Dopaminergic and serotonergic innervation of cockroach salivary glands:distribution and morphology of synapses and release sites

Abstract

SUMMARY The paired salivary glands in the cockroach are composed of acini with ion-transporting peripheral P-cells and protein-secreting central C-cells, and a duct system for the modification of the primary saliva. Secretory activity is controlled by serotonergic and dopaminergic neurons, whose axons form a dense plexus on the glands. The spatial relationship of release sites for serotonin and dopamine to the various cell types was determined by anti-synapsin immunofluorescence confocal microscopy and electron microscopy. Every C-cell apparently has only serotonergic synapses on its surface. Serotonergic and dopaminergic fibres on the acini have their release zones at a distance of ∼0.5 μm from the P-cells. Nerves between acinar lobules may serve as neurohaemal organs and contain abundant dopaminergic and few serotonergic release sites. Some dopaminergic and serotonergic release sites reside in the duct epithelium, the former throughout the duct system, the latter only in segments next to acini. These findings are consistent with the view that C-cells respond exclusively to serotonin, P-cells to serotonin and dopamine, and most duct cells only to dopamine. Moreover, the data suggest that C-cells are stimulated by serotonin released close to their surface,whereas P-cells and most duct cells are exposed to serotonin/dopamine liberated at some distance.

Characterisation of neurotransmitter-induced electrolyte transport in cockroach salivary glands by intracellular Ca2+, Na+ and pH measurements in duct cells

“…Previous immunofluorescence studies have demonstrated that the ducts further downstream of the acini are innervated only by dopaminergic fibres that have some release sites (Baumann et al, 2002;Baumann et al, 2004). Thus, we expected that duct cells would respond to stimulation by DA, but not by 5-HT.…”

“…Salivation is controlled by dopaminergic and serotonergic neurons (Baumann et al, 2002;Baumann et al, 2004). Acinar peripheral cells are specialised for electrolyte and water transport and are innervated by dopaminergic and serotonergic neurons.…”

Morphology of salivary gland and distribution of dopamine and serotonin on red palm weevil (RPW), Rhynchophorus ferrugineus (Coleoptera: Curculionidae)

“…These biogenic amines were believed is vital in physiological events of salivary glands [5]. In cockroach, salivation is regulated by the salivary duct nerve that consists of two neurons: dopaminergic and serotonergenic [6][7][8]. Both of these compounds were found to stimulate the salivation in isolated SG [9][10].…”

Source, topography and excitatory effects of GABAergic innervation in cockroach salivary glands

“…Besides the SN1 and SN2 axons with a thickness of several micrometers, the SDN contains thinner axons that also project from the SOG towards the salivary gland. These thin axons contain serotonin (5-hydroxytryptamine; 5-HT) as neurotransmitter (Davis, 1985;Baumann et al, 2002;Baumann et al, 2004). An additional source of serotonergic innervation of the salivary gland is provided by the stomatogastric nervous system (Whitehead, 1971;Bowser-Riley et al, 1978;Baumann et al, 2002).…”

“…The P-cells are innervated by both dopaminergic and serotonergic fibers, and are responsible for ion and water transport. The C-cells are innervated solely by serotonergic fibers and are responsible for protein secretion (Baumann et al, 2002;Baumann et al, 2004). Thus, with dopamine stimulation, a protein-free saliva is produced in the acini whereas 5-HT stimulates the secretion of protein-containing saliva (Just and Walz, 1996;Marg et al, 2004;Rietdorf et al, 2005;Troppmann et al, 2007).…”