Grating acuity of the Mongolian gerbil (Meriones unguiculatus)

Retinal neuroanatomy of two emerging model organisms, the spiny mouse (Acomys dimidiatus) and the Mongolian gerbil (Meriones unguiculatus)

Current research using animal models to investigate retinal cell biology and model retinal degenerative diseases largely utilize small mammals that are nocturnal and lack the ability to restore lost vision. In contrast, the Mongolian gerbil (Meriones) is a diurnal rodent with good photopic vision, and the spiny mouse (Acomys) is a small desert-dwelling rodent with remarkable regenerative capabilities. The goal of this study was to identify antibodies that detect retinal cell classes in Meriones and Acomys, and to describe the retinal anatomy of these two species in comparison to outbred laboratory mice (Mus musculus). Immunohistochemistry was performed on retinal sections with antibodies for various retinal cell types. Sections were imaged by light, fluorescence, and confocal microscopy. Cell density, morphology, and placement were compared between species qualitatively and quantitatively. Our analyses revealed a classic assembly of retinal cells in Meriones and Acomys, with a few deviations compared to Mus. Meriones displayed the highest density of cones and Acomys the lowest. A higher density of bipolar cell bodies in the proximal portion of the inner nuclear layer was observed in both Acomys and Meriones compared to Mus, and both species exhibited an increase in amacrine cell density compared to Mus. Our results provide a foundation for future research into the visual system adaptations of these interesting species.

Superior semicircular canal dehiscence and subsequent closure induces reversible impaired decision-making

Background

Vestibular loss and dysfunction has been associated with cognitive deficits, decreased spatial navigation, spatial memory, visuospatial ability, attention, executive function, and processing speed among others. Superior semicircular canal dehiscence (SSCD) is a vestibular-cochlear disorder in humans in which a pathological third mobile window of the otic capsule creates changes to the flow of sound pressure energy through the perilymph/endolymph. The primary symptoms include sound-induced dizziness/vertigo, inner ear conductive hearing loss, autophony, headaches, and visual problems; however, individuals also experience measurable deficits in basic decision-making, short-term memory, concentration, spatial cognition, and depression. These suggest central mechanisms of impairment are associated with vestibular disorders; therefore, we directly tested this hypothesis using both an auditory and visual decision-making task of varying difficulty levels in our model of SSCD.

Methods

Adult Mongolian gerbils (n = 33) were trained on one of four versions of a Go-NoGo stimulus presentation rate discrimination task that included standard ("easy") or more difficult ("hard") auditory and visual stimuli. After 10 days of training, preoperative ABR and c+VEMP testing was followed by a surgical fenestration of the left superior semicircular canal. Animals with persistent circling or head tilt were excluded to minimize effects from acute vestibular injury. Testing recommenced at postoperative day 5 and continued through postoperative day 15 at which point final ABR and c+VEMP testing was carried out.

Results

Behavioral data (d-primes) were compared between preoperative performance (training day 8-10) and postoperative days 6-8 and 13-15. Behavioral performance was measured during the peak of SSCD induced ABR and c + VEMP impairment and the return towards baseline as the dehiscence began to resurface by osteoneogenesis. There were significant differences in behavioral performance (d-prime) and its behavioral components (Hits, Misses, False Alarms, and Correct Rejections). These changes were highly correlated with persistent deficits in c + VEMPs at the end of training (postoperative day 15). The controls demonstrated additional learning post procedure that was absent in the SSCD group.

Conclusion

These results suggest that aberrant asymmetric vestibular output results in decision-making impairments in these discrimination tasks and could be associated with the other cognitive impairments resulting from vestibular dysfunction.

