A. Buschges et H. Wolf, Phase-dependent presynaptic modulation of mechanosensory signals in the locust flight system, J NEUROPHYS, 81(2), 1999, pp. 959-962
In the locust flight system, afferents of a wing hinge mechanoreceptor, the
hindwing tegula, make monosynaptic excitatory connections with motoneurons
of the elevator muscles. During flight motor activity, the excitatory post
synaptic potentials (EPSPs) produced by these connections changed in amplit
ude with the phase of the wingbeat cycle. The largest changes occurred arou
nd the phase where elevator motoneurons passed through their minimum membra
ne potential. This phase-dependent modulation was neither due to flight-rel
ated oscillations in motoneuron membrane potential nor to changes in motone
uron input resistance. This indicates that modulation of EPSP amplitude is
mediated by presynaptic mechanisms that affect the efficacy of afferent syn
aptic input. Primary afferent depolarizations (PADs) were recorded in the t
erminal arborizations of tegula afferents, presynaptic to elevator motoneur
ons in the same hemiganglion. PADs were attributed to presynaptic inhibitor
y input because they reduced the input resistance of the afferents and were
sensitive to the gamma-aminobutyric acid antagonist picrotoxin. PADs occur
red either spontaneously or were elicited by spike activity in the tegula a
fferents. In summary, afferent signaling in the locust flight system appear
s to be under presynaptic control, a candidate mechanism of which is presyn
aptic inhibition.