Lurcher Mutant Mice Research Articles

Olivocerebellar fiber maturation in normal and lurcher mutant mice: Defective development in lurcher

Olivocerebellar fiber maturation was examined in normal and lurcher mutant mice between postnatal day 5 (P5) and P15, using the anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) from the inferior olive. Immunocytochemistry for the Purkinje cell marker PEP-19 was used to demonstrate Purkinje cell development in the same material. In mutant and normal animals, a regional developmental variation is observed such that, when compared at a given age, cortex lining the vermal fissures appears developmentally advanced over cortex in the cerebellar hemispheres. In the primary fissure of the normal animals, the first recognizable Purkinje cell dendrites appear on P6, and the olivocerebellar fibers first enter the climbing stage of their development on P9. In lurcher animals Purkinje cell development proceeds on this schedule, but olivocerebellar fibers are never observed to enter the molecular layer. These afferents maintain dense perisomatic nests around Purkinje cells, even in P13-15 lurchers. Examination of P14 lurchers by transmission electron microscopy indicates that the olivocerebellar fibers form synapses on Purkinje cell somatic spines and that the basket cell axons fail to form their typical perisomal nests around Purkinje cells. In addition, parallel fibers can be observed to synapse on dendritic spines on the Purkinje cell primary dendrites. We interpret these results as indicating a recognition defect between olivocerebellar fibers and Purkinje cell dendrites. An analysis of this defect in lurcher may reveal how the normal transformation of olivocerebellar fibers, from perisomal to dendritic terminals, is achieved.

Does the mutant mouse lurcher have deficits in spatially oriented behaviours?

Lurcher mutant mice, in comparison to normal mice, had directional deficits in the Morris milk tank test and in a water-maze spatial alternation task. The lurcher mutants also showed an initial lack of spontaneous alternation and did not alternate in one behavioral condition when the inter-trial interval was lengthened. Lurcher mice were slower to learn a simple left/right position response to escape a T-maze by swimming although their motor coordination was good. Paradoxically, no deficit was observed in learning to select a left or right position for food in the same T-maze although the goal-directed locomotion was very ataxic. Overall, the lurcher mutants have difficulty in guiding themselves in the water toward a visible goal.

Spontaneous alternation and habituation in lurcher mutant mice

There is a spontaneous degeneration of Purkinje cells, granule cells and inferior olivary neurons in lurcher mutant mice. It was found that, in comparison to littermate controls, the lurcher mutants alternated less often in a discrete two-trial procedure of spontaneous alternation and did not habituate to maze stimuli in a T-maze. Results are discussed in terms of a possible role for the cerebellum in spatial learning.

On the location of γ-aminobutyrate and benzodiazepine receptors in the cerebellum of the normal C3H and Lurcher mutant mouse

Binding of γ-aminobutyrate and benzodiazepine receptor ligands has been studied in the cerebellum of adult normal (C3H) and Lurcher mutant mice. The adult mutant has lost all Purkinje cells and more than 90% of the granule cells in the cerebellar cortex. When compared with their normal littermates Lurcher mice displayed large decreases in the number of high-affinity binding sites for [ 3H]muscimol, a synaptic γ-aminobutyrate receptor ligand, in washed cerebellar homogenates. This observation was consistent with the extensive loss of γ-aminobutyrate receptive Purkinje and granule cells from the Lurcher cerebellum. However, specific binding of the benzodiazepine-receptor ligand [ 3H]flunitrazepam to Lurcher cerebellum remained unchanged. Indeed quantitative autoradiography, employing [ 3H]flunitrazepam as a photoaffinity label, showed no significant differences in the density of labelling between Lurcher and normal littermate mice in any region of the cerebellum. These benzodiazepine binding sites in washed homogenates or tissue sections displayed a γ-aminobutyrate-induced enhancement of [ 3H]flunitrazepam binding which occurred to the same extent in both Lurcher and normal cerebellum, a facilitatory effect which could be blocked by the addition of bicuculline methobromide. Our results suggest that a large proportion of the high-affinity, specific benzodiazepine binding sites in mouse cerebellum are not coupled to the synaptic γ-aminobutyrate receptors thought to be labelled by high affinity [ 3H]muscimol binding. Further, that benzodiazepine binding sites do not appear to be enriched on either the soma or dendrites of Purkinje cells, as has been suggested from previous studies. Investigations at the electron microscope level are now required to elucidate the cellular location of benzodiazepine binding sites in the cerebellar cortex and to examine whether or not they are likely to be exposed to γ-aminobutyrate in vivo.

Binding studies in the lurcher mutant suggest an uneven distribution of putative benzodiazepine receptor subclasses in the mouse cerebellum

Binding studies using [ 3H]flunitrazepam in the cerebellum of normal and Lurcher mutant mice indicate that about 90% of the total benzodiazepine receptor population reside on the Purkinje and granule cells. Moreover, the specific binding of the BZ 1 receptor subclass specific ligand [ 3H]propyl-β-carboline-3-carboxylate suggests that neuronal elements of the mouse cerebellum other than the Purkinje and granule cells contain about 18% of the BZ 1 receptors but only about 7% of the BZ 2 receptors of the mouse cerebellum.

