Studies on developing and transplanted monoaminergic neurons using an "ultra-thin" slice preparation

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An attempt was made to identify living monoaminergic neurons for electrophysiology in a brain slice preparation in the hope that the procedure would enable to study the sequence of events which might occur in the course of functional maturation of developing an transplanted monoaminergic neurons. Thin (80-100 mu thick) brain-stem slices obtained from young rats (5-25 days old) were treated with a serotonin analogue, 5, 7-dihydroxytryptamine (5, 7-DHT). Neurons accumulating the substance fluoresced under ultraviolet light. The localization of labelled cells in the raphe nuclei suggested that they were serotonerigc neurons. No cells were labelled in the dopamine neuron-containing substantia nigra. Intracellular recording also revealed that the responsed of labelled neurons conformed to those reported for serotonergic raphe neurons ; the spike potential of the neurons was slow in time course, showing a hump on its falling phase, and their membrane time constant was long. Application of 5, 7-DHT slightly broadened the spike width and depressed the transient outward rectification of the labelled neurons, but the neurons were still identifiable by their pattern of responses.The time course of maturation of sprotonergic raphe neurons was studied using the above-mentioned procedure. The neurons showed the main traits of their character even at the early postnatal periods. The data, along with those obtained from dopaminergic nigral neurons, suggested that brain-stem monoaminergic neurons were functionally fairly mature at birth, although further 2 weeks seemed to be necessary for their full matumration. Concerning the changes in property of monoaminergic neurons transplanted in vivo, definitive results have not yet been obtained and further studies are needed.