Neuropathology of cervical dystonia

The aim of this study was to search for neuropathological changes in postmortem brain tissue of individuals with cervical dystonia (CD). Multiple regions of formalin-preserved brains were collected from patients with CD and controls and examined with an extensive battery of histopathological stains in a two-stage study design. In stage one, 4 CD brains underwent a broad screening neuropathological examination. In stage two, these 4 CD brains were combined with 2 additional CD brains, and the subjective findings were quantified and compared to 16 age-matched controls. The initial subjective neuropathological assessment revealed only two regions with relatively consistent changes. The substantia nigra had frequent ubiquitin-positive intranuclear inclusions known as Marinesco bodies. Additionally, the cerebellum showed patchy loss of Purkinje cells, areas of focal gliosis and torpedo bodies. Other brain regions showed minor or inconsistent changes. In the second stage of the analysis, quantitative studies failed to reveal significant differences in the numbers of Marinesco bodies in CD versus controls, but confirmed a significantly lower Purkinje cell density in CD. Molecular investigations revealed 4 of the CD cases and 2 controls to harbor sequence variants in non-coding regions of THAP1, and these cases had lower Purkinje cell densities regardless of whether they had CD. The findings suggest that subtle neuropathological changes such as lower Purkinje cell density may be found in primary CD when relevant brain regions are investigated with appropriate methods.

Localization of hypoxanthine-guanine phosphoribosyltransferase mRNA in the mouse brain by in situ hybridization

Congenital deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) in humans results in a severe neurogenetic disorder known as the Lesch-Nyhan syndrome. Since little information concerning the precise localization of HPRT in the brain is currently available, we have used in situ hybridization to examine the expression of HPRT mRNA in the mouse brain. The results showed that HPRT mRNA is expressed in many regions of the normal mouse brain, with high levels in most, but not all neurons. In contrast, glial cells did not express detectable levels of HPRT mRNA. No HPRT mRNA was detected in the brains of mutant mice carrying a deletion in the HPRT gene.

Primary episodic ataxias: diagnosis, pathogenesis and treatment

Primary episodic ataxias are autosomal dominant channelopathies that manifest as attacks of imbalance and incoordination. Mutations in two genes, KCNA1 and CACNA1A, cause the best characterized and account for the majority of identified cases of episodic ataxia. We summarize current knowledge of clinical and genetic diagnosis, genotype-phenotype correlations, pathophysiology and treatment of episodic ataxia syndromes. We focus on unresolved issues including phenotypic and genetic heterogeneity, lessons from animal models and technological advancement, rationale and feasibility of various treatment strategies, and shared mechanisms underlying episodic ataxia and other far more prevalent paroxysmal conditions such as epilepsy and migraine.

Expression of catecholaminergic mRNAs in the hyperactive mouse mutant coloboma

The SNAP-25 deficient mouse mutant coloboma (Cm/+) is an animal model for investigating the biochemical basis of locomotor hyperactivity. The spontaneous hyperactivity exhibited by coloboma is three times greater than control mice and is a direct result of the SNAP-25 deletion. SNAP-25 is a presynaptic protein that regulates exocytotic neurotransmitter release; coloboma mice express only 50% of normal protein concentrations. Previous research has determined that there is an increase in the concentration of norepinephrine but a decrease in dopamine utilization in the striatum and nucleus accumbens of coloboma mice. In situ hybridization analysis revealed that there were corresponding increases in tyrosine hydroxylase (TH) mRNA expression in noradrenergic cell bodies of the locus coeruleus of Cm/+ mice. In contrast, TH mRNA expression in substantia nigra appeared normal in the mutant mouse. alpha(2)-Adrenergic receptors are important modulators of central noradrenergic function and dopamine release. In situ hybridization data revealed that alpha(2A)-adrenergic receptor mRNA expression is upregulated in Cm/+ mice. These results suggest an underlying abnormality in noradrenergic regulation in this hyperactive mouse mutant.

Iron deficiency decreases dopamine D1 and D2 receptors in rat brain

Iron deficiency (ID) in early life is known to alter neurological development and functioning, but data regarding specific effects on dopamine biology are lacking. The objective of this study was to determine the extent of functional alterations in dopamine receptors in two dopaminergic tracts in young, growing, iron-deficient rats. Forty male and 40 female weanling Sprague-Dawley rats were fed either an iron-deficient (ID) diet or control (CN) diet for 6 weeks. ID decreased densities of D(1) and D(2) receptors in the caudate-putamen and decreased D(2) receptor densities in the nucleus accumbens. There were no apparent effects of ID on the affinities for the ligands in either receptor in several brain regions. In situ hybridization studies for both dopamine receptors revealed no significant effect of ID on mRNA expression for either receptor. Iron-deficient rats had a significantly higher ED(50) for raclopride-induced hypolocomotion in male and female rats compared to control rats of each sex. The loss of iron in the striatum due to dietary ID was significantly correlated with the decrease in D(2) receptor density; however, this relationship was not apparent in other brain regions. These experiments thus demonstrate abnormal dopamine receptor density and functioning in several brain regions that are related to brain regional iron loss. Importantly, the impact of ID on dopamine was more pronounced in males than females, demonstrating sex-related different sensitivities to nutrient deprivation.

Abnormal presynaptic catecholamine regulation in a hyperactive SNAP-25-deficient mouse mutant

The consequences of a reduction in the presynaptic protein, SNAP-25, were investigated to determine the neurochemical basis of the marked hyperlocomotor activity in coloboma (Cm/+) mice. SNAP-25 is part of the minimal presynaptic machinery necessary for exocytotic neurotransmitter release. Reserpine treatment was used to deplete vesicular stores of catecholamines. Coloboma mice were more sensitive to the effects of reserpine than control mice. However, presynaptic regulation of dopamine (DA) release, as assessed by low-dose apomorphine challenge, was intact. There were region-specific reductions in in vivo tyrosine hydroxylation and the DA metabolites homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum and nucleus accumbens of Cm/+ mice. While hyperactivity is often associated with changes in DA concentration, norepinephrine (NE) concentration was significantly increased in the striatum and nucleus accumbens of the hyperactive mutant. The increase in NE may regulate the hyperactivity in these mice, as suggested by current hypotheses of the mechanisms underlying attention-deficit hyperactivity disorder (ADHD) and Tourette's syndrome.

