Central inhibition of lateral line input in the medulla of the goldfish by neurones which control active body movements

Abstract

1. Recordings were made from efferent neurones in the posterior lateral line nerve, and from second order afferent neurones in the lateral line lobe of the medulla, in goldfish during gross stimulation of the spinal cord and selective stimulation of neurones in the medulla (including the Mauthner cells), which control active body movements. 2. Brief bursts of 2–4 compound efferent action potentials were recorded from the proximal stump of the transected posterior lateral line nerve after a latency of 6–9 ms whenever either Mauthner neurone was excited, either antidromically by spinal cord stimulation, or by depolarizing current pulses injected into the Mauthner neurones through intracellular recording electrodes (Figs. 2 and 3). 3. Other large neurones in the medulla, which were antidromically excited by spinal cord stimulation, also evoked efferent impulses in the lateral line nerves when they were selectively excited by the injection of depolarizing current pulses through the intracellular recording electrodes. Some of these neurones were injected with Procion yellow and identified as vestibular spinal and reticular spinal neurones. 4. Latency measurements indicate that the lateral line efferent neurones are not electrically coupled to the vestibular and reticular spinal neurones. 5. Spontaneous activity, and impulses evoked in second order afferent neurones in the lateral line lobe through mechanical stimulation of their sensory fields, or electrical stimulation of the posterior lateral line nerve, were inhibited for at least 40 ms after a latency of 10–12 ms following stimulation of either Mauthner cell. IPSPs with similar latency and duration and 4–6 mV in amplitude were recorded intracellularly from the second order afferent neurones. The duration of the inhibition coincides with the rapid phase of the “tail flip” elicited by Mauthner cell stimulation. 6. Primitive Purkinje-like neurones in the crista cerebralis, which are also excited by lateral line stimulation, are not inhibited by Mauthner cell stimulation. 7. Second order afferent neurones adapt to prolonged and/or excessive mechanical stimulation. If stimulation of the Mauthner cells is timed so that the responses of second order neurones to the first few cycles of phasic mechanical stimulation of their sensory fields are inhibited, then the adaptation, which is usually associated with the responses of the neurones to later phases of mechanical stimulation, is reduced.