1994 — 1998 |
Hales, Tim G |
R29Activity Code Description: Undocumented code - click on the grant title for more information. |
Modulatory Sites On Gaba a Receptors @ University of California Los Angeles
GABA-A receptors are modulated by many intravenous general anesthetics (IV GAs), at clinically relevant doses. Low concentrations of IV GAs, such as the anesthetic steroids, barbiturates and propofol, potentiate GABA responses in neurons. Higher concentrations, present in blood during total IV anesthesia, directly activate GABA-A receptors opening Cl- channels and thus reducing neuronal excitability. This represents a mechanism by which some IV GAs may achieve anesthesia. GABA-A receptors are heterogeneous consisting of five subunits. Each subunit could be one of fifteen varieties cloned so far. Using the patch- clamp technique to record GABA responses from single cells, GABA-A receptors with different subunit combinations have been found to possess distinct pharmacological properties. Preliminary data indicate that GABA-A receptor combinations, expressed by the neuronal GT1-7 cell line are not directly activated by high concentrations of IV GAs. To study the subunit specificity of GABA-A receptor modulation and activation by IV GAs, GABA-A receptor subunit cDNAs will be transfected into cell lines lacking endogenous receptors. The cells will first be transfected with homomeric receptors. These will be tested using the patch-clamp technique to determine whether homomeric receptors are functional (Specific Aim l). Having determined the subunits required for a receptor to respond to GABA, the subunits needed for potentiation of GABA-responses by IV GAs will be investigated (Specific Aim 2). If additional subunits are required for functional receptors, or modulation of GABA-A receptors by IV GAs, these will be co-transfected into cells. The subunits tested will be those for which mRNAs have been identified in GT1-7 cells using molecular techniques. Finally, recombinant GABA-A receptors will be tested to define the subunits required for direct activation by IV GAs (Specific Aim 3). In future, having established the subunit specificities for GABA-A receptor direct activation by GABA and IV GAs, and modulation by IV GAs, these will be compared to the subunit specificity for the similar actions of volatile agents at this receptor. An understanding of the subunit specificity of GABA-A receptor modulation by GAs and the distribution of these subunits in the brain may suggest areas involved in anesthesia. Once the target site(s) for GAs are defined it may be possible to develop more efficacious and safer agents.
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1997 — 2002 |
Hales, Tim G |
P50Activity Code Description: To support any part of the full range of research and development from very basic to clinical; may involve ancillary supportive activities such as protracted patient care necessary to the primary research or R&D effort. The spectrum of activities comprises a multidisciplinary attack on a specific disease entity or biomedical problem area. These grants differ from program project grants in that they are usually developed in response to an announcement of the programmatic needs of an Institute or Division and subsequently receive continuous attention from its staff. Centers may also serve as regional or national resources for special research purposes. |
Core--Tissue Culture Core @ University of California Los Angeles |
0.934 |
1997 — 2002 |
Hales, Tim G |
P50Activity Code Description: To support any part of the full range of research and development from very basic to clinical; may involve ancillary supportive activities such as protracted patient care necessary to the primary research or R&D effort. The spectrum of activities comprises a multidisciplinary attack on a specific disease entity or biomedical problem area. These grants differ from program project grants in that they are usually developed in response to an announcement of the programmatic needs of an Institute or Division and subsequently receive continuous attention from its staff. Centers may also serve as regional or national resources for special research purposes. |
Mechanisms &Importance of Opioid and Orl1 Receptor Coupling to Ca2+ Channels @ University of California Los Angeles |
0.934 |
2000 — 2003 |
Hales, Tim G |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
The Role of Epsilon Subunit in Gabaa Receptor Function @ George Washington University