Amperometric analysis of exocytosis at chromaffin cells from genetically distinct mice

Amperometry is a very powerful technique for investigating the role(s) specific proteins play in exocytosis at the single-cell level. In this study, amperometry has been used to investigate possible changes in exocytosis at chromaffin cells isolated from coloboma and tottering mutant mice. Coloboma mice possess a deletion mutation that encompasses the gene for the presynaptic protein SNAP-25 and tottering mice carry a mutation of the alpha(1A) subunit gene, which encodes the pore-forming region of P/Q-type calcium channels. Although amperometric data measured from tottering and coloboma cells are not significantly different from that measured at wild-type control cells, significant differences are found when groups of wild-type chromaffin cells are analyzed at room temperature and at 37 degrees C. Due to the large variability inherent to amperometric data, it is possible that changes in release resulting from some genetic differences cannot be detected. To fully exploit the technical advantages of using mouse chromaffin cells, experimental guidelines are described which should maximize changes in release resulting from genetic differences and increase the likelihood of detecting a change in amperometric data.

Calcium channel agonists and dystonia in the mouse

Systemic administration of the L-type calcium channel agonists +/-Bay K 8644 or FPL 64176 causes a characteristic pattern of motor dysfunction in normal C57BL/6J mice that resembles generalized dystonia. There is no associated change in the electroencephalogram, confirming that the motor disorder does not reflect epileptic seizures. However, the electromyogram reveals an increase in baseline motor unit activity with prolonged phasic discharges consistent with dystonia. The duration and severity of dystonia is dependent on the dose administered and the age of the animal at testing. The effects are transient, with the return of normal motor behavior 1-4 hours after treatment. Similar effects can be provoked by intracerebral administration of small amounts of the drugs, indicating a centrally mediated response. Dystonia can be attenuated by co-administration of dihydropyridine L-type calcium channel antagonists (nifedipine, nimodipine, and nitrendipine) but not by non-dihydropyridine antagonists (diltiazem, verapamil, and flunarizine). These results implicate abnormal function of L-type calcium channels in the expression of dystonia in this model.

Quantitative and statistical analysis of the shape of amperometric spikes recorded from two populations of cells

Previously used methods of comparing amperometric spike characteristics from two separate groups of cells have entailed pooling all the values for a spike characteristic from each group of cells and then statistically comparing the two samples. Although this approach has indicated that there are significant differences between the spike characteristics from coloboma and control mouse chromaffin cells, the results are not consistent between experiments. We have reexamined the assumptions of the statistical tests used as well as the variability inherent in amperometric data measured from two groups of cells. Our findings indicate that when comparing amperometric spike characteristics between groups of cells, it is more appropriate to compare samples of mean spike values. This method consistently indicates that there is no difference between coloboma and control amperometric spikes. These results have been validated by using samples of mean spike characteristics to detect changes in the shape of amperometric spikes from both mouse chromaffin cells at 37 degrees C and PC12 cells previously exposed to 50 microM L-3,4-dihydroxyphenylalanine and by the use of an additional analysis method, the nested ANOVA. Together, these results indicate that pooled samples of amperometric spike characteristics can give results that may confound the interpretation of amperometric data.

Tottering mouse motor dysfunction is abolished on the Purkinje cell degeneration (pcd) mutant background

Tottering (tg) mice inherit a recessive mutation of the calcium channel alpha 1A subunit gene, which encodes the pore-forming protein of P/Q-type voltage-sensitive calcium channels and is predominantly expressed in cerebellar granule and Purkinje neurons. The phenotypic consequences of the tottering mutation include ataxia, polyspike discharges, and an intermittent motor dysfunction best described as paroxysmal dystonia. These dystonic episodes induce c-fos mRNA expression in the cerebellar circuitry, including cerebellar granule and Purkinje neurons, deep cerebellar nuclei, and the postsynaptic targets of the deep nuclei. Cellular abnormalities associated with the mutation include hyperarborization of brainstem nucleus locus ceruleus axons and abnormal expression of L-type calcium channels in cerebellar Purkinje cells. Here, the role of these two distinct neural pathways in the expression of tottering mouse intermittent dystonia was assessed. Lesion of locus ceruleus axons with the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzyl-amine (DSP-4) did not affect the frequency of tottering mouse dystonic episodes. In contrast, removal of cerebellar Purkinje cells with the Purkinje cell degeneration (pcd) mutation by generation of tg/tg; pcd/pcd double mutant mice completely eliminated tottering mouse dystonia. Further, the c-fos expression pattern of tg/tg; pcd/pcd double mutants following restraint was indistinguishable from that of wild-type mice, suggesting that the pcd lesion eliminated an essential link in this abnormal neural network. These data suggest that the cerebellar cortex, where the mutant gene is abundantly expressed, contributes to the expression of tottering mouse dystonic episodes.

Characterization and distribution of ferritin binding sites in the adult mouse brain

Studies on iron uptake into the brain have traditionally focused on transport by transferrin. However, transferrin receptors are not found in all brain regions and are especially low in white matter tracts where high iron concentrations have been reported. Several lines of research suggest that a receptor for ferritin, the intracellular storage protein for iron, may exist. We present, herein, evidence for ferritin binding sites in the brains of adult mice. Autoradiographic studies using 125I-recombinant human ferritin demonstrate that ferritin binding sites in brain are predominantly in white matter. Saturation binding analyses revealed a single class of binding sites with a dissociation constant (K(D)) of 4.65 x 10(-9) M and a binding site density (Bmax of 17.9 fmol bound/microg of protein. Binding of radiolabeled ferritin can be competitively displaced by an excess of ferritin but not transferrin. Ferritin has previously been shown to affect cellular proliferation, protect cells from oxidative damage, and deliver iron. The significance of a cellular ferritin receptor is that ferritin is capable of delivering 2,000 times more iron per mole of protein than transferrin. The distribution of ferritin binding sites in brain vis-à-vis transferrin receptor distribution suggests distinct methods for iron delivery between gray and white matter.

