Ph.d.

Bibliography: leaves 181-233. / 233 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates pharmacological control of transient lower oesophagal sphincter relaxations as a treatment of gastro-oesophageal reflux. Two major classes of pharmaceutical agents were explored; anticholinergic agents and the GABAb agonist, baclofen. / Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1999

Chapter 1 provides a general introduction on the role of bioisosterism of fluorine aiming to improve the pharmacokinetics properties of lead compounds. GABAA receptors specifically, synaptic GABAA receptors, extrasynaptic GABAA receptors and GABAA rho receptors are then presented. Compounds that exhibit agonist and partial agonist effects at these receptors are also discussed. The applications of some compounds as GABAA receptor PET radiotracers are also described. Chapter 2 details the synthesis of two fluorinated analogues of muscimol, fluoromuscimol and trifluoromethylmuscimol. Fluoromuscimol was obtained from the lithiation of a Boc-protected isoxazole followed by in-situ fluorination using NFSI, whereas trilfuoromethylmuscimol was obtained from the coupling of a heteroaryl iodide with trifluoromethylcopper species, which was generated in-situ from MFSDA in the presence of CuI. Fluoromuscimol and trifluoromethylmuscimol were assessed on human synaptic, (α₁β₂γ₂), extrasynaptic, (α₄β₂δ) and ρ₁ subunits of the GABAA receptor. The biological results show that fluoromuscimol exhibits greater maximum response in comparison to GABA at the extrasynaptic GABAA receptors (α₄β₂δ), but lower overall potency, whereas trifluoromethylmuscimol was inactive at all the tested GABAA receptors. Chapter 3 discusses the synthesis and late stage fluorination of diaryliodonium salts as precursors to fluoromuscimol. Application of iodonium salts as precursors for nucleophilic fluorination in PET studies are also highlighted. The last part of this chapter focuses on the synthesis of iodomuscimol as a potential alternative SPECT radiotracer to fluoromuscimols in probing GABA binding sites on GABAA receptors.

GABA is the main inhibitory neurotransmitter of the central nervous system. GABA[subscript A]Rs are multimeric transmembrane receptors, which are composed of 5 subunits. It is known that there are 19 subunits that can make up the GABA[subscript A]Rs, allowing for a vast array of receptor subtypes. In addition to the GABA binding site GABA[subscript A]Rs have distinct allosteric binding sites for benzodiazepines, barbiturates, ethanol, certain general anaesthetics and neuroactive steroids. The molecular heterogeneity of the GABA[subscript A]R is accompanied by distinct pharmacological profiles of the different receptor subtypes. The advance of transgenic mouse models has allowed the functional significance of this heterogeneity to be studied in vivo. Therefore, this thesis utilises a variety of transgenic mouse models carrying either mutations or deletions of certain subunits to study the functional significance of the receptor heterogeneity. Mice lacking the α1 subunit (α1[superscript(-/-)]), carrying a point mutation of the α1 subunit (α1H101R), and mice lacking the δ subunit (δ[superscript(-/-)]) have been utilised to investigate the role of these subunits in the sedative actions of benzodiazepines and the GABA[subscript A]R agonist THIP. Although there are limitations to the interpretation of these results due genetic background of the α1[superscript(-/-)] and α1H101R, experiments suggest that the α1H101R mutation is not behaviourally silent as previously suggested and provide further evidence that the α1 subunit mediates the sedative properties of benzodiazepines. These experiments also reveal that the extrasynaptic δ containing receptors are responsible for mediating the sedative effects of THIP, and these findings combined with evidence from collaborators, implicates the thalamus as an anatomical mediator of these effects. An investigation of the putative cognitive enhancing effects of THIP using an attentional set-shifting task for mice suggested that pre-treatment with THIP reduces the number of errors to reach criterion. δ[superscript(-/-)] mice could not be trained to perform the task, therefore further behavioural investigation of these mice was performed, which suggested a heightened level of anxiety and reduced motivation for a food reward. This thesis has furthered our understanding of the functional role of GABA[subscript A]R subtypes. With the advance in genetic manipulations that allow for regionally selective mutations of the receptor the anatomical structures involved in these functions can be identified.

