A Drosophila model of Parkinson's disease

Parkinson's disease is a common neurodegenerative syndrome characterized by loss of dopaminergic neurons in the substantia nigra, formation of filamentous intraneuronal inclusions (Lewy bodies) and an extrapyramidal movement disorder. Mutations in the alpha-synuclein gene are linked to familial Parkinson's disease and alpha-synuclein accumulates in Lewy bodies and Lewy neurites. Here we express normal and mutant forms of alpha-synuclein in Drosophila and produce adult-onset loss of dopaminergic neurons, filamentous intraneuronal inclusions containing alpha-synuclein and locomotor dysfunction. Our Drosophila model thus recapitulates the essential features of the human disorder, and makes possible a powerful genetic approach to Parkinson's disease.

Dopaminergic loss and inclusion body formation in alpha-synuclein mice: implications for neurodegenerative disorders

To elucidate the role of the synaptic protein alpha-synuclein in neurodegenerative disorders, transgenic mice expressing wild-type human alpha-synuclein were generated. Neuronal expression of human alpha-synuclein resulted in progressive accumulation of alpha-synuclein-and ubiquitin-immunoreactive inclusions in neurons in the neocortex, hippocampus, and substantia nigra. Ultrastructural analysis revealed both electron-dense intranuclear deposits and cytoplasmic inclusions. These alterations were associated with loss of dopaminergic terminals in the basal ganglia and with motor impairments. These results suggest that accumulation of wild-type alpha-synuclein may play a causal role in Parkinson's disease and related conditions.

Dopamine reward circuitry: two projection systems from the ventral midbrain to the nucleus accumbens-olfactory tubercle complex

Anatomical and functional refinements of the meso-limbic dopamine system of the rat are discussed. Present experiments suggest that dopaminergic neurons localized in the posteromedial ventral tegmental area (VTA) and central linear nucleus raphe selectively project to the ventromedial striatum (medial olfactory tubercle and medial nucleus accumbens shell), whereas the anteromedial VTA has few if any projections to the ventral striatum, and the lateral VTA largely projects to the ventrolateral striatum (accumbens core, lateral shell and lateral tubercle). These findings complement the recent behavioral findings that cocaine and amphetamine are more rewarding when administered into the ventromedial striatum than into the ventrolateral striatum. Drugs such as nicotine and opiates are more rewarding when administered into the posterior VTA or the central linear nucleus than into the anterior VTA. A review of the literature suggests that (1) the midbrain has corresponding zones for the accumbens core and medial shell; (2) the striatal portion of the olfactory tubercle is a ventral extension of the nucleus accumbens shell; and (3) a model of two dopamine projection systems from the ventral midbrain to the ventral striatum is useful for understanding reward function. The medial projection system is important in the regulation of arousal characterized by affect and drive and plays a different role in goal-directed learning than the lateral projection system, as described in the variation-selection hypothesis of striatal functional organization.

Induction of midbrain dopaminergic neurons from ES cells by stromal cell-derived inducing activity

We have identified a stromal cell-derived inducing activity (SDIA) that promotes neural differentiation of mouse ES cells. SDIA accumulates on the surface of PA6 stromal cells and induces efficient neuronal differentiation of cocultured ES cells in serum-free conditions without use of either retinoic acid or embryoid bodies. BMP4, which acts as an antineuralizing morphogen in Xenopus, suppresses SDIA-induced neuralization and promotes epidermal differentiation. A high proportion of tyrosine hydroxylase-positive neurons producing dopamine are obtained from SDIA-treated ES cells. When transplanted, SDIA-induced dopaminergic neurons integrate into the mouse striatum and remain positive for tyrosine hydroxylase expression. Neural induction by SDIA provides a new powerful tool for both basic neuroscience research and therapeutic applications.

Neurodegeneration prevented by lentiviral vector delivery of GDNF in primate models of Parkinson's disease

Lentiviral delivery of glial cell line-derived neurotrophic factor (lenti-GDNF) was tested for its trophic effects upon degenerating nigrostriatal neurons in nonhuman primate models of Parkinson's disease (PD). We injected lenti-GDNF into the striatum and substantia nigra of nonlesioned aged rhesus monkeys or young adult rhesus monkeys treated 1 week prior with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Extensive GDNF expression with anterograde and retrograde transport was seen in all animals. In aged monkeys, lenti-GDNF augmented dopaminergic function. In MPTP-treated monkeys, lenti-GDNF reversed functional deficits and completely prevented nigrostriatal degeneration. Additionally, lenti-GDNF injections to intact rhesus monkeys revealed long-term gene expression (8 months). In MPTP-treated monkeys, lenti-GDNF treatment reversed motor deficits in a hand-reach task. These data indicate that GDNF delivery using a lentiviral vector system can prevent nigrostriatal degeneration and induce regeneration in primate models of PD and might be a viable therapeutic strategy for PD patients.

