Injections Of Wheat Germ Agglutinin Conjugated To Horseradish Peroxidase Research Articles

Organization of the projections of a circumventricular organ: the area postrema in the rat.

The projections of the rat area postrema were analysed using anterograde and retrograde axonal transport techniques. Discrete injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the area postrema produced anterograde labeling in specific medullary and pontine nuclei. In the medulla, anterograde labeling was present in the internal solitary zone and dorsal division of the medial solitary nucleus, both of which also contained a small number of retrogradely labeled perikarya. Prominent projections to the dorsal motor nucleus of the vagus were seen only if the WGA-HRP injections in the area postrema invaded dorsal solitary nuclei. In the pons, anterograde labeling was present in the parabrachial nuclei, the dorsolateral tegmental nucleus, and the pericentral division of the dorsal tegmental nucleus. By far the major pontine projection was to the dorsolateral region of the middle one-third of the rostrocaudal extent of the parabrachial nuclei. Retrograde fluorescent tracing studies indicated that most area postrema neurons take part in this parabrachial projection. The area postrema projection to the parabrachial nuclei was bilaterally distributed, whereas that from the dorsal solitary nuclei was primarily ipsilateral. The external solitary zone, immediately subadjacent to the area postrema, neither received area postrema projections nor participated in the projections to the parabrachial nuclei. Fluorescent retrograde double labeling studies confirmed the bilateral nature of the area postrema projection to the parabrachial nuclei. In addition, because no doubly labeled neurons were observed it appears that individual area postrema neurons project to either side but not both sides of the dorsal pons. Thus, numerous neuronal pathways exist for the transfer of blood-borne information (that cannot cross the blood-brain barrier) from the area postrema to other brain regions.

The terminations of the spinothalamic tract in the cat

The termination sites of the spinothalamic tract (STT) in the cat have been examined using the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Cats which received an injection of WGA-HRP at the spinal cervical level (C7–C8) displayed anterograde labelling in the ventral posterior lateral (VPL), ventrolateral, lateral posterior, limitans, suprageniculate, medial geniculate pars magnocellularis, central lateral, paracentral, centrum medianum, submedius, central medial, reuniens, rhomboid and periventricular thalamic nuclei. Lumbar injection (L2–L3) produced a similar although less intense pattern of labelling, with only the VPL displaying an obvious topological organization. Although the STT terminations in the cat appear to be less dense than those observed in the rat or monkey the present results demonstrate that in the cat a widely variety of thalamic nuclei receive a direct STT projection and that the cat VPL, like rat, monkey and man receives a direct STT input.

The use of wheat germ agglutinin-horseradish peroxidase conjugates for studies of anterograde axonal transport

Injection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the hemisected spinal cord of the rat, cat and monkey consistently resulted in the intense anterograde labeling of ascending spinal projections such as the spinothalamic tract and spinocerebellar tracts and their terminal fields. Injections of WGA-HRP in the dorsal column nuclei resulted in the anterograde labeling of the medial lemniscus and its terminal fields in the thalamus. Injection of similar amounts of horseradish peroxidase alone (HRP) in hemisected animals or the dorsal column nuclei resulted in little anterograde labeling. The rate of the anterograde transport of WGA-HRP in cut axons appears to be greater than 200 mm/day. Small amounts of transneuronal labeling appeared to occur after injection of WGA-HRP in both cut axons and undamaged cell bodies. These results suggest that the amount of anterograde labeling observed after injection of WGA-HRP into both cut axons and undamaged cell bodies is significantly greater than the anterograde labeling observed after injections of HRP alone. Therefore, in the central nervous system WGA-HRP appears to be a far more effective anterograde tracer than HRP alone.