Biology Reference
In-Depth Information
the observed results, so that in a particular neuron, some peptides and
transcripts are strongly and consistently expressed, and others are weakly
but consistently expressed. In other cases a peptide or transcript may be
very weakly expressed to the extent that there are some samples of that
neuron that do not reveal any detectable gene product. The significance of
this variability is unclear. It is possible that the differences generate
differences in behavior, but it is also possible that the neural circuitry is
robust against such variations
comparable variability, yet stability in
overall function, has been reported in the stomatogastric ganglion of
crustacea.
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e
Bioactivity of Ascaris Neuropeptides
Several different assays have been used to assess the physiological
effects of peptides in A. suum: (1) injection of peptide into the intact worm,
and observation of effects on locomotory behavior and body length, either
in unconstrained worms,
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or in worms in a glass tube (18 mm internal
diameter) after the worms were ligatured approximately 5 mm posterior
to the pharynx
this procedure induced regular anterior propagating
waveforms (the basis for this response is not understood; similar effects
are induced by decapitation, so perhaps removal of the head ganglia and/
or the pharynx and constriction of the “neck” have mechanisms in
common);
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(2) muscle strip assays where the effects of peptides on
muscle contraction are either due to the peptide alone or on the amplitude
of ACh-induced contraction; (3) assays of peptide-induced changes in
cyclic AMP and GMP;
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(4) electrophysiological changes in motor-
neurons;
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(5) contraction of the A. suum ovipositor/ovijector;
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and
(6) effects on spike activity and contraction in the A. suum pharynx. The
currently available results of these assays have been very recently
reviewed and will not be further summarized here.
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An additional imaginative assay was developed by Martin, who
noticed blebs (irregular bulges of the plasma membrane) that appeared
after collagenase treatment of A. suum, and showed that they were large
vesicles of muscle cell membrane that were suitable for patch recording,
and characterization of single channel properties.
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These preparations,
or preparations in which the membranes of muscle cell bags were cleaned
by enzyme digestion with collagenase, have been used to show the effects
of AF2 (KHEYLRFamide) on voltage-activated channels in A. suum
muscle.
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The majority of the peptides tested for their effects on behavior lead to
paralysis, or drastic reduction in the amplitude and frequency of loco-
motory waveforms. One set of peptides has very different effects
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the six
peptides AF3, AF4, AF10, AF13, AF14, and AF20, all products of the afp-1
(As-flp-1) transcript, and sharing a PGVLRFamide C-terminus, produce
exaggerated high amplitude waveforms, and the waveforms extend
e
