Modulation of Neunte Outgrowth by Intact and Axotomized Adult Neurons ofHehsoma

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Abstract
SYNOPSIS. The abilty of adult molluscan neurons to exhibit neunte outgrowth and form synaptic connections after axotomy has been thoroughly investigated in recent years More recently we have asked whether such remodeling of neuronal form and function can occur within the intact nervous system In this essay, we describe our observations regarding the neunte outgrowth from an intact neuron (buccal neuron 5) in the pond snail Hehsoma which occurs on exposing the animal to specific forms of stress As a result of initial experiments the possibility arose that this form of neunte outgrowth was asso ciated with altered osmoregulation This hypothesis was tested by placing Helisoma in environments of different osmolanty which have known consequences in terms of blood osmoregulation When animals are placed in a hypertonic environment (20% seawater) neuron 5 exhibits the sprouting and retraction of a neunte similar to that seen after other forms of stress This observation gave rise to the hypothesis that a blood-borne agent might be responsible for the induction of sprouting Our chromatographic analysis of blood from Helisoma exposed to 20% seawater indicated that a rise and fall of blood acidic amino acids corresponded to the time course of neunte outgrowth Recently we tested glutamate at physiological levels for possible neurotrophic actions and have observed that it can promote neunte outgrow th from axotomized neurons We conclude that this classical transmitter can act in a neurotrophic fashion and discuss possible implications of our observations in terms of the form and function of neurons within the intact nervous system.

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