Investigations into the role of the metabotropic glutamate receptor, mGluR5, in incentive learning and some behavioural and neurobiological effects of cocaine

The metabotropic glutamate receptor, mGluR5, is densely expressed in brain regions involved in incentive learning processes. There is considerable evidence to suggest that following exposure to addictive drugs such as cocaine, adaptations in these brain areas may underlie the development and maintenance of behavioural responses related to addictive processes. The present thesis examines the role of mGluR5 in both incentive learning processes and some behavioural and neurobiological effects of cocaine. First, using a novel mutant mouse line in which mGluR5 is selectively knocked down in cells that express dopamine D1 receptors (D1R), I argue that this mGluR5 population is critically important for specific incentive learning processes. By blocking mGluR5 in wild-type mice with a selective antagonist, I then propose mGluR5 as necessary for the acquisition, but not the expression of an incentive association. Next, I present data showing that mGluR5 on dopaminoceptive neurons are not necessary for the „conditioned rewarding‟ properties of cocaine, measured in the conditioned place preference model, but do contribute to the psychomotor activating effects of cocaine. Finally, I present an immunohistochemistry study that examines cocaine-induced activation of the extracellular-signal related kinase (ERK) pathway. In the mGluR5 knock-down mice, activation of the ERK pathway in the striatum is disrupted following an acute injection of cocaine. Given the importance of the ERK pathway in establishing and maintaining long term memories, I propose that disruption of this pathway could contribute, in part, to some findings reported in the present thesis. Taken together, this thesis will argue that signalling through mGluR5 on D1R expressing neurons is important for the formation of incentive associations, and may contribute to neural adaptations necessary for the development and maintenance of behavioural responses related to addictive processes

Characterising the molecular response of Agaricus bisporus to mushroom virus X infection

Agaricus bisporus is a globally cultivated crop produced and consumed worldwide. This monoculture system and the advancement of consolidated growth of pre-colonised A. bisporus compost has coincided with the outbreak of a novel commercial disease, mushroom virus X (MVX). MVX constitutes a virome of 18 distinct single-stranded RNA viruses, of which select members cause detrimental disease phenotypes in infected mushrooms of A. bisporus. Scant focus has been placed on the molecular responses from the host during infection. The work presented herein provides novel genomic, transcriptomic, proteomic and cellular resources to help address the gaps in knowledge concerning MVX and A. bisporus. The first whole genome sequencing and analysis of a wild A. bisporus var. bisporus was provided as a new resource for A. bisporus breeding research, revealing to be most closely related to the commercial white variety with a large accessory genome compared to other A. bisporus genomes. Dual-culture assays revealed the potential for MVX to transmit through hyphal fusion (anastomosis) into a variety of strains, whereas diagnostics of fruit bodies revealed different susceptibilities in certain strains with wild germ plasms. Mechanisms of anastomosis were revealed in varietal interactions and showed evidence of hyphae remodelling in compatible strains, metabolic starvation responses in competing interactions and antagonistic oxidative stresses in vegetative incompatible interactions. Molecular responses revealed increased regulation in gene expression, vesicle transport and ER-stress responses in virus infected fruit bodies, with less susceptible strains revealing increases of antiviral protein responses, general stress responses, lipid metabolism. The intracellular localisation of two of these viruses related to different symptomologies in infected fruit bodies revealed distinct patterns of virus distribution and characteristics related to persistent nature of infection. This work has provided novel insights into the molecular aspects of A. bisporus and MVX and the challenges they pose for the mushroom industry

Effect of lower body negative pressure on physiological, perceptual and affective responses during self regulated exercise

Purpose: Lower body negative pressure (LBNP) treadmill exercise was developed for health maintenance during periods of microgravity. It involves exercising on a treadmill within a waist-high pressure chamber connected to a pump. LBNP treadmill exercise generates a pressure differential between the upper and lower body increasing ground reaction forces (GRFs). This study compared the physiological, perceptual and affective responses in women during 30 min of self-regulated treadmill walking with and without LBNP

Incentive learning underlying cocaine relapse requires mGluR5 receptors located on dopamine D1 receptor-expressing neurons

