Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2008.

Stress in adolescence is a putative risk factor for developing mental illnesses such as schizophrenia and mood disorders. Symptoms for these illnesses first emerge in late adolescence and early adulthood, with both incidence and severity being sexually dimorphic. Animal models can shed light on the neurobiological underpinnings of these disorders by allowing one to explore the relationship between a risk factor such as stress, and development of symptoms. In the current work the role of adolescent stress is explored in the development of biomarkers that are associated with adolescent-onset illnesses using Long Evans rats. Repeated exposure to predator odour was combined with social isolation during adolescence to create a novel stressor model. The specific objectives of this study were to determine (i) if repeated predator odour exposure altered measures related to sensorimotor gating (measured as prepulse inhibition, PPI), startle, and emotionality, and (ii) whether social support affected the outcome of predator odour stress. Predator odour elicited immediate avoidance, which did not habituate with repeated exposures, suggesting a strong behavioural stress response. In contrast to past work, few significant long-term effects were observed in animals exposed to predator odour compared with ones exposed to a non-threatening odour. Unexpectedly, animals exposed to a no odour (control) condition displayed altered PPI, startle response, anxiety-related behaviour, and memory, compared to rats exposed to a non-threatening, control odour or a predator odour. Moreover, the no odour animals showed altered expression of dopamine D2R receptor protein in the medial prefrontal cortex. The outcomes for this group were remarkably similar to those seen in animals raised in social isolation, suggesting an underlying similarity in the neurobiological mechanisms associated with these experiences that likely can be traced to being raised in environments lacking adequate social and physical complexity. Sex differences were noted in PPI, startle response, tests of anxiety- and depression-like behaviour, memory, and levels of dopamine D2R receptors, although the sex of the animal did not interact with stressor treatment to affect these measures. In conclusion, results of the current work provide further evidence for the importance of the social and physical environment to normal development during adolescence, as well as the importance of being male versus female.

Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2008.

The two-hit hypothesis of schizophrenia proposes that the development of the illness involves an early neurodevelopmental stress component which increases vulnerability to later stressful life events, in combination leading to overt disease. This thesis describes a two-hit animal model, comprising of an early first hit in the form of 24 hours maternal deprivation on postnatal day 9, and a late second hit simulated by 2 weeks of corticosterone administration from 8 to 10 weeks of age in rats. The project included behavioural studies on prepulse inhibition (PPI) regulation, locomotor activity, and learning and memory, and neurochemical and molecular studies on dopaminergic parameters, brain-derived neurotrophic factor (BDNF) and glucocorticoid receptor (GR) expression. / In the two-hit animals, there was little effect on baseline PPI or locomotor activity. However, the effect of acute treatment with the dopaminergic stimulants, apomorphine, amphetamine and quinpirole, was markedly diminished. There were differential effects of either maternal deprivation or corticosterone administration on the action of these drugs. However, there was no change in any of the groups in the effect of the serotonin-1A receptor agonist, 8-OH-DPAT, on PPI, or the effect of amphetamine and phencyclidine on locomotor activity. (For complete abstract open document)

