Quinpirole attenuates the striatal immediate early gene expression, but not the hyperactivity, induced by the serotonin agonist RU-24969

Systemic administration of the mixed 5-HT(1A/1B) agonist RU-24969 has been shown to produce a dramatic increase in locomotor activity and to induce robust c-Fos expression in the rat striatum. Previous studies have also shown that pretreatment with the D2-like dopamine agonist quinpirole virtually abolishes RU-24969-induced striatal c-Fos expression. The present study was undertaken to determine whether the effects of RU-24969 on immediate early gene expression extend to the additional Fos family transcription factors FosB and Fra-2. Additionally, this study quantitatively examined the effect of quinpirole pretreatment on the ability of RU-24969 to induce both locomotor hyperactivity and striatal immediate early gene expression. RU-24969 alone produced elevations in locomotor activity and induced clear expression of c-Fos, FosB and Fra-2 throughout the entire striatal complex. Quinpirole pretreatment virtually abolished RU-24969-induced expression of all three transcription factors, but did not alter the elevated locomotor activity produced by RU-24969. These results demonstrate that the effects of RU-24969 on locomotor activity can be dissociated from its effects on immediate early gene expression within the striatum.

Dopamine genes and ADHD

Family, twin, and adoption studies have documented a strong genetic basis for ADHD/HKD, but these studies do not identify specific genes linked to the disorder. Molecular genetic studies can identify allelic variations of specific genes that are functionally associated with ADHD/HKD, and dopamine genes have been the initial candidates based on the site of action of the stimulants drugs, which for a half century have provided the primary pharmacological treatment for ADHD/HKD. Two candidate dopamine genes have been investigated and reported to be associated with ADHD/HKD: the dopamine transporter (DAT1) gene [Cook et al., American Journal of Human Genetics 1995;56:993-998, Gill et al., Molecular Psychiatry 1997;2:311-313] and the dopamine receptor D4 (DRD4) gene [LaHoste et al., Molecular Psychiatry 1996;1:121-124: Smalley et al., 1998;3:427-430; Swanson et al., Molecular Psychiatry 1998;3:38-41]. Speculative hypotheses [Swanson and Castellanos, NIH Consensus Development Conference: Diagnosis and Treatment of Attention Deficit Hyperactivity Disorder, November 1998. p. 37-42] have suggested that specific alleles of these dopamine genes may alter dopamine transmission in the neural networks implicated in ADHD/HKD (e.g. that the 10-repeat allele of the DAT1 gene may be associated with hyperactive re-uptake of dopamine or that the 7-repeat allele of the DRD4 gene may be associated with a subsensitive postsynaptic receptor). These and other variants of the dopamine hypothesis of ADHD will be discussed.

[The influence of genes on the development of personality]

Antisocial behavior and personality disorders are both heterogeneous and the product of interacting genetic and environmental factors acting at different levels of causation. Heritability studies show that individual differences in predisposition to antisocial behavior are transmitted by genetic mechanisms in families. Direct gene analysis and genetic linkage analysis have identified structural variants in genes involved in neurotransmitter function, and some progress has been made towards relating these genetic variants to antisocial personality and other behaviors. The monoamine oxidase-A variant leads to aggressive behavior in one family. Direct gene analyses have revealed amino acid substitutions and structural variants at DRD2, DRD3 and DRD4 dopamine receptors and 5-HT2A, 5-HT2C serotonin receptors, serotonin transporter gene, and genes for enzymes, metabolizing biogenic amines MAO-A, MAO-B. The stage is set to identify the phenotypic significance of these as well as genetic variants at other loci which may be relevant as candidate genes for antisocial behavior and related behavioral differences.

