Neuronal control of nematocyst discharge in hydra
This dissertation research seeks to understand how the neuronal circuitry of the battery cell complex in hydra functions in order to accomplish the basic biological necessity of food acquisition through its effector organelles, the nematocysts. ^ A behavioral assay was used to discharge individual nematocysts from the tentacles of Hydra vulgaris. Cnidocils were mechanically deflected using a piezoelectrically driven glass probe. Standard immunohistochemical methods were used to localize the N-methyl-D-aspartate receptor in hydras tissues. ^ Desmonemes and stenoteles differentially responded to imposed forces on the cnidocil. Desmonemes discharged when the cnidocil was struck with a force of at least 3.7 × 10−3 Newton's; stenoteles required a force of at least 1.9 × 10−2 Newton's. Desmonemes discharged at distances from the stimulation point of another desmonemes both within the battery cell complex and at distant battery cell complexes. We also report that desmonemes responded to vibrating probes in a frequency dependent manner and that tentacles of whole hydra will attack vibrating probes. Video analysis revealed that desmonemes and stenoteles required only a single strike of the cnidocil to elicit discharge. ^ The effects of Glutamate and GABA were studied on nematocyst discharge. Bath applied GABA at concentrations ranging from 100μM–10nM had no effect on stenotele discharge but did affect desmoneme discharge. The effect was excitatory only at distant points from stimulation both within the battery cell of the stimulated desmoneme and at distant battery cells. This was mimicked by baclofen and inhibited by phaclofen. Glutamate had no effect on desmonemes but did have an effect on stenoteles. Glutamate at concentrations of 100μM and 1μM caused significant increases in the number of stenoteles that responded to mechanical stimuli. This was mimicked by the addition of NMDA + kainate and NMDA + AMPA. The effect was blocked by the addition of either DAP5 or CNQX. The specific ionotropic glutamate agonists gave no significant results alone. Serotonin, dopamine, glycine, acetylcholine, and epinephrine were tested and did not significantly alter the discharge probability of desmonemes and stenoteles. ^ This study also shows specific localization of N-Methyl-D-aspartic acid receptor subunit 1, NMDAR1 to nematocytes, epithelial, nerve, and interstitial cells. ^
A. A. Scappaticci,
"Neuronal control of nematocyst discharge in hydra"
Dissertations and Master's Theses (Campus Access).