New Animal Models for Understanding FMRP Functions and FXS Pathology

Fragile X encompasses a range of genetic conditions, all of which result as a function of changes within the FMR1 gene and abnormal production and/or expression of the FMR1 gene products. Individuals with Fragile X syndrome (FXS), the most common heritable form of intellectual disability, have a full-mutation sequence (>200 CGG repeats) which brings about transcriptional silencing of FMR1 and loss of FMR protein (FMRP). Despite considerable progress in our understanding of FXS, safe, effective, and reliable treatments that either prevent or reduce the severity of the FXS phenotype have not been approved. While current FXS animal models contribute their own unique understanding to the molecular, cellular, physiological, and behavioral deficits associated with FXS, no single animal model is able to fully recreate the FXS phenotype. This review will describe the status and rationale in the development, validation, and utility of three emerging animal model systems for FXS, namely the nonhuman primate (NHP), Mongolian gerbil, and chicken. These developing animal models will provide a sophisticated resource in which the deficits in complex functions of perception, action, and cognition in the human disorder are accurately reflected and aid in the successful translation of novel therapeutics and interventions to the clinic setting.

The Organization of Somatostatin-Immunoreactive Cells in the Visual Cortex of the Gerbil

Somatostatin (SST) is widely expressed in the brain and plays various, vital roles involved in neuromodulation. The purpose of this study is to characterize the organization of SST neurons in the Mongolian gerbil visual cortex (VC) using immunocytochemistry, quantitative analysis, and confocal microscopy. As a diurnal animal, the Mongolian gerbil provides us with a different perspective to other commonly used nocturnal rodent models. In this study, SST neurons were located in all layers of the VC except in layer I; they were most common in layer V. Most SST neurons were multipolar round/oval or stellate cells. No pyramidal neurons were found. Moreover, 2-color immunofluorescence revealed that only 33.50%, 24.05%, 16.73%, 0%, and 64.57% of SST neurons contained gamma-aminobutyric acid, calbindin-D28K, calretinin, parvalbumin, and calcium/calmodulin-dependent protein kinase II, respectively. In contrast, neuropeptide Y and nitric oxide synthase were abundantly expressed, with 80.07% and 75.41% in SST neurons, respectively. Our immunocytochemical analyses of SST with D₁ and D₂ dopamine receptors and choline acetyltransferase, α₇ and β₂ nicotinic acetylcholine receptors suggest that dopaminergic and cholinergic fibers contact some SST neurons. The results showed some distinguishable features of SST neurons and provided some insight into their afferent circuitry in the gerbil VC. These findings may support future studies investigating the role of SST neurons in visual processing.

Graded remapping of hippocampal ensembles under sensory conflicts

Hippocampal place cells are thought to constitute a cognitive map of space derived from multimodal sensory inputs. Alteration of allocentric (visual) cues in a fixed environment is known to induce modulations of place cell activity to varying degrees from rate changes to global remapping. To determine how hippocampal ensembles combine multimodal sensory cues, we examine hippocampal CA1 remapping in Mongolian gerbils in a 1D virtual reality experiment, during which self-motion cues (locomotor, vestibular, and optic flow information) and allocentric visual cues are altered. We observe that self-motion cues are over-represented, but responsiveness to allocentric visual cues, although task-irrelevant, elicits both rate and global remapping in the hippocampal ensemble. We propose that remapping can be reconciled by considering global, partial, and rate remapping on a continuous scale on which the graded change of activity in the entire CA1 population can be interpreted as the expectancy about the animal's spatial environment.

Auditory-induced visual illusions in rodents measured by spontaneous behavioural response

When two brief sounds are presented with a short flash of light, we often perceive that the flash blinks twice. This phenomenon, called the “sound-induced flash illusion”, has been investigated as an example of how humans finely integrate multisensory information, more specifically, the temporal content of perception. However, it is unclear whether nonhuman animals experience the illusion. Therefore, we investigated whether the Mongolian gerbil, a rodent with relatively good eyesight, experiences this illusion. The novel object recognition (NOR) paradigm was used to evaluate the gerbil’s natural (i.e., untrained) capacity for multimodal integration. A light-emitting diode embedded within an object presented time-varying visual stimuli (different flashing patterns). The animals were first familiarised with repetitive single flashes. Then, various sound stimuli were introduced during test trials. An increase in exploration suggested that the animals perceived a flashing pattern differently only when the contradicting sound (double beeps) was presented simultaneously with a single flash. This result shows that the gerbil may experience the sound-induced flash illusion and indicates for the first time that rodents may have the capacity to integrate temporal content of perception in a sophisticated manner as do humans.