DESCRIPTION: (Applicant's Abstract) The gamma-aminobutyric type A (GABAA) receptor is the major inhibitory neurotransmitter receptor in the brain. General anesthetics modulate GABAA receptors through an unknown site and it is widely believed that this is their mechanism of action. This theory has been impossible to test by virtue of a lack of antagonists to anesthetic binding sites. GABAA receptors each consist of five subunits and there are 15 known varieties of these polypeptides in mammals, providing the potential for numerous receptor subtypes. Different subunit combinations can form receptors with distinct properties, and heterogeneous subunit distribution throughout the brain provides regional differences in the sensitivity of GABAA receptors to various therapeutic agents. The sensitivity of GABAA receptors to anesthetics was thought to lack subunit specificity until the identification of a new polypeptide (e). The e subunit has a distinctive distribution in the brain and may confer novel properties to the neurons in which it is expressed. Indeed, when the subunit is combined with others to form recombinant receptors in cell lines, these GABAA receptors exhibit a resistance to modulation by anesthetics. The e subunit shares most sequence identity with the gamma subunit, although the properties conferred to GABAA receptors by these two polypeptides are quite distinct. Most notably the gamma subunit supports anesthetic and benzodiazepine modulation of GABAA receptors while the e subunit does not. This project seeks to determine the role of the e subunit in controlling GABAA receptor function. The subunit will be used to define the amino acid motifs involved in the regulation of GABAA receptor function by anesthetics. A major goal of the project is to produce a subunit that can in future studies be introduced into transgenic mice which will functionally antagonize anesthetic regulation of GABAA receptors causing the minimum possible change in other GABAA receptor properties. Specific aim 1 will determine whether the e subunit displaces the gamma subunit from GABAA receptors. In Aim 2 chimeric e/gamma2 constructs will be used to probe the relationship between structure and the properties conferred by these subunits, with particular emphasis on identifying the anesthetic site. Specific aim 3 will examine whether general anesthetics use similar mechanisms to regulate the function of other ionotropic receptors related to the GABAA receptor. Particular emphasis will be placed on the 5-HT3 receptor. This receptor is of considerable interest as it is thought to be the site of action of several anti-emetic agents. Human homomeric and heteromeric 5-HT3 receptors are modulated by the intravenous anesthetic propofol which is reported to have anti-emetic properties.
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2007 — 2008 |
Hales, Tim G |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
The Role of Epsilon Subunit in Gaba Receptor Function @ George Washington University
[unreadable] DESCRIPTION (provided by applicant): The GABAA receptor provides the major inhibitory drive to neurons in the mammalian central nervous system. Mutations in GABAA subunit genes that reduce the function or expression of these receptors can cause epilepsy. On the other hand anticonvulsant benzodiazepines and anesthetics that increase GABAA receptor activity are anticonvulsant. Seizures alter the expression of several GABAA receptor subunits including the e subunit. Recombinant GABAA receptors containing the e subunit are relatively insensitive to anesthetics and benzodiazepines. Functionally the e subunit mimics the actions of anesthetics on GABAA receptors causing spontaneous gating, increased GABA affinity and prolonged deactivation. Our preliminary data suggest that e subunits participate in spontaneous (tonic) GABAA receptor activity in hippocampal neurons, which is seen in the absence of exogenous GABA. Quantitative PCR, immunocytochemistry with an E subunit specific antibody, and pharmacological studies suggest that hippocampal pyramidal neurons express native GABAA receptors containing e subunits. Furthermore, up regulation of e subunit expression in hippocampal pyramidal neurons following epileptiform electrical activity (EEA) may contribute to GABAA receptor remodeling. The specific aims of the proposal are to: 1) Examine the functional contribution of the e subunit to synaptic (phasic) and extrasynaptic (tonic) receptors in hippocampal pyramidal neurons, 2) Examine the functional properties of phasic and tonic GABAA receptors following EEA or introduction of the epilepsy mutant y2(R43Q) subunit, 3) Use chimeric e/y2 constructs to determine the & subunit's structure/function relationship. We will test the hypothesis that the e subunit confers anesthetic resistance to extrasynaptic GABAA receptors and alters receptor gating and kinetics by inducing an anesthetic-bound receptor conformation. These experiments will help uncover important structural determinants of GABAA receptor function. A better understanding of GABAA receptors and their potential for adaptation will help increase our understanding of changes in neuronal inhibition during epilepsy. [unreadable] [unreadable] [unreadable]
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