The GABAA α4-subunit is found co-assembled with δ subunits in extrasynaptic GABAA receptors (α4-GABAARs). Within the striatum α4-GABAARs are most highly expressed in the Nucleus Accumbens (NAc) where they mediate tonic inhibition thought to control the excitability of accumbal medium spiny neurons (MSNs). Experiments presented in this thesis use genetic techniques in mice to investigate the role of α4-GABAARs in modulating binge-like ethanol consumption and the potentiation of locomotor behaviours by cocaine. We have generated several transgenic mouse lines in which the Gabrα4 gene, encoding the α4 subunit, has been deleted either constitutively or within specific neural populations expressing D1 or D2 type dopamine receptors via cre/loxp recombination. Using quantitative rt-PCR and in-situ-hybridisation methods to compare Gabrα4 mRNA levels in brain sections from each genotype we confirmed that the α4 subunit was deleted either globally or in the expected cell type within conditional knockouts. We also generated an Adeno Associated Virus (AAV) carrying Cre-recombinase to knockdown α4 locally by infusing it into in specific brain regions of ‘floxed'-α4 mice. Deletion of the α4 subunit in mice significantly reduced alcohol consumption in a pre-clinical model of binge-drinking, known as drinking in the dark (DID). Moreover, targeted deletion of Gabrα4 in the NAc was sufficient to mediate this effect. We did not observe any effects on alcohol consumption in mice where α4 was deleted conditionally in D1 or D2 type neurons. This data indicates that α4- GABAARs in the NAc are an important mediator of alcohol consumption. Deletion of GABAAR α4-subunits from dopamine D1-expressing neurons facilitated cocaine's ability to potentiate locomotor activity and operant responding for natural rewards. Deletion of GABAAR α4-subunits from dopamine D2-expressing neurons had no such effects. Deletion of GABAAR α4-subunits from dopamine D1- expressing neurons also accelerated the acquisition of behavioural sensitisation to cocaine. This effect was associated with increased cFos expression in the NAc core following acute cocaine, whilst in cocaine-sensitised mice it was associated with increased cFos in both the NAc Core and Shell. A similar altered pattern of cFos expression was observed in mice with a global knockout of α4 subunits however they showed no behavioural effects. This may imply that a balance of α4-GABAARmediated inhibition in D1 and D2 neurons is required for normal behavioural sensitisation to cocaine. The data presented within this thesis indicate that α4- GABAAR-mediated inhibition of D1- and D2-expressing neurons plays an important physiological role in controlling behavioural responses to cocaine.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:751888 |
| Date | January 2018 |
| Creators | Robertson, Johnathan |
| Publisher | University of Sussex |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://sro.sussex.ac.uk/id/eprint/77213/ |
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