Inhibitory interactions between motoneurone terminals in neonatal rat lumbrical muscle.

Abstract

SUMMARY1. Evoked synaptic potentials and currents were recorded in neonatal rat fourth deep lumbrical muscle during the period of polyneuronal innervation. Signs of inhibitory interactions between converging mononeurone terminals were detected.2. Muscle fibres innervated bv axons from the lateral plantar nerve (LPN) and from the sural nerve (SN) were studied. In unblocked preparations the muscle contracted, and electrode tips were mounted on flexible wires to prevent loss of impalements.3. In voltage recordings from unblocked preparations, paired two-shock stimulation of one nerve revealed synaptic depression: the second response was smaller than the first. XVhen the two stimuli were delivered to different nerves (SN and LPN), the second response was smaller than its own control. 4 5. The inhibition was not constant during the tail of the test end-plate current (EPC). Instead, it declined during the EPC tail, suggesting that the mechanism of inhibition was active, though diminishing, throughout the time course of the test EPC.6. The amount of inhibition was not noticeably affected by altering the muscle membrane potential (two cells studied).7. Treatment with curare or a-bungarotoxin to block most ACh receptors reduced the inhibition. In about half of the fibres studied, no inhibition was evident: in the others, up to 50% inhibition was observed. The average inhibition for all receptorblocked fibres was about 15 %.8. In six a-bungarotoxin-treated cells. multiple conditioning stimuli were t To whom all correspondence should be addressedl.II1Is5 7i

Co‐regulation of synaptic efficacy at stable polyneuronally innervated neuromuscular junctions in reinnervated rat muscle

“…4D). The physiological occlusion of the convergent inputs, similar to that reported in neonatal muscles by Betz et al (1989) A, EPP amplitudes corrected for non-linear summation plotted against nerve terminal area for LPN (1) and SN (0). The two measures are expressed as a percentage of the arithmetic sum of the EPP amplitudes and terminal areas, respectively.…”

Hebbian Mechanisms Revealed by Electrical Stimulation at Developing Rat Neuromuscular Junctions

“…This so-called "heterosynaptic suppression" does not occur if the two neurons are tetanized synchronously. Similar acute effects have been shown in multiply innervated fibers of adult rat muscle (Betz et al, 1989). However, the relationship of these immediate effects with the much slower developmental process of synapse elimination is not known.…”

Spike timing plays a key role in synapse elimination at the neuromuscular junction

“…5C, Inset shows that the two EPPs occluded one another, as reported for polyneuronal innervation of developing (38) and reinnervated adult (34) mammalian NMJs. Furthermore, it is known that occlusion is associated with intimate contact (38) and intermingling (34) between terminals, although the underlying mechanism remains speculative. Interestingly, the occlusion of the EPPs in the asynchronously activated both-nerves fields was significantly smaller than that in the synchronously activated fields (Fig.…”