The development of swimming behavior in the neurological mutant weaver mouse

Maturation of Purkinje cell firing properties relies on neurogenesis of excitatory neurons

Preterm infants that suffer cerebellar insults often develop motor disorders and cognitive difficulty. Excitatory granule cells, the most numerous neuron type in the brain, are especially vulnerable and likely instigate disease by impairing the function of their targets, the Purkinje cells. Here, we use regional genetic manipulations and in vivo electrophysiology to test whether excitatory neurons establish the firing properties of Purkinje cells during postnatal mouse development. We generated mutant mice that lack the majority of excitatory cerebellar neurons and tracked the structural and functional consequences on Purkinje cells. We reveal that Purkinje cells fail to acquire their typical morphology and connectivity, and that the concomitant transformation of Purkinje cell firing activity does not occur either. We also show that our mutant pups have impaired motor behaviors and vocal skills. These data argue that excitatory cerebellar neurons define the maturation time-window for postnatal Purkinje cell functions and refine cerebellar-dependent behaviors.

Interactions Between Purkinje Cells and Granule Cells Coordinate the Development of Functional Cerebellar Circuits

Cerebellar development has a remarkably protracted morphogenetic timeline that is coordinated by multiple cell types. Here, we discuss the intriguing cellular consequences of interactions between inhibitory Purkinje cells and excitatory granule cells during embryonic and postnatal development. Purkinje cells are central to all cerebellar circuits, they are the first cerebellar cortical neurons to be born, and based on their cellular and molecular signaling, they are considered the master regulators of cerebellar development. Although rudimentary Purkinje cell circuits are already present at birth, their connectivity is morphologically and functionally distinct from their mature counterparts. The establishment of the Purkinje cell circuit with its mature firing properties has a temporal dependence on cues provided by granule cells. Granule cells are the latest born, yet most populous, neuronal type in the cerebellar cortex. They provide a combination of mechanical, molecular and activity-based cues that shape the maturation of Purkinje cell structure, connectivity and function. We propose that the wiring of Purkinje cells for function falls into two developmental phases: an initial phase that is guided by intrinsic mechanisms and a later phase that is guided by dynamically-acting cues, some of which are provided by granule cells. In this review, we highlight the mechanisms that granule cells use to help establish the unique properties of Purkinje cell firing.

Behavioral effects of neonatal lesions on the cerebellar system

Several rodent models with spontaneous mutations causing cerebellar pathology are impaired in motor functions during the neonatal period, including Grid2(Lc), Rora(sg), Dab1(scm), Girk2(Wv), Lmx1a(dr-sst), Myo5a(dn), Inpp4a(wbl), and Cacna1a(rol) mice as well as shaker and dystonic rats. Deficits are also evident in murine null mutants such as Zic1, Fgfr1/FgFr2, and Xpa/Ercc8. Behavioral deficits are time-dependent following X-irradiated- or aspiration-induced lesions of the cerebellum in rats. In addition, motor functions are deficient after lesions in cerebellar-related pathways. As in animal subjects, sensorimotor disturbances have been described in children with cerebellar lesions. These results underline the importance of the cerebellum and its connections in the development of motor functions.

Enrichment from birth accelerates the functional and cellular development of a motor control area in the mouse

Background

There is strong evidence that sensory experience in early life has a profound influence on the development of sensory circuits. Very little is known, however, about the role of experience in the early development of striatal networks which regulate both motor and cognitive function. To address this, we have investigated the influence of early environmental enrichment on motor development.

Methodology/Principal Findings

Mice were raised in standard or enriched housing from birth. For animals assessed as adults, half of the mice had their rearing condition reversed at weaning to enable the examination of the effects of pre- versus post-weaning enrichment. We found that exclusively pre-weaning enrichment significantly improved performance on the Morris water maze compared to non-enriched mice. The effects of early enrichment on the emergence of motor programs were assessed by performing behavioural tests at postnatal day 10. Enriched mice traversed a significantly larger region of the test arena in an open-field test and had improved swimming ability compared to non-enriched cohorts. A potential cellular correlate of these changes was investigated using Wisteria-floribunda agglutinin (WFA) staining to mark chondroitin-sulfate proteoglycans (CSPGs). We found that the previously reported transition of CSPG staining from striosome-associated clouds to matrix-associated perineuronal nets (PNNs) is accelerated in enriched mice.

Conclusions/Significance

This is the first demonstration that the early emergence of exploratory as well as coordinated movement is sensitive to experience. These behavioural changes are correlated with an acceleration of the emergence of striatal PNNs suggesting that they may consolidate the neural circuits underlying these behaviours. Finally, we confirm that pre-weaning experience can lead to life long changes in the learning ability of mice.