Research Doctorate - Doctor of Philosophy (PhD) / This thesis investigates mechanisms of brain maturation by utilising the special advantages offered by the protracted maturation of neural circuits in chicken forebrain. Biochemical, behavioural and electrophysiological techniques are used in behaving animals to investigate the functional consequences of maturation changes at the molecular, behavioural and physiological levels. Two issues are addressed: (1) do immature (2 week) and mature (8 week) chickens employ different molecular mechanisms to produce changes in neuronal function after learning a behavioural task; and (2) can quantitative non-invasive measures of neuronal function be used to monitor maturation changes in chicken forebrain? Biochemical investigation of subcellular fractions using antibodies and western blots of chicken forebrain and intermediate medial mesopallium (IMM) revealed regional differences in expression levels of a number of components of the glutamatergic neurotransmitter system. The discriminative taste aversion learning (DTAL) task was used to assess whether an animal learns the same task at different ages using different intracellular signalling pathways. The patterns of biochemical change seen in the IMM after DTAL training was very different at 2 weeks and 8 weeks. Two major differences were observed. Firstly, the same type of training induced changes occurred at both ages in GluR1 and CaMKII but they occurred faster at 8 weeks. Secondly the difference in ERK and CREB responses is consistent with a change in the relative contribution made by the ERK signalling pathway and CREB requirement to learning at these two ages. These results imply that the molecular changes induced by learning a behavioural task are faster in mature than immature brain and may involve a different balance of intracellular signalling pathways. In order to be able to investigate biological mechanisms controlling maturation and to use the chicken as an animal model in which pharmacological and/or environmental agents can be screened for potentially harmful effects on brain maturation two non-invasive measures of neuronal function were investigated. One was behavioural (prepulse inhibition: PPI) and the other was electrophysiological (auditory evoked related potentials: AERP). PPI in the chicken was examined electromyographically and via whole body movement with a stabilimeter apparatus. In two strains of chicken (a meat breed and a laying breed) PPI was identified but shown to be small and variable compared to that in the rat. The results indicate that the phenomenon of PPI in the chicken is too small and variable to be used as a quantitative measure of neural circuit maturation. Quantitative analysis of the chicken AERP revealed a significant decrease in amplitude of the positive AERP component and a decrease in latency of the negative AERP component with maturation. These maturation changes were comparable to developmental changes seen in human and other mammal AERPs. Such changes may reflect changes in the intracortical synaptic organisation of the auditory cortex. This technique allowed for repeated measures to be undertaken on the same animal over a number of weeks and enabled developmental changes to be monitored. This technique was extended to investigate perturbed maturation via the induction of chemically induced hypothyroidism. Results from this study showed that the induction of late onset hypothyroidism produces measurable effects on the chicken AERP consistent with perturbation in maturation of neuronal circuits and synapses. This suggests that AERPs may be useful non-invasive functional measures of brain maturation that can be used to study the effects of endogenous or exogenous factors on brain maturation in the chicken. Since human brain also exhibits a protracted maturation period the availability of a well characterised animal model for protracted brain maturation provides an opportunity to identify molecules, genes and environmental factors that are important in the regulation of maturation. Such a model may provide the basis for developing rational therapies or prevention strategies for some neurodevelopmental disorders. The protracted maturation of neuronal circuits observed in chicken forebrain offers such a model.

abstract: Patients with schizophrenia have deficits in sensorimotor gating, the ability to gate out irrelevant stimuli in order to attend to relevant stimuli. Prepulse inhibition (PPI) of the startle response is a reliable and valid model of sensorimotor gating across species. Repeated D2-like agonist treatment alleviates prior PPI deficits in rats, termed a PPI recovery, and is observable 28 days after treatment. The aim of the current project is to illuminate the underlying mechanism for this persistent change of behavior and determine the clinical relevance of repeated D2-like agonist treatment. Our results revealed a significant increase in Delta FosB, a transcription factor, in the nucleus accumbens (NAc) 10 days after repeated D2-like agonist treatment. Additionally, we investigated if Delta FosB was necessary for long-lasting PPI recovery and discovered a bilateral infusion of dominant-negative Delta JunD prevented PPI recovery after repeated D2-like agonist treatment. To further develop the underlying mechanism of PPI recovery, we observed that dominant negative mutant cyclic adenosine monophosphate (cAMP) response biding element protein (CREB) prevented repeated D2-like agonist-induced Delta FosB expression in the NAc. We then compared our previous behavioral and intracellular findings to the results of repeated aripiprazole, a novel D2-like partial agonist antipsychotic, to determine if repeated D2-like receptor agonist action is a clinically relevant pharmacological approach. As compared to previous PPI recovery and Delta FosB expression after repeated D2-like agonist treatment, we found similar PPI recovery and Delta FosB expression after repeated aripiprazole treatment in rats. We can conclude that repeated D2-like agonist treatment produces persistent PPI recovery through CREB phosphorylation and Delta FosB, which is necessary for PPI recovery. Furthermore, this pharmacological approach produces behavioral and intracellular changes similar to an effective novel antipsychotic. These findings suggest the underlying intracellular mechanism for sustained PPI recovery is clinically relevant and may be a potential target of therapeutic intervention to alleviate sensorimotor gating deficits, which are associated with cognitive symptoms of schizophrenia. / Dissertation/Thesis / Ph.D. Psychology 2013