L-type calcium channels contribute to the tottering mouse dystonic episodes

Tottering mice inherit a recessive mutation of the calcium channel alpha1A subunit that causes ataxia, polyspike discharges, and intermittent dystonic episodes. The calcium channel alpha1A subunit gene encodes the pore-forming protein of P/Q-type voltage-dependent calcium channels and is predominantly expressed in cerebellar granule and Purkinje neurons with moderate expression in hippocampus and inferior colliculus. Because calcium misregulation likely underlies the tottering mouse phenotype, calcium channel blockers were tested for their ability to block the motor episodes. Pharmacologic agents that specifically block L-type voltage-dependent calcium channels, but not P/Q-type calcium channels, prevented the inducible dystonia of tottering mutant mice. Specifically, the dihydropyridines nimodipine, nifedipine, and nitrendipine, the benzothiazepine diltiazem, and the phenylalkylamine verapamil all prevented restraint-induced tottering mouse motor episodes. Conversely, the L-type calcium channel agonist Bay K8644 induced stereotypic tottering mouse dystonic at concentrations significantly below those required to induce seizures in control mice. In situ hybridization demonstrated that L-type calcium channel alpha1C subunit mRNA expression was up-regulated in the Purkinje cells of tottering mice. Radioligand binding with [3H]nitrendipine also revealed a significant increase in the density of L-type calcium channels in tottering mouse cerebellum. These data suggest that although a P/Q-type calcium channel mutation is the primary defect in tottering mice, L-type calcium channels may contribute to the generation of the intermittent dystonia observed in these mice. The susceptibility of L-type calcium channels to voltage-dependent facilitation may promote this abnormal motor phenotype.

Influence of age and strain on striatal dopamine loss in a genetic mouse model of Lesch-Nyhan disease

Lesch-Nyhan disease is a neurogenetic disorder caused by deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). Affected individuals exhibit a characteristic pattern of neurological and behavioral features attributable in part to dysfunction of basal ganglia dopamine systems. In the current studies, striatal dopamine loss was investigated in five different HPRT-deficient strains of mice carrying one of two different HPRT gene mutations. Caudoputamen dopamine concentrations were significantly reduced in all five of the strains, with deficits ranging from 50.7 to 61.1%. Mesolimbic dopamine was significantly reduced in only three of the five strains, with a range of 31.6-38.6%. The reduction of caudoputamen dopamine was age dependent, emerging between 4 and 12 weeks of age. Tyrosine hydroxylase and aromatic amino acid decarboxylase, two enzymes responsible for the synthesis of dopamine, were reduced by 22.4-37.3 and 22.2-43.1%, respectively. These results demonstrate that HPRT deficiency is strongly associated with a loss of basal ganglia dopamine. The magnitude of dopamine loss measurable is dependent on the genetic background of the mouse strain used, the basal ganglia subregion examined, and the age of the animals at assessment.

Cerebellar circuitry is activated during convulsive episodes in the tottering (tg/tg) mutant mouse

Tottering (tg) is an autosomal recessive mutation of the calcium channel alpha1A subunit in the mouse that results in epileptic spike and wave discharges, mild ataxia and paroxysmal episodes of involuntary spasms of the limbs, trunk and face. These convulsions have been especially difficult to characterize because of their unpredictable occurrence and lack of electroencephalographic correlates. However, it is, in fact, possible to induce these convulsions, making this facet of the tottering phenotype amenable to controlled experimentation for the first time. Here, the neuroanatomical basis of the convulsions in tottering mice has been identified using in situ hybridization for c-fos messenger RNA to chart abnormal neuronal activity. Convulsion-induced c-fos messenger RNA expression was most prominent in the cerebellum of convulsing tottering mice. Additionally, cerebral cortex and principal cerebellar relay nuclei were also activated during a convulsion. The c-fos activation in the cerebellum temporally preceded expression in cerebral cortex, suggesting that cerebral cortex is not driving the expression of convulsions. These results suggest that the cerebellum, a region not classically associated with paroxysmal events, is important in the generation and/or maintenance of the intermittent convulsions in tottering mutant mice.

Rapid genotyping of mutant mice using dried blood spots for polymerase chain reaction (PCR) analysis