Protection and repair of the nigrostriatal dopaminergic system by GDNF in vivo

Glial-cell-line-derived neurotrophic factor (GDNF), a recently cloned new member of the transforming growth factor-beta superfamily, promotes survival of cultured fetal mesencephalic dopamine neurons and is expressed in the developing striatum. There have, however, been no reports about effects of GDNF in situ. We have used the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces parkinsonian symptoms in man, to determine whether GDNF might exert protective or regenerative effects in vivo in the adult nigrostriatal dopamine system in C57/B1 mice. GDNF injected over the substantia nigra or in striatum before MPTP potently protects the dopamine system, as shown by numbers of mesencephalic dopamine nerve cell bodies, dopamine nerve terminal densities and dopamine levels. When GDNF is given after MPTP, dopamine levels and fibre densities are significantly restored. In both cases, motor behaviour is increased above normal levels. We conclude that intracerebral GDNF administration exerts both protective and reparative effects on the nigrostriatal dopamine system, which may have implications for the development of new treatment strategies for Parkinson's disease.

Expression of ghrelin receptor mRNA in the rat and the mouse brain

Ghrelin is a hormone that stimulates growth hormone secretion and signals energy insufficiency via interaction with its receptor, the growth hormone secretagogue receptor (GHSR). The GHSR is located in both the central nervous system and the periphery. Its distribution in the CNS, as assessed by in situ hybridization histochemistry (ISHH), has been described previously in a few mammalian species, although these studies were limited by either the detail provided or the extent of the regions examined. In the present study, we systematically examined the distribution of GHSR mRNA in the adult rat and mouse brains and cervical spinal cords by using ISHH with novel cRNA probes specific for the mRNA encoding functional GHSR (the type 1a variant). We confirmed GHSR mRNA expression in several hypothalamic nuclei, many of which have long been recognized as playing roles in body weight and food intake. GHSR also was found in several other regions previously unknown to express GHSR mRNA, including many parasympathetic preganglionic neurons. Additionally, we found GHSR mRNA within all three components of the dorsal vagal complex, including the area postrema, the nucleus of the solitary tract, and the dorsal motor nucleus of the vagus. Finally, we examined the coexpression of GHSR with tyrosine hydroxylase and cholecystokinin and demonstrate a high degree of GHSR mRNA expression within dopaminergic, cholecystokinin-containing neurons of the substantia nigra and ventral tegmental area.

Structure and evolution of calcium-modulated proteins

This review suggests that the intracellular functions of calcium are best understood in terms of calcium's functioning as a second messenger. Further, when functioning as a second messenger, calcium completes its mission not by transferring charge nor by binding to lipid but by binding to specific targets, calcium-modulated proteins. This concept is broadly interpreted to include proteins involved in calcium transport. There is strong evidence that many, if not all, of these calcium-modulated proteins are homologs. Their structures and properties are contrasted to those of extracellular calcium-binding proteins which are not homologous to one another or to the intracellular calcium-modulated proteins. Finally, this line of thought leads to a suggestion of the evolutionary reason for the choice of calcium as the sole inorganic second messenger.

Differential co-existence of neuropeptide Y (NPY)-like immunoreactivity with catecholamines in the central nervous system of the rat

The distribution of neuropeptide Y immunoreactive cell bodies in relation to various types of catecholamine-containing cell bodies in the rat brain was analyzed immunohistochemically using antisera to tyrosine hydroxylase, dopamine beta-hydroxylase and phenylethanolamine N-methyltransferase. Coexistence of the peptide in catecholamine cell bodies was established by using an elution-restaining procedure. Neuropeptide Y-like immunoreactivity was observed in most noradrenergic cell bodies of the Al/Cl cell groups in the ventro lateral medulla oblongata. Similarly this peptide immunoreactivity was also observed in the majority of the adrenergic cell bodies of the C2 group. In the dorsal and dorsal-lateral part of the nucleus of the solitary tract, where a group of small adrenergic cells is present, several small neuropeptide Y immunoreactive cells were also observed. The possibility of coexistence of adrenaline and neuropeptide Y in these cells remains to be established. The majority of the noradrenergic cell bodies of the A2 group, as well as the presumptive dopaminergic cells within its ventromedial part, seemed to lack neuropeptide Y-like immunoreactivity. Many noradrenergic cell bodies of the A6 group in the locus coeruleus proper were neuropeptide Y-immunoreactive, whereas the peptide could not be observed in the subcoeruleus group. Neither the A5 and A7 noradrenergic cells in the pons, nor any of the dopaminergic cell groups in the mesencephalon and forebrain (A8-A15) seemed to contain a neuropeptide Y-like peptide. The findings indicate that central catecholamine neurons can be subdivided into distinct sub-groups based upon the coexistence of a specific peptide.

