A site-specific mutation of tyrosine hydroxylase reduces feedback inhibition by dopamine in genetically modified cells grafted in parkinsonian rats

Distinct effects of ketamine and acetyl L-carnitine on the dopamine system in zebrafish

Ketamine, a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist is commonly used as a pediatric anesthetic. We have previously shown that acetyl L-carnitine (ALCAR) prevents ketamine toxicity in zebrafish embryos. In mammals, ketamine is known to modulate the dopaminergic system. NMDA receptor antagonists are considered as promising anti-depressants, but the exact mechanism of their function is unclear. Here, we measured the levels of dopamine (DA) and its metabolites, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the zebrafish embryos exposed to ketamine in the presence and absence of 0.5 mM ALCAR. Ketamine, at lower doses (0.1-0.3 mM), did not produce significant changes in DA, DOPAC or HVA levels in 52 h post-fertilization embryos treated for 24 h. In these embryos, tyrosine hydroxylase (TH) mRNA expression remained unchanged. However, 2 mM ketamine (internal embryo exposure levels equivalent to human anesthetic plasma concentration) significantly reduced DA level and TH mRNA indicating that DA synthesis was adversely affected. In the presence or absence of 2 mM ketamine, ALCAR showed similar effects on DA level and TH mRNA, but increased DOPAC level compared to control. ALCAR reversed 2 mM ketamine-induced reduction in HVA levels. With ALCAR alone, the expression of genes encoding the DA metabolizing enzymes, MAO (monoamine oxidase) and catechol-O-methyltransferase (COMT), was not affected. However, ketamine altered MAO mRNA expression, except at the 0.1 mM dose. COMT transcripts were reduced in the 2 mM ketamine-treated group. These distinct effects of ketamine and ALCAR on the DA system may shed some light on the mechanism on how ketamine can work as an anti-depressant, especially at sub-anesthetic doses that do not affect DA metabolism and suppress MAO gene expression.

Microdialysis in central nervous system disorders and their treatment

Central nervous system (CNS) insults elevate endogenous toxins and alter levels of indicators of metabolic disorder. These contribute to neurotrauma, neurodegenerative diseases and chronic pain and are possible targets for pharmaceutical treatment. Microdialysis samples substances in the extracellular space for chemical analysis. It has demonstrated that toxic levels of glutamate are released and that toxic levels of the reactive species O(2)(-), H(2)O(2), HO. NO and HOONO are generated upon CNS injury. Agent administration by microdialysis can also help elucidate mechanisms of damage and protection, and to identify targets for clinical application. Microdialysis sampling indicates that circuits descending from the brain to the spinal cord transmit and modulate pain signals by releasing neurotransmitter amines and amino acids. Efforts are under way to develop microdialysis into a technique for intensive care monitoring and predicting outcomes of brain insults. Finally, microdialysis sampling has demonstrated in vivo elevation of glial cell line-derived neurotrophic factor following grafting of primed fetal human neural stem cells into brain-injured rats, the first in vivo demonstration of the release of a neurotrophic factor by grafted stem cells. This increased release correlated with significantly improved spatial learning and memory.

The Neurotransmitter Cycle and Quantal Size

Changes in the response to release of a single synaptic vesicle have generally been attributed to postsynaptic modification of receptor sensitivity, but considerable evidence now demonstrates that alterations in vesicle filling also contribute to changes in quantal size. Receptors are not saturated at many synapses, and changes in the amount of transmitter per vesicle contribute to the physiological regulation of release. On the other hand, the presynaptic factors that determine quantal size remain poorly understood. Aside from regulation of the fusion pore, these mechanisms fall into two general categories: those that affect the accumulation of transmitter inside a vesicle and those that affect vesicle size. This review will summarize current understanding of the neurotransmitter cycle and indicate basic, unanswered questions about the presynaptic regulation of quantal size.

Engineered protein function by selective amino acid diversification

Almost all protein engineering methods rely upon making changes to naturally occurring proteins that already possess some of the desired properties. This will probably remain the case as long as we lack a complete understanding of the way that an amino acid sequence gives rise to a protein with a precisely defined biological function. Common to all methods for altering an existing protein is the selection of a subset of amino acids in the protein for variation and a choice of which substitutions to make at each position. Variants are then tested empirically and further variants are created based upon their performance. Differences between protein engineering methods are the ways in which amino acids are chosen for variation, the protocols followed for creating the variants, and how information regarding variant properties is used in creating subsequent variants. In this article, we describe these differences and provide examples of how the experimental parameters of specific projects determine which method is most suitable.

Gene therapy in Parkinson?s disease

Gene therapy in Parkinson's disease appears to be at the brink of the clinical study phase. Future gene therapy protocols will be based on a substantial amount of preclinical data regarding the use of ex vivo and in vivo genetic modifications with the help of viral or non-viral vectors. To date, the supplementation of neurotrophic factors and substitution for the dopaminergic deficit have formed the focus of trials to achieve relief in animal models of Parkinson's disease. Newer approaches include attempts to influence detrimental cell signalling pathways and to inhibit overactive basal ganglia structures. Nevertheless, current models of Parkinson's disease do not mirror all aspects of the human disease, and important issues with respect to long-term protein expression, choice of target structures and transgenes and safety remain to be solved. Here, we thoroughly review available animal data of gene transfer in models of Parkinson's disease.

Potential of gene therapy for pediatric neurotransmitter diseases: lessons from Parkinson's disease

Gene therapy methods have continued to develop rapidly, and many initial limitations that hampered clinical application have been overcome. Thus serious consideration of clinical application of gene therapy is warranted for selected disorders in which the pathogenesis is well defined. Parkinson's disease has been the most extensively studied target of gene therapy for central nervous system disorders and shares many features with pediatric neurotransmitter diseases. Neurotransmitter replacement therapy using catecholamine-synthesizing genes and delivery of neurotrophic factors such as glial cell line-derived neurotrophic factors has been successful in animal models of Parkinson's disease. Application of gene therapy for pediatric neurotransmitter diseases will require delineating the optimal set of genes to correct the consequences of the deficiencies. The optimal anatomical targets and proper timing of the gene replacement must be understood. Safety of gene therapy vehicles and the ability to regulate gene expression will be essential for eventual clinical application.