RAPID COMMUNICATION Convergent Chemical and Electrical Synaptic Inputs From Proprioceptive Afferents Onto an Identified Intersegmental

Convergent chemical and electrical synaptic inputs from proprio- that excite LG, however, are chemically mediated and de-ceptive afferents onto an identified intersegmental interneuron in pression prone, but protected from this depression to some the crayfish. J. Neurophysiol. 77: 2826–2830, 1997. Synaptic extent by presynaptic inhibitory pathways (Kennedy et al. transmission between proprioceptive afferents from a chordotonal 1974; Kirk and Wine 1984; Newland et al. 1996). These organ in the tailfan of the crayfish and an identified ascending intersegmental interneurons in turn excite LG via electricalinterneuron, interneuron A, in the terminal abdominal ganglion synapses (Zucker 1972). The combined mono- and disynap-was analyzed. Interneuron A is part of a disynaptic pathway from tic electrical inputs from sensory afferents onto LG sum toprimary afferent neurons to the lateral giant interneuron involved evoke spikes and thus initiate the tail-flip escape response.in producing the characteristic ballistic escape behavior of crayfish. Interneuron A received short and long latency excitatory postsyn- A proprioceptor, the exopodite-endopodite chordotonal aptic potentials (EPSPs) from chordotonal afferents. Short latency organ, containing 12 sensory neurons that project to the EPSPs occurred with little central synaptic delay, were unchanged terminal abdominal ganglion (Nagayama and Newland by hyperpolarizing current injection of 02 nA, and remained at a 1993), monitors the movements of the exopodite relative to constant amplitude when the nervous system was bathed in saline the endopodite of the tailfan (Field et al. 1990). One particu-with a low calcium concentration or saline containing the nicotinic lar intersegmental ascending interneuron that excites LG, antagonist curare. These EPSPs are thus thought to be mediate