3. AUTONOMIC NERVOUS SYSTEMS
123
ent species. The sympathetic chains are connected to spinal nerves
by both gray and white rami communicantes. The chains extend caudally
to the end of the tail and also extend rostrally into the cranium where
connections arc usually made with the IIIrd, Vth, VIIth, IXth, and Xth
cranial nerves ( Fig. 2 ) . The gastrointestinal tract is mainly innervated
by an anterior splanchnic nerve, leaving the right sympathetic chain, but
a posterior splanchnic nerve has bcen found in trout ( Burnstock, 195813).
Genital and vcsical nerves leave the posterior regions of the chains,
supplying thc urinary and genital ducts via periarterial nerve plexuses.
A sympathetic innervation of the iris occurs in teleosts, but it has
never been observed in selachians. The fibers involved leave the spinal
cord in the anterior spinal nerves and run rostrally up the chain to form
synapses in the sympathetic ganglion in the trigeminal nerve (Uranoscopus; Young, 1931a; Fig. 2 ) . Stimulation of the sympathetic chain
cause's pupilloconstriction. The response is prevented by treatment with
atropinc, indicating that the nerves are cholinergic ( Young, 1931a,
1933b). The sympathetic also appears to provide a motor innervation
to the striated extraocular muscles in teleosts because sympathetic section
causes abnormal protrusion of the eyeball (Young, 1931a). There is
no evidence concerning the transmitter substance mediating this effect,
but it has been found that sympathetic adrenergic fibers can cause contraction of thc superior rectus muscle in a mammal (Eakins and Katz,
1967 ) .
It has long been denied that there is a sympathetic innervation of the
hcart in fish (see Johansen and Martin, 1965; Randall, 1968). However,
duorescence histochemical studies of the heart of teleosts have now
shown that in spite of one report to the contrary (von Mecklenburg,
1966, cited in Falck et al., 1966) there is an adrenergic innervation of
the cardiac chambers (Govyrin and Leont’eva, 1965; Gannon and Burnstock, 1969; Fig. 5). Nerve fibers containing small granular vesicles,
typical of adrenergic nerves in other animals, have been seen during an
electron microscopic investigation of the trout heart (Yaniauchi and
Burnstock, 1968). The adrenergic nerve fibers appear to come both from
the vagi and along the coronary arterics and occur most densely in the
sinus venosus and auricle. Gannon and Bumstock (1969) have confirmed Kulaev’s report (1957) that stimulation of the vagi can cause
cardioacceleration in teleosts. They have also shown that this response
is prevented by treatment with the adrenergic neuron-blocking drugs,
bretylium and gunnethidine, or with an epinephrine-blocking drug,
propranolol, a congener of which inhibits cardiac responses to catecholamines in plaice (Falck et al., 1966). As in the case of the vagal
adrenergic innervation of the swim bladder, it is probably safest to assume
123
ent species. The sympathetic chains are connected to spinal nerves
by both gray and white rami communicantes. The chains extend caudally
to the end of the tail and also extend rostrally into the cranium where
connections arc usually made with the IIIrd, Vth, VIIth, IXth, and Xth
cranial nerves ( Fig. 2 ) . The gastrointestinal tract is mainly innervated
by an anterior splanchnic nerve, leaving the right sympathetic chain, but
a posterior splanchnic nerve has bcen found in trout ( Burnstock, 195813).
Genital and vcsical nerves leave the posterior regions of the chains,
supplying thc urinary and genital ducts via periarterial nerve plexuses.
A sympathetic innervation of the iris occurs in teleosts, but it has
never been observed in selachians. The fibers involved leave the spinal
cord in the anterior spinal nerves and run rostrally up the chain to form
synapses in the sympathetic ganglion in the trigeminal nerve (Uranoscopus; Young, 1931a; Fig. 2 ) . Stimulation of the sympathetic chain
cause's pupilloconstriction. The response is prevented by treatment with
atropinc, indicating that the nerves are cholinergic ( Young, 1931a,
1933b). The sympathetic also appears to provide a motor innervation
to the striated extraocular muscles in teleosts because sympathetic section
causes abnormal protrusion of the eyeball (Young, 1931a). There is
no evidence concerning the transmitter substance mediating this effect,
but it has been found that sympathetic adrenergic fibers can cause contraction of thc superior rectus muscle in a mammal (Eakins and Katz,
1967 ) .
It has long been denied that there is a sympathetic innervation of the
hcart in fish (see Johansen and Martin, 1965; Randall, 1968). However,
duorescence histochemical studies of the heart of teleosts have now
shown that in spite of one report to the contrary (von Mecklenburg,
1966, cited in Falck et al., 1966) there is an adrenergic innervation of
the cardiac chambers (Govyrin and Leont’eva, 1965; Gannon and Burnstock, 1969; Fig. 5). Nerve fibers containing small granular vesicles,
typical of adrenergic nerves in other animals, have been seen during an
electron microscopic investigation of the trout heart (Yaniauchi and
Burnstock, 1968). The adrenergic nerve fibers appear to come both from
the vagi and along the coronary arterics and occur most densely in the
sinus venosus and auricle. Gannon and Bumstock (1969) have confirmed Kulaev’s report (1957) that stimulation of the vagi can cause
cardioacceleration in teleosts. They have also shown that this response
is prevented by treatment with the adrenergic neuron-blocking drugs,
bretylium and gunnethidine, or with an epinephrine-blocking drug,
propranolol, a congener of which inhibits cardiac responses to catecholamines in plaice (Falck et al., 1966). As in the case of the vagal
adrenergic innervation of the swim bladder, it is probably safest to assume