'How to insert label at bottom of axis MatPlotLib

Somehow I cannot understand how I can force Matplotlib to label the bottom edge of the axis...Visually it's really disconcerting how the 400 is close to the top but there is all this unused label space along the y axis at the bottom. I'd like the labeling to somehow start...earlier? I'm a beginner, please be kind. :D

p.s. I removed the x axis as it's not used in the plot which is why it's missing.

What I have: plot

What I want: wanted plot



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