Synaptic coupling into the production and storage of a neuronal memory trace

Abstract

AN adequate model for the nature of the memory trace at the neuronal level should provide for a sequence of physiological mechanisms which would include ‘read-in’ of the neuronal change, ‘storage’ processes that impart an enduring quality, and ‘read-out’ of the change in the form of an altered neuronal response to an appropriate neural input. The framework for such a neuronal model seems to be provided by the features of a novel heterosynaptic interaction in a mammalian sympathetic ganglion. It had been found previously that one synaptic transmitter (the catecholamine dopamine, DA) could produce a specific and enduring enhancement, lasting for at least several hours, of the subsequent responses to another synaptic transmitter (acetylcholine, ACh)¹. We have now found that the retention of this DA-induced change can be disrupted by cyclic GMP in a strikingly time-dependent manner that is similar, in principle, to the well known disruptability feature of the memory storage process^2,3. Additional evidence indicates that the production and storage of the enduring change initiated by DA are mediated intraneuronally by cyclic AMP. We present here a scheme which outlines the cellular pathways postulated to carry out the sequence of events from ‘read-in’ through to ‘read-out’.