Spontaneous neurologic mutations in the mouse provide powerful tools for the study of mammalian central nervous system development. The study of mouse neurologic mutants has led to a better understanding of the complex mechanisms involved in the development of the nervous system. Because few of these mutations have been identified, molecular probes distinguishing heterozygotes from homozygotes are generally unavailable. Further, most neurologic mouse mutants breed poorly as homozygotes, making it necessary to breed heterozygotes and select homozygous mutant progeny based on phenotype. The requirement for heterozygous breeding and the lack of molecular markers specific for the mutation have hampered developmental studies because the underlying neurologic perturbations occur before the mutant mice can be identified by phenotype. The recent identification and chromosomal assignment of simple sequence repeats (SSRs), repetitive sequences of DNA found at a high density throughout the mouse genome, provide the tools for mapping mutations in the mouse and for subsequent genotyping of potential mutants prior to phenotype onset. The SSRs are useful because these markers are polymorphic (for review see Weber, J.L., Human DNA polymorphisms based on length variations in simple-sequence tandem repeats. In: K.E. Davies and S.M. Tilghman (Eds.), Genetic and Physical Mapping. Genome Analysis, Vol. I, Cold Spring Harbor Laboratory Press, Plainview, NY, 1990, pp. 159-181 [16]), that is, the size of the individual SSRs differs among strains of mice. Following polymerase chain reaction (PCR) amplification of an SSR and separation of PCR products by polyacrylamide gel electrophoresis, one can easily visualize differences in the size of the PCR product between mouse strains. Many mutations in the mouse arose spontaneously on inbred strains and were subsequently backcrossed onto a different strain. After many generations of congenic backcrosses, the only DNA retained from the original mutant strain is composed of the mutant gene and closely linked regions. Thus, it is possible to cross the mutant strain to a different mouse strain and map the mutation by correlating mutant phenotype to SSRs the same size as the original mutant strain. We have mapped the tottering (tg), Purkinje cell degeneration (pcd), and nervous (nr) mutations using SSRs in backcrossed mouse strains. The SSRs distinguishing mutant from normal strains can then be used to genotype potential mutant pups before the onset of the mutant phenotype. The protocol described below can be adapted to almost any mutation congenically inbred for genotyping. Here we describe a method for selecting primers appropriate for genotyping potential mouse mutants and a rapid protocol for genotype screening. Even with SSRs distinguishing mutant from normal mice, genotyping several mice simultaneously can be a daunting task. This is primarily because the protocols available for preparing DNA for PCR amplification are time-consuming, requiring several purification steps including phenol extractions. Although kits are commercially available for DNA preparation without organic extractions, these kits tend to be expensive. The protocol described is a rapid, inexpensive method of determining the genotype of mice using PCR analysis of dried blood spots. The protocol only requires PCR primers distinguishing among alleles and is therefore ideal for the rapid identification of potential mutants for those mouse mutations which have been mapped using microsatellite markers. The DNA preparation protocol may also be used in rapid screening of potential transgenic mice.

Cloning and characterization of the Bg/II restriction-modification system reveals a possible evolutionary footprint

Bg/II, a type II restriction-modification (R-M) system from Bacillus globigii, recognizes the sequence 5'-AGATCT-3'. The system has been cloned into E. coli in multiple steps: first the methyltransferase (MTase) gene, bglIIM, was cloned from B. globigii RUB561, a variant containing an inactivated endonuclease (ENase) gene (bglIIR). Next the ENase protein (R.BglII) was purified to homogeneity from RUB562, a strain expressing the complete R-M system. Oligonucleotide probes specific for the 5' end of the gene were then synthesized and used to locate bglIIR, and the gene was isolated and cloned in a subsequent step. The nucleotide sequence of the system has been determined, and several interesting features have been found. The genes are tandemly arranged, with bglIIR preceding bglIIM. The amino acid sequence of M.BglII is compared to those of other known MTases. A third gene encoding a protein with sequence similarity to known C elements of other R-M systems is found upstream of bglIIR. This is the first instance of a C gene being associated with an R-M system where the R and M genes are collinear. In addition, open reading frames (ORFs) resembling genes involved with DNA mobility are found in close association with BglII. These may shed light on the evolution of the R-M system.

The Use of Transgenes and Mutations in the Mouse to Study the Genetic Basis of Locomotor Hyperactivity

As the mouse genome becomes more accessible to experimental manipulation, it is becoming feasible to assess how genes influence the expression of specific behavioral traits. The mouse mutant coloboma exhibits extreme hyperactivity resulting from an approximately 2-cM deletion on mouse Chromosome 2. This deletion includes the gene encoding SNAP-25, a neuron-specific protein implicated in exocytotic neurotransmitter release. Because a deficit in this gene product might contribute to the expression of hyperactivity, a transgene expressing SNAP-25 was bred into the coloboma mouse genome to replace the missing SNAP-25 and rescue the hyperactivity. The Snap transgene was indeed sufficient to ameliorate the locomotor excesses exhibited by these mice, suggesting that SNAP-25 plays a central role in the expression of hyperactivity. In the course of designing and executing this experiment, several methodologic issues pertinent to manipulating the mouse genome in the context of a behavioral question were presented. These issues are discussed in light of the unique properties of the mouse as a behavioral genetic tool.

Cloning and sequence comparison of AvaI and BsoBI restriction-modification systems

AvaI and BsoBI restriction endonucleases are isoschizomers which recognize the symmetric sequence 5'CYCGRG3' and cleave between the first C and second Y to generate a four-base 5' extension. The AvaI restriction endonuclease gene (avaIR) and methylase gene (avaIM) were cloned into Escherichia coli by the methylase selection method. The BsoBI restriction endonuclease gene (bsoBIR) and part of the BsoBI methylase gene (bsoBIM) were cloned by the "endo-blue" method (SOS induction assay), and the remainder of bsoBIM was cloned by inverse PCR. The nucleotide sequences of the two restriction-modification (RM) systems were determined. Comparisons of the predicted amino acid sequences indicated that AvaI and BsoBI endonucleases share 55% identity, whereas the two methylases share 41% identity. Although the two systems show similarity in protein sequence, their gene organization differs. The avaIM gene precedes avaIR in the AvaI RM system, while the bsoBI R gene is located upstream of bsoBI M in the BsoBI RM system. Both AvaI and BsoBI methylases contain motifs conserved among the N4 cytosine methylases.

Mouse model of hyperkinesis implicates SNAP-25 in behavioral regulation

Although hyperkinesis is expressed in several neurological disorders, the biological basis of this phenotype is unknown. The mouse mutant coloboma (Cml+) exhibits profound spontaneous locomotor hyperactivity resulting from a deletion mutation. This deletion encompasses several genes including Snap, which encodes SNAP-25, a nerve terminal protein involved in neurotransmitter release. Administration of amphetamine, a drug that acts presynaptically, markedly reduced the locomotor activity in coloboma mice but increased the activity of control mice implicating presynaptic function in the behavioral abnormality. In contrast, the psychostimulant methylphenidate increased locomotor activity in both coloboma and control mice. When a transgene encoding SNAP-25 was bred into the coloboma strain to complement the Snap deletion, the hyperactivity expressed by these mice was rescued, returning these corrected mice to normal levels of locomotor activity. These results demonstrate that the hyperactivity exhibited by these mice is the result of abnormalities in presynaptic function specifically attributable to deficits in SNAP-25 expression.

