Neurophysiological and behavioural characterisation of a 16p11.2 microdeletion rat model of autism spectrum disorder

Deletion of an approximately 600kb region of the 16p11.2 chromosome is commonly associated with autism spectrum disorder and intellectual disability. The effects of 16p11.2 microdeletion are highly variable and complex, as a result of the diversity of the 30 genes found at this locus. 16p11.2 deletion mice have shown deficits in a range of hippocampal and prefrontal-dependent behavioural paradigms, including those testing learning and memory, sociability, and cognitive flexibility. In exploring possible mechanisms underlying these deficits, aberrant interneuron development has been implicated in 16p11.2 deletion pathology; somatostatin (SST)-expressing interneurons of the hippocampus are intrinsically hyperexcitable in the rat model of the deletion. Additionally, research has demonstrated that developing interneurons in the human fetal prefrontal cortex express disproportionally high numbers of 16p11.2 locus genes, making them potentially vulnerable to 16p11.2 microdeletion. In this thesis I characterise a Sprague-Dawley rat model of the deletion by applying electrophysiological approaches to investigate common pathophysiological signatures of medial prefrontal cortex (mPFC) dysfunction. Additionally, I apply a battery of tests assessing various behaviours to explore whether 16p11.2 microdeletion results in the emergence of altered behavioural phenotypes in rats. A comprehensive neurophysiological dissection of alterations to the mPFC circuit was performed using electrophysiological approaches that employed the whole-cell patch-clamp recording technique. I assessed the intrinsic cellular properties of pyramidal neurons and interneurons of the mPFC over a developmental time course and found that SST interneurons of 16p11.2 deletion rats were hyperexcitable at a specific developmental timepoint. However, inhibitory synaptic inputs onto pyramidal neurons and excitatory synaptic inputs onto interneurons showed no differences. The proportions of different subtypes of interneurons within the mPFC were quantified to explore whether altered interneuron subtype numbers may stem from or compensate for SST interneuron hyperexcitability, however the densities of neurons and interneurons did not differ between genotypes. Rats went through a behavioural pipeline that assessed reflexes at the pup stage, and an array of behaviours in the adult rats. Across development, 16p11.2 deletion rats were shown to have lower body weights compared to wildtype controls. Deficits were revealed in a negative geotaxis, a reflex that requires motor coordination and vestibular input. No differences were observed in tests of social interaction or marble interaction, but 16p11.2 deletion rats showed alterations in their performance of prey capture, a complex paradigm that allows rats to hunt live crickets and engages motor coordination, reward-seeking behaviours, attention and motivation. 16p11.2 microdeletion rats successfully catch more prey than wildtype rats but further exploration into which facet of 16p11.2 rats’ behaviour underlies this phenotype is needed. Lastly, an auditory fear conditioning paradigm revealed that 16p11.2 deletion rats display less freezing when recalling fearful memories, pointing to a deficit in either the formation or recall of fear memory (processes which were previously shown to engage SST interneurons) in this rat model. In summary, this thesis provides a characterisation of some of the cellular excitability, synaptic physiology and behavioural phenotypes of a rat model of 16p11.2 microdeletion. In particular, it provides evidence for the effect of 16p11.2 microdeletion on SST-expressing interneurons in the mPFC during development. Furthermore, this work reveals novel behavioural phenotypes of this rat model of ASD/ID, which taken together add to the understanding of the varied pathophysiology associated with 16p11.2 microdeletion.

Grantor dc:publisher

The University of Edinburgh

Year dc:date.issued

2024

Author dc:creator

• Petrović, Nina

Advisors dc:contributor.advisor

• Wyllie, David
• Wood, Emma
• Kind, Peter
• Torsney, Carole

• Autism spectrum disorders
• ASD/ID-related disorder
• 16p11.2 microdeletion
• rat model
• inhibitory neurons
• somatostatin-expressing neurons
• problems forming memories

Language dc:language.iso

en

Identifier URI

http://dx.doi.org/10.7488/era/5042

OAI identifier oai:identifier

oai:era.ed.ac.uk:1842/42324