INTRODUCTION: The process of sensorimotor gating is a neurological phenomenon referring to the brain’s ability to process and filter out stimuli in order to prevent an overflow of information. This phenomenon can be operationally measured by prepulse inhibition, which is the attenuation of a stimulus-induced startle response by introducing a milder preceding stimulus. Studies have shown that impairment of prepulse inhibition (PPI) has been correlated with diseases such as schizophrenia and autism spectrum disorder. Many brain areas, including the superior colliculus (SC), inferior colliculus (IC), mediodorsal thalamus (MD), basolateral amygdala (BLA), anterior cingulate cortex (ACC), and ventral hippocampus (VHPC), have been implicated in playing important roles in prepulse inhibition. While many studies have implicated GABA-A receptors in playing a role in PPI regulation, little work has been done on GABA-B receptors. An established rat model with induced prepulse inhibition impairment was used in this study. PPI impairment was induced via injection of the glutamate receptor antagonist dizocilpine. A subgroup of rats was also treated with the antihistamine pyrilamine to reverse the effects of dizocilpine. OBJECTIVES: The aims of this study are to: 1. Expand the understanding of prepulse inhibition in the context of neurological and developmental diseases such as autism spectrum disorder (ASD) and schizophrenia; 2. Identify potential significant differences within GABA-B receptor densities in the rat SC, IC, MD, BLA, ACC, or VHPC between treatment groups with and without dizocilpine and groups with and without pyrilamine. METHODS: Histological brain slides harvested from 36 Sprague-Dawley rats were provided by Dr. Edward Levin from Duke University’s Neurobehavioral Research Lab for this study. The brain slides were incubated in a radioligand solution specific for GABA-B receptors and exposed to autoradiograph film for approximately 12 weeks. The films were developed in a dark room and scanned electronically. GABA-B receptor densities were measured from the images and the data was analyzed using ANOVA and independent T tests. RESULTS: ANOVA testing revealed significant differences between treatment groups in the MD and VHPC. However, only the MD was found to have significant GABA-B receptor differences when comparing the dizocilpine and pyrilamine treatment groups to the control group. The VHPC was found to have significant differences in GABA-B receptor densities when directly comparing the dizocilpine group to the pyrilamine treatment group, rather than to the control group. There were no significant differences in GABA-B receptor densities as a result of either dizocilpine or pyrilamine treatment in the SC, IC, BLA, ACC, or VHPC. CONCLUSION: Changes in GABA-B receptor levels appear to play a role in both the impairment and rescue of PPI in the rat MD. It does not appear to play a role in the SC, IC, BLA, ACC, or VHPC for either the impairment or rescue of PPI function.

Toxoplasma gondii infection is common in humans and is a significant risk factor for developing the disease schizophrenia. Genetic risk factors are likely required for the disease of schizophrenia to develop. Nurr1 – heterozygous (+/-) mice and wild-type (+/+) mice were evaluated using immune activation of astrocytes within the prefrontal cortex, dopamine levels within the striatum, and measuring the acoustic startle response reaction time by using prepulse inhibition (PPI). T. gondii infected heterozygous (+/-) mice exhibited increased GFAP expression within the prefrontal cortex. Dopamine levels within the striatum were measured and T. gondii infected wild-type (+/+) mice exhibited increased dopamine levels. The acoustic startle response reaction time was measured using PPI and T. gondii infected mice exhibited slower reaction times when compared to controls. These data demonstrate that the Nurr1 (+/-) genotype predisposes mice to T. gondii-induced alterations in behaviors that involve dopamine neurotransmission and are associated with symptoms of schizophrenia.

No description available.

This study investigated the effects of the pharmacological manipulation of noradrenergic activities on dopaminergic phenotypes in aged rats. Results showed that the administration of L-threo-3,4-dihydroxyphenylserine (L-DOPS) for 21 days significantly increased the expression of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum and substantia nigra (SN) of 23-month-old rats. Furthermore, this treatment significantly increased norepinephrine/DA concentrations in the striatum and caused a deficit of sensorimotor gating as measured by prepulse inhibition (PPI). Next, old rats were injected with the α2-adrenoceptor antagonist 2-methoxy idazoxan or β2-adrenoceptor agonist salmeterol for 21 days. Both drugs produced similar changes of TH and DAT in the striatum and SN. Moreover, treatments with L-DOPS, 2-methoxy idazoxan, or salmeterol significantly increased the protein levels of phosphorylated Akt in rat striatum and SN. However, although a combination of 2-methoxy idazoxan and salmeterol resulted in a deficit of PPI in these rats, the administration of 2-methoxy idazoxan alone showed an opposite behavioral change. The in vitro experiments revealed that treatments with norepinephrine markedly increased mRNAs and proteins of ATF2 and CBP/p300 and reduced mRNA and proteins of HDAC2 and HDAC5 in MN9D cells. A ChIP assay showed that norepinephrine significantly increased CBP/p300 binding or reduced HDAC2 and HDAC5 binding on the TH promoter. The present results indicate that facilitating noradrenergic activity in the brain can improve the functions of dopaminergic neurons in aged animals. While this improvement may have biochemically therapeutic indication for the status involving the degeneration of dopaminergic neurons, it may not definitely include behavioral improvements, as indicated by using 2-methoxy idazoxan only.