D. Cattaert et al., Presynaptic inhibition and antidromic spikes in primary afferents of the crayfish: A computational and experimental analysis, J NEUROSC, 21(3), 2001, pp. 1007-1021
Primary afferent depolarizations (PADs) are associated with presynaptic inh
ibition and antidromic discharges in both vertebrates and invertebrates. In
the present study, we have elaborated a realistic compartment model of a p
rimary afferent from the coxobasipodite chordotonal organ of the crayfish b
ased on anatomical and electrophysiological data. The model was used to tes
t the validity of shunting and sodium channel inactivation hypotheses to ac
count for presynaptic inhibition. Previous studies had demonstrated that GA
BA activates chloride channels located on the main branch close to the firs
t branching point. We therefore focused the analysis on the effect of GABA
synapses on the propagation of action potentials in the first axonal branch
. Given the large diameters of the sensory axons in the region in which PAD
s were likely to be produced and recorded, the model indicates that a relat
ively large increase in chloride conductance (up to 300 nS) is needed to si
gnificantly reduce the amplitude of sensory spikes. The role of the spatial
organization of GABA synapses in the sensory arborization was analyzed, de
monstrating that the most effective location for GABA synapses is in the ar
ea of transition from active to passive conduction. This transition is like
ly to occur on the main branch a few hundred micrometers distal to the firs
t branching point. As a result of this spatial organization, antidromic spi
kes generated by large-amplitude PADs are prevented from propagating distal
ly.