[The number and form of cerebellar fastigial neurons projecting to the thalamic suprageniculate nucleus in cats studied using WGA-HRP tracing method].

This study was designed to investigate the number and form of cerebellar fastigial neurons projecting to the suprageniculate nucleus(Sg) by using retrograde axonal transport of wheat germ agglutinin-horseradish peroxidase(WGA-HRP). Six adult cats(weighing 2.5-3.5 kg) were anesthetized with ketamine hydrochloride(30 mg/kg, i.m.) and sodium pentobarbital(15 mg/kg, i.p.). In experiments using injected WGA-HRP in the Sg, retrogradely labeled neurons by WGA-HRP were found only in the caudal part of the bilateral fastigial nucleus (Ft) with ipsilateral predominance, and the ratio of labeled neurons in the contralateral Ft to that in the ipsilateral Ft in all cats was 496:670(1:1.35). Five types of Ft-Sg neurons were distinguished morphologicaly. Of the 246 labeled neurons that could be characterized, 6.1% were large stellate neurons, 43.5% medium stellate neurons, 24.0% bipolar neurons, 20.3% triangular neurons, and 6.1% granular neurons. Thus, we concluded that a mixed population of Ft neurons projects to the Sg. In summary, as shown in the Figure 4 the Ft-Sg connection is an important pathway joining two closed circuits, and can be part of the extrageniculate visual system. We also speculate that the Ft-Sg connections may have a role in sending visual modulating information.