TARGET NEURON SPECIFICATION OF SHORT-TERM SYNAPTIC FACILITATION AND DEPRESSION IN THE CRICKET CNS

We investigated the role of retrograde signals in the regulation of sh ort-term synaptic depression and facilitation by characterizing the fo rm of plasticity expressed at novel synapses on four giant interneuron s in the cricket cereal sensory system, We induced the formation of no vel synapses by transplanting a mesothoracic leg and its associated se nsory neurons to the cricket terminal abdominal segment. Axons of ecto pic leg sensory neurons regenerated and innervated the host terminal a bdominal ganglion forming monosynaptic connections with the medial gia nt interneuron (MGI), lateral giant interneuron (LGI), and interneuron s 7-1a and 9-2a, The plasticity expressed by these synapses was charac terized by stimulating a sensory neuron with pairs of stimuli at vario us frequencies or with trains of 10 stimuli delivered at 100 Hz and me asuring the change in excitatory postsynaptic potential amplitude reco rded in the postsynaptic neuron. Novel synapses of a leg tactile hair on 7-1a depressed, as did control synapses of cereal sensory neurons o n this interneuron, Novel synapses of leg campaniform sensilla (CS) se nsory 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 als o facilitated; however, the plasticity expressed by these sensory neur ons is dependent on the identity of the postsynaptic cell since the sy napses these same sensory neurons formed with LGI always depressed. We conclude that the form of plasticity expressed at these synaptic conn ections is determined retrogradely by the postsynaptic cell. (C) 1998 John Wiley & Sons, Inc.