M. V. L. BENNETT
460
is measured in grams rather than kilograms. When macromolecules of
excitable membranes are to be isolated, electric organs are probably a
good place to start. The ability to choose by choice of organ the type of
excitability present in terms of PSP or spike generating membrane may
be helpful in the future isolation procedures.
The electric organ of Torpedo is now being used for the isolation of
vesicles containing acetylcholine (Israel et al., 1968). Electric organs
seem to be much better tissues than guinea pig brain in which to look
for vesicles containing acetylcholine when only a very small fraction of
interneuronal synapses can involve this transmitter. Another probably
useful tissue for vesicle isolation is the electromotor lobe of the Torpedo
brain. Available evidence indicates that synapses on the electromotor
neurons are chemically transmitting, but the transmitter is unlikely to be
acetylcholine (see Section 111, B ) . The electromotor lobes provide a
tissue sample of up to a gram of what appear to be neurons of a single
type with a single class of synaptic ending on them. While the weight of
tissue is small compared to the kilograms of electric organ, the size is
very large compared to other neuronal groups of comparable
homogeneity.
111. NEURAL CONTROL OF ELECTRIC ORGANS
For most electric fish it is of considerable importance that the firing
of individual electrocytes be synchronous. Synchrony leads to an output
that is larger in terms of both voltage and power because inactive cells
act as a shunt or series resistance and thus reduce the amount of current
that active cells produce outside the fish. When the discharge is diphasic
or triphasic, synchronization is particularly important because slightly
out of phase addition leads to cancellation. As has been seen in the
section on electrocyte activity, organ discharge generally involves one
highly synchronized response of each cell. Only weakly electric organs of
marine fish appear to have discharges that involve fused and repetitive
activity of the electrocytes.
There is another fundamental consideration in control of organ discharge; namely, that two spike generating membranes arranged in series
tend to desynchronize each other’s activity. Inward current generated by
one excitable membrane tends to hyperpolarize the corresponding membrane of the next cell in series with it and thus prevent its firing (see
Fig. 2). To achieve synchronous activity each cell in series must be
separately innervated and its discharge controlled centrally. Of course,
cell membranes in parallel may tend to excite one another as an action
460
is measured in grams rather than kilograms. When macromolecules of
excitable membranes are to be isolated, electric organs are probably a
good place to start. The ability to choose by choice of organ the type of
excitability present in terms of PSP or spike generating membrane may
be helpful in the future isolation procedures.
The electric organ of Torpedo is now being used for the isolation of
vesicles containing acetylcholine (Israel et al., 1968). Electric organs
seem to be much better tissues than guinea pig brain in which to look
for vesicles containing acetylcholine when only a very small fraction of
interneuronal synapses can involve this transmitter. Another probably
useful tissue for vesicle isolation is the electromotor lobe of the Torpedo
brain. Available evidence indicates that synapses on the electromotor
neurons are chemically transmitting, but the transmitter is unlikely to be
acetylcholine (see Section 111, B ) . The electromotor lobes provide a
tissue sample of up to a gram of what appear to be neurons of a single
type with a single class of synaptic ending on them. While the weight of
tissue is small compared to the kilograms of electric organ, the size is
very large compared to other neuronal groups of comparable
homogeneity.
111. NEURAL CONTROL OF ELECTRIC ORGANS
For most electric fish it is of considerable importance that the firing
of individual electrocytes be synchronous. Synchrony leads to an output
that is larger in terms of both voltage and power because inactive cells
act as a shunt or series resistance and thus reduce the amount of current
that active cells produce outside the fish. When the discharge is diphasic
or triphasic, synchronization is particularly important because slightly
out of phase addition leads to cancellation. As has been seen in the
section on electrocyte activity, organ discharge generally involves one
highly synchronized response of each cell. Only weakly electric organs of
marine fish appear to have discharges that involve fused and repetitive
activity of the electrocytes.
There is another fundamental consideration in control of organ discharge; namely, that two spike generating membranes arranged in series
tend to desynchronize each other’s activity. Inward current generated by
one excitable membrane tends to hyperpolarize the corresponding membrane of the next cell in series with it and thus prevent its firing (see
Fig. 2). To achieve synchronous activity each cell in series must be
separately innervated and its discharge controlled centrally. Of course,
cell membranes in parallel may tend to excite one another as an action