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Fig. 5. Amine modulation of command-like neurons known to activate or inhibit
swimming. Bath application of a mixture of 5-HT and OA (50 µmol
l–1) caused the inhibition of cell Tr1
(Brodfuehrer and Friesen,
1986b) and SIN1 (Brodfuehrer
and Burns, 1995). (A) During perfusion of a saline baseline
(left), swim-trigger neuron Tr1 fired a train of action potentials just before
a swim episode (see swim motor neuron bursts in the DP nerve extracellular
recording). After a 30-min application of the 5-HT/OA mixture (middle), Tr1
became hyperpolarized (5 mV) and fired no action potentials. Furthermore, Tr1
appeared to receive less synaptic activity (i.e. fewer small and rapid
fluctuations in membrane potential) following mixture application. During
washout of the mixture (with saline, right), Tr1 partially repolarized and
synaptic inputs to Tr1 resumed. Tr1 spiked once preceding the onset of a swim
bout. (B) During perfusion of a saline baseline (left), swim-inhibitory neuron
SIN1 fired action potentials at a constant rate. After a 30-min application of
the mixture (middle), the membrane potential of SIN1 became inhibited (18 mV),
and large, rhythmic inhibitory inputs were observed. During washout of the
mixture (right), SIN1 partially repolarized and rhythmic membrane potential
fluctuations were phase-locked with swim-motor bursts in the DP nerve.
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