WILLIAM F. FRIEDMAN 
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FFTUS 
ADULT 
Figure 13. — Myocardial monoamine oxidase activities 
in the fetal lamb and adult sheep. Horizontal bars: 
mean values. 
varicosities and flouresced only weakly. The ap- 
pearance of large preterminal nerve trunks en- 
closing intensely flourescent, catacholamine- 
containing terminal varicosities suggests that 
the latter move into the heart during early de- 
velopment, perhaps in response to an increase 
in sensory input, and branch out and arborize to 
form the autonomic ground plexus. Since nor- 
epinephrine storage granules flow down cardiac 
adrenergic nerves from neuronal cell bodies in 
the cervical and thoracic sympathetic ganglia, 
the intense preterminal flourescence suggests 
that these ganglia are quite prepared to respond 
appropriately to central efferent impulse traffic. 
Moreover, it appears that a significant propor- 
tion of the norepinephrine measured in the fetal 
and newborn heart resides in the preterminal 
nerve trunks, and therefore may not be in close 
anatomic proximity to the adrenergic receptors 
of the myocardial cell. 
While one cannot stain specifically for acetyl- 
choline in tissues, it is possible to localize ace- 
tylcholinesterase histochemically, and it has 
been shown that reasonably good correlations 
exist between the concentrations of acetylcho- 
line, acetylcholinesterase, and choline acetylase 
in various regions of the peripheral and central 
nervous systems. The photomicrograph shown 
in Figure 16 has been stained for acetylcholin- 
esterase by the thiocholine technique after se- 
lective inhibition of pseudocholinesterase.^^ It 
would appear that a similar density of stained 
cholinergic fibers is present in atrial, SA and 
AV nodal and ventricular tissue in both the 
fetus and the adult. 
FETUS 
ADULT 
Figure 14. — Myocardial catachol-o-methyl transferase 
activities in the fetal lamb and adult sheep. Horizon- 
tal bars : mean values. 