Chromosomal localization of the neurological mouse mutations tottering (tg), Purkinje cell degeneration (pcd), and nervous (nr)

We have refined the map positions and identified molecular markers for three neurological mutations in the mouse, tottering (tg), Purkinje cell degeneration (pcd), and nervous (nr). These mutations were localized using simple sequence length polymorphisms between the mouse strain on which the mutation arose and the inbred strain onto which the mutation was bred. This approach to mutation mapping is generalizable to any mutant that has been backcrossed for several generations. The tg mutation was localized to the 1.1 cM region of chromosome 8 distal to simple sequence repeat (SSR) D8Mit103 and proximal to SSRs D8Mit79, D8Mit105, and D8Mit283. The pcd locus was mapped to the 5 cM interval of chromosome 13 between SSRs D13Mit139 and D13Mit67, and the nr locus was mapped between SSRs D8Mit155 and D8Mit18, a 5.6 cM region of chromosome 8. For each mutation, several SSRs distinguishing mutant from wild type chromosomes were identified within these regions. The definition of molecular markers distinguishing mutant from wild type alleles makes possible for the first time identification of tg, pcd, and nr mutants prior to behavioral manifestation of the mutant genotype. Thus, developmental studies of these mutants designed to describe or dissect the biochemical basis of the induction of the mutant phenotype are now feasible.

Absence of linkage of apparently single gene mediated ADHD with the human syntenic region of the mouse mutant Coloboma

Attention deficit disorder (ADHD) is a complex biobehavioral phenotype which affects up to 8% of the general population and often impairs social, academic, and job performance. Its origins are heterogeneous, but a significant genetic component is suggested by family and twin studies. The murine strain, coloboma, displays a spontaneously hyperactive phenotype that is responsive to dextroamphetamine and has been proposed as a genetic model for ADHD. Coloboma is a semi-dominant mutation that is caused by a hemizygous deletion of the SNAP-25 and other genes on mouse chromosome 2q. To test the possibility that the human homolog of the mouse coloboma gene(s) could be responsible for ADHD, we have carried out linkage studies with polymorphic markers in the region syntenic to coloboma (20p11-p12). Five families in which the pattern of inheritance of ADHD appears to be autosomal dominant were studied. Segregation analysis of the traits studied suggested that the best fitting model was a sex-influenced, single gene, Mendelian pattern. Several genetic models were evaluated based on estimates of penetrance, phenocopy rate, and allele frequency derived from our patient population and those of other investigators. No significant linkage was detected between the disease locus and markers spanning this chromosome 20 interval.

Deletion map of the coloboma (Cm) locus on mouse chromosome 2

The extent of the semidominant coloboma (Cm) mutation on mouse Chromosome 2 was determined by deletion mapping using interspecific hybrid mice. The Cm deletion mutation results in ophthalmic dysmorphology and behavioral deficits, including profound hyperactivity, and has been shown to encompass the gene Snap. In addition to Snap, the gene encoding phospholipase C beta-1 (Plcb-1), which maps 0.60 +/- 0.60 cM proximal to Snap, and simple sequence repeat (SSR) loci D2Mit19, D2Mit46, D2Mit28, and D2Mit136 were shown to be deleted at the Cm locus. In contrast, analysis of other closely linked SSRs and genes either proximal (Bmp-2a) or distal (Nec-1) to Snap, as well as a complementation test with the closely linked mutation lethal milk (lm), indicates that these gene sequences are unaffected by the Cm mutation. These data demonstrate that the Cm deletion represents a contiguous gene defect encompassing 1.1 to 2.2 cM that may be probed for genes, both in the mouse and in the syntenic region of human Chr 20, that independently affect elements of neurological behavior and eye development.

Spontaneous locomotor hyperactivity in a mouse mutant with a deletion including the Snap gene on chromosome 2

The gene encoding the synaptosomal-associated protein--25 kDa (SNAP-25) was mapped by analysis of somatic cell hybrids and an intersubspecies backcross to mouse Chromosome 2. To identify potential mutants for SNAP-25, mice bearing mutations mapping to this region of Chromosome 2 were screened for Snap gene abnormalities. Mice heterozygous for the semidominant mutation coloboma (Cm/+) were identified that carried a deletion of Snap gene sequence. Analysis of genomic DNA revealed that the Snap gene dosage in Cm/+ mice was 50% lower than control littermates. Additionally, SNAP-25 mRNA and protein expression were 50% lower in coloboma mice than control littermates. The coloboma mouse phenotype is characterized by small eyes and head bobbing; in addition, we observed that these mice were extremely hyperactive with spontaneous locomotor activity exceeding three times control mouse activity. The localization of the genetic abnormality in coloboma mice using the Snap gene marker will provide a powerful tool for studying the biologic basis of locomotor hyperactivity.

Tottering and leaner mutations perturb transient developmental expression of tyrosine hydroxylase in embryologically distinct Purkinje cells

The mouse mutants tottering and leaner exhibit neurologic disorders associated, in part, with global noradrenergic hyperinnervation. Therefore, the expression of tyrosine hydroxylase (TH) mRNA and protein was examined in mutant and control mice. TH expression was normal in the major catecholaminergic nuclei. However, TH was expressed in vermal Purkinje cells of adult mutant but not control mice. TH expression in the Purkinje cells of both mutants was first observed on P21 and persisted throughout adulthood; in contrast, Purkinje cells of normal mice expressed TH transiently during development from P21 to P35. Thus, tottering and leaner mice are deficient in suppressing the normal transient expression of TH in developing Purkinje cells, suggesting that the protein encoded by the tg locus may play a crucial role in neuronal development.

