342
J. DIAMOND
nerve inhibition, electrical and chemical, will reinforce on the contralateral cell any collateral inhibition coincidently activated. Nature
seems to have accepted the numerous possibilities of closely timed reexcitation of the Mauthner neurons, particularly by vibrational stimuli,
as a genuine hazard to the fish. The minimization of this hazard reinforces our view that the Mauthner reflex is prepotent and suggests that
the initiation of escape swimming after a startle-response (Section IX, C )
could be more valuable to the fish than the reexcitation of the Mauthner
reflex with its effective preclusion of coordinated swimming movements.
E. Functions in Different Species : Unanswered Questions
(1) As indicated in the introduction to this chapter, Mauthner cell
functions probably vary from one animal type to another. In this context,
it is interesting to note that in the hatchetfish (Gasteropelecus) other
giant nerve fibers intervene between the Mauthner axons and the motoneurons, and the reflex response to tapping the aquarium is a jump of
the fish into the air, achieved by the simultaneous contraction of pectoral
fin musculature on both sides and axial musculature on one side (Auerbach and Bennett, 1969a,b). Surprisingly, no spinal crossing inhibition
was reported. In this fish, too, a phenomenon analogous to that of
“fatigue” ( described above) was observed. The Mauthner axons excite
the giant axons chemically, and they in turn excite the motoneurons
electrically (here there was good evidence of the excitation of motoneurons by other motoneurons resulting from electrotonic coupling between
them). In the hatchetfish therefore the giant (non-Mauthner) axons
are analogous to the A1 units we have described. Comparative studies
on a variety of different animals will undoubtedly show that the Mauthner cells and those that they act upon can vary in their functions (cf.
Rovainen, 1967), and such studies will clarify the whole problem of
the role of Mauthner cells in general.
( 2 ) Certainly one important type of evidence lacking at present
is a full kinematic analysis of startle-responses with simultaneous recordings from the Mauthner cells themselves rather than the recording of
inadequately defined reflex movements or electrical potentials in the cord
or muscles ( cf. Berkowitz, 1956; Wilson, 1959).
( 3 ) The linkage of the swim bladder to vestibular systems, already
referred to, could provide more than simply a means of transmission of
mechanical stimuli originating in the environment. The results of Furukawa and Ishii (198713) suggest that possibly hearing sensitivity could
be influenced, or even controlled, by changing the abdominal pressure.
J. DIAMOND
nerve inhibition, electrical and chemical, will reinforce on the contralateral cell any collateral inhibition coincidently activated. Nature
seems to have accepted the numerous possibilities of closely timed reexcitation of the Mauthner neurons, particularly by vibrational stimuli,
as a genuine hazard to the fish. The minimization of this hazard reinforces our view that the Mauthner reflex is prepotent and suggests that
the initiation of escape swimming after a startle-response (Section IX, C )
could be more valuable to the fish than the reexcitation of the Mauthner
reflex with its effective preclusion of coordinated swimming movements.
E. Functions in Different Species : Unanswered Questions
(1) As indicated in the introduction to this chapter, Mauthner cell
functions probably vary from one animal type to another. In this context,
it is interesting to note that in the hatchetfish (Gasteropelecus) other
giant nerve fibers intervene between the Mauthner axons and the motoneurons, and the reflex response to tapping the aquarium is a jump of
the fish into the air, achieved by the simultaneous contraction of pectoral
fin musculature on both sides and axial musculature on one side (Auerbach and Bennett, 1969a,b). Surprisingly, no spinal crossing inhibition
was reported. In this fish, too, a phenomenon analogous to that of
“fatigue” ( described above) was observed. The Mauthner axons excite
the giant axons chemically, and they in turn excite the motoneurons
electrically (here there was good evidence of the excitation of motoneurons by other motoneurons resulting from electrotonic coupling between
them). In the hatchetfish therefore the giant (non-Mauthner) axons
are analogous to the A1 units we have described. Comparative studies
on a variety of different animals will undoubtedly show that the Mauthner cells and those that they act upon can vary in their functions (cf.
Rovainen, 1967), and such studies will clarify the whole problem of
the role of Mauthner cells in general.
( 2 ) Certainly one important type of evidence lacking at present
is a full kinematic analysis of startle-responses with simultaneous recordings from the Mauthner cells themselves rather than the recording of
inadequately defined reflex movements or electrical potentials in the cord
or muscles ( cf. Berkowitz, 1956; Wilson, 1959).
( 3 ) The linkage of the swim bladder to vestibular systems, already
referred to, could provide more than simply a means of transmission of
mechanical stimuli originating in the environment. The results of Furukawa and Ishii (198713) suggest that possibly hearing sensitivity could
be influenced, or even controlled, by changing the abdominal pressure.