Identification and characterization of a tachykinin-containing neuroendocrine organ in the commissural ganglion of the crabCancer productus

Abstract

SUMMARY A club-shaped, tachykinin-immunopositive structure first described nearly two decades ago in the commissural ganglion (CoG) of three species of decapod crustaceans has remained enigmatic, as its function is unknown. Here, we use a combination of anatomical, mass spectrometric and electrophysiological techniques to address this issue in the crab Cancer productus. Immunohistochemistry using an antibody to the vertebrate tachykinin substance P shows that a homologous site exists in each CoG of this crab. Confocal microscopy reveals that its structure and organization are similar to those of known neuroendocrine organs. Based on its location in the anterior medial quadrant of the CoG, we have named this structure the anterior commissural organ (ACO). Matrix-assisted laser desorption/ionization Fourier transform mass spectrometry shows that the ACO contains the peptide APSGFLGMRamide,commonly known as Cancer borealis tachykinin-related peptide Ia(CabTRP Ia). Using the same technique, we show that CabTRP Ia is also released into the hemolymph. As no tachykinin-like labeling is seen in any of the other known neuroendocrine sites of this species (i.e. the sinus gland, the pericardial organ and the anterior cardiac plexus), the ACO is a prime candidate to be the source of CabTRP Ia present in the circulatory system. Our electrophysiological studies indicate that one target of hemolymph-borne CabTRP Ia is the foregut musculature. Here, no direct CabTRP Ia innervation is present, yet several gastric mill and pyloric muscles are nonetheless modulated by hormonally relevant concentrations of the peptide. Collectively,our findings show that the C. productus ACO is a neuroendocrine organ providing hormonal CabTRP Ia modulation to the foregut musculature. Homologous structures in other decapods are hypothesized to function similarly.

A newly identified extrinsic input triggers a distinct gastric mill rhythmviaactivation of modulatory projection neurons

“…Whole mounts of the isolated STNS and the thoracic ganglion (TG) with attached cocs and CoGs were fixed in 4% paraformaldehyde (Electron Microscopy Sciences, Hatfield, PA, USA) for 12-24·h, rinsed at least five times, at 1-h intervals, in phosphate (P) buffer (0.1·mol·l -1 ) with 0.3% Triton X-100 (P-Triton) and then incubated for 24-72·h with a monoclonal rat anti-substance P antibody (1:300; Accurate Chemical and Scientific Corporation, Westbury, NY, USA; Abcam Incorporated, Cambridge, MA, USA) that has been used previously on this system (Goldberg et al, 1988;Christie et al, 1997;Messinger et al, 2005). The nervous system was then again rinsed in P-Triton, five times at 1·h intervals, after which the STNS preparations were incubated with goat anti-rat Alexa Fluor 488 or 647 (1:300; Invitrogen Corporation,·Carlsbad, CA, USA) for 12-16·h.…”

“…There is a dense CabTRP Ia-immunoreactive (CabTRP Ia-IR) arborization within the anterior CoG neuropil, called the anterior commissural organ (ACO; Fig.·8A) (Messinger et al, 2005). The ACO innervates each CoG via a population of small diameter axons that project as a bundle through the medial aspect of the coc TG (Goldberg et al, 1988;Messinger et al, 2005).…”

“…The ACO innervates each CoG via a population of small diameter axons that project as a bundle through the medial aspect of the coc TG (Goldberg et al, 1988;Messinger et al, 2005). This CabTRP Ia-IR bundle does not project through the coc B (Fig.·8A) (Goldberg et al, 1988;Messinger et al, 2005).…”

“…Our data further suggest that the POC excitation of MCN1 and CPN2 is mediated by the neuropeptide transmitter Cancer borealis tachykinin-related peptide Ia (CabTRP Ia). The POC neurons also appear to be the source of the CabTRP Ia-containing anterior commissural organ (ACO), a dense neurohemal structure in the CoG neuropil (Messinger et al, 2005). Some of this work was published previously in abstract form (White et al, 2005).…”

Muscles innervated by a single motor neuron exhibit divergent synaptic properties on multiple time scales

“…Similarly, relaxation kinetics are modulated, and the differences in summation between the three muscles could converge under a particular modulatory environment (Jing et al, 2010;Jorge-Rivera et al, 1998). Some inputs that activate gastric mill rhythms with distinct LG activity patterns also likely trigger hormonal release (Messinger et al, 2005) (D.M.B., unpublished observations). It will be interesting to determine whether coordinated peripheral and central modulation, such as that matching relaxation rate to rhythm speed in the Aplysia feeding system (Jing et al, 2010), changes synaptic plasticity to enable convergent responses of the LG muscles under some modulatory conditions.…”