Understanding the psychobiological basis of relapse remains a challenge in developing therapies for drug addiction. Relapse in cocaine addiction often occurs following exposure to environmental stimuli previously associated with drug taking. The metabotropic glutamate receptor, mGluR5, is potentially important in this respect; it plays a central role in several forms of striatal synaptic plasticity proposed to underpin associative learning and memory processes that enable drug-paired stimuli to acquire incentive motivational properties and trigger relapse. Using cell type-specific RNA interference, we have generated a novel mouse line with a selective knock-down of mGluR5 in dopamine D1 receptor-expressing neurons. Although mutant mice self-administer cocaine, we show that reinstatement of cocaine-seeking induced by a cocaine-paired stimulus is impaired. By examining different aspects of associative learning in the mutant mice, we identify deficits in specific incentive learning processes that enable a reward-paired stimulus to directly reinforce behavior and to become attractive, thus eliciting approach toward it. Our findings show that glutamate signaling through mGluR5 located on dopamine D1 receptor-expressing neurons is necessary for incentive learning processes that contribute to cue-induced reinstatement of cocaine-seeking and which may underpin relapse in drug addiction

Illumina MiSeq Phylogenetic Amplicon Sequencing Shows a Large Reduction of an Uncharacterised Succinivibrionaceae and an Increase of the Methanobrevibacter gottschalkii Clade in Feed Restricted Cattle

peer-reviewedPeriodic feed restriction is used in cattle production to reduce feed costs. When normal feed levels are resumed, cattle catch up to a normal weight by an acceleration of normal growth rate, known as compensatory growth, which is not yet fully understood. Illumina Miseq Phylogenetic marker amplicon sequencing of DNA extracted from rumen contents of 55 bulls showed that restriction of feed (70% concentrate, 30% grass silage) for 125 days, to levels that caused a 60% reduction of growth rate, resulted in a large increase of relative abundance of Methanobrevibacter gottschalkii clade (designated as OTU-M7), and a large reduction of an uncharacterised Succinivibrionaceae species (designated as OTU-S3004). There was a strong negative Spearman correlation (ρ = -0.72, P = <1x10-20) between relative abundances of OTU-3004 and OTU-M7 in the liquid rumen fraction. There was also a significant increase in acetate:propionate ratio (A:P) in feed restricted animals that showed a negative Spearman correlation (ρ = -0.69, P = <1x10-20) with the relative abundance of OTU-S3004 in the rumen liquid fraction but not the solid fraction, and a strong positive Spearman correlation with OTU-M7 in the rumen liquid (ρ = 0.74, P = <1x10-20) and solid (ρ = 0.69, P = <1x10-20) fractions. Reduced A:P ratios in the rumen are associated with increased feed efficiency and reduced production of methane which has a global warming potential (GWP 100 years) of 28. Succinivibrionaceae growth in the rumen was previously suggested to reduce methane emissions as some members of this family utilise hydrogen, which is also utilised by methanogens for methanogenesis, to generate succinate which is converted to propionate. Relative abundance of OTU-S3004 showed a positive Spearman correlation with propionate (ρ = 0.41, P = <0.01) but not acetate in the liquid rumen fraction.This study was supported by the Science Foundation Ireland (http://www.sfi.ie) (Contract number SFI 09/RFP/GEN2447-awarded to SMW) and Teagasc Walsh Fellowship Funding (www.teagasc.ie) (Teagasc project RMIS 6341-awarded to SMW)

Transmission of mushroom virus X and the impact of virus infection on the transcriptomes and proteomes of different strains of Agaricus bisporus

Cultivation of Agaricus bisporus is a large horticultural industry for many countries worldwide, where a single variety is almost grown exclusively. Mushroom virus X (MVX), a complex of multiple positive-sense single stranded RNA (ss(+)RNA) viruses, is a major pathogen of typical A. bisporus crops. MVX can manifest a variety of symptoms in crops and is highly infective and difficult to eradicate once established in host mycelium. Currently our knowledge regarding the molecular response of A. bisporus fruit bodies to MVX infection is limited. In order to study the response of different A. bisporus strains with different susceptibilities to MVX, we designed a model system to evaluate the in-vitro transmission of viruses in A. bisporus hyphae over a time-course, at two crucial phases in the crop cycle. The symptom expression of MVX in these varieties and the transcriptomic and proteomic response of fruit bodies to MVX-infection were examined. Transmission studies revealed the high potential of MVX to spread to uninfected mycelium yet not into the fruit bodies of certain strains in a crop. MVX affected colour and quality of multiple fruit bodies. Gene expression is significantly altered in all strains and between times of inoculation in the crop. Genes related to stress responses displayed differential expression. Proteomic responses revealed restriction of cellular signalling and vesicle transport in infected fruit bodies. This in-depth analysis examining many factors relevant to MVX infection in different A. bisporus strains, will provide key insights into host responses for this commercially important food crop