Lesions of hippocampal circuitry define synaptosomal-associated protein-25 (SNAP-25) as a novel presynaptic marker

Synaptosomal-associated protein, 25 kD, (SNAP-25) is a novel protein containing a possible transition metal binding site and encoded by a neuronal-specific mRNA. We examined the distribution of SNAP-25 mRNA and protein in the hippocampal formation of the adult rat following kainic acid, colchicine, and entorhinal lesions. The results show that destruction of granule cells of the dentate gyrus and CA3 pyramidal cells did not diminish SNAP-25 immunoreactivity in the dendritic fields of these cells. In contrast, lesioned neurons exhibited an extensive loss of immunoreactivity at the site of their axonal projections. These results support the identification of SNAP-25 as a novel presynaptic protein. In addition, SNAP-25 immunoreactivity was increased in afferent fibers which project to areas adjacent to the deafferented region, and expression of SNAP-25 mRNA was increased in neurons deafferented by the lesion. Examination of SNAP-25 immunoreactivity and mRNA expression may provide a useful marker of major hippocampal pathways and of axonal plasticity in neurological disorders such as Alzheimer's disease and temporal lobe epilepsy.

Chronic treatment with dopamine receptor antagonists: behavioral and pharmacologic effects on D1 and D2 dopamine receptors

Rats were treated for 21 d with the selective D1 dopamine receptor antagonist SCH23390, the selective D2 dopamine receptor antagonist spiperone, the nonselective dopamine receptor antagonist cis-flupentixol, or a combination of SCH23390 and spiperone. In addition, a group of rats received L-prolyl-L-leucyl-glycinamide (PLG) for 5 d after the 21 d chronic spiperone treatment. Chronic treatment with SCH23390 resulted in a significant increase in D1 dopamine receptor density with no change in the D2 dopamine receptor density. Conversely, spiperone treatment resulted in a significant increase in D2 dopamine receptors and no change in D1 dopamine receptor density. PLG treatment had no effect. SCH23390 plus spiperone treatment resulted in a significant increase in both D1 and D2 dopamine receptor densities. However, although in vitro cis-flupentixol has an equal affinity for D1 and D2 dopamine receptors, only the D2 dopamine receptor density increased after chronic treatment with cis-flupentixol. In vivo treatment with the protein-modifying reagent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), which irreversibly inactivates D1 and D2 dopamine receptors, was used to investigate the paradoxical, selective D2 dopamine receptor up-regulation induced by cis-flupentixol treatment. In vivo treatment with cis-flupentixol before EEDQ administration prevented the D1 and D2 dopamine receptor reductions induced by EEDQ. However, cis-flupentixol protected, in a dose-dependent manner, a greater percentage of D2 dopamine receptors than of D1 dopamine receptors from EEDQ-induced modification. These data indicate that, in vivo, cis-flupentixol preferentially interacts with D2 dopamine receptors and could explain why only D2 dopamine receptors were up-regulated following chronic treatment with cis-flupentixol. Rats were tested for their cataleptic response to the administered drug over the course of the chronic drug treatment. Catalepsy scores of rats receiving spiperone decreased over the course of treatment, with a significant reduction in catalepsy occurring by treatment day 5. The profound catalepsy observed in rats receiving SCH23390 did not change over the 21 d of treatment. Rats receiving cis-flupentixol demonstrated tolerance to its cataleptogenic effects, with a significant reduction in catalepsy observed by treatment day 7. During the 3 week treatment, the time between drug injection and a full cataleptic response to cis-flupentixol increased from 20 to 60 min, suggesting a tolerance to the D2, but not D1, dopamine receptor antagonism by cis-flupentixol.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopamine receptor subtype imbalance in schizophrenia

We have investigated the radioligand binding properties of D1 and D2 dopamine receptors in postmortem brains from schizophrenic patients. Consistent with previous reports, the schizophrenic population demonstrated a significant 56% increase in D2 dopamine receptor density. Importantly, the D1 dopamine receptor density was significantly reduced by 43%. These alterations in dopamine receptor densities resulted in a highly significant difference in the ratio of D2/D1 dopamine receptors between schizophrenic patients and controls. A correlation between D1 dopamine receptor density and age was apparent in the schizophrenic patients: D1 dopamine receptor density decreased markedly with age and the linear regressions of D1 dopamine receptor density versus age in both the controls and schizophrenic patients had similar slopes. These results may have clinical implications for the treatment of schizophrenia and tardive dyskinesia.

Differential modification of striatal D1 dopamine receptors and effector moieties by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline in vivo and in vitro

Both in vivo and in vitro treatments with the irreversible protein-modifying reagent, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), were used to investigate rat striatal D1 dopamine receptor/effector interactions. Peripherally administered EEDQ markedly reduced D1 dopamine receptor binding and D1 dopamine receptor-stimulated adenylate cyclase in a dose-dependent manner. However, EEDQ administered in vivo did not result in functional modification of either the guanine nucleotide-regulatory protein (Ns) or the catalytic subunit of striatal adenylate cyclase as assessed via guanine nucleotide- or forskolin-stimulated cAMP production. Interestingly, the loss in D1 dopamine receptor binding did not correlate directly with observed reductions in dopamine-stimulated adenylate cyclase activity; 40% of D1 dopamine receptor binding was lost with no significant reduction in the Vmax of dopamine-stimulated adenylate cyclase activity. Conversely, the reduction by EEDQ of the adenylate cyclase activity stimulated by the partial agonist SKF38393 was reduced in parallel with EEDQ-induced reductions in the D1 dopamine receptor Bmax. However, when SKF38393-stimulated adenylate cyclase activity was potentiated by forskolin, approximately 30% of receptors could be lost with no significant reduction in cAMP production, resembling the pattern observed utilizing the full agonist dopamine. In vivo pretreatment with the specific D1 antagonist, SCH23390, prevented reductions in dopamine-stimulated adenylate cyclase activity and D1 dopamine receptor binding, suggesting that EEDQ acts at the ligand recognition site of the receptor. Unlike in vivo treatment, in vitro EEDQ treatment resulted in dose-dependent decreases in catalytic subunit activity as assessed by forskolin-stimulated cAMP production, indicating that, in vitro, the adenylate cyclase catalytic subunit is vulnerable to EEDQ-induced modification. These data indicate that EEDQ is an effective tool for elucidating the mechanisms and biochemistry of D1 dopamine receptor/effector coupling.