Identification of a polymorphism in the promoter region of DRD4 associated with the human novelty seeking personality trait

Polymorphism in the human dopamine D4 receptor gene (DRD4) exon III has been associated in some but not all studies of the human personality trait of Novelty Seeking. We searched for polymorphisms in the 5' region of DRD4 and identified six polymorphisms as follows: -1217G Ins/Del, -809G/A, -616C/G, -603T Ins/Del, -602(G)8-9, and -521C/T. Associations between these polymorphisms and personality traits measured by the Temperament and Character Inventory (TCI) were investigated in 86 healthy Japanese volunteers. The -521C/T polymorphism was significantly associated with Novelty Seeking (P = 0.0001). Subjects with the C/C genotype exhibited the highest Novelty Seeking scores and those with the T/T genotype exhibited the lowest. A transient expression method revealed that the T variant of the C-521T polymorphism reduces transcriptional efficiency. The present study suggests a contribution of dopamine D4 receptor availability to individual differences in Novelty Seeking behavior. Molecular Psychiatry (2000) 5, 64-69.

Multiplex semi-quantitative reverse transcriptase-polymerase chain reaction of low abundance neuronal mRNAs

The sequential use of reverse transcriptase and the polymerase chain reaction (RT-PCR) has provided molecular biology research with an exquisitely sensitive and fast technique for studying gene expression. This method is particularly useful to study transcripts in the nervous system, which are on average present at low levels and the amount of tissue or cells to be analyzed is often limited. Here, we describe a RT-PCR assay which allows the simultaneous detection and semi-quantitation of several transcripts (multiplex). Multiple PCR primer pairs are used to detect different target transcripts in a single reaction, together with a pair of primers able to amplify the hypoxantine-phosphoribosyl-transferase (HPRT), a gene constitutively expressed at low levels throughout the nervous system. HPRT levels remain constant also during neurogenesis and it is thus apt to be used in developmental neurobiology. This internal standard is the mRNA of reference to evaluate sample variation in RT and PCR reactions and to monitor the degradation and recovery of RNAs. Normalization with respect to HPRT cDNA allows to estimate the relative abundance of each target mRNA.

Recent aspects in the genetic renal mechanisms involved in hypertension

The kidney plays an important role in the blood pressure regulation primarily by modulating tubular sodium reabsorption. Various hormones, vasoactive peptides, autacoids and transporters or channels in renal tubules are involved in this process. Genes associated with renal tubular sodium handling are possibly related to the development of hypertension. Genes of the renin-angiotensin-aldosterone system are thought to be especially important as causal genes of hypertension. Na-K-ATPase, biochemically equal to Na pump, exists on the basolateral membrane of renal epithelial cells. It plays a central role in Na reabsorption and creates a driving force for transepithelial transport. Na-K-ATPase activity is regulated by adducin, a membrane-bound skeletal protein, as well as by several hormones such as dopamine, endogenous ouabain-like factor or cytochrome P450 metabolites. Genes of these factors involved in Na-K-ATPase regulation should be related to the development of hypertension. The endothelin system, atrial natriuretic peptide and nitric oxide regulate the tonus of blood vessels as well as renal sodium excretion. Several reports have indicated that genes of these substances are crucial in the pathogenesis of hypertension.

Transgenic rescue of SNAP-25 restores dopamine-modulated synaptic transmission in the coloboma mutant