Early Sensory Loss Alters the Dendritic Branching and Spine Density of Supragranular Pyramidal Neurons in Rodent Primary Sensory Cortices

Multisensory integration in primary auditory (A1), visual (V1), and somatosensory cortex (S1) is substantially mediated by their direct interconnections and by thalamic inputs across the sensory modalities. We have previously shown in rodents (Mongolian gerbils) that during postnatal development, the anatomical and functional strengths of these crossmodal and also of sensory matched connections are determined by early auditory, somatosensory, and visual experience. Because supragranular layer III pyramidal neurons are major targets of corticocortical and thalamocortical connections, we investigated in this follow-up study how the loss of early sensory experience changes their dendritic morphology. Gerbils were sensory deprived early in development by either bilateral sciatic nerve transection at postnatal day (P) 5, ototoxic inner hair cell damage at P10, or eye enucleation at P10. Sholl and branch order analyses of Golgi-stained layer III pyramidal neurons at P28, which demarcates the end of the sensory critical period in this species, revealed that visual and somatosensory deprivation leads to a general increase of apical and basal dendritic branching in A1, V1, and S1. In contrast, dendritic branching, particularly of apical dendrites, decreased in all three areas following auditory deprivation. Generally, the number of spines, and consequently spine density, along the apical and basal dendrites decreased in both sensory deprived and non-deprived cortical areas. Therefore, we conclude that the loss of early sensory experience induces a refinement of corticocortical crossmodal and other cortical and thalamic connections by pruning of dendritic spines at the end of the critical period. Based on present and previous own results and on findings from the literature, we propose a scenario for multisensory development following early sensory loss.

Effects of adaptation to handling on the circadian rhythmicity of blood solutes in Mongolian gerbils

The Mongolian gerbil has been widely used in many research fields and has been reported to be a diurnal laboratory animal. The circadian rhythmicity of these gerbils was investigated in the present study by measuring two hormones that show daily oscillations, cortisol and ACTH, in serum using ELISA kits. The levels of the two hormones were highest at 8:00 am and their rhythmic changes were similar to those in humans. In addition, the influence of stress of handling and blood collection on the physiological parameters of the gerbils was examined. After adaptation to handling for 1 week, some serum parameters in the animals changed. Handling and blood collection did not impact significantly on the following parameters: creatine kinase (CK), lactate dehydrogenase (LD), alanine aminotransferase (ALT), aspartate transaminase (AST), blood urea nitrogen (BUN), and albumin (ALB). However, blood glucose (GLU), total protein (TP) and globulin (GLB) significantly increased while creatinine (CRE) and albumin/globulin (A/G) significantly decreased after adaptation. This work further confirms that the Mongolian gerbil is a diurnal animal and also indicates that a suitable adaptation procedure is necessary for getting reliable results when performing experiments using these animals.

De novo sequencing and initial annotation of the Mongolian gerbil (Meriones unguiculatus) genome

The Mongolian gerbil (Meriones unguiculatus) is a member of the rodent family that displays several features not found in mice or rats, including sensory specializations and social patterns more similar to those in humans. These features have made gerbils a valuable animal for research studies of auditory and visual processing, brain development, learning and memory, and neurological disorders. Here, we report the whole gerbil annotated genome sequence, and identify important similarities and differences to the human and mouse genomes. We further analyze the chromosomal structure of eight genes with high relevance for controlling neural signaling and demonstrate a high degree of homology between these genes in mouse and gerbil. This homology increases the likelihood that individual genes can be rapidly identified in gerbil and used for genetic manipulations. The availability of the gerbil genome provides a foundation for advancing our knowledge towards understanding evolution, behavior and neural function in mammals. ACCESSION NUMBER: The Whole Genome Shotgun sequence data from this project has been deposited at DDBJ/ENA/GenBank under the accession NHTI00000000. The version described in this paper is version NHTI01000000. The fragment reads, and mate pair reads have been deposited in the Sequence Read Archive under BioSample accession SAMN06897401.