Functional recovery of D1 dopamine receptor-mediated stimulation of rat striatal adenylate cyclase activity following irreversible receptor modification by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ): evidence for spare receptors

We report here the functional relationship between the time-dependent recovery of [3H]SCH 23390-labeled D1 dopamine receptors and the D1 receptor-mediated stimulation of rat striatal adenylate cyclase activity following irreversible receptor modification by in vivo administration of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline. Initial decreases in receptor density (-93%) and receptor-mediated enzyme activity (-78%) were accomplished without concomitant changes in guanosine triphosphate or forskolin-stimulated enzyme activity. The percentage of maximal D1 receptor-mediated enzyme activity was significantly greater than that of D1 receptor density at all recovery times. Dopamine-stimulated enzyme activity returned to control values by day 4, although D1 receptor density remained significantly below control levels at this time. No differences in the EC50's for dopamine stimulation of enzyme activity were observed at any of the recovery times. These data demonstrate that the stoichiometric relationship between the recovering D1 dopamine receptors and D1 receptor-mediated enzyme activity is not one to one, providing evidence for the presence of 'spare' D1 dopamine receptors in rat striatum.

Effects of chronic SCH23390 treatment on the biochemical and behavioral properties of D1 and D2 dopamine receptors: potentiated behavioral responses to a D2 dopamine agonist after selective D1 dopamine receptor upregulation

Chronic treatment of rats with SCH23390 (0.5 mg/kg/day s.c.), a D1 dopamine receptor antagonist, for 21 days resulted in an increase in D1 dopamine receptors but produced no change in D2 dopamine receptors. During habituation to locomotor activity cages the rats treated chronically with SCH23390 showed significantly higher locomotor activity than controls treated chronically with saline. When injected with the selective D1 dopamine receptor agonist SKF38393 (3 mg/kg), rats treated chronically with SCH23390 showed significantly greater stereotypy and locomotor activity responses. Surprisingly, rats treated chronically with SCH23390 also showed significantly higher locomotor activity and stereotypy responses when treated with the selective D2 dopamine receptor agonist, quinpirole (LY171555) (0.3 mg/kg). These results indicate that a selective increase in D1 receptors may not be necessary, but is sufficient, to lead to an enhanced behavioral response to either selective D1 or D2 dopamine receptor agonists. If, indeed, an enhanced stereotypy and locomotor activity response to dopaminergic agonists in rats after a brief chronic treatment with a neuroleptic drug is predictive of tardive dyskinesia potential in the clinical setting, these results can suggest that SCH23390 may also induce tardive dyskinesia in humans. Adenylate cyclase activity stimulated by guanine nucleotides, forskolin or dopamine was enhanced after chronic treatment with SCH23390. However, dopamine-stimulated adenylate cyclase activity was not potentiated detectably by the increase in receptor number over the more general increase in guanine nucleotide-stimulated cyclic AMP production. Additionally, no change was observed in dopamine competition for [3H]SCH23390 binding, with dopamine's RH/RL ratio remaining unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Forskolin potentiates the stimulation of rat striatal adenylate cyclase mediated by D-1 dopamine receptors, guanine nucleotides, and sodium fluoride

We report here that forskolin acts in a synergistic manner with dopaminergic agonists, guanine nucleotides, or sodium fluoride to potentiate the stimulation of rat striatal adenylate cyclase mediated by these reagents. In the presence of 100 microM GTP, 100 microM guanyl-5'-yl imidodiphosphate [Gpp(NH)p], or 10 mM NaF, there is a greater than additive increase in forskolin-stimulated enzyme activity as well as a concomitant decrease (two- to fourfold) in the EC50 value for forskolin stimulation of striatal enzyme activity. In the presence of various concentrations of forskolin (10 nM-100 microM), the stimulation of adenylate cyclase elicited by GTP, Gpp(NH)p, and NaF is potentiated 194-1,825%, 122-1,141%, and 208-938%, respectively, compared with the stimulation by these agents above basal activity in the absence of forskolin. With respect to 3,4-dihydroxyphenylethylamine (dopamine) receptor-mediated stimulation of striatal enzyme activity, the stimulation of enzyme activity by dopaminergic agonists, in the absence or presence of forskolin, was GTP-dependent and could be antagonized by the selective D-1 antagonist SCH23390 (100 nM), indicating that these effects are mediated by D-1 dopamine receptors. In the presence of 100 microM GTP, forskolin at various concentrations markedly potentiates the stimulation elicited by submaximal as well as a maximally effective concentrations of dopamine (100 microM) and SKF38393 (1 microM). At higher concentrations of forskolin (10-100 microM) the stimulation elicited by the partial agonist SKF38393 is comparable to that of the full agonist dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Guanine nucleotide regulation of agonist interactions at [3H]SCH23390-labeled D1 dopamine receptors in rat striatum

We report here the regulation of agonist interactions with [3H]SCH23390-labeled D1 dopamine receptors in rat striatum. Scatchard analyses of [3H]SCH23390 saturation data revealed a single high affinity binding site (KD = 0.49 nM) with a Bmax of 64 pmol/g tissue. The specific binding of 0.25 nM [3H]SCH23390 represented 90% of total binding. Antagonist competition for [3H]SCH23390 binding was monophasic (i.e. pseudo-Hill slope approximately 1) and the rank order of antagonists' affinities was consistent with the pharmacology of D1 dopamine receptors (e.g. cis-flupentixol greater than haloperidol greater than spiperone). In contrast, agonist competition curves were shallow (pseudo-Hill slope less than 1) and computer-assisted analysis indicated that, for all agonists, the data best fit a two-site model composed of a high (KH) and a low (KL) affinity component. In the presence of 0.3 mM GTP, the high affinity binding component (%RH) of various agonists was reduced by approximately 50%. No significant effect of 0.3 mM GTP on [3H]SCH23390 binding was observed. Additionally, it was noted that [3H]SCH23390 labels S2 serotonin receptors in extrastriatal brain regions. However, [3H]SCH23390 apparently does not have an affinity high enough to label S2 receptors at the concentration of [3H]SCH23390 employed in labeling striatal D1 dopamine receptors. These data indicate that [3H]SCH23390 represents a superior radioligand for labeling the two-state striatal D1 dopamine receptor in that its high percent specific binding makes it especially suitable for detailed mechanistic studies of this receptor.