Many of the molecular components constituting the exocytotic machinery responsible for neurotransmitter release have been identified, yet the precise role played by these proteins in synaptic transmission, and their impact on neural function, has not been resolved. The mouse mutation coloboma is a contiguous gene defect that leads to electrophysiological and behavioral deficits and includes the gene-encoding SNAP-25, an integral component of the synaptic vesicle-docking/fusion core complex. The involvement of SNAP-25 in the hyperactive behavior of coloboma mice, which can be ameliorated by the indirect dopaminergic agonist, amphetamine, has been demonstrated by genetic rescue using a SNAP-25 transgene. Coloboma mice also exhibit increased recurrent inhibition, reduced theta rhythm by tail-pinch and reduced long-term potentiation in the hippocampal dentate gyrus that, as the hyperkinesis seen in these mutants suggests, may reflect impaired monoaminergic modulation. We sought to identify neurophysiological correlates of the rescued hyperactivity within hippocampal synaptic circuitry of SNAP-25 transgenic coloboma mutant mice. In contrast to the differences between coloboma and wild-type mice, there was no significant difference in the duration or amplitude of theta rhythmic activity (4-6 Hz) induced by tail-pinch (10 s), afferent-evoked field potentials, or paired-pulse responses recorded in the dentate gyrus of SNAP-25 transgenic coloboma and wild-type mice. Amphetamine (3.0 mg/kg, i.p.) produced disinhibition of dentate paired-pulse responses in both SNAP-25 transgenic and wild-type mice but increased inhibition in non-transgenic coloboma mice. These findings support the hypothesis that alteration of monoaminergic neurotransmission, which can be reversed by the indirect agonist, amphetamine, is particularly sensitive to alterations in the expression of SNAP-25.

Alterations in serotonin receptors in the neostriatum of weaver mutant mice

Mice that carry the autosomal recessive gene weaver show a distinctive loss of nigrostriatal dopamine innervation, with the greatest deficits in the dorsal caudate-putamen and almost complete sparing in the nucleus accumbens and ventral caudate. In addition to loss of dopamine in this model, it has recently been shown that markers of serotonin (5-hydroxytryptamine, 5-HT) innervation including 5-HT content, synaptosomal uptake of [3H]5-HT and [3H]citalopram binding were elevated in the dorsal neostriatum of the weaver mutant mouse. Using quantitative autoradiography of specific ligands for dopamine and 5-HT uptake sites as well as serotonin 5-HT1 and 5-HT2A receptors, we found an increased density of 5-HT uptake sites and 5-HT1 receptors restricted to the dorsal portion of the neostriatum of the weaver mouse. In contrast, 5-HT2A receptors were increased in both the dorsal and ventral portions of the rostral neostriatum as well as the nucleus accumbens. The behavioural and functional relevance of these receptor changes is unclear, although, adaptations in 5-HT may play a role in certain aspects of spontaneous behaviour in the weaver mutant mouse.

Family-based association studies of bipolar disorder with candidate genes involved in dopamine neurotransmission: DBH, DAT1, COMT, DRD2, DRD3 and DRD5

The dopaminergic system has been implicated in the aetiology of mood disorders. We conducted family-based association studies for polymorphisms at three genes involved in the metabolism of dopamine: dopamine transporter (DAT1), dopamine-beta-hydroxylase (DBH) and catechol-O-methyl transferase (COMT); and three dopamine receptors: DRD2, DRD3 and DRD5. We used a sample of 122 parent-offspring trios of British Caucasian origin where the proband had bipolar disorder I (BPI), and analysed the results with the transmission/disequilibrium test (TDT) which is robust to hidden population stratification. No statistically significant differences were found between transmitted and not transmitted alleles for any of the polymorphisms studied.

Distribution of dopamine, its metabolites, and D1 and D2 receptors in heterozygous and homozygous weaver mutant mice

In weaver mice, besides a postnatal cerebellar developmental anomaly probably caused by alterations of an inwardly rectifying K+ channel, there is a progressive loss of mesencephalic dopaminergic neurons. To further evaluate this deficit, endogenous dopamine and its metabolites were measured in 22 brain regions from heterozygous (wv/+) and homozygous (wv/wv) mutants, and compared to wild type (+/+) mice. In both wv/+ and wv/wv mutants there were profound dopamine depletions in all regions; these changes were accompanied by decreases in metabolites but with an increase of turnover indexes. Dopamine D1 and D2 receptors were examined by autoradiography, and their distribution was conserved. The results show that the dopaminergic deficit is widespread to all areas of innervation, and is probably compensated for by an increased turnover. Abnormal developmental growth signals, or aberrant cellular responses, may result in defective neurite formation of the midbrain dopaminergic neurons, leading to their postnatal death.

