Transneuronal transport of WGA-HRP from the ipsi- to contralateral medial habenular nucleus through the interpeduncular nucleus in the rat.

Transneuronal transport of WGA-HRP from the ipsi- to contralateral medial habenular nucleus (mHb) through the interpeduncular nucleus (Ip) in the rat was examined by light and electron microscopy. At 2-3 days after unilateral injection of the tracer into the mHb, retrogradely labeled neurons were observed in the contralateral mHb. The labeling was assumed to be a result of an anterograde-retrograde transneuronal transport of the tracer through the Ip. At the fine structural level, astrocytes and terminal boutons were most readily labeled in the Ip with shorter survival periods, while neuronal somata and major dendrites were prominently labeled with longer survival times. This indicates that astroglia might be involved in the earliest stages of the transneuronal transport of the tracer.