Spiny lobsters

The relative importance of chemosensory input from the medial vs the
lateral antennular flagellae to the orientation behaviour of the spiny
lobster, Panulirus argus, is examined. The experimental results show
that the lateral filament, specifically the aesthetasc tuft of the
lateral filament, is necessary and sufficient to effect chemotaxis in
this organism. Results further demonstrate a role of lateral filament
input in both tropotactic and klinotactic mechanisms of odour orientation.

Periodic movements of the olfactory organs in the spiny lobster known
as antennular "flicking" temporally enhance the response of the olfactory
receptors to changes in the odor environment. The temporally
enhanced response onsets as a series of transient discharges phase
locked with the flick. This response pattern results from superimposed
increases in stimulus concentration at the receptor sites due
to flicking modulated permeability of a chemical diffusion barrier
surrounding the receptors, presumably created by the densely packed
nature of the receptor hair tuft. It is concluded that flicking
provides the lobster with a physiological mechanism to compensate
for the indiscrete temporal nature of chemical stimumi.

Antennular chemoreceptors of P. argus were surveyed electro-physiologically
to determine their relative sensitivity to low molecular
weight components of the shrimp, Penaeus duorarum. An ultrafiltrate
(less than 1,000 molecular weight) of shrimp extract did not differ
significantly in stimulus value from the total extract itself. A
mixture of the 19 amino acids present in the ultrafiltrate was slightly
less stimulatory than the total extract. Taurine alone approximated
the stimulus value of the amino acid mixture at its component concentration.
Taurine was also the most stimulatory of the 19 amino acids when
compared at the homogeneous 10^-3 M concentration. Taurine is the major
individual stimulant of shrimp extract but a contribution is also made
from other non-amino acid low molecular weight compounds.

The physiological effect of antennular flicking was analyzed
behaviorally and electrophysiologically in the spiny
lobster, Panulirus argus. Behavioral studies indicate
that glycine and L-glutamic acid cause a transient
concentration-dependent increase in flick rate. Electro-physiological
analysis of primary chemosensory afferents
indicates that flicking modulates ongoing chemically-elicited
activity in approximately half of the units
observed by causing either a brief increase or decrease
in the frequency of impulses. Responses of remaining units
were not altered by flicking. Antennular flicking is
discussed as a mechanism to prolong the address of the
peripheral chemoreceptors to the central nervous system
and allow the lobster to prolong its awareness of the
chemical environment.