Loss of peripheral contacts modifies electrical synapses among embryonic leech motor neurons.

ANTONIA MARIN BURGIN; SARAH RAOUFI; W. B. KRISTAN JR; K.A. FRENCH

Washington, DC

Congreso; Meeting of the society for neuroscience; 2005

Society for Neuroscience

During development, leech motor neurons sequentially establish electrical synapses in a very precise and specific way. Previous experiments have shown that in embryos severing one of the two pairs of roots that connect a leech ganglion to the periphery produces exuberant overgrowth in the central processes of some of the motor neurons that innervate the longitudinal muscles on that side. We investigated whether formation of electrical connections depends on each neuron’s predetermined ability to recognize and connect with its central postsynaptic targets or if depriving motor neurons of contact with their peripheral target would disrupt their ability to establish normal central synapses. We injected a combination of dextran-Alexafluor  488 and Neurobiotin into identified motor neurons either in ganglia in which the roots had been cut previously or in adjacent control ganglia. Cuts were made at different developmental stages. When roots were cut before the motor neurons formed electrical connections, subsequent fills revealed few or no cells dye-coupled to the filled motor neuron, whereas in control ganglia within the same embryo we saw several dye-coupled cells.  Cutting roots after motor neurons had begun to form electrical connections halted formation of additional connections: existing connections were maintained, but the ability to form new connections was abolished. We conclude that cutting the nerve roots deprives some—although not necessarily all--motor neurons of their ability to form new connections, but that these neurons retain any connections that were established prior to the surgery.