116
GRAEME CAMPBELL
caused by oculomotor nerve stimulation in mammals. There is no direct
evidence to show whether the response represents an inhibition of activity in the sphincter or an excitation of the dilator muscle. In Uranoscopus, both epinephrine and acetylcholine can cause both dilatation and
constriction of the pupil; in the selachians studied both epinephrine
and acetylcholine caused predominantly dilator reactions, and it has
been found that acctylcholine causes contraction of the isolated iris
dilator muscle of Scyllium (Young, 1931a, 1933a,b). Atropine inhibits
constrictions of Uranoscopus pupil caused both by sympathetic nerve
stimulation and by acetylcholine (Young, 1931a), but the effects of
blocking drugs on responses to oculomotor nerve stimulation have not
been tested. The most simple, but not necessarily the correct interpretation of these limitcd observations, is that both the sympathetic and the
oculomotor are cholinergic and that the sympathetic provides an excitatory innervation to the sphincter (in teleosts only) while oculomotor
stimulation excites the dilator muscle.
2. VAGUS NERVE
The posttrematic rami of the vagus nerve in teleosts (as well as of
the glossopharyngeal nerve in selachians ) almost certainly innervate
the branchial vascular bed. Dircct evidence of efferent innervation is
wanting, but elevations of branchial vascular resistance are known to
occur during, for instance, periods of anoxia ( Squalus acanthias, Satchell,
1962; Salmo gairdneri, Holeton and Randall, 1967). Determination of
whether this phenomenon is nerve mediated is made difficult by indications that the gill vasculature can constrict in direct response to
the anoxic conditions (Satchell, 1962). It is well established that catecholnmines dilate and acetylcholine constricts the branchial vasculature
in teleosts (Krawkow, 1913; Keys and Bateman, 1932; Ostlund and
Fange, 1962) and in dipnoans (Johansen et al., 1968), although no
vasomotor responses could be obtained from the isolated gills of the
selachian Squalus acantliias ( dstlund and Finge, 1962). Similar vasoconstrictor actions of acetylcholine have been obscrvcd in the amphibian
pulmonary vascular bed (Voigt, 1939; Brecht, 1947), a system derived
from branchial arch vasculaturc. It is then reasonable to suggest that
the vagi provide cholinergic vasoconstrictor fibrrs to the gills, if only
because of the analogy with the established cholinergic vasoconstriction
mediated by the vagi in amphibian lungs (Luckhardt and Carlson,
1921 ) .
The visceral vagal rami distribute efferent fibers to the heart, the
stomach, and usually no more than the most oral region of the intestine,
GRAEME CAMPBELL
caused by oculomotor nerve stimulation in mammals. There is no direct
evidence to show whether the response represents an inhibition of activity in the sphincter or an excitation of the dilator muscle. In Uranoscopus, both epinephrine and acetylcholine can cause both dilatation and
constriction of the pupil; in the selachians studied both epinephrine
and acetylcholine caused predominantly dilator reactions, and it has
been found that acctylcholine causes contraction of the isolated iris
dilator muscle of Scyllium (Young, 1931a, 1933a,b). Atropine inhibits
constrictions of Uranoscopus pupil caused both by sympathetic nerve
stimulation and by acetylcholine (Young, 1931a), but the effects of
blocking drugs on responses to oculomotor nerve stimulation have not
been tested. The most simple, but not necessarily the correct interpretation of these limitcd observations, is that both the sympathetic and the
oculomotor are cholinergic and that the sympathetic provides an excitatory innervation to the sphincter (in teleosts only) while oculomotor
stimulation excites the dilator muscle.
2. VAGUS NERVE
The posttrematic rami of the vagus nerve in teleosts (as well as of
the glossopharyngeal nerve in selachians ) almost certainly innervate
the branchial vascular bed. Dircct evidence of efferent innervation is
wanting, but elevations of branchial vascular resistance are known to
occur during, for instance, periods of anoxia ( Squalus acanthias, Satchell,
1962; Salmo gairdneri, Holeton and Randall, 1967). Determination of
whether this phenomenon is nerve mediated is made difficult by indications that the gill vasculature can constrict in direct response to
the anoxic conditions (Satchell, 1962). It is well established that catecholnmines dilate and acetylcholine constricts the branchial vasculature
in teleosts (Krawkow, 1913; Keys and Bateman, 1932; Ostlund and
Fange, 1962) and in dipnoans (Johansen et al., 1968), although no
vasomotor responses could be obtained from the isolated gills of the
selachian Squalus acantliias ( dstlund and Finge, 1962). Similar vasoconstrictor actions of acetylcholine have been obscrvcd in the amphibian
pulmonary vascular bed (Voigt, 1939; Brecht, 1947), a system derived
from branchial arch vasculaturc. It is then reasonable to suggest that
the vagi provide cholinergic vasoconstrictor fibrrs to the gills, if only
because of the analogy with the established cholinergic vasoconstriction
mediated by the vagi in amphibian lungs (Luckhardt and Carlson,
1921 ) .
The visceral vagal rami distribute efferent fibers to the heart, the
stomach, and usually no more than the most oral region of the intestine,