Tyrosine hydroxylase and regulation of dopamine synthesis

Tyrosine hydroxylase is the rate-limiting enzyme of catecholamine biosynthesis; it uses tetrahydrobiopterin and molecular oxygen to convert tyrosine to DOPA. Its amino terminal 150 amino acids comprise a domain whose structure is involved in regulating the enzyme's activity. Modes of regulation include phosphorylation by multiple kinases at four different serine residues, and dephosphorylation by two phosphatases. The enzyme is inhibited in feedback fashion by the catecholamine neurotransmitters. Dopamine binds to TyrH competitively with tetrahydrobiopterin, and interacts with the R domain. TyrH activity is modulated by protein-protein interactions with enzymes in the same pathway or the tetrahydrobiopterin pathway, structural proteins considered to be chaperones that mediate the neuron's oxidative state, and the protein that transfers dopamine into secretory vesicles. TyrH is modified in the presence of NO, resulting in nitration of tyrosine residues and the glutathionylation of cysteine residues.

Tyrosine hydroxylase-immunoreactive boutons in synaptic contact with identified striatonigral neurons, with particular reference to dendritic spines

Tyrosine hydroxylase-immunoreactive fibres in the rat neostriatum were studied in the electron microscope in order to determine the nature of the contacts they make with other neural elements. The larger varicose parts of such fibres contained relatively few vesicles and rarely displayed synaptic membrane specializations; however, thinner parts of axons (0.1-0.4 micron) contained many vesicles and had symmetrical membrane specializations, indicative of en passant type synapses. By far the most common postsynaptic targets of tyrosine hydroxylase-immunoreactive boutons were dendritic spines and shafts, although neuronal cell bodies and axon initial segments also received such input. Six striatonigral neurons in the ventral striatum were identified by retrograde labelling with horseradish peroxidase and their dendritic processes were revealed by Golgi impregnation using the section-Golgi procedure. The same sections were also developed to reveal tyrosine hydroxylase immunoreactivity and so we were able to study immunoreactive boutons in contact with the Golgi-impregnated striatonigral neurons. Each of the 280 immunoreactive boutons examined in the electron microscope displayed symmetrical synaptic membrane specializations: 59% of the boutons were in synaptic contact with the dendritic spines, 35% with the dendritic shafts and 6% with the cell bodies of striatonigral neurons. The dendritic spines of striatonigral neurons that received input from immunoreactive boutons invariably also received input, usually more distally, from unstained boutons that formed asymmetrical synaptic specializations. A study of 87 spines along the dendrites of an identified striatonigral neuron showed that the most common type of synaptic input was from an individual unstained bouton making asymmetrical synaptic contact (53%), while 39% of the spines received one asymmetrical synapse and one symmetrical immunoreactive synapse. It is proposed that the spatial distribution of presumed dopaminergic terminals in synaptic contact with different parts of striatonigral neurons has important functional implications. Those synapses on the cell body and proximal dendritic shafts might mediate a relatively non-selective inhibition. In contrast, the major dopaminergic input that occurs on the necks of dendritic spines is likely to be highly selective since it could prevent the excitatory input to the same spines from reaching the dendritic shaft. One of the main functions of dopamine released from nigrostriatal fibres might thus be to alter the pattern of firing of striatal output neurons by regulating their input.

Akt phosphorylates the Yes-associated protein, YAP, to induce interaction with 14-3-3 and attenuation of p73-mediated apoptosis

We have used an affinity purification method to identify substrates of protein kinase B/Akt. One protein that associates with 14-3-3 in an Akt-dependent manner is shown here to be the Yes-associated protein (YAP), which is phosphorylated by Akt at serine 127, leading to binding to 14-3-3. Akt promotes YAP localization to the cytoplasm, resulting in loss from the nucleus where it functions as a coactivator of transcription factors including p73. p73-mediated induction of Bax expression following DNA damage requires YAP function and is attenuated by Akt phosphorylation of YAP. YAP overexpression increases, while YAP depletion decreases, p73-mediated apoptosis following DNA damage, in an Akt inhibitable manner. Akt phosphorylation of YAP may thus suppress the induction of the proapoptotic gene expression response following cellular damage.

