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Other
Ascending Pathways
Previously we have emphasized the probable role of the spinothalamic
tract in transmitting noxious information from the heart. There
are other ascending pathways that could also be involved, although
none of them is as well-characterized as the spinothalamic tract.
The most prominent
of these is the spinoreticular tract (Figure
1).
Spinoreticular
neurons react similarly to spinothalamic neurons in response to
noxious chemicals applied to the heart as well as to coronary
artery occlusion (Blair
et al., 1984 a & b).
Considering the neuronal response patterns of the spinoreticular
tract, as well as its projections, this pathway is likely involved
in the transmission of neuronal activity that the brain ultimately
interprets as angina pectoris.
Another possible
pathway is the spinoparabrachial tract, which projects
to the parabrachial region of the pons (Figure
9).
The cell bodies
for the spinoparabrachial pathway are located primarily in the
uppermost region of the dorsal horn (lamina I), and the axons
terminate in the lateral parabrachial region (Blomquest
et al., 1989; Cechetto
et al., 1985; McMahon
et al., 1985; Panneton
and Burton, 1985; Menetrey
and DePommery, 1991; Gauriau
and Bernard, 2002). Neurons from the lateral parabrachial
region project to the amygdala and the hypothalamus (ventromedial
nucleus and retrochiasmatic region). These structures are likely
to participate in the emotional-affective responses to noxious
events, possibly including angina pectoris, as well as autonomic
responses to noxious events.
Some additional
pathways that could convey noxious information from the heart
include the spinomesencephalic, spinosolitary, and spinohypothalamic
tracts (Yezierski
and Broton, 1991; Yezierski
and Shwartz, 1986; Menetrey
and Basbaum, 1987; Burstein,
1996), but very little information is known about their possible
role in angina pectoris.
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