Effects of intraventricular injection of 6-hydroxydopamine in the developing kitten. III. Histochemical fluorescence and radioautographic studies of the noradrenaline hyperinnervation in the pons.

In the present study, using neonatal intraventricular injections of 6-hydroxydopamine (6-OHDA) and the fluorescence histochemical method for monoamines, it is observed that an extensive plexus of noradrenaline (NA) fibres develops in the pontine region of the cat brain subsequently to the neonatal destruction of the ascending NA bundles and of the NA innervation in the cerebral cortex by the neurotoxin. This plexus is only partly conserved 10 months after the 6-OHDA treatment. Generally, only a limited number of NA perikarya degenerate in the region of the locus coeruleus, the others (nucleus subcoeruleus senso lato) exhibiting the same strong fluorescence as the new NA fibres. Using the radioautographic method after intraventricular injections of [3H]NA, our work demonstrates also the transient disappearance (at least one month) of the uptake of [3H]NA in the pons, whose NA cell bodies and nerve terminals are no longer labeled in the same number as in control animals. The possibility of again labeling significantly NA perikarya and numerous nerve terminals occurred between 3 and 5 months of age, probably indicating both a re-establishment of normal uptake properties in the preserved NA perikarya and nerve terminals and some maturation of the uptake mechanisms in the abnormal NA fibres of the pons. This last observation is at variance with data from newborn animals showing that the uptake of NA develops in parallel with the accumulation of endogenous NA in catecholamine nerve terminals. The present results, however, do corroborate and complement previous biochemical data obtained in the cat after neonatal injection of 6-OHDA.