ATTENTION REGULATION AND BEHAVIOURAL FLEXIBILITY IN RATS WITH RELEVANCE TO SCHIZOPHRENIA

Schizophrenia is a neuropsychological disorder in which the neural systems which regulate attention allocation, primarily the dorsolateral prefrontal cortex, are

dysfunctional, resulting in deficient gating of attention to irrelevant inputs from the environment. This sensory processing dysfunction hinders goal-directed behaviour to the extent that the subsequent cognitive deficits of schizophrenia prevent many chronic patients from leading normal lives. It is the onus of neuroscience to understand the nature of deficits induced by the disorder, thus providing target mechanisms for remediation of those deficits in patients. To accomplish this, manipulations in rats with relevance to schizophrenia are examined in assays with translation to human neurobiology and behaviour. In this thesis, three manipulations with relevance to schizophrenia, were examined for attentional regulation in the attentional set-shifting task, and similar assays, to determine how different forms of schizophrenia-related pathology influence attentional regulation and behavioural flexibility.

The foremost findings of the experiments herein were that manipulations inducing schizophrenia-related neurobiology, resulted in impaired performance in

extradimensional set-shifting and reversal learning. These deficits were found following: acute inhibition of the mPFC in adult rats, in adult rats who had been exposed to a glutamate receptor antagonist during the neonatal period of development, and/or in adult rats who had gestational disruption of neuron proliferation. Across all three manipulations, a clear behavioural pattern of deficient sensory gating, evidenced by responding to irrelevant stimuli during the set-shifting task was found.

These findings suggest that at the core of the cognitive deficits in schizophrenia is the 'loosening of associations' such that patients suffer the inability to regulate

attention, and limit sensory processing to relevant information. The subsequent aberrant learning about irrelevant information then impairs performance during goal-

directed behaviours.

1.1 Overview  - - - - - - - - - - - - - - - - - - - - - - - - -   2 

1.2 Schizophrenia genetics and neurochemistry  - - - - - - - - - - - - - -   3 

1.2.1 Dopamine  - - - - - - - - - - - - - - - - - - - - - - -   5 

1.2.3 Glutamate  - - - - - - - - - - - - - - - - - - - - - - -   7 

1.2.4 GABA  - - - - - - - - - - - - - - - - - - - - - - - - .  9 

1.3 Schizophrenia neuroanatomy  - - - - - - - - - - - - - - - - - -   10 

1.4 Schizophrenia behavioural flexibility and attentional regulation  - - - - - - -   13 

1.4.1 Schizophrenia and the Wisconsin Card Sorting Test- - - - - - - - - -   14 

1.4.2 Schizophrenia and the Attentional Set-Shifting Task  - - - - - - - - - .  17 

1.5 Tasks used to measure behavioural flexibility in rodents  - - - - - - - - - .  21 

1.6 Thesis rationale  - - - - - - - - - - - - - - - - - - - - - -   25 

2.1 ASST protocol  - - - - - - - - - - - - - - - - - - - - - - -   28 

2.1.1 Apparatus  - - - - - - - - - - - - - - - - - - - - - - -   28 

2.1.2 Training - - - - - - - - - - - - - - - - - - - - - - -   28 

2.1.3 Standard 7-stage ASST testing  - - - - - - - - - - - - - - - -   29 

2.2 Histology - - - - - - - - - - - - - - - - - - - - - - - -   30 

2.3 Statistical analysis - - - - - - - - - - - - - - - - - - - - - .  32 

2.3.1 Frequentist approach: Null hypothesis testing  - - - - - - - - - - -   32 

2.3.2 Probability approach: Bayesian analysis  - - - - - - - - - - - - -   32 

3.1 Introduction to acute manipulations to induce 'schizophrenia-related' behaviour in 

rodents  - - - - - - - - - - - - - - - - - - - - - - - - - -   42 

3.1.1 Adult sub-chronic/acute NMDA receptor antagonist manipulations  - - - - .  42 

3.1.2 Stress-induced perturbations - - - - - - - - - - - - - - - - .  44 

3.1.3 Lesion experiments  - - - - - - - - - - - - - - - - - - - -   45 

3.1.4 Inactivation of the mPFC via designer receptors exclusively activated by designer 

drugs (DREADDs)  - - - - - - - - - - - - - - - - - - - - - -   47 

3.2 Rationale  - - - - - - - - - - - - - - - - - - - - - - - -   48

3.3 Methods and materials  - - - - - - - - - - - - - - - - - - - -   49 

3.3.1 Animals - - - - - - - - - - - - - - - - - - - - - - -   49 

3.3.2 Pharmacogenetic manipulation  - - - - - - - - - - - - - - - -   49 

3.3.3 Behavioural Testing - - - - - - - - - - - - - - - - - - - .  50 

3.4 Results  - - - - - - - - - - - - - - - - - - - - - - - - -   54 

3.4.1 mPFCin-rats have set-shifting deficits in the standard 7-stage ASST - - - - -   54 

3.4.2 Behavioural pattern analysis reveals increased irrelevant dimension responding in 

mPFCin-rats  - - - - - - - - - - - - - - - - - - - - - - - -   56 

3.4.3 mPFCin-rats attend to stimuli in the irrelevant dimension - - - - - - - -   58 

3.5 Discussion  - - - - - - - - - - - - - - - - - - - - - - - -   62 

3.5.1 Irrelevant dimension responding during set-shifting inducing enhanced learned 

irrelevance. - - - - - - - - - - - - - - - - - - - - - - - -   62 

3.5.2 Model of neural mechanisms of the mPFC-inhibition on ASST performance. - -   64 

3.5.3 Implications for theories of attention and associative learning  - - - - - -   70 

3.6 Histological Analysis of mPFC DREADDs - - - - - - - - - - - - - - -   73 

Rationale  - - - - - - - - - - - - - - - - - - - - - - - - - .  73 

3.7 Methods and materials  - - - - - - - - - - - - - - - - - - - -   73 

3.8 Results  - - - - - - - - - - - - - - - - - - - - - - - - -   74 

3.8.1 All rats exhibited clear DREADDs expression within the mPFC - - - - - -   74 

3.8.2 DREADDs are trafficked throughout the projections of the infected mPFC neurons.

 - - - - - - - - - - - - - - - - - - - - - - - - - - - -   75 

3.8.3 No difference in c-Fos immunoreactivity following clozapine-N-oxide 

administration.  - - - - - - - - - - - - - - - - - - - - - - -   77 

3.9 Discussion  - - - - - - - - - - - - - - - - - - - - - - - -   80 

3.9.1 Analysis of DREADDs expression.  - - - - - - - - - - - - - - - .  80 

3.9.2 Infected projections are consistent with the pattern of mPFC neuronal projections

 - - - - - - - - - - - - - - - - - - - - - - - - - - - -   80 

3.9.3 Inhibitory DREADDs can be effective without reduction in activity at the cell body

 - - - - - - - - - - - - - - - - - - - - - - - - - - - -   81 

4.1 Introduction to neonatal-NMDAR antagonism rats  - - - - - - - - - - -   84 

4.1.1 Neurochemistry - - - - - - - - - - - - - - - - - - - - -   85 

4.1.2 Brain structural abnormalities  - - - - - - - - - - - - - - - -   87 

4.1.3 Schizophrenia-related innate behaviour in neonatal-NMDAR blockaded rats  - -   87

4.