Individual medial and lateral nociceptive (N) cells of the leech have been paired with a variety of different target cells to determine the patterns and the properties of the connections made in culture.

Lateral nociceptive N cells did not make electrical or chemical connections with other N cells or with P sensory cells.

N cells made electrical connections with Retzius cells, anterior pagoda cells (AP) and annulus erector (AE) and L motor neurones in culture.

Lateral and medial N cells, which differ in the animal, exhibited consistent differences in culture. Well-established electrical junctions made by lateral N cells showed clear rectification. In contrast, medial N cells could make either non-rectifying or rectifying connections with target cells.

In spite of the presence of strong electrical coupling, evidence for chemically mediated synaptic interactions between N cells and other neurones was obtained on occasion.

These findings emphasize the specific nature of connections formed in culture. Unlike P sensory cells, N cells in culture did become electrically connected to Retzius cells and could make both rectifying and non-rectifying electrical junctions with appropriate targets.

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