Selective action of 6-hydroxydopa on noradrenergic terminals: Mapping of preterminal axons of the brain

Abstract

6-Hydroxydopa (i.v.) caused a marked reduction in mouse brain norepinephrine in 24 hours which remained reduced by 30% after 2 months. Fluorescence histochemical studies showed that there was a reduction in the number of noradrenergic terminals after 24 hours, in addition to an accumulation of intensely fluorescent noradrenergic preterminal axons, which suggests that degeneration of many of the noradrenergic terminals may have occurred. The noradrenergic cell bodies appeared normal and the dopaminergic neurons were unchanged. The appearance of catecholamine in the axons provides a method for mapping out the noradrenergic preterminal processes of the brain. The prominent tract of noradrenergic neurons was contained in the reticular formation from which smaller trunks emanate and ascend through the median forebrain bundle and internal capsule to innervate the forebrain. After 2–3 weeks norepinephrine-containing terminals reappeared in all areas except the cortex, cerebellum and hippocampus. It is suggested that 6-hydroxydopa has the ability to cause selective destruction and/or marked impairment of noradrenergic terminals, which in the brainstem, are capable of regeneration or replenishment of the neurotransmitter.