IMMUNOHISTOCHEMICAL LOCALIZATION OF THE NEUROPEPTIDE RFAMIDE IN THE HYPOSTOMAL NERVE NET OF \u3cem\u3eHYDRA VULGARIS\u3c/em\u3e

This study examined the distribution and localization of the neuropeptide arginine-phenylalanine-amide (RFamide) in the hypostomal and tentacular nerve net of the cnidarian polyp Hydra vulgaris. Immunohistochemical techniques were used to visualize three RFamide-positive distinct nerve ring structures, nerves and neurites throughout the ectoderm of the hypostome and tentacles of ablated hypostomes. Two RFamide-positive circumhypostomal nerve rings are reported here: an inner ring located near the mouth and an outer ring located beneath the tentacle attachment sites. Both rings are consistent with rings labeled with anti-α-tubulin; the outer ring is also coincident with a GABAB receptor-antibody-labeled ring previously described (Hufnagel and Kass-Simon, manuscript in preparation). A third, previously undescribed, set of nerve ring structures are reported, these are circumtentacular nerve rings located around the base of each tentacle. These circumtentacular rings were situated at the tentacle-hypostome junctions. Comparison preparations using anti-α- tubulin antibodies also showed circumtentacular ring structures. A continuous RFamide-labeled nerve net was seen throughout the hypostome and tentacles. RFamide labeled nerves were observed to be consistently associated with the nematocytes; this was especially apparent in the battery cell complexes within the tentacles. These results expand on the understanding of the role of RFamide in the chemical neurotransmission of hydra and suggest that RFamide leads to tentacular contractions during hydra feeding behaviors