Acetylcholine and lobster sensory neurones

Abstract

SUMMARYExperiments are presented in support of the hypothesis that acetylcholine functions as a sensory transmitter in the lobster nervous system.1. Several different peripheral sensory structures incorporate radioactive choline into acetylcholine. The preparation most enriched in sensory as opposed to other nervous elements (the antennular sense organs of the distal outer flagellum) does not incorporate significant amounts of glutamate, tyrosine or tryptophan into any of the other major transmitter candidates.2. There is a parallel between the distribution of the enzyme choline acetyltransferase and the proportion of sensory fibres in nervous tissue from many parts of the lobster nervous system. 3. Isolated sensory axons contain at least 500 times as much choline acetyltransferase per cm of axon as do efferent excitatory and inhibitory fibres.4. Abdominal ganglia and root stumps show a decline in the rate of incorporation of choline into acetylcholine 2 to 8 weeks after severing the first and second roots bilaterally (leaving the connectives and third roots intact). Extracts of the root stumps exhibit a significantly lower level of choline acetyltransferase 2 weeks after this operation.5. Curare and atropine partially block an identified sensory synapse in the lobster abdominal ganglion.

Acetylcholine in the crayfish optic lobe: concentration profile and cellular localization

“…In the lobster abdominal ganglia (and numerous other arthropods), there is good evidence that much of the ACh is associated with primary afferents, where ACh functions as a neurotransmitter. Similar findings are documented for the choline acetyltransferase activity in the brains and afferent roots of lobsters (Barker et al, 1972;Hildebrand et al, 1974) and the ACh-like immunoreactivity of crayfish brain (Wang-Bennett et al, 1988). The presence of 6 bilateral primary sensory neuropiles in the brain is presumably the basis of its high ACh concentration.…”

“…The reactivity of the antisera was assessed in several locations of the brain known to contain cholinergic primary afferents (Barker et al, 1972). ACh-like reactivity was observed in the primary afferent axons of the antenna1 and antennulary nerves and the most intense reactivity was observed in the primary afferent terminals of the sensory neuropiles (Wang-Bennett et al, 1988).…”

The physiological properties of amine‐containing neurones in the lobster nervous system.

“…The input has a cholinergic pharmacology, suggesting that it may be sensory (Barker et al 1972), and only a limited number of cells produce the synaptic response. In fact, we have no evidence that the synaptic input to an individual neurone comes from more than one fibre.…”

“…The three major types of through fibres known to be present in the second thoracic roots are efferent excitatory and inhibitory axons to exoskeletal muscles, probably using glutamate and GABA as neurotransmitters; and afferent sensory axons likely to use ACh as their transmitter substance (Barker, Herbert, Hildebrand & Kravitz, 1972). The possibility that the synaptic input to the root neurones might be from cholinergic sensory fibres in the root was examined next.…”

A Test of the Excitability-Gradient Hypothesis in the Swimmeret System of Crayfish

“…Because axons of many primary sensory afferents that enter each abdominal ganglion are cholinergic (Barker et al, 1972), a second alternative site of action would be on neurons postsynaptic to these afferents. There are hundreds of afferents from each swimmeret (Killian and Page, 1992), and perturbation of individual swimmerets during normal movements will cause changes in the coordinated activity of the system (West et al, 1979); therefore, this alternative is possible.…”