Target neuron specification of short-term synaptic facilitation and depression in the cricket CNS

Abstract

We investigated the role of retrograde signals in the regulation of short‐term synaptic depression and facilitation by characterizing the form of plasticity expressed at novel synapses on four giant interneurons in the cricket cercal sensory system. We induced the formation of novel synapses by transplanting a mesothoracic leg and its associated sensory neurons to the cricket terminal abdominal segment. Axons of ectopic leg sensory neurons regenerated and innervated the host terminal abdominal ganglion forming monosynaptic connections with the medial giant interneuron (MGI), lateral giant interneuron (LGI), and interneurons 7‐1a and 9‐2a. The plasticity expressed by these synapses was characterized by stimulating a sensory neuron with pairs of stimuli at various frequencies or with trains of 10 stimuli delivered at 100 Hz and measuring the change in excitatory postsynaptic potential amplitude recorded in the postsynaptic neuron. Novel synapses of a leg tactile hair on 7‐1a depressed, as did control synapses of cercal sensory neurons on this interneuron. Novel synapses of leg campaniform sensilla (CS) sensory neurons on MGI, like MGI's control synapses, always facilitated. The form of plasticity expressed by novel synapses is thus consistent with that observed at control synapses. Leg CS synapses with 9‐2a also facilitated; however, the plasticity expressed by these sensory neurons is dependent on the identity of the postsynaptic cell since the synapses these same sensory neurons formed with LGI always depressed. We conclude that the form of plasticity expressed at these synaptic connections is determined retrogradely by the postsynaptic cell. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 700–714, 1998

Auditory change detection by a single neuron in an insect

“…It is possible that the synaptic transmission properties of the receptor cells’ are influenced by the post-synaptic neuron; one receptor cell could form synapses with one interneuron that reliably transmit the repeated signal for extended periods, while synapses with another interneuron show simultaneously synaptic depression (Killian and Murphey 1998). However, such a situation seems unlikely in TN-1.…”

Dendritic calcium accumulation regulates wind sensitivity via short-term depression at cercal sensory-to-giant interneuron synapses in the cricket

“…Facilitation and depression at the cercal-to-giant synapses have been observed when paired-pulse stimulation or pulse train at over 100 Hz was applied (Davis and Murphey, 1993;Killian and Murphey, 1998). A quantal analysis of transmission at these synapses has demonstrated that this facilitation and depression are presynaptically regulated.…”

“…It is improbable that dendritic Ca 2ϩ elevation contributes to the Ca 2ϩ spike initiation in the GIs, because the time course of the [Ca 2ϩ ] i change induced by action potentials is much slower than that of the membrane potential change (Ogawa et al, 2000). On the other hand, synaptic depression and facilitation were found at the synapses between cercal sensory interneurons and GI (cercal-to-giant synapses) in the cricket (Davis and Murphey, 1993;Hill and Jin, 1998;Killian and Murphey, 1998). We presupposed that the dendritic Ca 2ϩ would be used as a second messenger for induction of the synaptic plasticity in the GI.…”