We so far reported that Purkinje cells in a small area (folium-p, fp) of rabbit cerebellar flocculus receive excitatory modulation via diffuse axons of hypothalamic orexinergic neurons (1). Rabbits were preferred because their flocculus has discernible regular folial divisions; this is not the case in rats or mice. We used albino rabbits weighing 1.0-3.1 kg. In the study to be reported, we used axonal transport of DiI and biotinylated dextran amine and found that these Purkinje cells project to the ventrolateral edge of the ipsilateral parabrachial nucleus (PBN), thus forming the fp-PBN microcomplex. Because stimulation of the classic defense area that activates hypothalamic orexinergic neurons induced, as part of defense reactions, redistribution of arterial blood flow between active muscles and visceral organs/resting muscles, we hypothesized that fp-PBN microcomplex adaptively controls the redistribution of arteriasl blood flow, which is primarily controlled by somatosympathetic reflexes (SSRs) and their supraspinal pathways. To support this hypothesis, we previously showed that climbing fiber signals to fp Purkinje cells were elicited by high arterial blood pressure or a high potassium concentration in muscles, both implying errors in redistribution of arterial blood flow (2). In the present study, we evoked defense reactions by applying electric foot shock stimuli to a conscious freely moving rabbit in a cage. The stimuli were 2-4mA, lasting 1-30 s in each trial and repeated once every 10 min 4-7 times in one session. These stimuli evoked quick turning around of the rabbit within the cage. Probes were chronically implanted to measure blood flow in femoral and celiac arteries under α-chloralose (60 mg/kg) and urethane (600 mg/kg) anesthesia. Another probe was implanted to measure blood pressure in femoral artery. Foot shock stimuli induced an increase in arterial blood flow in femoral muscles (FAF) and a reciprocal decrease in visceral organs (VAF). Both the increase and decrease were attenuated after systemic administration of orexin antagonists. After fp lesioning (with local kainate injection), FS-induced FAF increases became significantly larger, whereas FS-induced VAF decreases became significantly smaller and shorter- lasting. Apparently, under orexin neuromodulation, fp functions for effective balance of arterial blood flow in magnitude and time course between active muscles and visceral organs/resting muscles. Based on these collected data, we conclude that folium-p and PBN jointly form a unique microcomplex that is activated by orexin neuromodulation in defense behavior, and that the so activated microcomplex adaptively controls redistribution of arterial blood flow conforming to the high demand of arterial blood supply to active muscles in defense behavior.