Characterization of a C57BL/6 congenic mouse strain of mucopolysaccharidosis type IIIA

The original mucopolysaccharidosis type IIIA (MPS IIIA) mice were identified in a mixed background with contributions from four different strains. To ensure long-term stability and genetic homogeneity of this lysosomal storage disease (LSD) model, the aim of this study was to develop and characterize a C57BL/6 congenic strain. The B6.Cg-Sgsh(mps3a) strain compares favorably with the original mixed donor strain, exhibiting low liver sulfamidase activity and significant brain heparan sulfate-derived disaccharide elevation from birth. A rapid increase in brain disaccharide levels occurred after birth, with a plateau reached by 13 weeks of age at 110x the levels observed in brains of age-matched unaffected mice. Typical lysosomal inclusions were observed in cerebral cortical and cerebellar neurons and in liver hepatocytes and Kupffer cells. Ubiquitin-positive spheroids and GM(2)-ganglioside were also detected in brain. Using the Morris water maze in male mice, impaired memory and spatial learning was evident at 20 weeks of age in B6.Cg-Sgsh(mps3a) MPS IIIA mice. Other behavioral changes include motor, cognitive and sensory deficits, and aggression. Male B6.Cg-Sgsh(mps3a) MPS IIIA mice exhibited more behavioral abnormalities than B6.Cg-Sgsh(mps3a) MPS IIIA females, as observed previously in the original mixed background strain. Affected mice generally survive to 9 to 12 months of age, before death or euthanasia for humane reasons. Overall, minor differences were apparent between the new congenic and previously described mixed MPS IIIA strains. Availability of an in-bred strain will ensure more reproducible experimental outcomes thereby assisting in our goal of developing effective therapies for LSD with central nervous system disease.

Survival and engraftment of mouse embryonic stem cell-derived implants in the guinea pig brain

alpha-Mannosidosis is a lysosomal storage disease resulting from a deficiency of the enzyme alpha-D-mannosidase. A major feature of alpha-mannosidosis is progressive neurological decline, for which there is no safe and effective treatment available. We have a guinea pig model of alpha-mannosidosis that models the human condition. This study investigates the feasibility of implanting differentiated mouse embryonic stem cells in the neonatal guinea pig brain in order to provide a source of alpha-mannosidase to the affected central nervous system. Cells implanted at a low dose (1.5 x 10(3)cells per hemisphere) at 1 week of age were found to survive in very low numbers in some immunosuppressed animals out to 8 weeks. Four weeks post-implantation, cells implanted in high numbers (10(5) cells per hemisphere) formed teratomas in the majority of the animals implanted. Although implanted cells were found to migrate extensively within the brain and differentiate into mature cells of neural (and other) lineages, the safety issue related to uncontrolled cell proliferation precluded the use of this cell type for longer-term implantation studies. We conclude that the pluripotent cell type used in this study is unsuitable for achieving safe engraftment in the guinea pig brain.

Development of motor deficits in a murine model of mucopolysaccharidosis type IIIA (MPS-IIIA)

Mucopolysaccharidosis (MPS) type IIIA or Sanfilippo syndrome is a lysosomal storage disorder characterised by progressive neurological pathology. Patients exhibit aggression, disturbed sleep, hyperactivity and mental decline ultimately resulting in inanition and death. Recently, a mouse model of MPS-IIIA was discovered, and both the clinical signs and neuropathological changes mimic the human disease. This provides us with an opportunity to study the pathological progression of this disorder and to determine the efficacy of novel therapies, for at present all lysosomal storage disorders (LSD) affecting the brain are untreatable. Neuropathological changes have previously been described in areas of the brain involved in regulating motor function, therefore, in the present study we sought to determine whether quantifiable motor abnormalities were present in the MPS-IIIA mouse, and if so, at what age they became detectable. Tests of open-field locomotor activity, hindlimb gait, catalepsy, neuromuscular strength and negative geotaxis were administered to MPS-IIIA and normal male and female mice aged from 3 to 40 weeks of age. Significant changes in open-field activity were observed from 3 weeks in MPS-IIIA mice, whereas abnormalities in tests of gait, grip strength and in the assessment of the negative geotaxis response were observable from approximately 15 weeks of age. Behavioural changes were often detected in male MPS-IIIA mice before they appeared in females. Our observations provide insight into the chronology of pathological changes within the MPS-IIIA brain and this simple series of tests will prove useful in comparing mice following the administration of experimental therapies for this condition.

