9. THE MAUTHNER CELL
343
Clearly the depth of the fish might be an important consideration and
could perhaps influence the production of startle-responses to stimuli
associated with aquatic predators. More experiments are needed on
these important points.
(4) The type of muscle activated in the Mauthner reflex is not
known. It would certainly be of interest to have information on this and
also on how the same muscles could be activated in other, non-Mauthner
reflex activity (see Hudson, 1968). In addition the behavior and sources
of activation of fin muscles is largely unknown, certainly in relation to
startle-responses [except in the case of thc pectoral fins in the hatchetfish, see ( 1 ) above]. Comparative studies would be of great value here.
(5) It has been suggested that in any one animal there could be
differences in the size and shape of the two Mauthner neurons and
their axons (Moulton and Barron, 1967). This, of course, would be
very useful in helping to bring about a time difference in the initiation
of the Mauthner impulses and in their speed of conduction in the cord.
However, without statistical information the variability of such histological appearances in fixed tissues can hardly be adduced as good
evidence for true anatomical differences in the living animal. Physiologically, as we have said, no differences are usually found between the
two neurons or their axons. This point does however deserve further
study.
( 6 ) The morphology of the inputs to the Mauthner cells and their
distribution on the cell soma and dendrites varies in different species
( cf. Otsuka, 1962, 1964). Here there may be further clues as to functional
characteristics. Again a comparative analysis of the startle-responses of
different. fish and their correlation with the morphological features
relating to the Mauthner cells might give more understanding of the
whole of the Mauthner cell system and the reflex with which it is
concerned.
There are numerous other questions which we have raised in this
chapter and other investigations in which the Mauthner cells may be
(and have already been) of great value. We may mention here their usefulness in quantitative studies on synaptic pharmacology (Roper et d.,
1969). Developmental studies, too, may be more conveniently carried
out on the larger Mauthner neurons and their axons than on most
other central neurons (Stefanelli, 1951; Hibbard, 1965; Moulton et d.,
1968; Piatt, 1969), as may chemical investigations (Edstrom and
Sjostrand, 1969).
Clearly there is an important future for the Mauthner cells as the
neurons of choice in vertebrate central nervous systems, especially when
the investigation requires the ability to distinguish between somatic
and dendritic regions (Diamond, 1968); we can expect these cells to
343
Clearly the depth of the fish might be an important consideration and
could perhaps influence the production of startle-responses to stimuli
associated with aquatic predators. More experiments are needed on
these important points.
(4) The type of muscle activated in the Mauthner reflex is not
known. It would certainly be of interest to have information on this and
also on how the same muscles could be activated in other, non-Mauthner
reflex activity (see Hudson, 1968). In addition the behavior and sources
of activation of fin muscles is largely unknown, certainly in relation to
startle-responses [except in the case of thc pectoral fins in the hatchetfish, see ( 1 ) above]. Comparative studies would be of great value here.
(5) It has been suggested that in any one animal there could be
differences in the size and shape of the two Mauthner neurons and
their axons (Moulton and Barron, 1967). This, of course, would be
very useful in helping to bring about a time difference in the initiation
of the Mauthner impulses and in their speed of conduction in the cord.
However, without statistical information the variability of such histological appearances in fixed tissues can hardly be adduced as good
evidence for true anatomical differences in the living animal. Physiologically, as we have said, no differences are usually found between the
two neurons or their axons. This point does however deserve further
study.
( 6 ) The morphology of the inputs to the Mauthner cells and their
distribution on the cell soma and dendrites varies in different species
( cf. Otsuka, 1962, 1964). Here there may be further clues as to functional
characteristics. Again a comparative analysis of the startle-responses of
different. fish and their correlation with the morphological features
relating to the Mauthner cells might give more understanding of the
whole of the Mauthner cell system and the reflex with which it is
concerned.
There are numerous other questions which we have raised in this
chapter and other investigations in which the Mauthner cells may be
(and have already been) of great value. We may mention here their usefulness in quantitative studies on synaptic pharmacology (Roper et d.,
1969). Developmental studies, too, may be more conveniently carried
out on the larger Mauthner neurons and their axons than on most
other central neurons (Stefanelli, 1951; Hibbard, 1965; Moulton et d.,
1968; Piatt, 1969), as may chemical investigations (Edstrom and
Sjostrand, 1969).
Clearly there is an important future for the Mauthner cells as the
neurons of choice in vertebrate central nervous systems, especially when
the investigation requires the ability to distinguish between somatic
and dendritic regions (Diamond, 1968); we can expect these cells to