Catecholamine‐containing cells in the central nervous system and periphery of Aplysia californica

Abstract

Previous studies have suggested the presence of numerous catecholamine-containing cells in both the central ganglia and peripheral tissues of Aplysia, but they often offered conflicting or incomplete accounts of numbers, locations, and morphologies. The current study combines aldehyde-induced histofluorescence and tyrosine hydroxylase-like immunoreactivity together with confocal microscopy to provide details of these cells. Approximately 35-50 neurones in the cerebral ganglia, 4-8 neurones in the pedal ganglia, 5 neurones in the buccal ganglia, and numerous small fibres in various nerve trunks exhibited both immunoreactivity and aldehyde-induced fluorescence. Approximately 20 cells in the pedal ganglia and 4 cells in the buccal ganglia exhibited only immunoreactivity whereas 15-20 neurons in the cerebral ganglia exhibited only aldehyde-induced fluorescence. No somata in the pleural or abdominal ganglia exhibited aldehyde-induced fluorescence or immunoreactivity. Both aldehyde-induced histofluorescence and immunoreactivity also labelled what appeared to be two classes of catecholamine-containing cells in the gill, siphon, oesophagus, rhinophore, tentacle, and reproductive organs. The more numerous, but smaller cells had subepithelial somata and processes penetrating the overlying body wall, thus suggesting a sensory function. Another class of neurones had larger somata, often located more deeply within the tissue, and occasionally appeared to be multipolar. Processes from these various peripheral cells appeared to comprise the major component of afferent fibres and to form an extensive peripheral plexus, often associated with various muscles. The morphologies of the peripheral cells thus suggest involvement in both local and centrally mediated reflexes and responses, but additional studies must test such hypothesised functions and determine the sensory modalities that the cells mediate.

Developing Nervous Systems in Molluscs: Navigating the Twists and Turns of a Complex Life Cycle

“…Such evidence indicates that these cells might provide the sensory input that triggers settlement and metamorphosis, a possibility consistent with other evidence demonstrating that catecholamines are indeed involved in these processes [Coon et al, 1985;Bonar et al, 1990;Beiras and Widdows, 1995b;Pires et al, 2000;Pechenik et al, 2002]. However, similar peripheral catecholaminergic sensory cells are found in adult molluscs [Smith et al, 1998;Croll et al, 1999Croll et al, , 2003Croll, 2001], thus suggesting that the neurons are not responsive exclusively to specific cues for settlement and metamorphosis. For instance, they might be mechanoreceptive and determine the suitability of substrate for settlement of the larvae, but be responsive to general tactile cues in the adult, as has been suggested previously [Croll, 2001[Croll, , 2003.…”

“…However, similar peripheral catecholaminergic sensory cells are found in adult molluscs [Smith et al, 1998;Croll et al, 1999Croll et al, , 2003Croll, 2001], thus suggesting that the neurons are not responsive exclusively to specific cues for settlement and metamorphosis. For instance, they might be mechanoreceptive and determine the suitability of substrate for settlement of the larvae, but be responsive to general tactile cues in the adult, as has been suggested previously [Croll, 2001[Croll, , 2003. In addition to the peripheral innervation of structures that persist into adulthood, there is also the appearance at this time of the ganglia that will form the adult central nervous system.…”

Peripheral sensory cells in the cephalic sensory organs of Lymnaea stagnalis

“…Similarly, in Aplysia spp., an earlier study that found no evidence for PSCs in CSOs (Salimova et al, 1987), has been superseded by observations of TH-IR PSCs, corroborated by histochemistry (Croll, 2001). Moreover, autoradiographic Figure 11.…”

“…Histochemistry or immunohistochemistry have been used to describe putative catecholaminergic PSCs (Osborne and Cottrell, 1971;Salimova et al, 1987;Croll et al, 1999;Voronezhskaya et al, 1999;Croll, 2001;Croll et al, 2003), histaminergic PSCs (Hegedüs et al, 2004), nitregic PSCs (Elphick et al, 1995;Serfozo et al, 1998), FMRFamidergic PSCs (Nezlin et al, 1994a,b;Suzuki et al, 1997;Wollesen et al, 2007;Faller et al, 2008), and glutamatergic PSCs (Hatakeyama et al, 2007). In addition, putative chemosensory cells have been identified by using receptor signal transduction proteins (Mazzatenta et al, 2004;Cummins et al, 2009).…”

Dopamine stimulates snail albumen gland glycoprotein secretion through the activation of a D1-like receptor

“…Catecholaminergic axons have been shown to innervate the reproductive organs of various molluscs (Hartwig et al, 1980;Smith et al, 1998;Croll et al, 1999;Croll, 2001;Kiehn et al, 2001), and histochemical analyses have revealed that catecholaminergic cell bodies and axon processes are concentrated in the region of the exocrine albumen gland (AG) of the freshwater snails Bulinus truncatus Brisson, 1983) and Helisoma duryi (Kiehn et al, 2001). The AG is a female accessory reproductive gland that secretes a viscous substance known as the perivitelline fluid (PVF) around the individual eggs as they enter the carrefour, the area where the main duct of the AG empties.…”