Intracerebral injection of sulfamidase delays neuropathology in murine MPS-IIIA

Lysosomal storage disorders (LSD) are rare inherited metabolic diseases in which genetic alterations affect lysosomal proteins. Mucopolysaccharidosis type IIIA (MPS-IIIA) is an LSD characterized by reduced activity of sulfamidase (heparan-N-sulfatase, EC3.10.1.1), which degrades the sulfated glycosoaminoglycan heparan sulfate. The central nervous system (CNS) is the main site of pathology in MPS-IIIA, resulting in reduced neurological function and neurocognitive decline. Neuropathological changes include lysosomal vacuolation of heparan sulfate and lipids in neurons, glia, and perivascular cells and the formation of axonal spheroids and ectopic dendrites. At present there is no effective treatment for the CNS effects of LSD as enzyme administered intravenously cannot cross the blood-brain barrier. We have previously established and characterized a mouse model of MPS-IIIA, and in the present study, we injected recombinant human sulfamidase directly into the brain at 6, 12 or 18 weeks of age. Treatment reduced vacuolation and gliosis and delayed the onset of ubiquitin-positive neurodegenerative changes in widespread areas of MPS-IIIA brain, assessed at 24 weeks of age. However, ubiquitin-positive axonal spheroids already detectable by 6 weeks of age were unaffected by treatment at any age, suggesting their irreversibility and thus indicating the importance of early detection of MPS-IIIA and instigation of therapy.

In vitro characterization of genetically modified embryonic stem cells as a therapy for murine mucopolysaccharidosis type IIIA

The mucopolysaccharidoses (MPS) are lysosomal storage disorders resulting from the impaired catabolism of glycosaminoglycans (GAG). MPS type IIIA patients have dysfunctional sulfamidase enzyme leading to lysosomal storage of the GAG heparan sulfate, severe neurological symptoms including regression in learning, behavioural abnormalities, and premature death. We have engineered mouse D3 embryonic stem (ES) cells to over-express recombinant human sulfamidase. Human sulfamidase was correctly folded and secreted 2h post-labelling as determined by immunoprecipitation and SDS-PAGE analysis of transfected ES cells. Secreted human sulfamidase present in conditioned ES cell media was able to be taken up via mannose-6-phosphate-mediated endocytosis and restored sulfamidase enzyme activity in human MPS IIIA fibroblast cell lines. ES cells underwent directed differentiation to neural precursor populations and were capable of sustained human sulfamidase over-expression at all stages. Additionally, transfected and control cells were proliferative (Ki67+) and expressed several neural markers (nestin, MAP-2, and NF160) as determined by immunofluorescence. These findings suggest the possibility of ES cell-based therapy for the treatment of neurological pathology of MPS IIIA.

Dopamine receptors in the subthalamic nucleus are involved in the regulation of muscle tone in the rat

The effects of injecting an irreversible dopamine receptor antagonist, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) bilaterally into the subthalamic nucleus (STN) on changes in muscle tone and behaviour were investigated. Increased muscle tone (i.e. rigidity) was assessed quantitatively as increases in tonic electromyographic (EMG) activity in the hindlimb muscles of conscious, unrestrained rats. Significant, sustained increases in EMG activity were observed for 3-5 h post-injection in the tibialis and gastrocnemius muscles following injection of EEDQ into the STN. This effect was associated with 73% dopamine D1 and 66% dopamine D2 receptor occupancy in the STN, while dopamine receptors in surrounding regions were minimally occupied. These results provide new evidence that dopamine receptors located in the STN play an important role in the regulation of normal muscle tone.

Atropine reduces raclopride-induced muscle rigidity by acting in the ventral region of the striatum

Parkinson-like extrapyramidal motor side effects associated with the use of antipsychotic drugs, such as increased muscle rigidity, are thought to result from blockade of striatal dopamine D2 receptors. While anticholinergic medications (muscarinic receptor antagonists) ameliorate extrapyramidal side effects, the mechanisms underlying their effectiveness remain unclear. We investigated the site of action of atropine, a non-selective muscarinic receptor antagonist, in reducing increased muscle rigidity, assessed as increases in tonic electromyographic (EMG) activity, induced by the selective dopamine D2 receptor antagonist, raclopride. Atropine significantly reduced raclopride-induced EMG increases in rat hindlimb muscles, when injected into the ventral striatum, but not the dorsal striatum or the substantia nigra. Atropine's site of action was localised to a small area of muscarinic receptors within the ventral part of the striatum, using quantitative autoradiography. These findings provide new information about the regulation of motor control by muscarinic receptor antagonists and additional evidence about the functional heterogeneity of the striatum.

