Interconnections between hypothalamus and cerebellum.

The cerebellum and hypothalamus are interconnected through a multitude of direct (monosynaptic) and indirect (polysynaptic) pathways. Direct hypothalamocerebellar fibres are mainly uncrossed and reach all parts of the cerebellar cortex and nuclei. They are neither mossy fibres nor climbing fibres, but appear to terminate in all layers of the cerebellar cortex as multilayered fibres. At least some of the hypothalamocerebellar fibres are histaminergic, and it appears that a small proportion of the hypothalamocerebellar neurons contain GABA. Indirect hypothalamocerebellar connections may be relayed through various brain stem nuclei. The hypothalamo-ponto-cerebellar pathway, which has a contralateral predominance, appears to be the quantitatively most important of these. The direct cerebellohypothalamic projection originates from the cerebellar nuclei and terminates in the posterior hypothalamus, in the same regions where the direct hypothalamocerebellar pathway has its main origin. Indirect cerebellohypothalamic connections with brain stem relays have also been demonstrated. The functions of hypothalamocerebellar circuits are so far unknown. However, these pathways are probably involved in the coordination and integration of somatic as well as non-somatic responses to a given set of inputs.