Undergraduate Honors Theses

Thesis Defended

Spring 2018

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Psychology & Neuroscience

First Advisor

Robert Spencer

Second Advisor

Heidi E W Day

Third Advisor

Alison Jane Vigers

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Abstract

How the brain and body coordinate the phase of their internal clocks has remained elusive despite years of study. The discovery of clock genes showed how individual cells can keep time. The establishment of the suprachiasmatic nucleus as the master clock showed that in normal circumstances the brain relies on one nucleus to communicate time of day information to the rest of the body and brain. By what method the SCN accomplishes this is largely unknown. Glucocorticoid hormones are known to have a role in this communication, but evidence remains for a neuronal pathway between the SCN and extra SCN brain regions. The Paraventricular nucleus of the thalamus (PVT) might be an important interface between the SCN and extra SCN brain regions, such as the prefrontal cortex (PFC). This study provides further support for this role of the PVT by characterizing the diurnal variation of Per1 and Bmal1 mRNA expression in the PVT. To further research this possible connection this study also characterized the use of intersectional DREADDs in the study of the PVT and its possible circadian regulation of the infralimbic portion of the PFC. Twelve rats received 1µl micro infusions of retrograde AAV CRE recombinase into both hemispheres of the infralimbic PFC, and 1µl micro infusions of AAV8 vectors containing double FLEXED hM3Dq DREADD receptors into the PVT. This creates a system where only neurons receiving both CRE and DIO-DREADDs will express the mCherry fused DREADD receptors. Rats were split up into three treatment groups and given injections of either clozapine-N-oxide (CNO), vehicle or no injection 90 minutes before perfusions and tissue collection. Immunohistochemistry was performed to visualize FOS protein as a marker of neuronal activity. The specificity of this intersectional approach was made apparent as the entire extent of the infection was isolated to the PVT despite injecting almost 3 times the amount of virus used in other studies. Qualitatively the CNO injection increased the amount of FOS immunopositive cells.

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