Title

Investigating the Links Between Early-life Seizures, Stress, and Behavior in a Larval Zebrafish Model

Date of Award

2018

Degree Type

Thesis

Degree Name

Master of Science in Biomedical Sciences

First Advisor

Jocelyn Lippman-Bell, PhD

Second Advisor

Heather Montie, PhD

Third Advisor

Denah Appelt, PhD

Fourth Advisor

Marcus Bell, PhD

Abstract

Seizures and stress in early life disrupt normal brain development and often lead to long-term behavioral and cognitive deficits. Here, we compare the long-term behavioral consequences of early-life seizures induced by the chemoconvulsant pentylenetetrazol (PTZ) and handling stress in two larval zebrafish models to determine which of these paradigms will replicate the long-term behavioral deficits observed in humans and in rodent models. The first model, referred to here as the 1-day model, replicates an established larval zebrafish seizure model in which seizures were induced at 7 days post-fertilization (dpf) for 40 mins using an 8mM PTZ solution (PTZ group). In a second model, the 3-day model, fish were exposed to 5mM for 40 mins once per day from 5-7 dpf. Handling control zebrafish (HC) were exposed to normal tank water. A third group remained undisturbed until experimentation (untouched controls, UC). We next assessed three behavioral outcome measures in each group: shoaling/sociability at 30 dpf, learning/memory at 30 and 60 dpf, and anxiety at 30 and 60 dpf. In the 3-day model, the HC fish, but not the PTZ fish, showed significantly less shoaling behavior than UC fish. All three groups showed similar levels of learning and memory, as assessed by a y-maze task. However, the HC group showed a significantly increased prevalence of freezing, and anxiety behavior compared to the UC or PTZ groups at 30 dpf in the 3-day model. Substantiated by the fact that HC fish but not PTZ fish differed from the UC fish, we hypothesize that the observed differences may be due to stress and not specifically to the seizures. Further, seizures may inhibit the normal development of stress-response pathways. To investigate molecular links to these changes, we analyzed cell death markers, acute and long-term stress pathways, and synaptic plasticity-related gene expression. We found no differences in cell death or long-term stress between any groups. However, HC fish displayed significantly stronger acute stress responses compared to both other groups, as measured by cortisol release. Further, both the HC and PTZ groups showed a large change in synaptic plasticity-related gene expression compared to UC group, but HC fish showed larger magnitude changes than the PTZ fish. Taken together, we conclude that behavioral changes following early-life stress are related to the development of heightened acute stress responses, but that the development of these responses in inhibited following early-life seizures.

Comments

Full text will be posted on 8/21/2020.

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