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Fig. 5. Electrophysiological examination of motor nerve supplies and intracellular
muscle fibre recordings support anatomical and immunocytochemical data. (A)
Extracellular recordings from the nerves supplying M81 (bottom trace) and M59
(middle trace), and intracellular recording from an M59 muscle fibre (top
trace) during spontaneous activity illustrate two major features. First, there
are two classes of IPSPs in M59, with different amplitudes and shapes. Second,
the large-amplitude IPSPs exhibit a 1:1 relationship to spikes in the nerve
supplies of both, M59 and M81 (marked by arrowheads). The small-amplitude
IPSPs are related only to spike activity in the M59 motor nerve. (Bi)
Stimulating the motor nerve to M81 and M82 in a different experiment (N1D;
stimulus artefacts marked by arrow) elicits spikes in N1B (bottom trace) and
small-amplitude IPSPs in a fibre of M59 (top trace). (Bii) Large-amplitude
IPSPs in this same muscle fibre are not stimulus-related but occur in 1:1
relationship to spontaneous spikes, with slightly different shape and
amplitude when compared to those seen in Bi, bottom trace. Four traces each
from the same recording are superimposed in Bi and Bii. (C) Stimulating the
motor nerve to M59 (stimulus artefacts indicated by arrow) elicits
(small-amplitude) IPSPs in fibres of M60. Large-amplitude IPSPs (arrowhead)
occur spontaneously. (D) Simultaneous intracellular recordings from fibres of
M59 (top trace) and M60 (bottom trace) illustrate common inhibitory input. 1:1
relationship of IPSPs in the two muscle fibres is clearly discernible (dotted
lines mark the beginnings of IPSPs in M60), as is the unrelated occurrence of
larger-amplitude IPSPs in M59 (arrowheads; uncorrelated IPSPs were also
observed in M60 in other experiments). Scale bars, 20 mV, 275 ms (A); 10 mV,
32.5 ms (B); 10 mV, 25 ms (C); 20 mV, 250 ms (D).
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