112
GRAEME CAMPBELL
response could have been artifactual. On the other hand, Fange and
Johnels (1958) pointed out that they had allowed the animal to warm
up to room temperature (lSOC), and they suggested that the vagus
might be ineffective at this high temperature (see also Burnstock, 19S8a).
The only independent support for an inhibitory vagal innervation of the
gut is the observation that nicotine causes a relaxation of previously contracted Myxine intestine in uitro (Fange, 1948), which may indicate the
presence of inhibitory neurons in the gut wall. It has been postulated
elsewhere (Campbell and Burnstock, 1968) that the vagus nerve is primitively inhibitory to the vertebrate gastrointestinal tract and that the
inhibitory nerve fibers are of a nonadrenergic type recently demonstrated
in the mammalian gastric vagus (Martinson, 1965; Campbell, 1966).
The possibility has been raised that the vagus nerves contain adrenergic nerve fibers (Fange et al., 1963) since the vagus of hilyxine contains considerable concentrations of catecholamines, predominantly norepinephrine (von Euler and Fange, 1961). Adrenergic fibers have not
been found in the cranial autonomic outflow of any higher vertebrate,
but this does not necessarily mean that they will be absent in cyclostomes.
Alternatively, sympathetic adrenergic fibers could enter the vagi from
the spinal outflow, as claimed by Marcus (1910), since the vagi run
extremely close to the mixed ventral rami of the anterior spinal nerves
(see Peters, 1963). Finally, the catecholamines could be stored in chromaffin cells; the vaS;us contains many ganglion cells, and one must remember that the “ganglion cells” found in cyclostome hearts by Augustinsson et al. (1956) were later shown to be specialized chromaffin
cells (Johnels and Palmgren, 1960; Bloom et al., 1961; Hoffmeister et al.,
1961). A fluorescence histochemical study of this problem would be most
welcome.
B. Spinal Autonomic Nerves
There is still much confusion about the distribution of autonomic
nerve fibers from the spinal cord. Some of this confusion arises from
the fact that many peripheral nerve cell bodies have been observed in
cyclostomes, but it is not always clear which of these neurons are autonomic and which sensory. In addition, there are reports of fibers leaving
the spinal cord of Lnmpetru in both dorsal and ventral spinal nerves
and running directly, without an intervening ganglionic synapse, to
visceral structures (Johnels, 19S6). Whether all or any of these fibers
arc autonomic, i.e., effercnt, is unknown and will probably remain so
until physiological observations have been made.
GRAEME CAMPBELL
response could have been artifactual. On the other hand, Fange and
Johnels (1958) pointed out that they had allowed the animal to warm
up to room temperature (lSOC), and they suggested that the vagus
might be ineffective at this high temperature (see also Burnstock, 19S8a).
The only independent support for an inhibitory vagal innervation of the
gut is the observation that nicotine causes a relaxation of previously contracted Myxine intestine in uitro (Fange, 1948), which may indicate the
presence of inhibitory neurons in the gut wall. It has been postulated
elsewhere (Campbell and Burnstock, 1968) that the vagus nerve is primitively inhibitory to the vertebrate gastrointestinal tract and that the
inhibitory nerve fibers are of a nonadrenergic type recently demonstrated
in the mammalian gastric vagus (Martinson, 1965; Campbell, 1966).
The possibility has been raised that the vagus nerves contain adrenergic nerve fibers (Fange et al., 1963) since the vagus of hilyxine contains considerable concentrations of catecholamines, predominantly norepinephrine (von Euler and Fange, 1961). Adrenergic fibers have not
been found in the cranial autonomic outflow of any higher vertebrate,
but this does not necessarily mean that they will be absent in cyclostomes.
Alternatively, sympathetic adrenergic fibers could enter the vagi from
the spinal outflow, as claimed by Marcus (1910), since the vagi run
extremely close to the mixed ventral rami of the anterior spinal nerves
(see Peters, 1963). Finally, the catecholamines could be stored in chromaffin cells; the vaS;us contains many ganglion cells, and one must remember that the “ganglion cells” found in cyclostome hearts by Augustinsson et al. (1956) were later shown to be specialized chromaffin
cells (Johnels and Palmgren, 1960; Bloom et al., 1961; Hoffmeister et al.,
1961). A fluorescence histochemical study of this problem would be most
welcome.
B. Spinal Autonomic Nerves
There is still much confusion about the distribution of autonomic
nerve fibers from the spinal cord. Some of this confusion arises from
the fact that many peripheral nerve cell bodies have been observed in
cyclostomes, but it is not always clear which of these neurons are autonomic and which sensory. In addition, there are reports of fibers leaving
the spinal cord of Lnmpetru in both dorsal and ventral spinal nerves
and running directly, without an intervening ganglionic synapse, to
visceral structures (Johnels, 19S6). Whether all or any of these fibers
arc autonomic, i.e., effercnt, is unknown and will probably remain so
until physiological observations have been made.