Prefrontal cortical efferents in the rat synapse on unlabeled neuronal targets of catecholamine terminals in the nucleus accumbens septi and on dopamine neurons in the ventral tegmental area

Physiological and pharmacological studies indicate that descending projections from the prefrontal cortex modulate dopaminergic transmission in the nucleus accumbens septi and ventral tegmental area. We investigated the ultrastructural bases for these interactions in rat by examining the synaptic associations between prefrontal cortical terminals labeled with anterograde markers (lesion-induced degeneration or transport of Phaseolus vulgaris leucoagglutinin; PHA-L) and neuronal processes containing immunoreactivity for the catecholamine synthesizing enzyme, tyrosine hydroxylase. Prefrontal cortical terminals in the nucleus accumbens and ventral tegmental area contained clear, round vesicles and formed primarily asymmetric synapses on spines or small dendrites. In the ventral tegmental area, these terminals also formed asymmetric synapses on large dendrites and a few symmetric axodendritic synapses. In the nucleus accumbens septi, degenerating prefrontal cortical terminals synapsed on spiny dendrites which received convergent input from terminals containing peroxidase immunoreactivity for tyrosine hydroxylase, or from unlabeled terminals. In single sections, some tyrosine hydroxylase-labeled terminals formed thin and punctate symmetric synapses with dendritic shafts, or the heads and necks of spines. Close appositions, but not axo-axonic synapses, were frequently observed between degenerating prefrontal cortical afferents and tyrosine hydroxylase-labeled or unlabeled terminals. In the ventral tegmental area, prefrontal cortical terminals labeled with immunoperoxidase for PHA-L were in synaptic contact with dendrites containing immunogold reaction product for tyrosine hydroxylase, or with unlabeled dendrites. These results suggest that: (1) catecholaminergic (mainly dopaminergic) and prefrontal cortical terminals in the nucleus accumbens septi dually synapse on common spiny neurons; and (2) dopaminergic neurons in the ventral tegmental area receive monosynaptic input from prefrontal cortical afferents. This study provides the first ultrastructural basis for multiple sites of cellular interaction between prefrontal cortical efferents and mesolimbic dopaminergic neurons.

TAZ: a novel transcriptional co-activator regulated by interactions with 14-3-3 and PDZ domain proteins

The highly conserved and ubiquitously expressed 14-3-3 proteins regulate differentiation, cell cycle progression and apoptosis by binding intracellular phosphoproteins involved in signal transduction. By screening in vitro translated cDNA pools for the ability to bind 14-3-3, we identified a novel transcriptional co-activator, TAZ (transcriptional co-activator with PDZ-binding motif) as a 14-3-3-binding molecule. TAZ shares homology with Yes-associated protein (YAP), contains a WW domain and functions as a transcriptional co-activator by binding to the PPXY motif present on transcription factors. 14-3-3 binding requires TAZ phosphorylation on a single serine residue, resulting in the inhibition of TAZ transcriptional co-activation through 14-3-3-mediated nuclear export. The C-terminus of TAZ contains a highly conserved PDZ-binding motif that localizes TAZ into discrete nuclear foci and is essential for TAZ-stimulated gene transcription. TAZ uses this same motif to bind the PDZ domain-containing protein NHERF-2, a molecule that tethers plasma membrane ion channels and receptors to cytoskeletal actin. TAZ may link events at the plasma membrane and cytoskeleton to nuclear transcription in a manner that can be regulated by 14-3-3.

Projection-specific modulation of dopamine neuron synapses by aversive and rewarding stimuli

Midbrain dopamine (DA) neurons are not homogeneous but differ in their molecular properties and responses to external stimuli. We examined whether the modulation of excitatory synapses on DA neurons by rewarding or aversive stimuli depends on the brain area to which these DA neurons project. We identified DA neuron subpopulations in slices after injection of "Retrobeads" into single target areas of adult mice and found differences in basal synaptic properties. Administration of cocaine selectively modified excitatory synapses on DA cells projecting to nucleus accumbens (NAc) medial shell while an aversive stimulus selectively modified synapses on DA cells projecting to medial prefrontal cortex. In contrast, synapses on DA neurons projecting to NAc lateral shell were modified by both rewarding and aversive stimuli, which presumably reflects saliency. These results suggest that the mesocorticolimbic DA system may be comprised of three anatomically distinct circuits, each modified by distinct aspects of motivationally relevant stimuli.

