M. V. L. BENNETT
540
required are large, but the data are nevertheless suggestive of glutaminergic transmission.
D. Phasic Receptors in Gymnarchus
Two types of tuberous receptor are found in Gymnarchus. These may
correspond to large and medium receptors of mormyrids, but they have
not yet been adequately studied physiologically. In each receptor type
there is the peculiarity that the receptor cavity invaginates into the receptor cell. However, numerous microvilli increase the lumenal surface far
beyond that of the other surface (Mullinger, 1969), and action of the
lumenal face as a blocking capacity is not unreasonable. One type of
tuberous receptor (Szabo’s type B, Szabo, 1965) contains a single receptor cell but occurs in clusters innervated by a single fiber. The other kind
(Szabo’s type C) contains one large and one small receptor cell innervated by the same fiber, which may also innervate several neighboring
receptors of the same kind. It is tempting to homologize the latter receptors with the medium receptors of mormyrids (Szabo’s type B) because of the presence of two kinds of receptor cell. However, this type
of receptor is supposed to generate the spontaneous potentials on the skin
that resemble the potentials external to large receptors of mormyrids
( Szabo, 1962). The correspondence between receptor types in mormyrids
and Gymnarchus requires further study.
E. Amplification and Oscillation at Phasic Receptors
The external responses at phasic receptors of gymnotids show an interesting correlation with the organ discharge of the particular species.
The period of evoked oscillations at the receptors is similar to the duration
of each organ discharge (Bennett, 1967). The correlation holds whether
organ pulses are emitted at high or low frequency. The responsiveness
of the receptors appears to represent tuned amplification of the main
frequency components present in the discharge. Most phasic receptors
in the eel appear not to have regenerative electrical responses (Bennett,
1967). Perhaps the large voltages produced by even the weakly electric
organ do not require the amplification present in phasic receptor cells of
other gymnotids.
Given a regenerative responsiveness like that of phasic receptor cells,
it would not be surprising if maintained oscillations could be obtained
under suitable conditions. In fact, in a number of gymnotids, phasic re-
540
required are large, but the data are nevertheless suggestive of glutaminergic transmission.
D. Phasic Receptors in Gymnarchus
Two types of tuberous receptor are found in Gymnarchus. These may
correspond to large and medium receptors of mormyrids, but they have
not yet been adequately studied physiologically. In each receptor type
there is the peculiarity that the receptor cavity invaginates into the receptor cell. However, numerous microvilli increase the lumenal surface far
beyond that of the other surface (Mullinger, 1969), and action of the
lumenal face as a blocking capacity is not unreasonable. One type of
tuberous receptor (Szabo’s type B, Szabo, 1965) contains a single receptor cell but occurs in clusters innervated by a single fiber. The other kind
(Szabo’s type C) contains one large and one small receptor cell innervated by the same fiber, which may also innervate several neighboring
receptors of the same kind. It is tempting to homologize the latter receptors with the medium receptors of mormyrids (Szabo’s type B) because of the presence of two kinds of receptor cell. However, this type
of receptor is supposed to generate the spontaneous potentials on the skin
that resemble the potentials external to large receptors of mormyrids
( Szabo, 1962). The correspondence between receptor types in mormyrids
and Gymnarchus requires further study.
E. Amplification and Oscillation at Phasic Receptors
The external responses at phasic receptors of gymnotids show an interesting correlation with the organ discharge of the particular species.
The period of evoked oscillations at the receptors is similar to the duration
of each organ discharge (Bennett, 1967). The correlation holds whether
organ pulses are emitted at high or low frequency. The responsiveness
of the receptors appears to represent tuned amplification of the main
frequency components present in the discharge. Most phasic receptors
in the eel appear not to have regenerative electrical responses (Bennett,
1967). Perhaps the large voltages produced by even the weakly electric
organ do not require the amplification present in phasic receptor cells of
other gymnotids.
Given a regenerative responsiveness like that of phasic receptor cells,
it would not be surprising if maintained oscillations could be obtained
under suitable conditions. In fact, in a number of gymnotids, phasic re-