Serotonin in the developing stomatogastric system of the lobster, Homarus americanus

Abstract

We studied the development of the serotonergic modulation of the stomatogastric nervous system of the lobster, Homarus americanus. Although the stomatogastric ganglion (STG) is present early in embryonic development, serotonin immunoreactivity is not visible in the STG until the second larval stage. However, incubation of the STG with exogenous serotonin showed that a serotonin transporter is present in embryonic and early larval stages. Serotonin uptake was blocked by paroxetine and 0% Na(+) saline. The presence of a serotonin transporter in the embryonic STG suggests that hormonally liberated serotonin could be taken up by the STG, and potentially released as a "borrowed transmitter". Consistent with a potential hormonal role, serotonin is found in the pericardial organs, a major neurosecretory structure, by midembryonic development. The rhythmic motor patterns produced by embryonic and larval STGs were decreased in frequency by serotonin. Lateral Pyloric (LP) neuron-evoked excitatory junctional potentials (EJPs) in the embryos and the first larval stage (LI) were larger, slower, and more variable than those in the adult. The amplitude of adult LP neuron-evoked EJPs was increased more than twofold in serotonin, but in embryos and LI preparations this effect was negligible. In embryos and LI preparations, serotonin increased the occurrence of muscle fiber action potentials and altered the EJP wave-form. These data demonstrate that serotonin receptors are present in the stomatogastric nervous system early in development, and suggest that the role of serotonin changes from modulation of muscle fiber excitability early in development to enhancement of neurally evoked EJPs in the adult.

Dopamine and histamine in the developing stomatogastric system of the lobster Homarus americanus

“…We have recently shown that transporters for another biogenic amine, serotonin, exist in the STG before the ganglion is capable of actually synthesizing serotonin (Richards et al, 2003). TH is present in neurosecretory structures as early as E35 , so dopamine is probably present in the hemolymph in embryos and could be used as a "borrowed transmitter" by the STG before TH is present.…”

“…Despite the advantages of these species for studies of adult modulation, in these species it has not yet been possible to obtain embryos and larvae to study the early development of the STG. In contrast, studies of modulation of the adult STG in Homarus americanus and Homa-rus gammarus have lagged behind those in P. interruptus and C. borealis, but in H. americanus and H. gammarus developmental studies are feasible (Casasnovas and Meyrand, 1995), and it is possible to study the actions of neuromodulators as early as 50% of embryonic development (Le Feuvre et al, 1999;Richards et al, 1999Richards et al, ,2003Richards and Marder, 2000). Previous work has shown that some neuromodulators are already present early in embryonic development, whereas others appear only during larval times (Cournil et al, 1995;Fénelon et al, 1998Fénelon et al, ,1999Kilman et al, 1999;Li et al, 2002).…”

Inter-animal variability in the effects of C-type allatostatin on the cardiac neuromuscular system in the lobster Homarus americanus

“…The effects of a given neuromodulator on a specific pattern generator often vary somewhat among animals, but most studies have focused on mean responses, and have reported similarities in the direction of these effects across the animal population Kreissl et al, 1999;Mercier et al, 2003;Richards et al, 2003;Stevens et al, 2008;Stevens et al, 2009). While a number of factors could potentially underlie the quantitative variability in responses across animals, differences in response to a given modulator have most often been attributed to the 'state' of the system; this in turn is often reflected in the starting parameters of the pattern, notably cycle frequency (Dickinson et al, 2001;Fu et al, 2007;Medler and Hulme, 2009;Nadim et al, 2008;Nagy and Dickinson, 1983;Nusbaum and Marder, 1989b;Sargeant, 2007).…”

Arthropod 5-HT2Receptors: A Neurohormonal Receptor in Decapod Crustaceans That Displays Agonist Independent Activity Resulting from an Evolutionary Alteration to the DRY Motif

“…glion (Beltz et al, 1984;Marder and Eisen, 1984;Flamm and Harris-Warrick, 1986a,b;Harris-Warrick and Flamm, 1987;Harris-Warrick, 1989, 1990;Johnson and Harris-Warrick, 1990;Kiehn and Harris-Warrick, 1992a,b;Meyrand et al, 1992;Johnson et al, 1993;Turrigiano and Marder, 1993;Harris-Warrick, 1994, 1995;Christie et al, 1995;Hempel et al, 1996;Ayali and HarrisWarrick, 1999;Kilman et al, 1999;Tierney et al, 1999;Peck et al, 2001;Birmingham et al, 2003;Richards et al, 2003). To date, we have localized two serotonin receptors to the STG: 5-HT 2␤Pan and 5-HT 1Pan (Baro and M. C. Clark, unpublished observations).…”

“…More than 20 different substances modulate the pyloric circuit, with monoamines figuring prominently among them (HarrisWarrick et al, 1992a;Pulver et al, 2003;Richards et al, 2003). Monoamines can alter the strength of synaptic interactions between pyloric neurons and/or their intrinsic properties (HarrisWarrick et al, 1998).…”