Altered presynaptic gene expression in transgenic mice producing dopamine in the pineal gland

Neurotransmitters are known to play an important role in the development of the nervous system. We recently generated transgenic mice that ectopically express tyrosine hydroxylase (TH) and thereby produce dopamine (DA) de novo in pinealocytes of the pineal gland (PG). The transgenic PG also exhibited a dramatic decrease in TH-immunoreactive (IR) fibers putatively arising from the superior cervical ganglion (SCG) (Cho et al. [1996] Proc Natl Acad Sci USA 93:2862-2866). In the current study, however, we found that there was no reduction in the number of fibers immunostained for neurofilament protein or PGP9.5, markers known to be heavily localized in fibers, despite the reduction of TH fiber density. Therefore, we investigated whether the decreased TH-IR fiber density is the consequence of reduced sympathetic innervation, or a decrease in TH expression within innervating fibers. Immunohistochemical analysis comparing control and transgenic PG demonstrated no apparent differences in numbers of NPY- and aromatic-L-amino acid decarboxylase (AADC)-IR fibers, indicating that TH expression is decreased in a normal number of innervating fibers. Furthermore, presynaptic neurons in the transgenic SCG showed abnormal and heterogeneous TH immunoreactivity and reduced TH and norepinephrine transporter (NET) mRNA levels. These results show that ectopic DA production in the PG lowers TH and NET gene expression in the SCG without altering sympathetic innervation to the PG and suggest that the alteration of target neurotransmitter phenotype may influence gene expression of phenotype-specific proteins in projecting neurons.

Feeding behavior in dopamine-deficient mice

Mice that cannot make dopamine (DA), a condition caused by the selective inactivation of tyrosine hydroxylase in dopaminergic neurons, are born normal but gradually become hypoactive and hypophagic, and die at 3 weeks of age. We characterized the feeding and locomotor responses of these DA-deficient (DA-/-) mice to 3, 4-dihyroxy-L-phenylalanine (L-DOPA) to investigate the relationship between brain DA levels and these complex behaviors. Daily administration of L-DOPA to DA-/- mice stimulated locomotor activity that lasted 6 to 9 hr; during that time the mice consumed most of their daily food and water. The minimal dose of L-DOPA that was sufficient to elicit normal feeding behavior in the DA-/- mice also restored their striatal DA to 9.1% of that in the wild-type (WT) mice at 3 hr; then DA content declined to <1% of WT levels by 24 hr. This dose of L-DOPA induced locomotor activity that exceeded that of treated WT mice by 5- to 7-fold, suggesting that DA-/- mice are supersensitive to DA. Unexpectedly, DA-/- mice manifested a second wave of activity 24 to 48 hr after L-DOPA treatment that was equivalent in magnitude to that of WT mice and independent of DA receptor activation. The DA-/- mice approached, sniffed, and chewed food during this second period of activity, but they ate <10% of that required for sustenance. Therefore, DA-/- mice can execute behaviors necessary to seek and ingest food, but they do not eat enough to survive.

The catecholamines up (Catsup) protein of Drosophila melanogaster functions as a negative regulator of tyrosine hydroxylase activity

We report the genetic, phenotypic, and biochemical analyses of Catecholamines up (Catsup), a gene that encodes a negative regulator of tyrosine hydroxylase (TH) activity. Mutations within this locus are semidominant lethals of variable penetrance that result in three broad, overlapping effective lethal phases (ELPs), indicating that the Catsup gene product is essential throughout development. Mutants from each ELP exhibit either cuticle defects or catecholamine-related abnormalities, such as melanotic salivary glands or pseudotumors. Additionally, Catsup mutants have significantly elevated TH activity that may arise from a post-translational modification of the enzyme. The hyperactivation of TH in Catsup mutants results in abnormally high levels of catecholamines, which can account for the lethality, visible phenotypes, and female sterility observed in these mutants. We propose that Catsup is a component of a novel system that downregulates TH activity, making Catsup the fourth locus found within the Dopa decarboxylase (Ddc) gene cluster that functions in catecholamine metabolism.