Orexin A in the VTA is critical for the induction of synaptic plasticity and behavioral sensitization to cocaine

Dopamine neurons in the ventral tegmental area (VTA) represent a critical site of synaptic plasticity induced by addictive drugs. Orexin/hypocretin-containing neurons in the lateral hypothalamus project to the VTA, and behavioral studies have suggested that orexin neurons play an important role in motivation, feeding, and adaptive behaviors. However, the role of orexin signaling in neural plasticity is poorly understood. The present study shows that in vitro application of orexin A induces potentiation of N-methyl-D-aspartate receptor (NMDAR)-mediated neurotransmission via a PLC/PKC-dependent insertion of NMDARs in VTA dopamine neuron synapses. Furthermore, in vivo administration of an orexin 1 receptor antagonist blocks locomotor sensitization to cocaine and occludes cocaine-induced potentiation of excitatory currents in VTA dopamine neurons. These results provide in vitro and in vivo evidence for a critical role of orexin signaling in the VTA in neural plasticity relevant to addiction.

Evidence for coexistence of dopamine and CCK in meso-limbic neurones

Vanderhaeghen et al. reported the occurrence of gastrin-like immunoreactivity in the mammalian brain. Subsequent studies have revealed that this immunoreactivity corresponded mainly to the COOH-terminal octapeptide of cholecystokinin (CCK-8), which has a COOH-terminal pentapeptide identical to gastrin. Also, two peptides resembling the NH- and the COOH-terminal tetrapeptide fragments of CCK-8 are present in the central nervous system (CNS). Using COOH-terminal-specific antisera raised to gastrin and/or CCK, the distribution of CCK neurones has been described with immunohistochemical techniques. Although high numbers of cells and nerve terminals are found in cortical areas, the CCK systems are also present in most other parts of the brain and spinal cord. In the CNS, true gastrin molecules, gastrin-17 and gastrin-34 have been located only in the neurohypophysis, hypothalamus and occasionally in the medulla oblongata (unpublished results). We describe here the occurrence of peptides in meso-limbic dopamine neurones in the rat brain. Evidence has also been obtained that mesencephalic dopamine neurones in the human brain contain similar peptides.

A highly reproducible rotenone model of Parkinson's disease

The systemic rotenone model of Parkinson's disease (PD) accurately replicates many aspects of the pathology of human PD and has provided insights into the pathogenesis of PD. The major limitation of the rotenone model has been its variability, both in terms of the percentage of animals that develop a clear-cut nigrostriatal lesion and the extent of that lesion. The goal here was to develop an improved and highly reproducible rotenone model of PD. In these studies, male Lewis rats in three age groups (3, 7 or 12-14 months) were administered rotenone (2.75 or 3.0 mg/kg/day) in a specialized vehicle by daily intraperitoneal injection. All rotenone-treated animals developed bradykinesia, postural instability, and/or rigidity, which were reversed by apomorphine, consistent with a lesion of the nigrostriatal dopamine system. Animals were sacrificed when the PD phenotype became debilitating. Rotenone treatment caused a 45% loss of tyrosine hydroxylase-positive substantia nigra neurons and a commensurate loss of striatal dopamine. Additionally, in rotenone-treated animals, alpha-synuclein and poly-ubiquitin positive aggregates were observed in dopamine neurons of the substantia nigra. In summary, this version of the rotenone model is highly reproducible and may provide an excellent tool to test new neuroprotective strategies.

Dopamine-deficient mice are severely hypoactive, adipsic, and aphagic

Mice unable to synthesize dopamine (DA) specifically in dopaminergic neurons were created by inactivating the tyrosine hydroxylase (TH) gene then by restoring TH function in noradrenergic cells. These DA-deficient (DA-/-) mice were born at expected frequency but became hypoactive and stopped feeding a few weeks after birth. Midbrain dopaminergic neurons, their projections, and most characteristics of their target neurons in the striatum appeared normal. Within a few minutes of being injected with L-dihdroxyphenylalanine (L-DOPA), the product of TH, the DA-/- mice became more active and consumed more food than control mice. With continued administration of L-DOPA, nearly normal growth was achieved. These studies indicate that DA is essential for movement and feeding, but is not required for the development of neural circuits that control these behaviors.

Calcium signaling through protein kinases. The Arabidopsis calcium-dependent protein kinase gene family

In plants, numerous Ca(2+)-stimulated protein kinase activities occur through calcium-dependent protein kinases (CDPKs). These novel calcium sensors are likely to be crucial mediators of responses to diverse endogenous and environmental cues. However, the precise biological function(s) of most CDPKs remains elusive. The Arabidopsis genome is predicted to encode 34 different CDPKs. In this Update, we analyze the Arabidopsis CDPK gene family and review the expression, regulation, and possible functions of plant CDPKs. By combining emerging cellular and genomic technologies with genetic and biochemical approaches, the characterization of Arabidopsis CDPKs provides a valuable opportunity to understand the plant calcium-signaling network.