Rostral cuneiform nucleus and the defence reaction: Direct and indirect midbrain–medullary 5‐HT mechanisms in baroreflex inhibition

Background and Purpose Activation of the defence reaction inhibits baroreflex response via intermediate rostro-ventromedial medulla (B3 raphé) nucleus tractus solitarius (NTS). Our aim was to determine whether how inhibition, induced by disinhibition rostral cuneiform (part pathway), involves 5-HT neurons in B3 5-HT3 receptors NTS. Experimental Approach We performed immunohistochemistry anatomical experiments raphé cells expressing Fos were directly targeted nucleus. The effect blocking neurotransmission NTS on cuneiform-induced inhibition cardiac also analysed. Key Results Bicuculline, microinjected into nucleus, an increase double-labelled Fos-5-HT-IR both lateral paragigantocellular (LPGi) magnus. anterograde tracer Phaseolus vulgaris leucoaggutinin injected revealed a dense projection LPGi but not Cuneiform-induced prevented injection 8-OH-DPAT, selective 5-HT1A receptor agonist. Cuneiform failed inhibit bradycardia after microinjection antagonist granisetron knockout mice. Conclusion Implications participates direct activation magnus activate second-order neurons. These data bring new insights primary secondary mechanisms involved vital prevention during stress.