I would try to avoid changing the xticklabels
if possible, otherwise it can get very confusing if you for example overplot your histogram with additional data.
Defining the range of your grid is probably the best and with imshow
it can be done by adding the extent
keyword. This way the axes gets adjusted automatically. If you want to change the labels i would use set_xticks
with perhaps some formatter. Altering the labels directly should be the last resort.
fig, ax = plt.subplots(figsize=(6,6))
ax.imshow(hist, cmap=plt.cm.Reds, interpolation='none', extent=[80,120,32,0])
ax.set_aspect(2) # you may also use am.imshow(..., aspect="auto") to restore the aspect ratio