Diss. Linköping : Univ., 2003. / Härtill 4 uppsatser.

Indiana University-Purdue University Indianapolis (IUPUI) / It has been proposed that the GABAB receptor subtype plays a role in alcoholism and alcohol use disorders (AUDs) (Cousins et al., 2002; Agabio et al., 2012). Specifically, the GABAB agonist baclofen has been looked at extensively in clinical and pre-clinical studies. In various animal models of chronic and intermittent consumption, baclofen has been shown to both increase (Petry, 1997; Smith et al., 1999; Czachowski et al., 2006; Moore et al., 2007) and decrease (Colombo et al., 2000; 2002; 2005; Stromberg, 2004; Moore et al., 2009) drinking. A critical issue in determining pharmacological effects of a drug is using the appropriate animal model. The drinking-in-the-dark (DID) model, developed by Rhodes et al. (2005, 2007), produces high levels of drinking in a binge-like paradigm and has been used to assess many pharmacological targets (e.g. Kamdar et al., 2007; Gupta et al., 2008; Moore et al., 2007; 2009). While DID produces high-levels of binge drinking, it is unclear what areas of the brain are involved in this behavior. A direct way to target areas that are believed to be involved in the circuitry of particular behaviors is through microinjection of drugs (Kiianmaa et al., 2003). Of particular recent interest involving motivated behaviors and addiction is the nucleus accumbens (Acb) (Everitt & Robbins, 2005); specifically the accumbens shell (AcbSh) (e.g. Rewal et al., 2009, 2012; Nie et al., 2011; Leriche et al., 2008). The current study aimed to investigate the role of GABAB receptors in the AcbSh by examining the ability of two different enantiomers of baclofen to alter ethanol and saccharin intake in male C57BL/6J (B6) mice. B6 mice underwent bilateral cannulation surgery targeting the AcbSh. After 48 hours of recovery time, animals began a five day Drinking-in-the-Dark (DID) procedure where they received 20% ethanol or 0.2% saccharin for two hours, three hours into the dark cycle, each day. Throughout the five drinking sessions, animals were kept in home-cage locomotor activity chambers to monitor activity throughout the drinking cycle. Day 4 drinking was immediately preceded by a mock microinjection, whereas Day 5 drinking was immediately preceded by a drug microinjection. Microinjection of one of five doses of baclofen was given in ng/side dissolved in 200 µl of aCSF (aCSF alone, 0.02 R(+)-, 0.04 R(+)-, 0.08 S(-)-, or 0,16 S(-)-). Intake was recorded every twenty minutes on Days 4 and 5. Retro-orbital sinus blood samples were taken from ethanol animals immediately following the Day 5 drinking period to determine blood ethanol concentrations (BECs). A one-way ANOVA on total Day 4 ethanol consumption revealed no baseline differences between dose groups. A one-way ANOVA on total Day 5 ethanol consumption revealed that the 0.04 R(+)- baclofen dose reduced total drinking, but the 0.16 S(-)- baclofen dose increased total drinking (p’s<0.05). This pattern was reflected in the BECs; 0.04 R(+)- baclofen reduced BECs, whereas 0.16 S(-)- baclofen increased BECs (p’s<0.05). These results were also time-dependent, with R(+)-baclofen reducing drinking in the first 20 minutes of the session and S(-)- increasing drinking in the last 40 minutes of the session. There were no effects on saccharin intake. An issue with the locomotor activity boxes led to unreliable locomotor activity counts. However, because there were no drug effects on saccharin consumption, it was concluded that locomotor effects did not contribute to the decreases or increases in ethanol consumption. These results further implicate the role of GABAB receptors in modulating ethanol intake. The bidirectional effects shown highlight the importance of considering enantioselective drug effects when interpreting data. Finally, these results also support previous conclusions that the AcbSh plays an important role in modulating use of drugs of abuse, but not other reinforcers.