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W G Wright

Publications and source records attributed to W G Wright.

28 records · Page 2Linked to original sources
PubMed1990

Multiple forms of non-associative plasticity in Aplysia: a behavioural, cellular and pharmacological analysis.

A complete understanding of the cellular mechanisms underlying the formation of associations between stimuli, as occurs during classical conditioning, requires an understanding of the non-associative effects of the individual stimuli. The siphon withdrawal reflex of Aplysia exhibits both non-associative and associative learning when a tactile stimulus to the siphon serves as a conditioned stimulus, and tail shock serves as an unconditioned stimulus. In this chapter we describe experiments which examine the non-associative effects of tail shock at three different levels of analysis. At a behavioural level we found that the magnitude, and even the sign of reflex modulation induced by tail shock depended critically on three parameters: (i) the state of the reflex (habituated or non-habituated); (ii) the strength of the tail shock, and (iii) the time of testing after tail shock. Specifically, when non-habituated responses produced by water jet stimuli to the siphon were examined, tail shock produced transient inhibition 90 s later; facilitation of non-habituated responses (sensitization) only emerged after a considerable delay of 20-30 min. When habituated responses were examined, tail shock produced immediate facilitation (dishabituation); the amount of facilitation was inversely related to the strength of tail shock, with stronger shock producing no dishabituation. At a cellular level it was found that the complex excitatory postsynaptic potential (EPSP) in siphon motor neurons produced by water jet stimuli to the siphon provides a reliable cellular correlate of several of the non-associative effects of tail shock that we observe behaviourally. When non-decremented complex EPSPS were examined, strong tail shock produced transient inhibition at a test 90 s after shock.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Direct comparison of serotonin effects on siphon versus tail sensory neurons in Aplysia.

Modulation of the strength of siphon and tail withdrawal reflexes in Aplysia involves, in part, changes in the sensory neurons that initiate these reflexes. Different observations and experiments on modulation in siphon and tail sensory neurons together contribute to the working model of mechanisms of learning and memory in Aplysia, yet no direct comparison of modulation in these two classes of sensory neurons has yet been made. The purpose of the present study was to directly compare modulation between siphon and tail sensory neurons in the same experimental conditions. In particular, we focused on the effects of serotonin on two firing properties of sensory neurons: spike duration and excitability. We applied serotonin (5-HT) onto both siphon and tail sensory neurons under the same conditions and found that both spike duration and excitability were significantly enhanced. This enhancement was statistically indistinguishable between siphon and tail sensory neurons tested simultaneously in the same preparation. Thus, these two different classes of sensory neurons respond to 5-HT in very similar, if not identical, ways. We conclude that if there are differences in 5-HT induced modulation between siphon and tail sensory neurons at the biophysical level, such differences are not strongly manifested at the level of changes in firing properties.

Animals↗
PubMedDate not supplied

Inhibition of catalytic and glucan-binding activities of a streptococcal GTF forming insoluble glucans.

The ability of a range of potential inhibitors to affect the catalytic activity or binding of dextran by a glucosyltransferase (GTF-I) that synthesises insoluble alpha1,3-linked glucan was tested. Acarbose, deoxynojirimycin, N-dodecyldeoxynojirimycin and Tris, which are thought to interfere with the active site of the enzyme of GTF and related glycosidases, inhibited glucan synthesis but not glucan binding. Tris was found to act as a competitive inhibitor of GTF-I. The effectiveness of the active site inhibitors was not altered by immobilisation of GTF-I on saliva-coated hydroxyapatite. In contrast, three amine hydrofluorides were markedly less effective against immobilised GTF than soluble GTF. The pH of the reaction mixture was found to have a strong influence on inhibition by acarbose, Tris and amine hydrofluorides, a finding that is of direct relevance to use of inhibitors in vivo.

1-Deoxynojirimycin↗