Hypothalamic orexinergic neurons target Purkinje cells in a discrete cerebellar microzone (folium-p) that likely contributes to cardiovascular control associated with hypothalamic defense reactions

Abstract

In this study on anesthetized rabbits, we recorded from Purkinje cells in and around the folium-p on the left side, and determined the effects of defense area stimulation during the 1 sec poststimulation period of the peristimulus histogram. With stimulation of hypothalamus, about 40% of the cells tested were excited and about 45% inhibited. With PAG stimulation, about 30% of the cells tested were excited and about 70% inhibited. The excitation was blocked by iontophoretically applied orexin receptor-1 antagonists and was markedly depressed after orexinergic neurons were lesioned using saporin conjugated with orexin-B. We confirmed the presence of orexin-immunopositive neurons in the hypothalamus and their axons in the PAG and flocculus, in rabbits. These results indicate that axons of orexinergic hypothalamic neurons extending through PAG reach the flocculus and mediate excitation to folium-p Purkinje cells. DiI labeling showed that folium-p Purkinje cells project to the lateral parabrachial nucleus known as a sensitive pressor site. We propose the folium-p as a specific microzone involved in the brainstem cardiovascular control system. [J Physiol Sci. 2008;58 Suppl:S184]