Functional hyperdopaminergia in dopamine transporter knock-out mice

Dopamine is an important regulator of many central nervous system functions. Hyperfunction of the dopaminergic system is believed to be related to several pathological conditions. Genetic deletion of the dopamine transporter gene in mice results in a persistent extracellular hyperdopaminergic tone, that is functionally revealed as hyperactivity. The lack of a reuptake mechanism produces a marked increase in functional extracellular dopamine which results in profound plasticity of pre- and postsynaptic parameters of dopamine homeostasis. The mice lacking the dopamine transporter gene may represent an appropriate model to elucidate the molecular adaptive changes accompanying pathological states associated with hyperdopaminergic function.

Global variation of a 40-bp VNTR in the 3'-untranslated region of the dopamine transporter gene (SLC6A3)

BACKGROUND

The dopamine transporter (DAT) is the primary mechanism for dopamine clearance from the synapse in midbrain dopaminergic neurons, and the target of psychostimulant and neurotoxic drugs such as cocaine, amphetamine, and MPTP. Consequently, the gene for DAT (SLC6A3) has been the focus of many population-based case-control association studies using a 40-bp VNTR in the 3'-untranslated region. Results have differed depending on the population studied, suggesting allele frequency effects are involved. For this reason, a global survey of allele frequencies for this VNTR polymorphism was performed.

METHODS

Individuals (n = 1528) from 30 populations around the world were typed for this VNTR using PCR and agarose gel electrophoresis.

RESULTS

As with previous studies, the ten-repeat allele is most common, except for a Middle Eastern population in which the nine-repeat allele is most frequent. Frequencies of the nine- and ten-repeat alleles vary widely even among European populations.

CONCLUSIONS

Many previous association studies have used "white" or "black" U.S. populations. However, many different ethnic groups have contributed to these populations. The large variation in allele frequencies observed in this study emphasizes the inadequacy of most past studies using the case-control design and the importance of matching patient and control populations in future association studies.

Specification of dopaminergic and serotonergic neurons in the vertebrate CNS

The early specification of dopaminergic and serotonergic neurons during vertebrate CNS development relies on signals produced by a small number of organizing centers. Recent studies have characterized these early organizing centers, the manner in which they may be established, the inductive signals they produce, and candidate signaling systems that control the later development of the dopaminergic system.

Altered gene expression for catecholamine biosynthetic enzymes and stress response in rat genetic model of depression

Although stress is a major contributory factor in the development of depression, the relationship between stress and depression is still unclear. In this study, we evaluated basal mRNA levels of several genes involved in neurotransmitter biosynthesis and the effect of stress in Flinder's Sensitive Line (FSL), a genetic rat model of depression. In adrenals, basal levels of tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT) and GTP cyclohydrolase I (GTPCH) mRNAs were markedly elevated in FSL rats compared to the control strain. As opposed to control strain, immobilization stress (IMO) to FSL rats, did not further raise DBH, PNMT or GTPCH mRNAs and had relatively mild effect on TH. In contrast to enzymes involved in catecholamine biosynthesis, basal NPY and its response to IMO were unchanged in FSL rats. In the brain, the two major dopaminergic nuclei displayed differences. In substantia nigra, TH mRNA levels were similar in both strains, and elevated by IMO only in FSL rats. In ventral tegmental area in FSL rats, TH mRNA was 2-fold higher than in the control strain and not further elevated by IMO. These high basal mRNA levels and abnormal response to stress in several catecholaminergic cell types in FSL rats may be related to the manifestations of depression.