D2 dopamine receptor-mediated inhibition of forskolin-stimulated adenylate cyclase activity in rat striatum

Forskolin markedly stimulates striatal adenylate cyclase activity in a concentration-dependent manner, and at 10(-4) M produces an approximate 40-fold increase in enzyme activity above basal levels. Dopamine (in the presence of 100 nM SCH 23390), bromocryptine and quinpirole (LY 171555) significantly inhibit both basal and forskolin-stimulated adenylate cyclase activity. There is a significant increase in the absolute but not in the percent inhibition of enzyme activity by dopaminergic agonists as a function of forskolin concentration. This inhibition is agonist-concentration dependent and antagonized by the D2 antagonist, spiperone. These results suggest that forskolin may be used as a tool for amplifying the abolute D2-receptor-mediated inhibition of adenylate cyclase in rat striatal homogenates.

Purification and immunological characterization of a calcium pump from bovine brain synaptosomal vesicles

In previous work ( Papazian , D., H. Rahamimoff , and S. M. Goldin (1979) Proc. Natl. Acad. Sci. U. S. A. 76: 3708-3712), an ATP-dependent calcium transport activity derived from rat brain synaptosomes was reconstituted into artificial lipid vesicles and substantially purified by transport-specific fractionation. When this procedure was applied to bovine brain synaptosomes, the approximately 70-fold purified, reconstituted Ca2+ uptake system contained two major polypeptides of Mr = 230,000 (" C230 ") and 94,000 (" C94 ") as observed on sodium dodecyl sulfate (SDS) gels. Evidence is presented here that these polypeptides are immunologically related to one another and that the synaptosomal Ca2+ pump is immunologically distinct from Ca2+ pumps in non-neuronal cells. Antisera and monoclonal antibodies to the purified, reconstituted protein did not significantly cross-react with the Ca2+ pumps or any other components of bovine sarcoplasmic reticulum or erythrocytes. However, these antibodies did cross-react with a component of bovine brain axolemma-enriched membranes. A monoclonal antibody was produced that immunoprecipitated the Ca2+ transport activity, both in native, synaptosomal vesicles and in liposomes containing the reconstituted transport system. This antibody bound C230 more prominently than C94 on Western blots of SDS gels. An antiserum raised against C94 alone, obtained by elution from SDS gels, was also found to bind most prominently to C230 on Western blots. These results suggest that this synaptosomal Ca2+ pump is specific to nerve tissue and that C94 and C230 are structurally homologous components of this transport activity.

Molecular characterization, reconstitution, and "transport-specific fractionation" of the saxitoxin binding protein/Na+ gate of mammalian brain

The saxitoxin (STX) binding protein has been solubilized by sodium cholate, both from axolemma and from synaptosomal membranes of mammalian brain. On the basis of agarose gel filtration and sedimentation properties in H2O and 2H2O, the solubilized particle has the following molecular properties: Stokes radius, 120 A; partial specific volume, 0.85 cm3/g; mass, 1,020,000 daltons; frictional ratio f/fo, 1.6. The solubilized STX binding protein was incorporated into unilamellar (approximately 550-A) artificial phosphatidylcholine vesicles. Based on the expectation that the STX binding protein contains functional monovalent cation gating activity ("action potential Na+ gate") that can be activated by veratridine and inhibited by tetrodotoxin, a strategy was devised for partial purification of the reconstituted sodium gate/STX binding protein by "transport-specific fractionation." When the entire vesicle population was preloaded with 0.4 M cesium ion, addition of veratridine allowed Cs+ efflux from specifically those vesicles containing the ion gate; the concomitant reduction in intravesicular density permitted the ion gate/STX binding protein to be fractionated on density gradients. These observations demonstrate functional reconstitution and partial (30- to 50-fold) purification of the STX binding protein/Na+ gate of mammalian brain.

Studies on the relationship between the degradative rates of proteins in vivo and their isoelectric points

Acidic proteins tend to be degraded more rapidly than neutral or basic proteins in rat liver, skeletal muscle, kidney and brain and in mouse liver and skeletal muscle. We now report a similar relationship among soluble proteins from rat lung, heart and testes, and from human fibroblasts and mouse-embryo cells grown in culture. These findings indicate that the correlation between protein net charge and degradative rate is a general characteristic of intracellular protein degradation in mammals. This relationship between isoelectric point and half-life appears to be distinct from the previously reported correlation between subunit molecular weight and protein half-lives. The more rapid degradation of acidic proteins does not result from their being of larger molecular weight than neutral or basic proteins. Furthermore, proteins within specific isoelectric point ranges still exhibit a relationship between subunit size and half-life. Finally, a group of membrane or organelle-associated proteins that are insoluble in phosphate-buffered saline and water but soluble in 1% Triton X-100 exhibit a correlation between size and half-life, but not between net charge and half-life. The biochemical reasons for the relationship between protein isoelectric point and half-life are unclear, although several possible explanations are presented. It is not due to a greater sensitivity of acidic proteins to proteolytic attack since experiments with a variety of endoproteinases, including trypsin, chymotrypsin, Pronase, papain, chymopapain, Staphylococcus aureus V8 proteinase, pepsin and lysosomal cathepsins from rat liver, have failed to demonstrate more rapid digestion of acidic proteins.