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Title: SENSORY NEURONANATOMY OF A PASSIVELY INGESTED NEMATODE PARASITE, HAEMONCHUS CONTORTUS: AMPHIDIAL NEURONS OF THE FIRST STAGE LARVA

Author
item LI, J - UNIV OF PENNSYLVANIA
item ASHTON, F - UNIV OF PENNSYLVANIA
item Gamble, Howard
item SCHAD, G - UNIV OF PENNSYLVANIA

Submitted to: Journal of Comparative Neurology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Nematode parasites of livestock go through an obligatory free-living stage in soil. Egg passed from infected animals hatch and develop to infective larvae on pastures. When ingested by grazing animals, these worms begin a new phase of development which is triggered by environmental cues from the host. These developmental phases include molting, growth and feeding behaviors. Control of nematode development is based on sensory input, presumably through the parasite's nervous system. In this study we have constructed a map of the amphidial neurons of the nematode parasite Haemonchus contortus. This map includes all of the nerve cells which recognize sensory stimuli from the environment. Using this map, we are now employing microbeam laser technology to individually kill nerve cells and examine the consequences of ablation on parasite development. Armed with knowledge of nerve function, it should be possible to construct analog of nerve cell receptors which can be used for parasite control.

Technical Abstract: The infective larva of Haemonchus contortus, when ingested by a grazing host, is exposed to environmental changes in the rumen, which stimulate resumption of development. We hypothesize that resumption of development is under the control of the sensory neurons in the large, goblet-shaped sensilla known as the amphids. Using three-dimensional reconstructions from melectron micrographs of serial transverse sections, amphidial structure of the Ll is described. Each amphid of H. contortus is innervated by 12 neurons. The ciliated dendritic processes of ten neurons lie in the amphidial channel. Three of these end in double processes, resulting in thirteen sensory cilia in the channel. One process, that of the so-called finger cell, ends in a number of digitiform projections. Another specialized dendrite enters the amphidial channel, but leaves it to end within the sheath cell, a hollow, flask-shaped cell that forms the base of the amphidial channel. Although not flattened, the structure of this process is otherwise similar to that of the wing cells in C. elegans; we consider it to be one of this group. Each of the 12 amphidial neurons was traced to its cell body in the lateral ganglion, posterior to the worm's nerve ring. The positions of these bodies were similar to their counterparts in C. elegans; consequently, they were named according to C. elegans nomenclature. A map to be used to identify the amphidial cell bodies in the living LI was prepared.