The hippocampal code for space in Mongolian gerbils

Large parts of our knowledge about the physiology of the hippocampus in the intact brain are derived from studies in rats and mice. While many of those findings fit well to the limited data available from humans and primates, there are also marked differences, for example, in hippocampal oscillation frequencies and in the persistence of theta oscillations. To test whether the distinct sensory specializations of the visual and auditory system of primates play a key role in explaining these differences, we recorded basic hippocampal physiological properties in Mongolian gerbils, a rodent species with high visual acuity, and good low-frequency hearing, similar to humans. We found that gerbils show only minor differences to rats regarding hippocampal place field activity, theta properties (frequency, persistence, phase precession, theta compression), and sharp wave ripple events. The only major difference between rats and gerbils was a considerably higher degree of head direction selectivity of gerbil place fields, which may be explained by their visual system being able to better resolve distant cues. Thus, differences in sensory specializations between rodent species only affect hippocampal circuit dynamics to a minor extent, which implies that differences to other mammalian lineages, such as bats and primates, cannot be solely explained by specialization in the auditory or visual system.

Mongolian gerbils learn to navigate in complex virtual spaces

Virtual reality (VR) environments are increasingly used to study spatial navigation in rodents. So far behavioral paradigms in virtual realities have been limited to linear tracks or open fields. However, little is known whether rodents can learn to navigate in more complex virtual spaces. We used a VR setup with a spherical treadmill but no head-fixation, which permits animals not only to move in a virtual environment but also to freely rotate around their vertical body axis. We trained Mongolian gerbils to perform spatial tasks in virtual mazes of different complexity. Initially the animals learned to run back and forth between the two ends of a virtual linear track for food reward. Performance, measured as path length and running time between the virtual reward locations, improved to asymptotic performance within about five training sessions. When more complex mazes were presented after this training epoch, the animals generalized and explored the new environments already at their first exposure. In a final experiment, the animals also learned to perform a two-alternative forced choice task in a virtual Y-maze. Our data thus shows that gerbils can be trained to solve spatial tasks in virtual mazes and that this behavior can be used as a readout for psychophysical measurements.

Laminar firing and membrane dynamics in four visual areas exposed to two objects moving to occlusion

It is not known how visual cortical neurons react to several moving objects and how their firing to the motion of one object is affected by neurons firing to another moving object. Here we combine imaging of voltage sensitive dye (VSD) signals, reflecting the population membrane potential from ferret visual areas 17, 18, 19, and 21, with laminar recordings of multiunit activity, (MUA), when two bars moved toward each other in the visual field, occluded one another, and continued on in opposite directions. Two zones of peak MUA, mapping the bars' motion, moved toward each other along the area 17/18 border, which in the ferret maps the vertical meridian of the field of view. This was reflected also in the VSD signal, at both the 17/18 border as well as at the 19/21 border with a short delay. After some 125 ms at the area 19/21 border, the VSD signal increased and became elongated in the direction of motion in front of both of the moving representations. This was directly followed by the phase of the signal reversing and travelling back from the 19/21 border toward the 17/18 border, seemingly without respect for retinotopic boundaries, where it arrived at 150 ms after stimulus onset. At this point the VSD signal in front of the moving bar representations along the 17/18 border also increased and became elongated in the direction of object motion; the signal now being the linear sum of what has been observed in response to single moving bars. When the neuronal populations representing the bars were some 600 μm apart on the cortex, the dye signal and laminar MUA decreased strongly, with the MUA scaling to that of a single bar during occlusion. Despite a short rebound of the dye signal and MUA, the MUA after the occlusion was significantly depressed. The interactions between the neuronal populations mapping the bars' position, and the neurons in between these populations were, apart from 19/21 to 17/18 interaction, mainly lateral-horizontal; first excitatory and inducing firing at the site of future occlusion, then inhibitory just prior to occlusion. After occlusion the neurons that had fired already to the first bar showed delayed and prolonged inhibition in response to the second bar. Thus, the interactions that were particular to the occlusion condition in these experiments were local and inhibitory at short cortical range, and delayed and inhibitory after the occlusion when the bars moved further apart.

