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Dorsal
column and ventrolateral pathways
Another prominent
system that is not generally considered to transmit noxious visceral
or somatic input consists of the dorsal column pathways (Figure
10).
Recent evidence
suggests that the dorsal column pathways have a role in conveying
nociceptive visceral information, particularly from pelvic organs
(Al-Chaer
et al., 1996a, 1996b;
Al-Chaer
et al., 1997; Apkarian et
al., 1995; Berkley
and Hubscher, 1995).
Clinical studies
helped to elucidate the role of the dorsal columns. Eight patients
exhibited relief from pelvic cancer pain after a small lesion
was made in the midline of the dorsal column at the T10 spinal
level (Hirshberg
et al., 1996). In animal studies gentle or noxious stimulation
of reproductive organs or noxious colorectal distension excites
neurons in the gracile nucleus; the sensory input likely reached
the gracile nucleus via the postsynaptic dorsal column pathway
(Al-Chaer
et al., 1996a). The limited dorsal column lesion also reduced
the response of cells in the ventroposterolateral nucleus of the
thalamus in rats, showing that visceral input could be transmitted
via the dorsal columns (Al-Chaer
et al., 1996b).
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