In vivo Analysis of kir4.1 Channel Expression Following Photothrombotic Stroke and Antidepressant Therapy

Abstract

Stroke is one of the leading causes of death and disability in Canada. Despite increasing morbidity rates, current stroke treatments are ineffective outside of a three-to six-hour window following symptom onset, indicating a critical need for alternative approaches to the management of symptoms. One such alternative is the use of antidepressant therapy to treat post-stroke depression (PSD). A pilot survey conducted for this dissertation found that Canadian hospitals and stroke centers frequently prescribe antidepressants following strokes. This survey also demonstrated that antidepressant treatment improved respondents, experience in two outcome domains (depression and anxiety or mood swings) and may have an impact on further deterioration in two specific domains (pain or numbness and inattention to one side of the body). The two antidepressants commonly used to treat PSD, fluoxetine and nortriptyline, have previously been shown to inhibit an inward rectifying potassium channel, known as kir4.1. Following a stroke, the kir4.1 channel has been shown to be responsible for the rapid reuptake of potassium to return the cell to baseline levels. This dissertation sought to examine the impact of inhibiting kir4.1 channel activity, using two common antidepressants (fluoxetine and nortriptyline), on proteins involved in astrocytic inflammation and cell survival post-stroke. The developmental expression pattern was first characterized as many developmental factors are known to play an important role in plasticity following traumatic brain injuries. The expression pattern of IL-1β, kir4.1, p38, and pERK1/2 following stroke were also evaluated; these four proteins were also examined following treatment with antidepressants (fluoxetine or nortriptyline).Four major conclusions were drawn from the animal studies. First, the level of kir4.1 expression fluctuated with development, with higher expression observed at E18 and P7 compared to older timepoints, and at P21 compared to aged adults. Second, significant cell death was seen iii at the 24-hour and three-day timepoints, followed by substantial cellular recovery by day seven post-stroke. Thirdly, an increase in IL-1β was found to coincide with reduced expression of the kir4.1, p38β and pERK1/2 expression in the first six hours after stroke. Only pERK1/2 remained reduced after six hours. Finally, nortriptyline was found to significantly increase kir4.1 and pERK1/2 expression, and significantly decrease p38β expression, when compared to the fluoxetine and saline conditions. Findings from the animal studies provide support for the idea that tricyclic antidepressants may be more appropriate in the preventative treatment of post-stroke depression (PSD). The clinical significance of these relationships remains unknown; however, both antidepressants appear to be prescribed to individuals who have recently suffered a stroke. Furthermore, it is likely that the kir4.1 channel is involved in the astrocytic response to antidepressants treatment in the prevention of PSD. iv Acknowledgement...