Changes in muscle tone are regulated by D1 and D2 dopamine receptors in the ventral striatum and D1 receptors in the substantia nigra

Muscle rigidity associated with antipsychotic drug treatment is believed to result from reduced striatal dopamine neurotransmission. In the current study the regulatory roles of dopamine D1 and D2 receptor subfamilies in the dorsal (DSTR) and ventral striatum (VSTR) and substantia nigra (SN) were investigated on muscle tone, assessed as increases in tonic electromyographic (EMG) activity. Rats were injected with the irreversible D1/D2 antagonist N-ethoxycarbonyl-2-ethoxy, -1,2-dihydroquinoline (EEDQ), the reversible D1 antagonist SCH23390, or D2 antagonist sulpiride. Increased EMG activity was observed following injection of EEDQ and SCH23390 into the SN or VSTR, and sulpiride into the VSTR. Mapping, using quantitative autoradiographic analysis of dopamine receptor occupancy after striatal injections, showed D1 and D2 receptors in discrete ventral sites were associated with EMG increases. Overall the results support roles for dopamine D1 and D2 receptors in the ventral striatum, and D1 receptors in the substantia nigra, in the regulation of muscle tone.

Atropine acts in the ventral striatum to reduce raclopride-induced catalepsy

While muscarinic receptor antagonists are used to reduce motor side effects associated with the use of antipsychotic drugs, their site of action remains unclear. The study investigated the site of action of the non-selective muscarinic receptor antagonist atropine on catalepsy induced by the selective dopamine D2 receptor antagonist, raclopride. Initially, catalepsy and striatal muscarinic receptor occupancy was assessed 2 h following subcutaneous injection of raclopride and either atropine or vehicle. Catalepsy was significantly reduced by doses of atropine that occupied more than 69% of muscarinic receptors. Next, atropine was injected bilaterally into the ventral striatum, which produced a significant reduction in catalepsy, while injections into the dorsal striatum and substantia nigra had no effect. The site of atropine's action was localised to a discrete area of the ventral striatum through the use of quantitative autoradiographic techniques. These findings provide further evidence for the importance of the ventral striatum in the expression of behaviours.

An animal model of extrapyramidal side effects induced by antipsychotic drugs: relationship with D2 dopamine receptor occupancy

1. Muscle rigidity was assessed quantitatively and objectively as increases in electromyographic (EMG) activity (muscle rigidity) in the hindlimb muscles of the rat following subcutaneous administration of haloperidol, fluphenazine and thioridazine. 2. Behavioural changes were assessed as increases in the catalepsy score, defined as the time taken for an animal to move off an inclined grid. 3. Increased tonic EMG activity, or the presence of catalepsy was related to the level of occupancy of dopamine D2 receptors in the striatum and substantia nigra of the brain, measured using ex vivo quantitative autoradiography. 4. Increases in tonic EMG activity and the induction of catalepsy were associated with >80% occupancy of striatal and nigral D2 receptors by fluphenazine, while haloperidol increased tonic EMG activity at D2 occupancies of >57%. 5. Thioridazine at doses ranging from 1-15 mg/kg failed to increase EMG activity and occupied <61% of striatal D2 receptors. 6. Overall the findings support the hypothesis that muscle rigidity is observed when a threshold level of D2 receptors in the striatum and substantia nigra are occupied by antipsychotic drugs. 7. This conclusion is consistent with the results of positron emission tomography (PET) studies in humans, and those from our past studies in rats using raclopride, chlorpromazine and clozapine, in which a threshold of approximately 70% striatal and nigral D2 receptor occupancy has been demonstrated.

Raclopride and chlorpromazine, but not clozapine, increase muscle rigidity in the rat: relationship with D2 dopamine receptor occupancy

The aim of the present study was to investigate the relationship between effects on muscle tone and D2 receptor occupancy of two typical antipsychotic drugs, raclopride and chlorpromazine, and the atypical drug, clozapine. Increased muscle tone (i.e., muscle rigidity), was measured as increases in tonic electromyographic (EMG) activity of the antagonistic muscles of the rat hind limb. D2 dopamine receptor occupancy was assessed in the striatum and substantia nigra, areas involved in the regulation of muscle tone. Raclopride and chlorpromazine produced dose-dependent increases in EMG activity associated with D2 occupancy of 68%-80% in the striatum and 67%-76% in the nigra. No significant increases in EMG were observed with clozapine which showed low D2 occupancy. The results are consistent with those from human studies showing extrapyramidal side effects were associated with striatal D2 occupancy of > 70%.

The effects of an irreversible dopamine receptor antagonist, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), on the regulation of muscle tone in the rat: the role of the substantia nigra

Recent evidence has questioned the view that the increased muscle tone of Parkinson's disease results solely from reduced release of dopamine in the striatum, by emphasising the important role of the substantia nigra. The aim of the current study was to compare the effects on muscle tone of inactivating D1 and D2 dopamine receptors throughout the brain with those seen following their inactivation only in the substantia nigra. Inactivation of dopamine receptors by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline injected either intraperitoneally, or bilaterally into the substantia nigra, resulted in similar increases in muscle tone, measured as changes in tonic electromyographic (EMG) activity. The magnitude and onset of EMG increases was related to the level of dopamine receptor inactivation. The results are consistent with the hypothesis that nigral dopamine mechanisms play a key role in the maintenance of muscle tone.