FOS EXPRESSION IN THE RAT PARABRACHIAL AND KOLLIKER-FUSE NUCLEI AFTERELECTRICAL-STIMULATION OF THE TRIGEMINAL ETHMOIDAL NERVE AND WATER STIMULATION OF THE NASAL-MUCOSA

The present study examined the location of neurons in the lateral para brachial nucleus (PBL), Kolliker-Fuse nucleus (KF), nucleus of the sol itary tract (NTS), spinal trigeminal nucleus (Sp5C) and upper cervical cord possibly involved in the transmission of autonomic responses (ap nea, bradycardia and rise in arterial blood pressure) elicited by naso trigeminal stimulation in the rat. To identify these neurons we employ ed immunocytochemical detection of the transcription factor Fos. To in duce the expression of Fos protein, two kinds of stimuli and experimen tal controls were performed in chloralose/urethane-anesthetized animal s: (i) electrical stimulation of the trigeminal ethmoidal nerve (EN5) and, as sham controls, dissection of the EN5 without electrical stimul ation, (ii) stimulation of the nasal mucosa with water and, as control experiments, no stimulation. Both forms of stimulation lead to a cons istent pattern of Fos-positive neurons in the PBL and KF. Differences could be observed rostrally in the PBL and KF, where significantly hig her numbers of Fos-positive neurons were present after EN5 versus wate r stimulation. The EN5-stimulated group had a significantly higher num ber of Fos-immunoreactive neurons in the KF than the sham controls, es pecially in the midlevel region. In the PBL significant differences in the numbers of activated cells could be observed between EN5-stimulat ed versus sham controls. In the water-stimulated rats compared with th e anesthesia controls, a significantly higher number of Fos-immunoreac tive neurons was always observed at all rostrocaudal levels in the KF and in the midlevel PBL. Electrical EN5 stimulation induced Fos expres sion in the Sp5C at the level of the area postrema and caudally in the upper cervical cord. In contrast, after water stimulation Fos-positiv e neurons were exclusively found in the Sp5C. In addition, all forms o f stimuli and controls induced strong expression of Fos in the medial and commissural NTS. Linear correlations were found between the number s of Fos-immunoreactive neurons in the Sp5C versus the KF and the NTS versus the PBL. The activated neurons may belong to two functionally d iscrete pathways: the nasotrigeminal reflex circuit, which is activate d by nasal sensory afferents running through the EN5 via the Sp5C to t he KF, and a pathway activated most likely by bare-and chemoreceptor a fferents running through the NTS to the PBL. Our results indicate that the PB/KF plays a pivotal role in the mediation and maintenance of th e autonomic responses induced by the nasotrigeminal reflex.