Modulation of the Hering-Breuer reflex by raphe pallidus in rabbits

Activation of the pulmonary stretch receptors by lung inflation or vagal stimulation evokes Hering-Breuer (HB) reflex, which is characterized by inspiratory inhibition and expiratory prolongation. In this work, whether the HB reflex could be modulated by the serotonergic raphe pallidus (RP) was studied by comparing the strength of this reflex before and after electrical or chemical stimulation of the RP. Experiments were performed on urethane anesthetized adult rabbits. The HB reflex was simulated with electrical stimulation of the central end of cervical vagus nerve. The RP was stimulated electrically or chemically by microinjection of glutamate. We found that after either electrical stimulation or chemical stimulation of the RP, the inspiratory inhibition and expiratory prolongation of the HB reflex were significantly attenuated. This attenuation showed post-stimulation time dependency or short-term memory, as well as RP stimulation intensity dependency. Results of the present study suggested that the serotonergic RP could exert its respiratory effects by modulating the strength of HB reflex.