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

Noradrenaline and functional plasticity in kitten visual cortex: a re-examination

A quantitative re-examination was made of the influence of noradrenergic depletion on the epigenesis of kitten visual cortex. Two methods were used to deplete noradrenaline at the cortical level: stereotaxically controlled injection of 6-hydroxydopamine (6-OHDA) in the coeruleus complex, from which the noradrenergic input to visual cortex arises; intraventricular injection of 6-OHDA. The latter chemical lesion also depleted dopamine levels in the brain. Lesion of the noradrenergic or catecholaminergic systems was performed neonatally or at an age of 3-4 weeks in kittens submitted to five different rearing procedures: normal rearing, dark rearing, monocular rearing, monocular exposure following dark rearing and monocular deprivation following normal rearing. Forty-two kittens between 3 and 12 weeks of age were used for this biochemical and electrophysiological study. Noradrenaline and dopamine levels were measured by a radioenzymatic method in the primary visual cortex of twenty-six kittens. A total of 1263 cells were recorded in area 17 of twenty-six kittens. Combined biochemical and electrophysiological data were obtained in ten 6-OHDA-lesioned kittens. Whatever the mode of chemical lesion used, cortical noradrenergic depletion failed to block either maturation or vision-dependent processes which are known to affect orientation selectivity and/or ocular dominance during the critical period. However, in some cases, the amplitude of the epigenetic functional modifications was slightly reduced in 6-OHDA-treated kittens. The cortical effects of monocular deprivation starting from the age of 5 weeks were studied quantitatively both in lesioned and intact kittens. Disappearance of noradrenaline in area 17 did not prevent the loss of binocularity in cortical cells. However, even when monocular occlusion had been maintained for 2 or 3 weeks in 6-OHDA-treated kittens, ocular dominance shifts were limited to a stage equivalent to that observed in the intact kitten after 5-8 days of monocular occlusion. The amplitude of this partial protective effect was found to be unrelated either to the delay following the chemical lesion, or to the level of noradrenaline remaining in lesioned kitten cortex. Although a putative gating role of noradrenaline cannot be excluded in the development of the intact animal, this report shows that its presence is not required for functional plasticity to occur in kitten area 17.

Postnatal ontogenesis of the dopaminergic innervation in the rat anterior cingulate cortex (area 24). Immunocytochemical and catecholamine fluorescence histochemical analysis

The postnatal development of the dopaminergic input to the rat anterior cingulate cortex (area 24) was followed using anti-tyrosine hydroxylase immunocytochemistry and catecholamine fluorescence histochemistry in control and noradrenaline-depleted rats. Noradrenaline depletion in the cerebral cortex was obtained by peripheral injections of 6-hydroxydopamine (6-OHDA) at birth or N-2-chloroethyl-N-ethyl-2-bromobenzylamine (DSP4) at various postnatal ages and controlled by the absence of dopamine-beta-hydroxylase-labelled axons. The superficial and deep components of the anterior cingulate dopaminergic field developed at a different rate in control as well as lesioned rats. The deep supragenual dopaminergic field was already present at birth like the dopaminergic innervation of the prefrontal cortex area 32. In the superficial field, the molecular layer was reached first from postnatal day 3 (P3) on by positive axons running through the anterior hippocampal continuation and from P5-P6 on by another dopaminergic contingent coming through the deep dopaminergic field and giving off collaterals for layer III. The adult distribution pattern and striking varicose aspect were not reached until P21-P30 and a further increased density was observed until P60. The superficial cingulate dopaminergic field extended into the pregenual part of area 24b. The innervation of the superficial and deep layers of the rat anterior cingulate cortex by two distinct dopaminergic subpopulations, one of them closely related to that of prefrontal cortex area 32, could be compared with other laminar differences. The important functional implications of these data are further discussed.

Atlas of catecholamine perikarya, varicosities and pathways in the brainstem of the cat

By application of a modified glyoxylic acid--paraformaldehyde histofluorescence technique, catecholamine perikarya, varicosities, and pathways were delineated within the brainstem of kittens that were either untreated, pretreated pharmacologically, or injected intracerebrally with 6-OHDA. Three principle catecholamine cell groups were identified within the medulla and pons; the dorsomedial medullary cell group, the dorsolateral pontine cell group, and a ventrolateral cell group extending from the medulla into the pons. Induced axonal accumulation of catecholamines with intracerebral 6-OHDA injections revealed a major longitudinal catecholamine bundle which courses in a dorsolateral position through the entire brainstem tegmentum. The dorsomedial medullary and dorsolateral pontine cell groups contribute ascending and descending fibers to this bundle. Axons of the ventrolateral pontomedullary cells also feed into the bundle at successive levels through radially coursing transverse fibers. Via this major dorsolateral conduit and its ventrally and medially coursing tributaries, catecholamine fibers and terminals are distributed to multiple nuclei through the brainstem. The regions of the catecholamine cell groups and the serotonin raphe nuclei all receive a dense catecholamine innervation. Varicosities are also dense in the visceral cranial nerve nuclei, moderately dense in most somatic spinal and cranial nerve motor nuclei, and moderate to light in sensory cranial nerve and relay nuclei. The lateral and ventromedial reticular formation are moderately innervated by varicose catecholamine fibers that traverse these regions. The longitudinal catecholamine bundle continues caudally into the lateral funiculus to descend into and innervate the spinal cord. Rostrally it continues into the tegmental fascicles of the midbrain to ascend into and innervate the diencephalon and there join the medial forebrain bundle to ascend into the telencephalon. Thus, the catecholamine neurons utilize this dorsolateral longitudinal bundle to distribute collaterals to multiple bulbar nuclei and to travel beyond the brainstem to innervate the spinal cord and forebrain.

Destruction of noradrenergic cell bodies by intracerebral 6-hydroxydopamine in the newborn rat

Intracerebral injections of 6-hydroxydopamine directly in the nucleus locus coeruleus were performed in 4-day-old rats. The effects of such treatment on the subsequent development of this nucleus were analyzed and compared to those obtained in vehicle-injected age-paired controls. The 3 histological techniques used (Nissl, Glenner reaction, and histochemical fluorescence) indicated in the experimental group a progressive disappearance of the coerulean perikarya within 7 days postinjection. This lesion was permanent and did not induce any noradrenergic sprouting.