10. ELECTRIC ORGANS
373
respect to Astroscopus (Fig. 7). The responses of the electrocytes of
Torpedo are essentially the same as in Astroscopus (Bennett et d., 1961).
The active face is the innervated face, which however is on the ventral
side. Again, this face does not respond to depolarization; it is electrically
inexcitable. The response that is evoked by external stimulation is a
monophasic depolarization, that is, a PSP mediated by activity of the
presynaptic fibers. Its origin as a neurally mediated response is attested
to by the irreducible delay when stimulating with closely applied electrodes and by the block of the response when curare is applied to the
innervated face. In a column of tissue the response can be inverted
by polarizing currents [the first tissue in which PSPs were shown to
invert ( Albe-Fessard, 1951; Bennett et al., 196l)l. The uninnervated
face is of very low resistance and generates only a resting potential.
The area of this face is greatly increased by numerous invaginating
canaliculi ( Fig. 10).
The maximum response amplitude observed in a single cell is about
90 mV, which is somewhat larger than the recorded resting potentials.
However, the cells are very thin and the canaliculi extend across at
least half the cell thickness; a supposedly intracellular electrode might
always be partly in the extracellular space outside the uninnervated
face. Probably the full resting potentials are not recorded and like other
PSPs those in Torpedo do not overshoot the resting potential. The duration of the PSPs is about 5 msec. Their latency with locally applied
stimuli is 2-3 msec, an appreciable fraction of which may be conduction
time in fine branches of the innervating fibers.
The PSPs in Torpedo electrocytes are cholinergic in that they are
blocked by curare and dihydro-P-erythroidine and prolonged by the
cholinesterase inhibitors eserine and physostigmine. Also, the cells are
depolarized by actylcholine and carbamylcholine.
The synthesis of organ discharge from the responses of the single
electrocytes simply requires synchronous activation as in Astroscopus.
The duration of the PSPs is about the same as that of the organ discharge, and the amplitude of the PSPs is sufficient that the number of
cells in series could produce the discharge amplitude.
Narcine is a smaller relative of Torpedo. It has a bilateral electric
organ, the “main” organ, that resembles that of Torpedo both morphologically and physiologically ( Bennett and Grundfest, 1961a). Nurcine
has an additional (bilateral) electric organ, the accessory organ, that
lies at the posterior margin of the main organ (Mathewson et al., 1958).
This organ differs in one important respect from the main organ. The
responses to low frequency stimuli are very small, but when the nerve
is stimulated at up to 100/sec, the responses are considerably augmented
373
respect to Astroscopus (Fig. 7). The responses of the electrocytes of
Torpedo are essentially the same as in Astroscopus (Bennett et d., 1961).
The active face is the innervated face, which however is on the ventral
side. Again, this face does not respond to depolarization; it is electrically
inexcitable. The response that is evoked by external stimulation is a
monophasic depolarization, that is, a PSP mediated by activity of the
presynaptic fibers. Its origin as a neurally mediated response is attested
to by the irreducible delay when stimulating with closely applied electrodes and by the block of the response when curare is applied to the
innervated face. In a column of tissue the response can be inverted
by polarizing currents [the first tissue in which PSPs were shown to
invert ( Albe-Fessard, 1951; Bennett et al., 196l)l. The uninnervated
face is of very low resistance and generates only a resting potential.
The area of this face is greatly increased by numerous invaginating
canaliculi ( Fig. 10).
The maximum response amplitude observed in a single cell is about
90 mV, which is somewhat larger than the recorded resting potentials.
However, the cells are very thin and the canaliculi extend across at
least half the cell thickness; a supposedly intracellular electrode might
always be partly in the extracellular space outside the uninnervated
face. Probably the full resting potentials are not recorded and like other
PSPs those in Torpedo do not overshoot the resting potential. The duration of the PSPs is about 5 msec. Their latency with locally applied
stimuli is 2-3 msec, an appreciable fraction of which may be conduction
time in fine branches of the innervating fibers.
The PSPs in Torpedo electrocytes are cholinergic in that they are
blocked by curare and dihydro-P-erythroidine and prolonged by the
cholinesterase inhibitors eserine and physostigmine. Also, the cells are
depolarized by actylcholine and carbamylcholine.
The synthesis of organ discharge from the responses of the single
electrocytes simply requires synchronous activation as in Astroscopus.
The duration of the PSPs is about the same as that of the organ discharge, and the amplitude of the PSPs is sufficient that the number of
cells in series could produce the discharge amplitude.
Narcine is a smaller relative of Torpedo. It has a bilateral electric
organ, the “main” organ, that resembles that of Torpedo both morphologically and physiologically ( Bennett and Grundfest, 1961a). Nurcine
has an additional (bilateral) electric organ, the accessory organ, that
lies at the posterior margin of the main organ (Mathewson et al., 1958).
This organ differs in one important respect from the main organ. The
responses to low frequency stimuli are very small, but when the nerve
is stimulated at up to 100/sec, the responses are considerably augmented