Early development of an identified serotonergic neuron inHelisoma trivolvis embryos: Serotonin expression, de-expression, and uptake

Apical sensory neurones mediate developmental retardation induced by conspecific environmental stimuli in freshwater pulmonate snails

“…Two anterior monoaminergic sensory cells, which develop before the onset of the CNS formation, express 5-HT, innervate locomotory cilia, and degenerate after metamorphosis, have been described in various pulmonate embryos (Goldberg and Kater, 1989;Voronezhskaya and Elekes, 1993;Diefenbach et al, 1998;Voronezhskaya et al, 1999;Kuang and Goldberg, 2001;Koss et al, 2003;Voronezhskaya and Elekes, 2003), and are generally believed to be the remnants of the apical sensory organ (ASO), the structure characteristic for trochophore animals (Nielsen, 2001). The basic plan of the ASO is highly conserved regardless of the planctotrophic or intracapsular developmental mode (Kempf et al, 1997;Marois and Carew, 1997;Dickinson et al, 1999;Page and Parries, 2000;Nielsen, 2001;Schaefer and Ruthensteiner, 2001).…”

“…Throughout the intracapsular development, they have a limited number of easily identifiable neurones (reviewed by Croll, 2000). At the trochophore and veliger stages, only one pair of sensory neurones has been described (Diefenbach et al, 1998;Voronezhskaya et al, 1999). These neurones differ in their transmitter content: they express serotonin (5-HT) in Helisoma (Goldberg and Kater, 1989;Diefenbach et al, 1991;Diefenbach et al, 1995;Diefenbach et al, 1998;Voronezhskaya and Elekes, 1993;Koss et al, 2003), and dopamine (DA) and FMRFamide-related peptides in Lymnaea (Croll and Voronezhskaya, 1996;Voronezhskaya et al, 1999;Voronezhskaya and Elekes, 2003).…”

Identification and evolutionary implications of neurotransmitter–ciliary interactions underlying the behavioral response to hypoxia inLymnaea stagnalisembryos

“…The ENC1 neurons of H. trivolvis are sensory-motor neurons that function both in hypoxia sensation and cilioexcitation (Kuang and Goldberg, 2001;Kuang et al, 2002). These serotonergic neurons have a short apical dendrite tipped with a sensory specialization on the embryonic surface, as well as a primary descending axon that innervates both the dorsolateral and pedal bands of cilia (Diefenbach et al, 1998;Koss et al, 2003). The TAC neurons of L. stagnalis are thought to be homologues of ENC1, with similar features including cell body and dendritic morphology, embryonic location, time of occurrence, transient expression of amine neurotransmitter and innervation of ciliary tissues (Voronezhskaya et al, 1999).…”

“…The conversion to encapsulated direct development by freshwater pond snails required adaptations that likely involved the redeployment of existing cellular machinery into new roles. For instance, the embryonic neuron C1 (ENC1) of the pulmonate Helisoma trivolvis (also known as Planorbella trivolvis; family Planorbidae) (Brown, 1991) is thought to be derived from the paraampullary apical ganglion neurons described in marine gastropods (Kempf et al, 1997;Diefenbach et al, 1998). ENC1 mediates detection of hypoxia and egg capsule ventilation in H. trivolvis embryos , whereas the para-ampullary neurons participate in substrate detection and larval settlement in planktotrophic gastropod veligers (Hadfield et al, 2000).…”

“…For example, only L. stagnalis has a ciliated apical plate region, whereas both species have pedal and dorsolateral (prototrochal) ciliary bands (Voronezhskaya et al, 1999;Koss et al, 2003). Furthermore, the transient apical catecholaminergic (TAC) neurons of L. stagnalis, which are considered to be homologous to the ENC1 neurons of H. trivolvis, contain dopamine rather than serotonin and innervate the apical plate cilia rather than the other ciliary bands (Diefenbach et al, 1998;Voronezhskaya et al, 1999;Koss et al, 2003). Finally, application of either dopamine or serotonin stimulates embryonic rotation in L. stagnalis (Filla et al, 2009), whereas only serotonin does so in H. trivolvis (Diefenbach et al, 1991).…”