The dynamics of presynaptic transmitter release are often matched to the physiological properties and functions of the postsynaptic cell. In organisms ranging from cats to crickets, evidence suggests that retrograde signaling is essential for matching these presynaptic release properties to individual postsynaptic partners. We show that properties of facilitation and depression at the terminals of single sensory neurons (SNs) are correlated with the postsynaptic target cell in the cricket cercal sensory system. A quantal analysis applied to evoked transmitter release and demonstrates that facilitation and depression are presynaptic phenomena. Thus, single SNs are capable of making functionally distinct presynaptic terminals, simultaneously on different target cells. Furthermore, when the population of SNs contacting each target cell were sampled, all of the SNs were observed to have similar dynamic properties on a single target interneuron. This indicates that presynaptic release properties of SN terminals are specified locally, at the synapse, by an interaction with the target interneuron. A simple binomial model adequately described transmission at these synapses. We showed that the probability of release, p, varied systematically at the terminals of a single SN and is correlated with the target cell contacted. Low values of p were obtained for the contacts that facilitate at one target and higher values of p were obtained for the contacts that depressed at a second target. In addition, changes in p were primarily responsible for the dynamic changes in EPSP amplitude associated with paired pulse facilitation, depression and frequency depression. This indicates that p is regulated locally, at the synapses, by an interaction with the target cell and that this interaction influences the dynamic properties of presynaptic function. Finally, p is strongly correlated with the external calcium concentration in this system, suggesting that it reflects the activity of the calcium-dependent transmitter release mechanism. These results suggest that a retrograde signal modulates the calcium-dependent transmitter release machinery of presynaptic sensory neuron terminals, thereby matching presynaptic function to identified postsynaptic partners.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-8914 |
| Date | 01 January 1994 |
| Creators | Davis, Graeme Wentworth |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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