Journal de physiologie
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Journal de physiologie · Apr 1990
Prolonged primary afferent induced alterations in dorsal horn neurones, an intracellular analysis in vivo and in vitro.
1.) Peripheral tissues injury produces long lasting sensory and motor disturbances in man that present as the post-injury hypersensitivity syndrome with a reduction in the threshold required to elicit either pain or the flexion withdrawal reflex and an exaggeration of the normal response to suprathreshold stimuli. 2.) Two mechanisms contribute to these changes; sensitization of the peripheral terminals of high threshold primary afferents and an increase in the excitability of the spinal cord; a phenomenon known as central sensitization. 3.) Central sensitization has previously been shown by our laboratory to be the consequence of activity in unmyelinated primary afferents. Brief (20 s) C-fibre strength conditioning stimuli have the capacity to produce both a prolonged heterosynaptic facilitation of the flexion reflex and an alteration in the response properties of dorsal horn neurones, that long outlast the conditioning stimulus. 4.) In the adult decerebrate-spinal rat preparation we have, using intracellular recordings of dorsal horn neurones, examined the time course of the central effects of different types of orthodromic inputs. ⋯ Such a conditioning stimulus results however in an expansion in the size and an alteration in the response properties of the receptive fields of dorsal horn neurones that lasts for tens of minutes. 8.) In dorsal horn neurones recorded intracellularly in the isolated hemisected spinal cord, both intrinsic membrane properties and the orthodromic responses to primary afferent input can be studied. Repeated stimulation of a dorsal root produces in some neurones a prolonged heterosynaptic facilitation with both an augmentation of the response to the conditioning root (homosynaptic potentiation) and to adjacent test roots (heterosynaptic potentiation).(ABSTRACT TRUNCATED AT 400 WORDS)
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Journal de physiologie · Apr 1990
Neuronal mechanisms of learning in an in vitro Aplysia preparation: sites other than the sensory-motor neuron synapse are involved.
Classical conditioning of the gill withdrawal reflex can be demonstrated in two different in vitro Aplysia preparations. The data obtained show that as conditioning of the gill withdrawal reflex proceeds there are changes in synaptic efficacy at the central sensory-motor neurone synapse. These changes in synaptic efficacy, however, are not necessary nor are they sufficient for the observed changes in gill reflex behaviour. ⋯ In control preparations that received an explicitly unpaired stimulus paradigm (which does not lead to classical conditioning of the reflex) there was a decrease in the efficacy of a gill motor neurone to elicit a gill withdrawal response. There are a number of possible sites within the integrated central (CNS) and peripheral (PNS) nervous systems where changes could occur to bring about the alterations in motor neurone efficacy. Our results suggest that changes in neuronal activity which underlie learning occur at multiple sites within the nervous system and that a complete understanding of the mechanisms of associative learning can only be obtained when all of these sites are taken into account.