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First published online April 18, 2008
Journal of Experimental Biology 211, 1434-1447 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.016998

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The pyloric neural circuit of the herbivorous crab Pugettia producta shows limited sensitivity to several neuromodulators that elicit robust effects in more opportunistically feeding decapods

Patsy S. Dickinson^1,2,*, Elizabeth A. Stemmler³ and Andrew E. Christie^4,5

¹ Department of Biology, Bowdoin College, 6500 College Station, Brunswick, ME 04011, USA
² Friday Harbor Laboratories, University of Washington, 620 University Road, Friday Harbor, WA 98250, USA
³ Department of Chemistry, Bowdoin College, 6600 College Station, Brunswick, ME 04011, USA
⁴ Department of Biology, University of Washington, Box 351800, Seattle, WA 98195-1800, USA
⁵ Mount Desert Island Biological Laboratory, PO Box 35, Old Bar Harbor Road, Salisbury Cove, ME 04672, USA

^* Author for correspondence (e-mail: pdickins{at}bowdoin.edu)

Accepted 21 February 2008

Modulation of neural circuits in the crustacean stomatogastric nervous system (STNS) allows flexibility in the movements of the foregut musculature. The extensive repertoire of such resulting motor patterns in dietary generalists is hypothesized to permit these animals to process varied foods. The foregut and STNS of Pugettia producta are similar to those of other decapods, but its diet is more uniform, consisting primarily of kelp. We investigated the distribution of highly conserved neuromodulators in the stomatogastric ganglion (STG) and neuroendocrine organs of Pugettia, and documented their effects on its pyloric rhythm. Using immunohistochemistry, we found that the distributions of Cancer borealis tachykinin-related peptide I (CabTRP I), crustacean cardioactive peptide (CCAP), proctolin, red pigment concentrating hormone (RPCH) and tyrosine hydroxylase (dopamine) were similar to those of other decapods. For all peptides except proctolin, the isoforms responsible for the immunoreactivity were confirmed by mass spectrometry to be the authentic peptides. Only two modulators had physiological effects on the pyloric circuit similar to those seen in other species. In non-rhythmic preparations, proctolin and the muscarinic acetylcholine agonist oxotremorine consistently initiated a full pyloric rhythm. Dopamine usually activated a pyloric rhythm, but this pattern was highly variable. In only about 25% of preparations, RPCH activated a pyloric rhythm similar to that seen in other species. CCAP and CabTRP I had no effect on the pyloric rhythm. Thus, whereas Pugettia possesses all the neuromodulators investigated, its pyloric rhythm, when compared with other decapods, appears less sensitive to many of them, perhaps because of its limited diet.

Key words: stomatogastric nervous system, neurohormone, neuropeptide, amine, feeding