Interaction of granule, Purkinje and inferior olivary neurons in Lurcher chimaeric mice : I.Qualitative studies

Heterozygous lurcher (+/Lc) mutant mice lose 100% of their Purkinje cells (PCs), 90% of their granule cells, and 75% of their inferior olivary neurons. In order to determine the primary site of Lc gene action, lurcher in equilibrium wild-type aggregation chimaeras were produced. The cerebella of the three chimaeras examined were intermediate or normal in size compared to +/Lc and wild-type cerebella. The PCs were reduced in number. Using the beta-glucuronidase locus (Gus) as a cell marker, all of the PCs present were identified as having descended from the wild-type embryo. It appears that all of the +/Lc PCs degenerated. Hence, the Lc gene acts directly on PCs to cause their degeneration. The inferior olivary nuclei of the chimaeras seemed to have fewer neurons than wild-type but more than +/Lc animals. As revealed by beta-glucuronidase histochemistry, both +/+ and +/Lc cells were present, and the ratio of genotypes was similar to the ratio seen in other regions of the brain. The evidence suggests that the death of olivary neurons in lurcher is secondary to another defect, probably the loss of PCs. Beta-glucuronidase is not an accurate cell marker for granule cells, and so no conclusion concerning the action of the Lc gene on granule cells could be made with these chimaeras.

The identification of mossy fibres and their cells of origin in the normal and Lurcher mutant mouse

The behavioural mutant mouse Lurcher survives to adult life as the heterozygote (Lc/+) and shows a disorder of gait. The neurological lesion has been shown to involve degeneration of Purkinje cells and inferior olivary neurones (Caddy and Biscoe 1976). It follows that the climbing fibre input is reduced and we wished to know if the mossy fibre input was also affected. Heterozygote Lurcher mutants were compared with the wild type in all experiments. Mossy fibre glomeruli were identified in the cerebellum of the mutant mouse by electron microscopy. Horseradish peroxidase (HRP) was injected into the cerebellum and was found in the cells of Clarke's column in the spinal cord. Electrophysiological experiments showed that following stimulation of the sciatic nerve evoked responses could be recorded in the cerebellum. It is concluded that the mossy fibre input to the cerebellum is intact in the Lurcher mutant mouse.

Electrophysiological studies on interpositus neurones in the normal and Lurcher mutant mouse

The response characteristics of interpositus neurones (IP) to sciatic nerve stimulation were studied in normal and Lurcher mutant mice under pentobarbitone anaesthesia. The response of IP neurones in the normal mouse was a short latency bimodal excitation (E1-I1-E2) followed by a depression of the firing rate (I2) and ending with a longer latency excitation (E3) which was completed within 225 msec. The response of the majority of IP neurones in the Lurcher mouse was a short latency unimodal excitation (LE1) which corresponded in time to the E1-I1-E2 phase in the normal. This was followed by a pause in the excitation. The response ended with a longer latency excitation (LE2) corresponding in time to the E3 phase in the normal mouse but which persisted for a considerably greater period of time. The response of IP neurones in normal and Lurcher mice appear to be similar to those observed in the normal and experimentally cerebellar decorticate cat, respectively.

Cerebellar histogenesis in the lurcher (Lc) mutant mouse.

The postnatal development of the cerebellar cortex of normal and lurcher (Lc) mutant mice was studied by neurohistological and autoradiographic techniques at ages ranging from 2 days through 18 days after birth. Lurcher shows severe defects in the granule cells and Purkinje cells soon after birth. A decrease in the generative layers of the external granular layer is seen as early as two days in the lobulus simplex and by six days of age in the uvula. Granule cell death is common before and during granule cell migration, from 2 to 18 days of age. Loss of granule cells is reflected in reduced growth of the molecular and granular layers. Purkinje cell abnormalities appear at three to four days after birth in the form of crowding failure of nuclear growth, and condensed or lessened cytoplasm; Purkinje cell death is apparent at four to six days of age depending on the region of the cerebellum.

A quantitative study of the purkinje cells and olive neurones in the normal and lurcher mutant mouse

A quantitative study of the purkinje cells and olive neurones in the normal and lurcher mutant mouse

The number of Purkinje cells and olive neurones in the normal and Lurcher mutant mouse

The number of Purkinje cells and olive neurones in the normal and Lurcher mutant mouse

Brain abnormalities in the lurcher (Lc) mutant mouse.

Le cervelet des souris heterozygotes de la mutation «lurcher» (Lc) presentent des anomalies. Il est reduit et deforme, en particulier l'uvula vermis. On peut detecter ces anomalies chez le nouveau-ne de 3 jours avant l'apparition des aberrations du comportement.