicate that acute administration of sub-anesthetic doses of ketamine, an NMDA receptor antagonist, provokes schizophrenic-like symptoms in healthy volunteers, and exacerbates existing symptoms in individuals with schizophrenia. These and other findings suggest that NMDA receptor hypofunction might participate in the pathophysiology of schizophrenia, and have prompted the development of rodent pharmacological models for this disorder based on acute or subchronic treatment with NMDA receptor antagonists, as well as the development of novel pharmacotherapies based on increasing extrasynaptic glycine concentrations. In the present study, we tested whether acute hyperlocomotory behavior and/or deficits in the novel object recognition (NOR) task, induced in male rabbits by the acute subcutaneous (s.c.) administration of MK-801 (0.025 and 0.037 mg/kg s.c., respectively), were prevented by prior administration of the atypcial antipsychotic, clozapine (0.2mg/kg, s.c.), or the glycine pro-drug glycinamide (56 mg/kg, s.c.). We found that clozapine fully prevented the MK-801-induced hyperlocomotion, and both clozapine and glycinamide prevented MK-801-induced deficits in the NOR task. The present results show that MK-801-induced hyperlocomotion and deficits in the NOR task in the domestic rabbit demonstrate predictive validity as an alternative animal model for symptoms of schizophrenia. Moreover, these results indicate that glycinamide should be investigated in pre-clinical models of neuropsychiatric disorders such as schizophrenia, obsessive compulsive disorder and anxiety disorders, where augmentation of extrasynaptic glycine concentrations may have therapeutic utility.