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Fig. 5. Morphological correlates of hormone secretion are present in the anterior
cardiac plexus. This transmission electron micrograph shows portions of
several nerve terminals at high magnification. Both dense-core (DCV) and
electron-lucent (ELV) vesicles are present in these terminals. In this image,
one DCV is docked to the plasma membrane. Likewise, several DCVs have fused
with the plasma membrane and are in the process of exocytosing their contents.
This exocytosis creates characteristic ultrastuctural features on the plasma
membrane commonly referred to as omega (
)-figures. The docked DCV and
the three -figures visible in this micrograph create a pseudo-time
course of hormone secretion. First, a DCV docks to the plasma membrane (1) and
subsequently fuses with it, releasing its dense-core and forming an
-figure (1). The membrane of the DCV rapidly is incorporated
into the plasma membrane of the terminal and the -figure subsides
(2 and 3). Note that this micrograph is from a different
preparation to that shown in Fig.
4. Scale bar, 200 nm.
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