Pyloric Neuron Morphology in the Stomatogastric Ganglion of the Lobster, <i>Panulirus interruptus</i>

Abstract

The pyloric network of decapod crustaceans has been intensively studied electrophysiologically in the infraorders Astacidea, Brachyura, and Palinura. The morphology of some or all pyloric neurons has been well described in Astacidea and Brachyura, but less so in Palinura. Given the large evolutionary distance between these three groups, and the large amount of electrophysiology that has been performed in palinuroid species, it is important to fill this gap. We describe here the gross morphology of all six pyloric neuron types in a palinuroid, P. interruptus. All pyloric neurons had complicated, extended dendritic trees that filled the majority of the neuropil, with most small diameter processes present in a shell near the surface of the ganglion. Certain neuron types showed modest preferences for somata location in the ganglion, but these differences were too weak to use as identifying characteristics. Quantitative measurements of secondary branch number, maximum branch order, total process length, and neuron somata diameter were also, in general, insufficient to distinguish among the neurons, although AB and LP neuron somata diameters differed from those of the other types. One neuron type (VD) had a distinctive neurite branching pattern consisting of a small initial branch followed shortly by a bifurcation of the main neurite. The processes arising from these two branches occupied largely non-overlapping neuropil. Electrophysiological recordings showed that each major branch had its own spike initiation zone and that, although the zones fired correlated spikes, they generated spikes independently. VD neurons in the other infraorders have similar morphologies, suggesting that having two arbors is important for the function of this neuron. These data are similar to those previously obtained in Brachyura and Astacidea. It thus appears that, despite their long evolutionary separation, neuron morphology in these three infraorders has not greatly diverged.

D2 receptors receive paracrine neurotransmission and are consistently targeted to a subset of synaptic structures in an identified neuron of the crustacean stomatogastric nervous system

“…Consistent with a previous report (Thuma et al, 2009), the length and trajectory of the primary neurite varied, possibly due to different soma locations (e.g., anterior vs. middle vs. posterior region of the STG) and the need for the primary process to extend throughout the neuropil. Each PD neuron had 9–10 secondary branches arising from the primary neurite.…”

“…These, in turn, can continue to divide beyond the 16th branch order (see below), ultimately generating small-diameter processes. The large-diameter processes are in the central core of the ganglion (coarse neuropil), whereas the higher order branches reside in the fine neuropil layered between the coarse neuropil and somata (Thuma et al, 2009). …”

Robust circuit rhythms in small circuits arise from variable circuit components and mechanisms

“…That said, at a finer scale of analysis, intracellular dye-fills of identified neurons in invertebrates show clear evidence of animal-to-animal variations in soma positions and branching patterns [27, 28, 29]. For example, a recent study of the Anterior Gastric Receptor (AGR) neuron in the crab stomatogastric ganglion (STG) shows large variations in the number of branches that AGR makes in the STG neuropil [28].…”

A multi-scale strategy for discovery of novel endogenous neuropeptides in the crustacean nervous system

“…The California spiny lobster Panulirus interruptus has long served as an important animal model for many areas of research in endocrinology and neurobiology [22-24], but its genome has not been sequenced yet and there is no protein/cDNA database. In particular, its stomatogastric ganglion has been utilized as a powerful model system to understand the cellular mechanisms of rhythmic pattern generation in neuronal networks [22].…”

“…In particular, its stomatogastric ganglion has been utilized as a powerful model system to understand the cellular mechanisms of rhythmic pattern generation in neuronal networks [22]. Many studies reported that neurotransmitters and neuropeptides regulate the functional output of these well-defined neuronal circuits [25-28].…”