Cellular mechanisms governing synapse formation: lessons from identified neurons in culture

Abstract

The accessibility of embryonic and adult neurons within invertebrate nervous systems has made them excellent subjects for neurobiological study. The ability to readily identify individual neurons, together with their great capacity for regeneration, has been especially beneficial to investigations of synapse formation and the specificity of neuronal connectivity. Many invertebrate neurons survive for long periods following isolation into primary cell culture. In addition, they readily extend new neuritic arbors and form electrical and chemical connections at sites of contact. Thus, cell culture approaches have allowed neuroscientists greater access to, and resolution of, events underlying neurite outgrowth and synaptogenesis. Studies of identified neuromuscular synapses of Helisoma have determined a number of signaling mechanisms involved in transsynaptic communication at sites of neuron-target contact. At these sites, both anterograde and retrograde signals regulate the transformation of growth cones into functional presynaptic terminals. We have found that specific muscle targets induce both global and local changes in neurotransmitter secretion and intracellular calcium handling. Here we review recent studies of cultured Helisoma synapses and discuss the mechanisms thought to govern chemical synapse formation in these identified neurons and those of other invertebrate species.

In VitroSynaptogenesis between the Somata of IdentifiedLymnaeaNeurons Requires Protein Synthesis But Not Extrinsic Growth Factors or Substrate Adhesion Molecules

“…Specifically, the isolated somata of neurons B5 and B19 juxtaposed in culture developed inhibitory soma-soma synapses. Although these synapses do not exist in vivo, this model nevertheless provided insights into the secretory assembly that mediated synaptic transmission between these neurons (Man-Son-Hing et al, 1989;Zoran et al, 1993;Zoran and Poyer, 1996). Recently, Klein (1994) used this approach to reconstructed specific synapses between the Aplysia sensory and motor neurons that are appropriate and similar to those seen in vivo.…”

Neurite outgrowth, RGD-dependent, and RGD-independent adhesion of identified molluscan motoneurons on selected substrates

“…Despite the extensive use of the molluscan nervous system in the study of various aspects of neuronal development and regeneration (e.g., Fain- zilber et al, 1996;Moffett, 1995;Ridgway et al, A small well (surface area approximately 1 cm 2 ) was 1991; Townsel and Thomas, 1987;Wildering et al, created in the center of each culture dish by securing a 1995; Zoran and Poyer, 1996), little is known of polypropylene ring cut from a 1.5-mL Eppendorf tube to the existence of integrins nor of the functional rele- Between 10 and 20 RPA neurons were plated within way. As a positive control, cells were plated on untreated the center well of each dish along the inner rim of the polystyrene culture dishes (Falcon 3001).…”

Transient electrical coupling regulates formation of neuronal networks

“…Neuron 19 does not form chemical synapses with other buccal neurons in culture (Haydon and Zoran, 1991;Zoran and Poyer, 1996) and did not form chemical synaptic connections with neuron 110 in either two-cell or three-cell configurations. Therefore, in this study, all chemical synaptic connectivity refers to cholinergic neurotransmission of neuron 110.…”