TIIE PHYSIOLOGY OF ABCIDIANS
103
P. A'gnaptic tmnsmimio.rL
Several workers have nttmi ptetl to idcntify the chemical nature of
the substances involved in synciptir tmnemission. their research being
focused on an attempt to detcrmine whether cliolinergic nerves are
present, in the system. The problem was first tackled by Bacq (1935b,
1936c, 1939, 1941, 1947) who pointcd out that if cholinergic nerves are
present it should be possible to identify acetylcholine or related substances in extracts of nervous tissue and to identify cholinesterase in
whole tissue or muscle extracts. In addition nervous transmission or
muscle action ahould bu inhibited by ciirarc, atropine and similar
blocking agcnts, while the response mechanism should be attenuated
in the presence of eserine which inhibits cholinesterases. He was unable
to identify any acc?tylcholint~ in ascidian extracts and cholinesterase was
only found in small quantity in whole animal extracts of Ciona intestinnlis or in thc riiitscle of one species studied, Rtyela plicata ; eserine had
no effect on Ciona intestinalisr and Halocynthia papilloaa and Bacq
concluded that cholinergic nerves were absent in these animals.
Similarly no effect on muRcle action occurred in the presence of curare.
(Por summaries of his findings s ~ e
Bacq, 1941 and 1947.)
Ihrante ( 1966) reported the presence in embryos of Ciona intestinalie
of cholinesterases in the musclc system only and not in the nervous
system, but she found that thesc enzymes disappeared completely at
the time of metamorphosis. Scudder and Karczmar (1966) also working
with C. intestinaliu used histochemical techniques to seek cholinesterases
and obtained positive results but the enzyme appeared diffusely spread
in tissues other than nerves and was in very low concentrations.
Furthermore, while this substance hydrolyzed acetylcholine it was
unaeected by normal inhibitors of cholinesterases and therefore must be
different from the normal cholinesterases. They did also report finding
a cholinesterase in the ganglion of C. intevtinalis but came to the rather
curious conclusion t h a t it was probably derived from detritus in the
neural gland which was homogenized with the ganglion. We shall see
later (p. 112) that it is most unlikely that detritus would accumulate in
the neural gland.
&udder et nl. (1966) used the siphonal clohing mechanism as an
indicator of muscle activity and tested t h e effects of acetylcholine and
anticholinergic agents by direct injection into the surrounding water.
Their results led them to bclievo that cholinergic nerves were absent,
but there is nothing in thcir experimental techniques to Ruggcst that the
substances preclcnted had an opportunity to reach the n e u r o m ~ ~ c ~ l a r
system involvccl.
103
P. A'gnaptic tmnsmimio.rL
Several workers have nttmi ptetl to idcntify the chemical nature of
the substances involved in synciptir tmnemission. their research being
focused on an attempt to detcrmine whether cliolinergic nerves are
present, in the system. The problem was first tackled by Bacq (1935b,
1936c, 1939, 1941, 1947) who pointcd out that if cholinergic nerves are
present it should be possible to identify acetylcholine or related substances in extracts of nervous tissue and to identify cholinesterase in
whole tissue or muscle extracts. In addition nervous transmission or
muscle action ahould bu inhibited by ciirarc, atropine and similar
blocking agcnts, while the response mechanism should be attenuated
in the presence of eserine which inhibits cholinesterases. He was unable
to identify any acc?tylcholint~ in ascidian extracts and cholinesterase was
only found in small quantity in whole animal extracts of Ciona intestinnlis or in thc riiitscle of one species studied, Rtyela plicata ; eserine had
no effect on Ciona intestinalisr and Halocynthia papilloaa and Bacq
concluded that cholinergic nerves were absent in these animals.
Similarly no effect on muRcle action occurred in the presence of curare.
(Por summaries of his findings s ~ e
Bacq, 1941 and 1947.)
Ihrante ( 1966) reported the presence in embryos of Ciona intestinalie
of cholinesterases in the musclc system only and not in the nervous
system, but she found that thesc enzymes disappeared completely at
the time of metamorphosis. Scudder and Karczmar (1966) also working
with C. intestinaliu used histochemical techniques to seek cholinesterases
and obtained positive results but the enzyme appeared diffusely spread
in tissues other than nerves and was in very low concentrations.
Furthermore, while this substance hydrolyzed acetylcholine it was
unaeected by normal inhibitors of cholinesterases and therefore must be
different from the normal cholinesterases. They did also report finding
a cholinesterase in the ganglion of C. intevtinalis but came to the rather
curious conclusion t h a t it was probably derived from detritus in the
neural gland which was homogenized with the ganglion. We shall see
later (p. 112) that it is most unlikely that detritus would accumulate in
the neural gland.
&udder et nl. (1966) used the siphonal clohing mechanism as an
indicator of muscle activity and tested t h e effects of acetylcholine and
anticholinergic agents by direct injection into the surrounding water.
Their results led them to bclievo that cholinergic nerves were absent,
but there is nothing in thcir experimental techniques to Ruggcst that the
substances preclcnted had an opportunity to reach the n e u r o m ~ ~ c ~ l a r
system involvccl.