Early stages of uptake and transport of horseradish‐peroxidase by cortical structures, and its use for the study of local neurons and their processes

Abstract

It is well known that, when horseradish-peroxidase (HRP) is injected into the central nervous system, it is taken up by nerve terminals and retrogradely transported to their cells of origin. We have now injected HRP into the visual cortex of cats in order to study light-microscopically the pattern of its spread, the neural structures that take it up locally, and the initial steps of its retrograde descent towards the dorsal lateral geniculate nucleus (LGNd). Special attention was given to post-injection times of ten minutes to eight hours, but animals with up to five days' survival were also analyzed.It was found that the brown spot produced by the initial spread (primary diffusion) of HRP remains constant in size for about two hours and then spreads out (secondary diffusion) to involve neighboring visual cortical areas. Secondary diffusion, however, does not result in further retrograde labelling of LGNd neurons. Local nervous structures labelled during primary diffusion of HRP include a large number of infracortical axons, many of which show bifurcations directed towards the cortex. As HRP descends within these axons, fewer and deeper axonal branchings appear labelled, as though, after initial uptake, HRP were no longer taken up. The possible reasons for the lack of further HRP uptake, including observed local inflammatory reactions, are discussed. Intracortical labelled structures include neuron somata and processes. These resemble Golgi-impregnated structures and, particularly a t short survival times, show fine details such as dendritic spine necks, terminal bouton stalks, synaptic contacts, and a remarkable degree of axonal preterminal and terminal branching. Some of these structures were also examined electron-microscopically.

Morphological Evidence for Secondary Vestibular Afferent Connections to the Dorsal Cochlear Nucleus in the Rabbit

“…It has been suggested that only the dark central core represents the real injection site [Vanegas et al, 1978;Mesulam, 1982;Sweet et al, 1985], although the peripheral diffusion zone could also be the effective area for the uptake and subsequent transport of the tracer [Ahlsén, 1981]. In many cases of our large injections into the dCo, we observed accidental spread of the tracer to the dorsal regions of MVr, MVc, LV, IV and inferior cerebellar peduncle.…”

Identification of pericellular baskets in the cat striate cortex: Light and electron microscopic observations after uptake of horseradish peroxidase

“…Light microscopically, the basket elements and the pyramidal cell had the brown appearance of nervous structures directly labelled with HRP (Vanegas et al, 1978;Vanegas & Hollander, 1980), the pyramid being much lighter than the basket. Electron microscopically, the basket elements and the pyramidal cell showed the typical increased electron density of HRP diffuse labelling (Vanegas et al, 1978) the basket elements being again much darker than the pyramid (Fig.…”

“…It has been found (Vanegas et al, 1978;Vanegas & Hollander, 1980) that injection of horseradish peroxidase (HRP) into the visual cortex results, within the first 2 h after injection, in a very fine labelling of neurons and neuronal processes located near the site of injection. This labelling is comparable to that obtained with Golgi impregnation methods, with the advantage that the HRP-labelled elements retain their intracellular structural details, and thus lend themselves to combined light and electron microscopic analysis.…”

Photochemically stimulated blood-borne factors induce blood-brain barrier alterations in rats.

“…3033 - 35 Because our recipient rats were allowed to survive for only 15 minutes after blood infusion, the fate of the flooded neurons remains uncertain. Nevertheless, the fact that neuronal alterations were documented suggests that acute neuronal dysfunction may be a direct consequence of altered vascular permeability.…”