Biomedical Engineering Reference
In-Depth Information
6.3
NO Release from the Nervous System
In this section, we present an imaging technique for visualizing neuronal function,
especially signal transduction. Several types of fl uorescent indicators have been
developed and applied in neuroethological studies. Ca indicators have been used to
visualize multi-neuron activity in the nervous system, and some of their applica-
tions are presented in another chapter of this topic. We, therefore, present other
kinds of fl uorescent dyes in this chapter.
NO is responsible for various types of neuromodulation in vertebrate and inver-
tebrate nervous systems (for reviews, Garthwaite and Boulton
1995
; Jaffrey and
Snyder
1995
). NO was also found to be involved in the chemical modifi cation of
serotonin into inactivate forms (Blanchard et al.
1997
). For example, the neuro-
modulatory effect of serotonin on cholinergic synapses in the buccal ganglion of
Aplysia
is reduced in the presence of an NO donor due to serotonin inactivation by
NO-derived nitrogen oxide (Fossier et al.
1999
). In the distal colon of the guinea
pig, the secretion of chloride by serotonin is possibly induced via the activation of
NO-producing neurons (Kadowaki et al.
1996
; Kuwahara et al.
1998
). Evidence of
a physiological interaction between NO and serotonin is also supported by the mor-
phological relationships between NO synthase -containing neurons and serotoner-
gic neurons (Kadowaki et al.
1999
).
At the present time, there are two plausible methods to detect NO: NO-sensitive
dye staining and NO-selective microelectrodes. The fi rst method is convenient for
screening the production of NO, and the second method is useful for the quantitative
evaluation of NO release from the nervous system.
We successfully showed that the VNC of the earthworm produces NO as a neu-
romodulator by visualizing the spatial pattern of NO production in the VNC using
an NO-specifi c fl uorescent dye, DAF-2 DA (Kitamura et al.
2001a
,
b
). The mecha-
nism for detecting NO with DAF-2 DA and typical imaging of spontaneous NO
production in the ventral nerve cord (VNC) of the earthworm are illustrated in
Fig.
6.3a, b
, respectively. This previous study revealed that the VNC contains
approximately 70 nitrergic neurons on the ventral side, which were identifi ed using
nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemis-
try, and suggested that basal NO production from these neurons is relatively high
compared with other previously reported nervous systems (Moroz et al.
1995
;
Kobayashi et al.
2000a
,
b
). It also showed that high K
+
stimulation induces further
NO production, resulting in the diffusion of NO to the giant fi bers on the dorsal side.
The axons of the ventrolateral serotonergic cells in the VNC are connected to the
MGF (Lubics et al.
1997
), and the propagation of action potentials in the MGF can
be modulated by the addition of 10
M serotonin. These fi ndings suggest a physi-
ological interaction between NO and serotonin in the earthworm VNC. However,
the role of serotonin in the mechanism of NO production in nervous systems,
including that of the earthworm VNC, has not been investigated. Recently, we found
that inhibition of serotonin-induced NO production causes the suppression of
μ