The effect of ecologically relevant variations in light level on the performance of Mongolian gerbils on two visual tasks

Tests of rodent visual capacities are typically performed under standard laboratory illumination. However, light level can have subtle and complex effects on behavior in rodents. We tested Mongolian gerbils (Meriones unguiculatus) - a species that shows individual differences in activity pattern - on visual tasks at three ecologically relevant levels of ambient illuminance: approximating moonlight (1 lx), dawn or dusk (10 lx), and low daylight (100 lx). A jumping task and a grating discrimination quantified depth perception and grating acuity, respectively. Illuminance variations had important effects on behavior. Gerbils jumped faster in lower light on the depth discrimination task, but were also less accurate than in bright light. Daytime activity levels (possibly reflecting variations in activity pattern) mediated these effects, with animals that were awake during a lower proportion of daytime hours exhibiting a trend toward jumping faster with lower light level as compared to more day-active gerbils. Moreover, while illuminance did not affect acuity overall, it interacted with activity levels in a complex way: in both the darkest and lowest light levels, animals that were awake during a greater proportion of daytime hours showed higher acuity levels than animals that were less active during the day. These results indicate that gerbils show behavioral profiles in vision tasks that represent an interaction between visual ability and illuminance-sensitive motivational or emotional actors, perhaps including chronotype. Thus, the most ecologically relevant assessments of the visual performance of rodents will likely be achieved by testing at species-specific preferred light levels.

Discriminative performance of the domestic hen in a visual acuity task

The performance of 6 domestic hens on a visual acuity task was studied using a spatial discrete-trial conditional discrimination procedure. Gray stimuli and vertical square-wave gratings, ranging in spatial frequency from 1 to 10 cycles per millimeter, were presented in a descending and ascending series of probes. On each trial, either a grating or gray stimulus was presented. Only one spatial frequency of grating was presented during each session. Between probe sessions, training continued at the coarsest grating value. Stimulus discriminability, measured as values of log d, changed with changes in grating spatial frequency for both probe series. Fitted lines described the linear portion of the psychometric functions. Thresholds estimated from the lines generally ranged from four to six cycles per degree, with slightly greater estimates from data from the descending probe series. There were no systematic changes in response bias as a function of grating spatial frequency.

Testing the spatial- versus object-learning distinction: water-maze performance of male rats exposed to ethanol during the brain growth spurt

This study investigated the effects of exposure to ethanol during the brain growth spurt on a visual-discrimination (VD) and a place-learning task (PL) using intra-maze cues in the water maze. Artificially reared male Long-Evans rats were exposed to ethanol (ET) in a binge pattern from postnatal days 6-9 (6.5 g kg(-1) x day(-1); BAC approximately 330 mg/dl) or an isocaloric maltose-dextrin solution (gastrostomy control). A third suckled control group was reared by lactating dams. In experiment 1, rats were trained to discriminate horizontal- (H) versus vertical-striped (V) cues, with the positive cue providing escape from water. Groups did not differ with V+, but ET rats made more errors with H+. In experiment 2, the ET group was impaired in learning the spatial location of a submerged platform relative to intra-maze cues. In both tasks, acquisition deficits among ET rats were characterized by impairment emerging at trial 2, with intact reference memory on trial 1, and the ET group reached a comparable level of performance to controls by the end of training. In summary, because impairment was related to task characteristics, a clear distinction between impaired spatial- versus cue-based learning was not supported. However, these findings do support an effect of exposure to ethanol during the brain growth spurt on recent event, but not reference, memory.