Regional brain variations of cytochrome oxidase activity and motor coordination in Girk2Wv (Weaver) mutant mice

The Girk2(Wv) (weaver) phenotype, caused by a mutated inward rectifying potassium channel, is characterized by degeneration of cerebellar granule cell population as well as midbrain dopamine-containing cells of the nigrostriatal pathway. To investigate the regional brain metabolic consequences of this combined pathology, cytochrome oxidase (CO) activity was measured by histochemistry from brain regions of wild-type and homozygous Girk2(Wv) mutant mice and correlated with motor performances. CO activity of Girk2(Wv) mutants was abnormal in cerebellar cortex, dentate nucleus, and brainstem regions (medial and lateral vestibular nuclei, prepositus, superior colliculus, lateral cuneiform nucleus, and reticular nuclei) implicated in the gaze system. CO activity increased in midbrain dopaminergic regions after correcting for tissue density, regions with severe depletion of tyrosine hydroxylase activity. Forebrain regions were relatively spared in term of CO activity, except for subthalamic nucleus, lateral geniculate nucleus, and cortical eye field. Similarly to the Rora(sg) cerebellar mutant, metabolic alterations in cerebellar and vestibular regions were linearly correlated with poor motor coordination, underlining the sensitivity of these tests to cerebellar dysfunction.

Spontaneous and induced mouse mutations with cerebellar dysfunctions: behavior and neurochemistry

Grid2(Lc) (Lurcher), Grid2(ho) (hot-foot), Rora(sg) (staggerer), nr (nervous), Agtpbp1(pcd) (Purkinje cell degeneration), Reln(rl) (reeler), and Girk2(Wv) (Weaver) are spontaneous mutations with cerebellar atrophy, ataxia, and deficits in motor coordination tasks requiring balance and equilibrium. In addition to these signs, the Dst(dt) (dystonia musculorum) spinocerebellar mutant displays dystonic postures and crawling. More recently, transgenic models with human spinocerebellar ataxia mutations and alterations in calcium homeostasis have been shown to exhibit cerebellar anomalies and motor coordination deficits. We describe neurochemical characteristics of these mutants with respect to regional brain metabolism as well as amino acid and biogenic amine concentrations, uptake sites, and receptors.

Grooming in Lurcher mutant mice

Lurcher mutant mice, characterized by degeneration of cerebellar Purkinje cells and granule cells, were compared to normal littermate controls for different facets of grooming and nongrooming behaviors after a brief period of water immersion. By comparison to normal controls, the number and the duration of several grooming components were decreased in Lurcher mutant mice, namely, licking the forelimb, the abdomen, the back, and the hindlimb. By contrast, the number and duration of body-shaking episodes were not reduced. Lurcher mutants had fewer grooming elements for bouts with at least five elements. However, the serial organization of grooming, as determined by the order of appearance of grooming elements, was maintained in Lurcher mutants. These results indicate that the cerebellar cortex is involved in the appearance of various grooming elements but not in the organization of the cephalocaudal sequence.

Neurobehavioral evaluation of lurcher mutant mice during ontogeny

Lurcher mutant mice were compared to normal littermate controls for body weight, body righting, negative geotropism, sensorimotor coordination (rotating grid, wire suspension, rotorod), and visuomotor coordination requiring swimming toward a pole during postnatal (P) days 0-30. Lurcher mutants had a lower body weight on P20-P30 and were slower before performing the complete body righting response on P13-P30. Because of postural instability during the negative geotropism test, lurcher mutants turned quicker up the slope than normal mice. The mutants fell sooner from the rotating grid on P11-P14, from the horizontal wire on P15-P16, and from the rotorod on P14-P30. Lurcher mutants were also slower before swimming to the pole or climbing to the top of the pole and were inferior in pole climbing height on P22-P30. These results indicate test-selective and time-selective neurobehavioral deficits during ontogeny in a spontaneous cerebellar mutant.

Separation of activation and pattern in grooming development of weaver mice

The effects of environmental conditions and age on grooming behavior were examined in weaver mutant mice and control littermates. Due to deficits in both the cerebellum and the dopaminergic system, weaver mice provide an opportunity to investigate how both of these systems are involved in grooming. Although homozygous weaver (wv/wv mice display deficiencies in grooming behavior, our results indicate that these effects are both context and age dependent. Overall wv/wv mice spent less time grooming than did controls. However, during the post-swim period wv/wv, after day 13, reached the grooming levels of pre-swim control mice. After day 15 wv/wv mice showed a higher number of post-swim grooming bouts relative to pre-swim, and in fact exceeded the number of bouts performed by controls in either pre- or post-swim conditions. Although controls displayed longer bouts than mutants overall, during the post-swim period wv/wv mice, after day 13, produced bouts as long as the control animals did pre-swim. This could in part reflect activation by previous swimming. Our data indicate these activational effects can be separated from balance or posture problems. From examination of the individual grooming stroke types used by the two groups, it is evident that the strokes used by mutant animals clustered around the early grooming sequence phase. In contrast, some of the later strokes were never used by the wv/wv mice during the entire developmental period studied. Our results emphasize the importance of using multiple measures of an action sequence and testing under different conditions.