Cerebellar connections to the dorsomedial and posterior nuclei of the hypothalamus in the rat

The stimulation or ablation of cerebellar structures has produced a variety of visceral responses, indicating a cerebellar role in visceral functions. Studies using anterograde and retrograde tracing methods have revealed con nections between the hypothalamus and cerebellar structures. The aim of thi s study is to investigate the cerebellar connections of the dorsomedial (DM H) and posterior hypothalamic nuclei using retrograde axonal transport of h orseradish peroxidase (HRP). In the present study, micro-injection of HRP r estricted within the borders of the DMH showed that the projections of this nucleus are not uniform throughout its extent. The posterior DMH receives projections from the cerebellum whereas the anterior DMH does not. These pr ojections were from the (greatest to least concentration) lateral (dentate) , anterior interposed (emboliform), and medial (fastigial) cerebellar nucle i. In addition, both the anterior and posterior DMH receive projections fro m various areas of the brainstem which confirms earlier studies and provide s detailed descriptions. This study also demonstrates the distribution of l abelled neurons to cerebellar and brainstem nuclei following HRP injection into the posterior hypothalamic nucleus. It provides clear evidence for a d irect cerebellar nuclei-posterior DMH and cerebellar nuclei-posterior hypot halamic nucleus connections. We suggest that the brainstem reticular nuclei and other connections, such as the solitary, trigeminal and vestibular nuc lei, of both DMH and posterior hypothalamus may contribute to the indirect cerebellohypothalamic connections. These observations offer a new perspecti ve on the question of how the cerebellum may influence autonomic activity.