Behavioral assessment of visual acuity in mice and rats

We have developed a simple computer-based discrimination task that enables the quick determination of visual acuities in rodents. A grating is displayed randomly on one of two monitors at the wide end of a trapezoidal-shaped tank containing shallow water. Animals are trained to swim toward the screens, and at a fixed distance, choose the screen displaying the grating and escape to a submerged platform hidden below it. Both mice and rats learn the task quickly. Performance falls below 70% when the spatial frequency is increased beyond 0.5 cycles in most C57BU6 mice, and around 1.0 cycles per degree (cpd) in Long-Evans rats.

The effects of cortical lesions on recognition of object context in a visuomotor task in the Mongolian gerbil

Two experiments were carried out in order to determine the effects of either parietal or temporal lesions on performance in a depth vision task in which gerbils normally use retinal image size (RIS) as a cue to distance. In the first experiment, gerbils were trained to jump to two training targets that differed in size and which were always presented with distinctive local features and in a particular spatial location. After lesions, gerbils were presented with further training trials and sets of probe trials in which they were presented with targets that differed in width from the training targets, and sets of local features and distal cues that either matched or mismatched those presented during training. Shams and temporal animals made predictable over- or underjumps when local feature and distal information matched, and stopped using retinal image size when they did not match. Parietal animals did not use retinal image size either during the match or the mismatch conditions. In a second experiment, gerbils with parietal lesions were shown capable of using retinal image size in a simpler task that did not contain distinguishing local features or distal cues. Taken together, these results suggest that parietal lesions in gerbils disrupt object recognition, when the purpose of the recognition process is to complete a distance estimate for a visuomotor act.

Sensitivity to ultraviolet light in the gerbil (Meriones unguiculatus): characteristics and mechanisms

In earlier electrophysiological experiments on the Mongolian gerbil (Meriones unguiculatus) evidence was obtained to suggest that the retina of this rodent contains only a single type of cone. The cones were found to have peak sensitivity of about 493 nm. Gerbil rods have peak sensitivity of about 500 nm, yielding a Purkinje shift that is small in magnitude and reversed in direction from that conventionally found among mammals. In a series of experiments we extended electrophysiological and behavioral measurements to include UV stimulation and this reveals a second photopic mechanism. Several pieces of evidence suggest this second mechanism is a cone having peak sensitivity of about 360 nm. Results from adaptation experiments show that the sensitivities of the two cone mechanisms can be independently manipulated, and thus they presumably reflect the operation of two types of cone photopigment. The results from behavioral experiments verify that the gerbil UV mechanism provides information that can be used to make visual discriminations based on intensity differences. A test of color vision additionally suggests that the two cone pigments can support some color discriminations.

Visual factors in sound localization in mammals

The ability of mammals to localize sound varies widely among species. During the past decade, evidence has accumulated that this variation cannot be accounted for simply on the basis of the availability of the physical cues for locus. Evidence is presented that a major factor in sound localization is the need to direct the field of best vision to a sound source for further scrutiny. Thus, species with broad fields of best vision (such as visual streaks) require less accurate information regarding the location of a sound source than do species with very narrow fields of best vision (such as foveae). To support this suggestion, data are reported for the width of the field of best vision in the form of retinal ganglion cell isodensity contours for thirteen species of mammals. The possible contribution of other factors including binocular fields, visual acuity, and the degree to which a species is predatory in lifestyle, is also examined.

The role of image size and retinal motion in the computation of absolute distance by the Mongolian gerbil (Meriones unguiculatus)

In a series of experiments in which Mongolian gerbils were trained to jump over a variable gap, it was demonstrated that computation of the distance to be jumped was dependent on both image size and retinal motion, the latter cue being generated by the production of vertical translation movements of the head (head bobs). When image size was not a reliable cue, the animals produced more head bobs, thereby increasing the availability of retinal motion cues. The performance of the gerbils on various probe trials strongly suggested that they computed absolute distance by combining information about the velocity (or amplitude) of their head bobs with information about the velocity (or displacement) of the moving image of the landing platform.

