Competition regulates the efficacy of an identified synapse in crickets

The efficacy of the synaptic contact between an identified sensory neuron and an identified interneuron in crickets is increased when neighboring afferent synapses are removed early in postembryonic life. The physiological changes are correlated with changes in the structure of the presynaptic neuron's axonal arborizations: When neighboring axons are destroyed, there is a shift of the remaining axonal arbors into deafferented regions and an increase in the number of putative contacts with the postsynaptic neuron. Changes in the structure of the presynaptic neuron also directly affect the probability of formation of this synaptic connection. The connection was found in 67% of the control specimens, but it was present in 100% of the partially deafferented specimens. The results demonstrate that interactions between growing sensory neurons can influence both the probability of synapse formation and the strength of those connections. This is the first case in which the effects of competition on the structure of a single, identified, presynaptic neuron can be directly related to its synaptic efficacy

Synaptic rearrangement during postembryonic development in the cricket

Synaptic rearrangement during development is a characteristic of the vertebrate nervous system and was thought to distinguish vertebrates from the invertebrates. However, examination of the wind-sensitive cercal sensory system of the cricket demonstrates that some identified synaptic connections systematically decrease in strength as an animal matures, while others increase in strength over the same period. Moreover, a single sensory neuron could increase the strength of its synaptic connection with one interneuron while decreasing the strength of its connection with another interneuron. Thus, rather than being a hallmark of the vertebrate nervous system, synaptic rearrangement is probably characteristic of the development of many if not all nervous systems