Postnatal development of striatal connections in the rat: a transport study with wheat germ agglutinin-horseradish peroxidase

This paper deals with the postnatal development of afferent and efferent connections of the rat striatum as revealed by the transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP). Tracer was injected weekly from birth to the end of the first postnatal month in the head of the caudate nucleus. To control for transport from cortical areas contaminated by the micropipette, injections in newborn rats were made by either vertical or lateral penetrations. In addition some newborn and 14-day-old animals were injected only in the cortex. The results showed that at birth there was retrograde transport to the thalamus, substantia nigra and raphe nuclei. Labelling in the cortex was seen at birth but was probably due to cortical contamination. Transport from the striatum was clearly established on day 7, when a few labelled neurons were observed on both the ipsi and contralateral sides. These neurons increased in number and were distributed through layers III to VI by day 14. At this time labelled cell bodies were observed in the claustrum and lateral amygdaloid nucleus as well as in the globus pallidus and entopeduncular nucleus. On day 21 the contralateral labelling of the lateral amygdaloid nucleus was apparent. The anterograde transport from the striatum to globus pallidus, entopeduncular nucleus and substantia nigra was already visible at birth although its intensity increased during the first postnatal month.