Overexpression of human a-synuclein in model systems, including cultured neurons, drosophila and mice, leads to biochemical and pathological changes that mimic synucleopathies including Parkinson's disease. We have overexpressed both wild-type (WT) and mutant alanine53 fi threonine (A53T) human a-synuclein by transgenic injection into Caenorhabditis elegans. Motor deficits were observed when either WT or A53T a-synuclein was overexpressed with a pan-neuronal or motor neuron promoter. Neuronal and dendritic loss were accelerated in all three sets of C. elegans dopaminergic neurons when human a-synuclein was overexpressed under the control of a dopaminergic neuron or panneuronal promoter, but not with a motor neuron promoter.There were no significant differences in neuronal loss between overexpressed WT and A53T forms or between worms of different ages (4 days, 10 days or 2 weeks). These results demonstrate neuronal and behavioral perturbations elicited by human a-synuclein in C. elegans that are dependent upon expression in specific neuron subtypes. This transgenic model in C. elegans, an invertebrate organism with excellent experimental resources for further genetic manipulation, may help facilitate dissection of pathophysiologic mechanisms of various synucleopathies. Keywords: a-synuclein, model organism, motor neuron, neurodegeneration, worm transgenic. Synucleopathies represent a large range of neuropathologically defined conditions that include Parkinson's disease (PD), dementia with Lewy bodies, Pick's disease and multiple system atrophy ( Spillantini et al. 1997Spillantini et al. , 1998Baba et al. 1998;Takeda et al. 1998). PD is a neurodegenerative disorder that affects 1% of the population over the age of 50 years. PD neurodegeneration is found predominantly in dopaminergic neurons of the substantia nigra where the pathological hallmark is the appearance of intracellular inclusions termed Lewy bodies. These bodies consist of protein complexes that include neurofilaments, ubiquitin and a-synuclein (Forno 1996 2 ; Spillantini et al. Abbreviations used: A53T, mutant alanine53 fi threonine; ADE, anterior deirid; CEP, cephalic neurons; GFP, green fluorescent protein; PD, Parkinson's disease; PDE, posterior deirid; UCHL1, ubiquitin carboxyl-terminal hydrolase L1; TBSB, Tris-buffered saline with 0.5% bovine serum albumin; WT, wild type.

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Background and purpose: Pharmacological validation of novel functions for the a 2A -, a 2B -, and a 2C -adrenoceptor (AR) subtypes has been hampered by the limited specificity and subtype-selectivity of available ligands. The current study describes a novel highly selective a 2C -adrenoceptor antagonist, JP-1302 (acridin-9-yl-[4-(4-methylpiperazin-1-yl)-phenyl]amine). Experimental approach: Standard in vitro binding and antagonism assays were employed to demonstrate the a 2C -AR specificity of JP-1302. In addition, JP-1302 was tested in the forced swimming test (FST) and the prepulse-inhibition of startle reflex (PPI) model because mice with genetically altered a 2C -adrenoceptors have previously been shown to exhibit different reactivity in these tests when compared to wild-type controls. Key results: JP-1302 displayed antagonism potencies (K B values) of 1,500, 2,200 and 16 nM at the human a 2A -, a 2B -, and a 2C -adrenoceptor subtypes, respectively. JP-1302 produced antidepressant and antipsychotic-like effects, i.e. it effectively reduced immobility in the FST and reversed the phencyclidine-induced PPI deficit. Unlike the a 2 -subtype non-selective antagonist atipamezole, JP-1302 was not able to antagonize a 2 -agonist-induced sedation (measured as inhibition of spontaneous locomotor activity), hypothermia, a 2 -agonist-induced mydriasis or inhibition of vas deferens contractions, effects that have been generally attributed to the a 2A -adrenoceptor subtype. In contrast to JP-1302, atipamezole did not antagonize the PCPinduced prepulse-inhibition deficit. Conclusions and implications:The results provide further support for the hypothesis that specific antagonism of the a 2C -adrenoceptor may have therapeutic potential as a novel mechanism for the treatment of neuropsychiatric disorders.

Atipamezole is an alpha2-adrenoceptor antagonist with an imidazole structure. Receptor binding studies indicate that its affinity for alpha2-adrenoceptors and its alpha2/alpha1 selectivity ratio are considerably higher than those of yohimbine, the prototype alpha2-adrenoceptor antagonist. Atipamezole is not selective for subtypes of alpha2-adrenoceptors. Unlike many other alpha2-adrenoceptor antagonists, it has negligible affinity for 5-HT1A and I2 binding sites. Atipamezole is rapidly absorbed and distributed from the periphery to the central nervous system. In humans, atipamezole at doses up to 30 mg/subject produced no cardiovascular or subjective side effects, while at a high dose (100 mg/subject) it produced subjective symptoms, such as motor restlessness, and an increase in blood pressure. Atipamezole rapidly reverses sedation/anesthesia induced by alpha2-adrenoceptor agonists. Due to this property, atipamezole is commonly used by veterinarians to awaken animals from sedation/anesthesia induced by alpha2-adrenoceptor agonists alone or in combination with various anesthetics. Atipamezole increased sexual activity in rats and monkeys. In animals with sustained nociception, atipamezole increased pain-related responses by blocking the noradrenergic feedback inhibition of pain. In tests assessing cognitive functions, atipamezole at low doses has beneficial effects on alertness, selective attention, planning, learning, and recall in experimental animals, but not necessarily on short-term working memory. At higher doses atipamezole impaired performance in tests of cognitive functions, probably due to noradrenergic overactivity. Recent experimental animal studies suggest that atipamezole might have beneficial effects in the recovery from brain damage and might potentiate the anti-Parkinsonian effects of dopaminergic drugs. In phase I studies atipamezole has been well tolerated by human subjects.