124
R. W. MURRAY
posterior to a deletion of the spinal cord over 1-2 segments in the region
of the anal fin.
Confirmation of the role of the cutaneous nerves has been provided
by tests in which fish were trained to swim away from a normal resting
position in the center of an experimental tank when touched by a warmed
rod and not to move if the rod was at tank temperature (Bardach, 1956).
When the rod was 2°C warmer than the tank, consistent responses were
obtained from almost the whole of the body surface, including the fins,
and they were not restricted to the region close to the lateral line. A
similar conclusion follows from Sullivan’s records of the behavior of
trout in a temperature gradient (Sullivan, 1954); the rate and extent of
turning and the frequency of moving vary with temperature in such a
way that the fish remain mostly in a certain “optimal” region. This
optimum is maintained even if the lateral line nerves are cut, but it is
lost after treatment of the skin with cocaine.
If temperature reception in teleosts is normally mediated by the
general cutaneous innervation, as indeed it is in most other vertebrates
(see, for example, Murray, 1962), then Rubin’s implication of the lateral
line has to be explained. He found that the temperature at which a
gradual warming of the water elicited an escape response in five different
species was raised from about 27°C to over 34°C (in fact to a lethal
level) by cutting both the trunk lateral line nerves (Rubin, 1935).
The first point which can be made is that the response is clearly a
nociceptive one (i.e., “painful”) and does not involve the kind of sensitive thermoreception that is involved in threshold experiments; and
it may well be that excessive activity of all lateral line organs, however
initiated, is a stimulus eliciting escape and there need be no identification
of the stimulus as thermal. Second, the responses were unconditioned,
and in such an experiment there is always the possibility that it is the
responsiveness of the animal which has altered and not the stimulus. The
removal of the tonic effect of the trunk lateral line system might well be
expected to depress the responsiveness of the central nervous system
(CNS), and there was no control showing that escape responses to other
modalities of stimulus were unchanged. There is also a third possibility
(Dijkgraaf, 1940), that detection of convection currents by the lateral line
could have been involved.
A further series of experiments ( Andrews, 1952) which apparently
connect the lateral line with thermoreception can be criticized along the
same lines. A number of species lose their normal light avoidance behavior
when the water gets too hot (the exact level depends on the acclimation
temperature), and this critical level was raised by about 4°C when the
trunk lateral line nerves were cut.
R. W. MURRAY
posterior to a deletion of the spinal cord over 1-2 segments in the region
of the anal fin.
Confirmation of the role of the cutaneous nerves has been provided
by tests in which fish were trained to swim away from a normal resting
position in the center of an experimental tank when touched by a warmed
rod and not to move if the rod was at tank temperature (Bardach, 1956).
When the rod was 2°C warmer than the tank, consistent responses were
obtained from almost the whole of the body surface, including the fins,
and they were not restricted to the region close to the lateral line. A
similar conclusion follows from Sullivan’s records of the behavior of
trout in a temperature gradient (Sullivan, 1954); the rate and extent of
turning and the frequency of moving vary with temperature in such a
way that the fish remain mostly in a certain “optimal” region. This
optimum is maintained even if the lateral line nerves are cut, but it is
lost after treatment of the skin with cocaine.
If temperature reception in teleosts is normally mediated by the
general cutaneous innervation, as indeed it is in most other vertebrates
(see, for example, Murray, 1962), then Rubin’s implication of the lateral
line has to be explained. He found that the temperature at which a
gradual warming of the water elicited an escape response in five different
species was raised from about 27°C to over 34°C (in fact to a lethal
level) by cutting both the trunk lateral line nerves (Rubin, 1935).
The first point which can be made is that the response is clearly a
nociceptive one (i.e., “painful”) and does not involve the kind of sensitive thermoreception that is involved in threshold experiments; and
it may well be that excessive activity of all lateral line organs, however
initiated, is a stimulus eliciting escape and there need be no identification
of the stimulus as thermal. Second, the responses were unconditioned,
and in such an experiment there is always the possibility that it is the
responsiveness of the animal which has altered and not the stimulus. The
removal of the tonic effect of the trunk lateral line system might well be
expected to depress the responsiveness of the central nervous system
(CNS), and there was no control showing that escape responses to other
modalities of stimulus were unchanged. There is also a third possibility
(Dijkgraaf, 1940), that detection of convection currents by the lateral line
could have been involved.
A further series of experiments ( Andrews, 1952) which apparently
connect the lateral line with thermoreception can be criticized along the
same lines. A number of species lose their normal light avoidance behavior
when the water gets too hot (the exact level depends on the acclimation
temperature), and this critical level was raised by about 4°C when the
trunk lateral line nerves were cut.