Landmark learning and visuo-spatial memories in gerbils

The aim of this study is to understand what a rodent (Meriones unguiculatus) learns about the geometrical relations between a goal and nearby visual landmarks and how it uses this information to reach a goal. Gerbils were trained to find sunflower seeds on the floor of a light-tight, black painted room illuminated by a single light bulb hung from the ceiling. The position of the seed on the floor was specified by an array of one or more landmarks. Once training was complete, we recorded where the gerbils searched when landmarks were present but the seed was absent. In such tests, gerbils were confronted either with the array of landmarks to which they were accustomed or with a transformation of this array. Animals searched in the appropriate spot when trained to find seeds placed in a constant direction and at a constant distance from a single cylindrical landmark. Since gerbils look in one spot and not in a circle centred on the landmark, the direction between landmark and goal must be supplied by cues external to the landmark array. Distance, on the other hand, must be measured with respect to the landmark. Tests in which the size of the landmark was altered from that used in training suggest that distance is not learned solely in terms of the apparent size of the landmark as seen from the goal. Gerbils can still reach a goal defined by an array of landmarks when the room light is extinguished during their approach. This ability implies that they have already planned a trajectory to the goal before the room is darkened. In order to compute such a trajectory, their internal representation of landmarks and goal needs to contain information about the distances and bearings between landmarks and goal. For planning trajectories, each landmark of an array can be used separately from the others. Gerbils trained to a goal specified by an array of several landmarks were tested with one or more of the landmarks removed or with the array expanded. They then searched as though they had computed an independent trajectory for each landmark. For instance, gerbils trained with an array of two landmarks were tested with the distance between two landmarks doubled. The animals then searched for seeds in two positions, which were at the correct distance and in the right direction from each landmark.(ABSTRACT TRUNCATED AT 400 WORDS)

Some effects of early monocular deprivation in the Mongolian gerbil

The effects of short- and long-term early monocular deprivation were investigated in 4 Mongolian gerbils using interocular differences in grating acuity as a measure of deprivation-induced impairment. All gerbils showed acuity deficits in the initially deprived eye, ranging in magnitude from 0.24-1.40 octaves. One month of monocular deprivation from eye opening proved sufficient to induce a permanent acuity impairment.

The gerbil: a unique model for research on aging

The Mongolian gerbil (Meriones unguicultatus) is suggested as a model for aging research because of its unique physiological attributes, ease of handling, and because of data previously collected. Factors that demonstrate the gerbils' suitability in fulfulling practical and scientific considerations important in determining a model for aging research are listed. Additionally, several unique physiological attributes of gerbils are described. Based on these attributes and on review of research in gerbils, it is suggested that gerbils can serve as animal models for behavioral and biological processes, and for normative and pathological aspects for aging.

Distance estimation in the Mongolian gerbil: the role of dynamic depth cues

The role of dynamic depth cues in distance estimation was investigated in the Mongolian gerbil. Animals were trained to jump randomly varied distances on a jumping stand under both binocular and monocular conditions. Videotape analysis revealed that prior to jumping, the gerbils executed a series of vertical head movements, the amplitude and velocity of which were related to the gap distance and to each animal's accuracy. This suggested that the gerbils were employing motion parallax cues to judge distance. An inverse relation between the magnitude of forward movement and the frequency of vertical head movements suggested that loom cues were also being used to judge distance. This hypothesis received support from a second experiment in which forward movements were constrained by a short take-off platform. In this condition, frequency of vertical head movements increased, suggesting that a compensation had occurred for the loss of information from loom.

The development of visual acuity in the Mongolian gerbil (Meriones unguiculatus)

The development of visual acuity for vertically oriented gratings was followed in gerbil pups from 34 days of age until adulthood using a jumping stand procedure. Acuity was found to improve gradually from an initial level of about 0.7 cycles/degree to asymptotic values of 1.2-1.6 cycles/degree by 70 days of age. Acuity did not vary as a function of viewing distance over the range tested (17.5-46 cm). Practice was found to play some role in the acuity changes seen but cannot alone explain the results. The contributions of other performance variables and of neural development are considered.