Motor and learning dysfunction during postnatal development in mice defective in dopamine neuronal transmission

Mice lacking expression of tyrosine hydroxylase (TH), the first and rate-limiting enzyme of the catecholamine biosynthetic pathway, in dopaminergic neuronal cell types were generated by a transgenic rescue approach to clarify the role of dopamine signaling during postnatal development. Introduction of the TH transgene directed by the dopamine beta-hydroxylase gene promoter into TH knockout mice restored noradrenaline and adrenaline synthesis, preventing perinatal lethality and cardiac dysfunction in the knockout mice. Lack of TH expression in the cells that normally express the dopaminergic phenotype resulted in a marked reduction of dopamine accumulation in the tissues, which led to multiple behavioral abnormalities at the juvenile stage. These abnormalities were characterized by a reduction in spontaneous locomotor activity, blockade of methamphetamine-induced hyperactivity, cataleptic behavior, and defects in active avoidance learning. In contrast, development of the pituitary gland as well as production and secretion of the pituitary peptide hormones dependent on hypothalamic dopaminergic control were normally maintained, despite defective dopamine synthesis. These results demonstrate that dopamine neurotransmission is essential for controlling spontaneous and voluntary movement and associative learning during postnatal development through the nigrostriatal and mesocorticolimbic pathways.

Molecular characterization of human and rat RGS 9L, a novel splice variant enriched in dopamine target regions, and chromosomal localization of the RGS 9 gene

A novel splice variant of RGS 9 was isolated from a rat hypothalamus, human retina, and a human kidney (Wilm's) tumor. This variant, termed RGS 9L, differs from the retinal form (termed RGS 9S) identified previously in that it contains a 211- (rat) or 205- (human) amino acid proline-rich domain on the carboxyl terminus. The pattern of RGS 9 mRNA splicing was tissue specific, with striatum, hypothalamus- and nucleus accumbens expressing RGS 9L, whereas retina and pineal expressed RGS 9S almost exclusively. This pattern of mRNA splicing seemed to be highly conserved between human and rodents, suggesting cell-specific differences in the function of these variants. Transient expression of RGS 9L augmented basal and beta-adrenergic receptor-stimulated adenylyl cyclase activity while suppressing dopamine D2 receptor-mediated inhibition. Furthermore, RGS 9L expression greatly accelerated the decay of dopamine D2 receptor-induced GIRK current. These results indicate RGS 9L inhibits heterotrimeric Gi function in vivo, probably by acting as a GTPase-activating protein. The human RGS 9 gene was localized to chromosome 17 q23-24 by radiation hybrid and fluorescent in situ hybridization analyses. The RGS 9 gene is within a previously defined locus for retinitis pigmentosa (RP 17), a disease that has been linked to genes in the rhodopsin/transducin/cGMP signaling pathway.

Modification of alcohol withdrawal by the A9 allele of the dopamine transporter gene

OBJECTIVE

Determinants of individual vulnerability to alcohol withdrawal symptoms are largely unknown. Because of the substantial role of monoaminergic transporters in limiting time and space effects of synaptic neurotransmission, the dopamine transporter gene (DAT1; locus symbol: SLC6A3) was studied as a candidate gene possibly related to symptoms of uncomplicated alcohol withdrawal.

METHOD

In 48 chronically intoxicated alcoholics (diagnosed according to ICD-10), withdrawal symptoms were examined and the presence of a variable-number tandem repeat in the 3' untranslated region of the DAT1 gene was determined.

RESULTS

Withdrawal syndromes were more pronounced in the 22 patients carrying the nine-copy repeat than in the 26 patients without this variant. Multiple regression analysis revealed that 4% of the variance of withdrawal was explained by this genotype, whereas 16% was due to the amount of alcohol the patients reported having consumed in the month before detoxification.

CONCLUSIONS

The A9 allele of the dopamine transporter gene is associated with more severe effects of alcohol withdrawal, possibly because of modifications of the brain's capacity to compensate for long-term effects of ethanol on cerebral function.

