Formation of novel central and peripheral connections between molluscan central neurons in organ cultured ganglia.

An in vitro organ culture system for buccal ganglia of the adult snail, Helisoma, is described. The system supports: (1) maintenance of characteristic electrophysiological parameters of identified neurons over seven days of culture; (2) choline metabolism including uptake and synthesis over the same duration; (3) sprouting and growth of neurons in response to axotomy; (4) the formation of novel central electrotonic connections between identified neurons as a result of sprouting and growth. These observations on neuronal growth and the formation of connections are similar to those made with in vivo culture. The use of in vitro culture allows precise manipulations not previously possible. When buccal ganglia are cultured in vitro with the cut distal ends of peripheral nerve trunks held closely apposed, axons of neurons 5R and 5L in the nerve trunks are capable of forming electrotonic connections similar to central connections. The capability of these neurons to form electrotonic connections via their peripheral axons implies that special structures (i.e., central neurites) are not required for the formation of connections; and neither are special environments (i.e., the central neuropile) required for these connections.