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Fig. 6. Impaired sympathetic innervation and altered AANAT induction in pineal
glands from Egr3-/- mice. The pineal glands from (A)
wild-type and (A') Egr3-/- mice appeared
histologically indistinguishable. Immunohistochemistry for TH showed robust
sympathetic innervation to the (B) wild-type pineal glands that was
either highly diminished or absent in most pineal glands from
Egr3-/- mice (B'). Similar results were obtained with
the lacZ sympathetic reporter that showed a robust network of
sympathetic axons in (C) wild-type pineal glands that was barely
detectable in (C') pineal glands from most Egr3-/-
mice. (D) AANAT is induced by increased sympathetic activity to the
pineal upon entry into the dark phase of the light-dark cycle. In 10D:14L
light cycle entrained wild-type mice, AANAT expression was induced as expected
during the dark phase of the light-dark cycle and returned to low basal levels
when sympathetic activity to the pineal gland decreased with the onset of the
light phase of the cycle. However, in Egr3-/- pineal glands AANAT
was induced to 
18% of the wild-type level, consistent with a
physiological impairment of sympathetic innervation to the gland. The white
and black bar along the horizontal axis depicts the time during the light-dark
cycle when the lights are on and off, respectively. Zeitgeber time (ZT)
represents the 24 hour elapsed time in the light-dark cycle relative to the
time of dark-light transition (ZT0). (AANAT expression representative of three
independent experiments and qPCR performed in triplicate; the peak wild-type
value at ZT21 was considered 100% maximal AANAT induction in this paradigm;
scale bars: 25 µm.)
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