316
J. DIAMOND
1
Fig. 32. Responses recorded in Mauthner cell following stimulation of the
ipsilateral VIIIth nerve. ( A ) Electrode in cell body. Superimposed traces made
at various stimulation intensities. Note spike firing from early e.p.s.p. The later
e.p.s.p.’s seen as delayed hump( s ) in subthreshold traces. Calibrations: vertical,
10.0 mV; horizontal, 0.5 msec. From Furshpan (1964). ( B ) Electrode in lateral
dendrite, 325 p from axon hillock. Stimulus intensity near threshold for excitation
of Mauthner cell spike. The latter fires from the second e.p.s.p; since this was
smaller than the first, the spike must have been generated at a distant point (i.e,,
the initial segment of the Mauthner axon) where the first e.p.s.p. was smaller than
the second. This means that the first e.p.s.p. mainly resulted from synaptic activity
near the recording electrode in the lateral dendrite. Calibrations: vertical, 5 mV;
horizontal, 1 msec. From Diamond ( 1968).
ipsilateral Mauthner cell, and the evidence now indicates that their
synapses are electrically transmitting (Furshpan, 1964). Figure 32 shows
responses recorded intracellularly from two different Mauthner cells
when their ipsilateral VIIIth nerves were excited directly by stimulating
electrodes. Quite often in such experiments there are at least two phases
of e.p.s.p., and the Mauthner impulse can arise from either of these,
e.g., the first in Fig. 32A but the second in Fig. 32B. The earliest e.p.s.p.
can have a synaptic delay which is almost immeasurably brief. Figure 33
shows evidence that this early e.p.s.p. results from the excitation of
VIIIth nerve fibers synapsing directly on the lateral dendrite (see also
Fig. 32B and legend) and that the synaptic transmission is electrical
in nature. The early e.p.s.p. is very similar in time course to the impulse
recorded directly by an electrode inside an VIIIth nerve fiber itself. The
fastest conducting fibers, presumably the large myelinated ones forming the club endings, have a relatively low resistance coupling to the
lateral dendrite since an electrical signal in the dendrite is detectable in
J. DIAMOND
1
Fig. 32. Responses recorded in Mauthner cell following stimulation of the
ipsilateral VIIIth nerve. ( A ) Electrode in cell body. Superimposed traces made
at various stimulation intensities. Note spike firing from early e.p.s.p. The later
e.p.s.p.’s seen as delayed hump( s ) in subthreshold traces. Calibrations: vertical,
10.0 mV; horizontal, 0.5 msec. From Furshpan (1964). ( B ) Electrode in lateral
dendrite, 325 p from axon hillock. Stimulus intensity near threshold for excitation
of Mauthner cell spike. The latter fires from the second e.p.s.p; since this was
smaller than the first, the spike must have been generated at a distant point (i.e,,
the initial segment of the Mauthner axon) where the first e.p.s.p. was smaller than
the second. This means that the first e.p.s.p. mainly resulted from synaptic activity
near the recording electrode in the lateral dendrite. Calibrations: vertical, 5 mV;
horizontal, 1 msec. From Diamond ( 1968).
ipsilateral Mauthner cell, and the evidence now indicates that their
synapses are electrically transmitting (Furshpan, 1964). Figure 32 shows
responses recorded intracellularly from two different Mauthner cells
when their ipsilateral VIIIth nerves were excited directly by stimulating
electrodes. Quite often in such experiments there are at least two phases
of e.p.s.p., and the Mauthner impulse can arise from either of these,
e.g., the first in Fig. 32A but the second in Fig. 32B. The earliest e.p.s.p.
can have a synaptic delay which is almost immeasurably brief. Figure 33
shows evidence that this early e.p.s.p. results from the excitation of
VIIIth nerve fibers synapsing directly on the lateral dendrite (see also
Fig. 32B and legend) and that the synaptic transmission is electrical
in nature. The early e.p.s.p. is very similar in time course to the impulse
recorded directly by an electrode inside an VIIIth nerve fiber itself. The
fastest conducting fibers, presumably the large myelinated ones forming the club endings, have a relatively low resistance coupling to the
lateral dendrite since an electrical signal in the dendrite is detectable in