Neurotoxic destruction of the serotoninergic innervation of the rat subcommissural organ is followed by reinnervation through collateral sprouting of non-monoaminergic neurons.

Specific neurotoxic destruction of the serotoninergic innervation of the subcommissural organ of the rat is followed by an efficient reinnervation by collateral sprouting of non-monoaminergic axons, which normally do not innervate the SCO cells. Morphologically, the reinnervating fibres totally replace the serotoninergic synapses lost by the lesion, but, functionally, they fail to substitute for the potent inhibitory control of secretory activity normally exerted by the serotoninergic innervation. It is possible that the observed reinnervation by foreign synapses explains why the regrowing serotoninergic neurons fail to re-establish their connections with the SCO.