Fig. 1. Schematic representation of the organization of the cockroach salivary gland and of its serotonergic and dopaminergic innervation pattern. (A) The salivary glands are paired and consist of several lobules of secretory acini. The ducts of each gland unite to a single efferent salivary duct (4) that fuses with the opposite duct to form the main salivary duct. Innervation of the salivary gland is via the salivary duct nerve containing a single dopaminergic and several serotonergic axons and via branches of the oesophageal nerve containing serotonergic axons. Dopaminergic nerve fibres (blue) reside on the surface of the acinar tissue (1), ramify extensively in nerves that interlink adjacent acinar lobules (2) and extend to the various sections of the duct system. Serotonergic nerve fibres (red) reside on the acinar tissue (1), penetrate deeply into the acinar lobules and are also associated with sections of the duct system adjacent to the acinar tissue (3). (B) Each acinus consists of two peripheral cells (P-cells) with long microvilli and several central cells (C-cells) with numerous secretory granules. Triple black lines indicate the position of septate junctions (Just and Walz, 1994). Each acinus is covered by dopaminergic (blue) and serotonergic (red) nerve fibres. Serotonergic nerve fibres (red) extend deep into the acini between the C-cells. The apical surface of the C-cells is covered by a sheath of flattened fenestrated centroacinar cells. The duct cells have basal and apical infoldings and form a simple tubule. Dopaminergic nerve fibres (blue) extend into the epithelial layer of duct cells.