Mutational and biochemical analysis of dopamine in dystonia: evidence for decreased dopamine D2 receptor inhibition

The dystonias are a group of serious movement disorders characterized by involuntary muscle spasms of different parts of the body. We recently proposed that hypofunction of dopamine D2 receptor-mediated inhibition of the indirect output pathway of the basal ganglia can result in dystonia. In this review, we discuss the results of a variety of genetic and biochemical studies in light of this hypothesis. Several forms of early-onset dystonia show distinct autosomal dominant, recessive, or X-linked genetic transmission patterns. Late onset forms of dystonia, though not showing clear Mendelian transmission patterns, also appear to be highly familial. Recently, several genetic-linkage locations have been identified for early-onset dystonia and for two of these loci, mutations decreasing dopamine synthesis have been demonstrated. Biochemical studies of monkeys and man also demonstrate that several types of dystonia occur in a dopamine-deficiency state. Similarly, mice strains developed to be deficient in several dopamine-pathway components have motor abnormalities consistent with dystonia. Hypofunction of the dopamine D2 receptor-mediated inhibition of the indirect output pathway of the putamen may be a common feature of many of these heritable and secondary dystonic syndromes.

Dopamine markers and general cognitive ability

Because general cognitive ability (g) is among the most heritable behavioural traits, it is a reasonable target for a search for quantitative trait loci (QTLs). We used a selected-extremes design to test candidate genes for allelic association with g. Polymorphisms in four genes in the dopamine system (DRD2, DRD3, DRD4, DAT1) were genotyped for 51 high g children with IQ scores > 130 and for 51 average g control children. No significant allelic or genotypic differences were found between the high g and average g groups for these markers of the dopamine system, even though the selected-extremes design provides power to detect QTL associations that involve a relative risk of about 1.5.

Differential modification of dopamine transporter and tyrosine hydroxylase mRNAs in midbrain of subjects with Parkinson's, Alzheimer's with parkinsonism, and Alzheimer's disease

The molecular characteristics of midbrain dopamine (DA) neurons have been extensively studied in Parkinson's disease (PD). No such studies of the characteristics of midbrain DA neurons in Alzheimer's disease (AD) or Alzheimer's disease with parkinsonism (AD/Park) have been published. We examined the levels of tyrosine hydroxylase (TH) protein, and the expression of TH and dopamine transporter (DAT) mRNAs, in midbrain neurons of PD, AD, and AD/Park cases. In PD, the loss of TH protein in the ventral tier of the substantia nigra pars compacta (SNpc) of the PD group in accompanied by severe losses in the number of neurons that express TH mRNA and DAT mRNA (74% loss). Remaining neurons show a shift to higher concentrations of TH mRNA but a shift to lower concentrations of DAT mRNA per cell. Hence, there is evidence that compensation in the remaining neurons can elevate concentrations of TH mRNA and lower DAT mRNA. Alternatively, there may be a predilection for a loss of neurons with high levels of DAT mRNA and low TH mRNA levels within the SNpc of PD cases. There was no change in TH protein but an elevation of TH mRNA concentrations per neuron without any change in concentrations of DAT mRNA in the AD group. The AD/Park group did not exhibit changes in the level of TH protein, but showed a small loss (26%) of neurons in the SNpc and a greater loss in other regions of the midbrain (43-53%). Remaining DA neurons showed a marked shift to lower concentrations of DAT mRNA per neuron and a nonsignificant shift in cellular concentration of TH mRNA to higher levels. This is consistent with our previous work showing that with AD/Park there is a significant reduction in the number of DAT sites located on DA terminals in the striatum, but the midbrain neurons have not died. Our results indicate that the differential regulation of mRNAs encoding TH and DAT is similar in the parkinsonian disorders (PD and AD/Park) even though the degree of cell death is very different. This might suggest that compensatory events occur in these DA neurons in AD/Park that are similar to those in PD and that result in differential effects on mRNAs encoding TH and DAT proteins.